Reading for MRL Course Theories of Motor Control

8/2/2019 Reading for MRL Course Theories of Motor Control

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6 S ec tio n I T H E O R E T I C A L F R A M E W O R K

Figure 1.2 . Mrs. Johnson is a 67-year-old wom an referred for therapy because of a r ight cerebral vascularaccident resulting in a left hemiparesis. Pictured is herhabitual sitting posture.

f u n c t i o n , spec i f i ca l ly the i n a b i l i t y t o ac t ive lye x t e n d t h e e l b o w, t o b ep r i m a r i l y t h e r e s u l t o fs p a s t i c i t y, d e f i n e d a s a release of the stretchreflex, i n the e lb ow f lexors.

H a s y o u r t h e o r e t i c a l f r a m e w o r k h e l p e d

y o u t o c o r r e c t l y i n t e r p r e t t h i s p a t i e n t ' s b e h a vi o r ? O n l y i f t h i s p a t i e n t ' s p r o b l e m s a r e i n f a c ts o l e l y t h e r e s u l t o f s p a s t i c it y. T h e t h e o r y h a sn o t h e l p e d y o u a s a c l i n i c i a n i f i t h asl i m i t e dy o u r a b i l i t y t o e x p l o r e o t h e r p o s s i b l e e x p l an a t i o n s f o r y o u r p a t i e n t ' s b e h a v i o r. W h a t a r esome o f t h e o t h e r f a c t or s t h a t p o t e n t i a l l y i mpa i r a r m f u n c t i o n i n y o u r st r o k e p a ti e nt ? L a t e ri n t h i s c h a p t e r w e w i l l d i scuss o the r theor i e so f m o t o r c o n t r o l t h a tw i l l p r o v i d e a l t e r n a t i v ee x p l a n a t i o n s f o r loss o f f u n c t i o n .

G U I D E F O R C L I N I C A L A C T I O N

T h e o r i e s p r o v i d e t h e r a p i s t sw i t h a poss i b l e g u i d e f o r a c t i o n . C l i n i c a l p r a c t i ce s d es i g n e d t o t r e a t t h e p a t i e n t w i t h m o t o r d y s-c o n t r o l ar e based o n a n u n d e r s t a n d i n g o f t h en a t u r e a n d cause o f n o r m a l m o v e m e n t , a sw e l las a n u n d e r s t a n d i n g o f t h ebasis f o r ab n o r m a lm o v e m e n t . T h e r a p e u t i c s t ra te g ie s a i m e d a tr e t r a i n i n g m o t o r c o n t r o l r e f l e ct t h i sbasic u nd e r s t a n d i n g . I n t h e a b o v e e x a m p l e , s p a s t i c it y

i s a s s u m e d t o b e a m a j o r d e t e r m i n a n t o f abn o r m a l f u n c t i o n . A s a r e s u l t , n u m e r o u s a p

p r o a c h e s h a v e b e e n d e v e l o p e d t oassess a n dt r e a t s p a s t ic i t y i n t h e c o u r s e o f r e t r a i n i n gf u n c t i o n . H o w e v e r , because t h e r e ar e m a n yd i f f e r e n t t h e o r i e s a b o u t t h e n a t u r e a n dcauseo f m o v e m e n t , t h e r e ar e p o t e n t i a l l y m a n yo t h e r t h e r a p e u t i c a p p r o a c he s f o r r e t r a i n i n gm o t o r d y s c o n t r o l .

N E W I D E A S : D Y N A M I CA N DE V O L V I N G

T h e o r i e s a r e d y n a m i c , a n dchange t o r ef le ct g r e a t e r k n o w l e d g e r e l a t i n g t o t h e t h e o r y.H o w does t h i s a ff ec t c l in i c a l p rac t i ces r e l a t edt o r e t r a i n i n g m o t o r d ys c o nt r o l? C h a n g i n gan d e x p a n d i n g t h e o r i es o f m o t o r c o n t r o l n e e dn o t b e a s o u r c e o ff r u s t r a t i o n t o c l in i c i ans . Exp a n d i n g t h e o r i e s c a n b r o a d e n a n d e n r i c h t h ep o s s i b i l i t ie s f o r c l i n i c a l p r a c t i c e . N e wideas f o rt h e assessment a n d t r e a tm e n t o f m o t o r d ysc o n t r o l w i l l e v o l v e t o r e f l e c t n e wideas a b o u tt h e n a t u r e a n d cause o f m o v e m e n t .

W O R K I N G H Y P O T H E S E S F O RA S S E S S M E N T A N D T R E A T M E N T

A t h e o r y is n o t d i r e c t l y t e s t a b l e ,since i ti s abs t r ac t . Ra the r, t heor i e sgenerate h y p o t heses, w h i c h a re t es t ab l e . I n f o r m a t i o n g a i n e dt h r o u g h hypo thes i s t e s t ing i s u sed to va l ida teo r i n v a l i d a t e a t h e o r y. T h i ssame a p p r o a c h i suse f u l in c l in i ca l p rac t i ce . So-ca l l edhypothesis-driven clinical practice ( 4 ) t r a n s f o r m s t h et h e r a p i s t i n t o a n a ct iv e p r o b l e m s o lv e r . U s i n gth i s a p p r o a c h t o r e t r a i n m o t o r d y s c o n t r o l c all sf or t h e t h e r a p i s t t o generate m u l t i p l e h y p o t heses ( e x p l a n a ti o n s ) f o r w h y p a t ie n t s m o v e ( o rd o n ' t m o v e ) i n w a y s t o a c h ie v e f u n c t i o n a l i nd e p e n d e n c e . D u r i n g t h e c o u r s e o f t h e r a p y t h et h e r a p i s t w i l l test v a r i o u s h y p o t h e s e s , d i s c a r di n g s o m e , a n d g e n e r a t i n g n e w e x p l a n a t i o n st h a t a re m o r e c o n s i s t e n tw i t h t h e i r r e s u l t s .

T H E O R I E S O F M O T O R

C O N T R O L

T h e r e is t r e m e n d o u s e n t h u s i a s m a m o n gt h e r a p i s t s f o r c r i t i c a l l y e x a m i n i n g t h e m o d e l s

u p o n w h i c h m u c hT h e r a p i s t s a r e re c

pas t t heor i e s ando f n e w s o l u t i o n s to r c o n t r o l a n d r

I n t h i s sec t im o t o r c o n t r o l ani t a t i o n s a n d p o s s ii m p o r t a n t t o u n du n i f i e d by the desan d cause o f m o vt h e a p p r o a c h . I t five m en t r y i n g t of u n c t i o n o f an esys temat i ca l ly s t u d

e r y t h i n g t he re i s an d f u n c t i o n o f tn a t u r e a n d f u n c tt a i l . Each i n h i s otial i n f o r m a t i o n e v e r , a t r u e u n dan d f u n c t i o n o fb y c o m b i n i n gi n ft h i s sp i r i t , w e appo n t h e o r i e s o ftions, an d possib

R e

Si r Char l e so l o g i s t i n t h e lw r o t e t h e b o o kNervous System i nt h e e x p e r i m e n t af lex th eor y o f moref lexes were thp l e x b e h a v i o r. R

Receptor}

Stimulus

Figure 1.3 . The bareceptor, a conduct


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Chapter O n e T H E O R I E S O FM O T O R C O N T R O L 7

t o re-e t h e o r y,

s r e l a t edC h a n g i n g

t r o l n e e dc i a n s . E x-n r i c h t h e

w ideas foro t o r d y s -eas abou t

T

e . since i te h y p o t h -

r. gainedo va l ida ter r o a c h is

bypothes i s -

f o r m s t h ec r. U s i n gn r r o l callse h y p o t h -m ov e (o rt i o n a l i n -e r a p y t h e

s . d i s c a r d -p l a n a t i o n sresul ts .

O R

u p o n w h i c h m u c h o f c l i n i c a lprac t i ce i s based .T h e r a p i s t s a re r e c o g n i z i n g t h el i m i t a t i o n s o f

pas t theor ies an d the exp and ing po ss ib i l i t i e so f n e w s o l u t i o n s based o n n e w m o d e l s o f m ot o r c o n t r o l a n d r ec o v e r y o ff u n c t i o n .

I n t h i s s e c t i o n w ew i l l r e v i e w t h e o r i e s o fm o t o r c o n t r o l a n d e x p l o r e s o m e o f t h e i rl i mi t a t i o n s and poss ib le c l in ica li m p l i c a t i o n s .I t isi m p o r t a n t t o u n d e r s t a n d t h a t a ll m o d e l s a reu n i f i e d b y t h e d e si re t o u n d e r s t a n d t h e n a t u r ea n d cause o f m o v e m e n t . T h e d i f f e r e n c e i s i nt h e a p p r o a c h . I t i s n o tu n l i k e t h e s t o r y o f t h efive m e n t r y i n g t o u n d e r s t a n d t h e n a t u r e a n df u n c t i o n o f a n e l e p h a n t . O n e c a r e f u l l y a n dsys temat ica l ly s tud ies th et r u n k , and learns ev-e m h i n g there is to k n o w a b o u t t h e n a t u r ea n d f u n c t i o n o f t h e t r u n k . A n o t h e r s t u d ie s t h en a t u r e a n d f u n c t i o n o f t h e f e e t ; a n o t h e r, t h et a i l . E a c h i n h is o w n w a y h asp r o v i d e d essen-t i a l i n f o r m a t i o n a b o u t t h e e l e p h a n t . H o we v er, a t r u e u n d e r s t a n d i n g a b o u t t h e n a t u r ea n d f u n c t i o n of an e lephan t i s o n l y poss ib le

c o m b i n i n g i n f o r m a t i o n f r o m a l l sources . I nth is sp i r i t , w e a p p r o a c h t h e f o l l o w i n g s e c t i o no n t h e o ri e s o f m o t o r c o n t r o l , t h e i rl i m i t ations, a n d p o s s i b le c l i n i c a l a p p l i c a t i o n s .

Reflex TheoryS ir C h a r l e s S h e r r i n g t o n , a n e u r o p h y s i -

o l o g i s t in the l a t e 1800s and ea r ly 1900s,w r o t e t h e b o o k The Integrative Action of theNervous System i n 1 9 0 6 . H i s r e se a r ch f o r m e dt h e e x p e r i m e n t a l f o u n d a t i o n f o r aclassic r e - e x t h e o r y o fm o t o r c o n t r o l . F o r S h e r r i n g t o n ,re f lexes wer e the b u i l d i n g b l o c k s o f c o mplex b e h a v i o r. Reflexes w o r k e d t o g e t h e r , o r

Stimulus Response' (stimulus)Response(stimulus)

=eceptor}

5: ~ulus

Muscle/effector

Response

a m o n ge m o d e l s

Figure 1.3 . The basic structure of a reflex consists of awreptor, a conductor, and an effector.

Figure 1 .4 . Reflex chaining as a basis for action. A stim-ulus leads to a response, which becomes the stimulus forthe next response, which becomes the stimulus for thenext response.

i n s e q u e n c e , t o ac h ie v e a c o m m o n p u r p o s e( 5 ) .

S h e r r i n g t o n p e r f o r m e d e l eg a n t e x p e r im e n t s w i t h cats, d o g s , a n d m o n k e y s t o s h o wt h e existence o f the re f l ex , and to ca re fu l ly des c r ib e a n d d e f in e r e fl e xe s . T h e c o n c e p t i o n o fa r e f l ex requ i res th ree d i ff e re n t s t ruc tu res , ass h o w n i n F i g u r e 1 . 3 : a r e c e p t o r, a c o n d u c t i n gn e r v o u s p a t h w a y, a n d a n e f f e c t o r. T h e c o nd u c t o r consis ts o f a tleast tw o ne rve cel l s , onec o n n e c t e d t o t h e e f fe c t o r, t h e o t h e r c o nnec ted to the recep to r. The re f l ex a rc thenc o n si st s o f t h e r e c e p t o r, t h e c o n d u c t o r , a n dt h e e f f e c t o r ( 6 ) .

S h e r r i n g t o n w e n t o n t o d es c ri b e c o mp l e x b e h a v i o r i n t e r m s o f c o m p o u n d r e f l ex e s,a n d t h e i r successive combination o r chainingt o g e t h e r. S h e r r i n g t o n g a ve t h ef o l l o w i n g exa m p l e o f af r o g ca p t u r ing and ea t in g a fly. P ict u r e M r . T o a d s i t t i n g in the sun on h i s l i lyp a d . A l o n g comes the fly; seeing the fly( s t i mu l u s ) r e su l t s in the re f l ex ac t iva t io n o f thet o n g u e d a r t i n g o u t t o c a p t u r e t h e f l y ( r esponse ) . I f he is successfu l , t he co n tac t o f thefly o n t h e t o n g u e causes r e f l ex c losure o f them o u t h , a n d c l o s u r e o f t h e m o u t h r e su l t s inref lex s w a l l o w i n g .

S h e r r i n g t o n c o n c l u d e d t h a t w i t h t h ew h o l e n e r v o u s s y st e m i n t a c t , t h e r e a c t i o n o fthe va r iou s pa r t s o f tha t sys tem, the s imp lere f l exes , a re combined i n t o grea te r ac t ions ,w h i c h c o n s t i t u t e t h e b e h a v i o r o f t h ei n d i v i d

u a l as a w ho le . F igu re 1 .4 r ep resen t s th i s co nc e p t o f r e f l e x c h a i n i n g . S h e r r i n g t o n ' sv i e w o fa ref lexive basis f o r m o v e m e n t p e r s i s t e d u nc h a l l e n g e d f o r 5 0 y e a r s, a n d c o n t i n u e s t o i nfluence t h i n k i n g a b o u t m o t o r c o n t r o l t o d a y.

L I M I T A T I O N S

Because S h e r r i n g t o n lo o k e dp r i m a r i l y atre f l exes , and asked ques t ions ab ou t the cen t ra l


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8 Section I T H E O R E T I C A L F R A M E W O R K

n e r v o u s s y st e m ( C N S ) r e l a t e d t oreflexes, h ed r e w a p i c t u r e o f t h e C N S a n d m o t o r c o n t r o lt h a t w a s sk e w e d t o w a r d s r e fl e x c o n t r o l .Therea re a n u m b e r o f l i m i t a t i o n s o f a r e f l ex t h e o r yo f m o t o r c o n t r o l ( 1 ) .

T h e r e f l e xcannot be cons ide re d the ba -sic u n i t o f b e h a v i o r i f b o t hspontaneous a n dv o l u n t a r y m o v e m e n t s a r e r e c o g n i z e d as a c-ceptable classes o f b e h a v i o r , since t he r e f l exmus t be ac t iva ted by an ou t s ideagent.

A n o t h e r l i m i t a t i o n o f t h e r ef l ex t h e o r yo f m o t o r c o n t r o l is t h a t i tdoes n o t a d e q u a t e l ye x p l a i n a n d p r e d i c t m o v e m e n t t h a toccurs i nt h e absence o f a sensory s t i m u l u s . M o r e r e -cen t ly, i t has been s h o w n t h a t a n i m a l s c a nm o v e i n a r e l a t i v e l y c o o r d i n a t e d f a s h i o n i n t h eabsence o f sensory i n p u t ( 7 ) .

Ye r a n o t h e r l i m i t a t i o n i s t h a t t h e t h e o r ydoes n o t e x p l a i n fast m o v e m e n t s , t h a t i s , se -quences o f m o v e m e n t s t h a toccur t o o r a p i d l yt o a l l o w f o r sensory feedback f r o m th e p r e -c e d i n g m o v e m e n t t o t r i g g e r t h e n e x t . F o r e x -a m p l e , a n experienced a n d p r o f i c i e n t t y p i s tmoves f r o m o n e k e y t o t h e n e x t s o r a p i d l y t h a tt h e r e i s n ' t t i m e f o rsensory i n f o r m a t i o n f r o mone keys t roke t o ac t iva te the n ex t .

A n a d d i t i o n a ll i m i t a t i o n i s t ha t t he r e f l ex

c h a i n i n g m o d e l f a i l s t o e x p l a i n t h efact t h a t as i n g l e s t i m u l u s c a n r e s u l t i n v a r y i n gresponsesd e p e n d i n g o n c o n t e x t a n d d e s c e n di n g c o m -m a n d s . F o r e x a m p l e , t h e r e a r e t i m e s w h e n w eneed t o o v e r r i d e reflexes t o achieve a g o a l . F o re x a m p le , n o r m a l l y t o u c h i n g so m e t h i n g h o tre su l t s i n the r e f l ex ivew i t h d r a w a l o f t h e h a n d .H o w e v e r , i f ou r ch i ld i s i n a f ir e, we m ay ove r-r i d e t h e r e fl e xi v e w i t h d r a w a l t op u l l t h e c h i l do u t .

F i n a l l y, r e f l e x c h a i n i n gdoes n o t e x p l a i nt h e a b i li t y t o p r o d u c e n o v e l m o v e m e n t s .N o v e l m o v e m e n t s p u t t o g e t h e r u n i q u e c o m -

b i n a t i o n s o f s t i m u l i a n dresponses a c c o r d i n gt o r u l e s p r e v i o u s l y l e a r n e d . A v i o l i n i s t , w h ohas l ea rned a piece o n t h e v i o l i n , a n d alsok n o w s t h e t e c h n i q u e o f p l a y i n g t h e c e l lo , c a np l a y t h a t piece p e r f e c tl y o n t h e ce l lo w i t h o u tnecessarily h a v i n g p r a c t i c e d t h epiece o n t h ece l lo . Th e v io l in i s t has l ea rn ed the ru le s fo rp l a y i n g t h e piece a n d h as a p p l i e d t h e m t o an o v e l o r n e w s i t u a t i o n .

C L I N I C A L I M P L I C A T I O N S

H o w m i g h t a r e fl e x t h e o r y o f m o t o rc o n t r o l be used t o i n t e r p r e t a p a t i e n t ' sbehav-i o r , a n d serve as a gu ide fo r the the rap i s t ' sactions?

I f c h a in e d o r c o m p o u n d e d reflexes ar eth e basis f o r f u n c t i o n a l m o v e m e n t , c l i n ic a lstrategies d e s i g n e d t o test reflexes s h o u l d a l -l o w t h e r a p is t s t o p r e d i c t f u n c t i o n . I n a d d i -tion, a p a t i e n t ' s m o v e m e n t b e h a v i o r sw o u l db e i n t e r p r e t e d i n t e r m s o f t h epresence or ab -sence o f c o n t r o l l i n greflexes. F i n a l l y, r e t r a i n -i n g m o t o r c o n t r o l f o r f u n c t i o n a l sk il lsw o u l dfocus o n e n h a n c i n g o r r e d u c i n g th eeffect orv a r i o u s reflexes d u r i n g m o t o r tasks. A p p l y i n ga r e fl e x t h e o r y t o in t e r p r e t i n g m o t o r d y s c o n -t r o l w a s s h o w n i n o u r p r e v i o u sexample o fM r s . Johnson. C l i n i c a l strategies f o r i m p r o v -i n g m o t o r c o n t r o l u s i n g a r e fl e x m o d e lw o u l dfocus o n m e t h o d s t o reduce flexor spasticity,w h i c h s h o u l d enhance n o r m a l m o v e m e n t c a-p a c i t y.

D e s p i t e t h e U m i t a t i o n s i n S h e r r i n g t o n ' sc o n c l u s i o n s , m a n y o f h i s a s s u m p t i o n s a b o u th o w t h e C N S c o n t r o l s m o v e m e n thave beenr e i n f o r c e d a n dhave i n f l u e n c e d c u r r e n t c l i n i c a lpractices.

Hierarchical Theory

M a n y researchers c o n t r i b u t e d t o t h ev i e w t ha t t he ne rvou s sys t em i s o rg an ize d a sa h i e ra r ch y. A m o n g t h e m , H u g h l i n g sJack-s o n , a n E n g l i s h p h y s i c i a n , a rg u e d t h a t t h eb r a i n h as h i g h e r , m i d d l e , a n d l o w e rlevels o fc o n t r o l , equated w i t h h i g h e r association ar -e a s , t h e m o t o rcortex a n d s p i n a l levels o f m o -t o r f u n c t i o n ( 8 ) .

H i e r a r c h i c a l c o n t r o l i n g e n e r a l h asbeen

d e f i n e d a s a n o rg a n i z a t i o n a l s t r u c t u r e t h a t i stop down. T h a t i s , each successively h i g h e rl e v e l exerts c o n t r o l o v e r t h e l e v e l b e l o w i t , ass h o w n i n F i g u r e 1 . 5 . I n a s t r i c t v e r t i c a l h i e r -a r c h y, l i n e s o f c o n t r o l d o n o tcross a n d t h e r eis never b o t t o m u p c o n t r o l .

I n t h e 1920s, R u d o l f M a g n u s began t oe x p l o r e t h e f u n c t i o n o f d i f fe r e n treflexesw i t h i n d i f f e r e n t p a r t s o f t h e n e r v o u s s y s te m .


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t m t M . - .mmtmmn m m m m m m m m m u

Chapter O ne T H E O R I E S O F M O T O R C O N T R O L 9

Top

A A

r i g i i L. 1 - 5 . T h e hierarchical control structure is char-" z-zow n structure, where higher centers

a e a h a a v * in charge of lower centers.

r ~ : t ha t reflexes c o n t r o l l e d b y l o w e ri r c c b o f t h e n e u r a l h i e r a r c h y a re o n l y p r e s e n tw m e n c o r t i c a l centers a r e d a m a g e d . These r e -

l i t e r i n t e r p r e t e d t o i m p l y t ha t r e -- : : : r i r t o f a h i e r a r c h y o f m o t o r c o n t r o l ,r w- ; - r r g r e r centers n o r m a l l yi n h i b i t these

k p c r ref lex centers (9-10).

G e o rg S c h a l t e n b r a n d ( 11 ) u s e d~c : ~ ; : r t - d e v e lo p e d b y M a g n u s t o e x p l a inr : : . .-. r r t e n t o f m o b i l i t y i n c h i l d r e n a n dd C _ r : H : d e s cr i b ed t h e d e v e l o p m e n t o f h u -n s r m o b i l i t y i n t e r m s o f t h eappearance a n dm LTCci .- i r.ee o f a p ro gress io n o freflexes. H ew e n t o n f u r t h e r t o s ay t h a t p a t h o l o g y o f t h eb r a n I R Z Y r e su l t i n the persistence o f p r i m i t i v e

: " : : H ; suggested t h a t a c o m p l e t e u n -. : : - - . : : r . f all the reflexes w o u l d a l l o w t h e; . : - : - i t : r. o f the neur a l age o f a ch i ld o r

p n b e n t .

I n t he l a t e 1930s, Stephan We i s z ( 1 2 )x_r:rEed on ref lexreactions t ha t he f e l t were

r -j si s fo r e q u i l i b r i u m i n h u m a n s . H e d e -


5/16

1 0 S ec ti on I T H E O R E T I C A L F R A M E W O R K

Neuroanatomicalstructures

Postural reflexdevelopment

Motordevelopment

Cortex Equilibriumreactions

Bipedalfunction

Midbrain

Rightingreactions

Quadrupedalfunction

Brainstemspinal cord Primitive

reflex

Apedalfunction

Figure 1.6. Neuromaturat ional theory of motor control a t t r ibutes motor development to the maturat ion of neuralprocesses, includ ing the progressive appearan ce and disappearan ce of ref lexes.

a m p l e o f b o t t o m - u p c o n t r o l . T h u s , o n e m u s tb e c a u t i o u s a b o u t a s s u m p t i o n s t h a t a l l l o w -l eve l behav io r s a re p r i m i t i v e , i m m a t u r e , a n dn o n a d a p t i v e , w h i l e a l l h ig her l eve l ( co r t i ca l )b e h a v i o r s a r e m a t u r e , a d a p t i v e , a n da p p r o p r iate .

C L I N I C A LI M P L I C A T I O N S

A b n o r m a l i t i e s o f r e f l e x o rg a n i z a t i o nhave been used by many c l in ic ians to exp la ind i s o r d e r e d m o t o r c o n t r o l i n th e n e u r o l o g i c a lp a t i e n t . B e r t a B o b a t h , a n E n g l i s h p h y s i c a lt h e r a p i s t , in he r d i scussions o f ab no rm al post u r a l r e f l ex ac t iv i ty i n c h i l d r e n w i t h ce rebra lpalsy, states t h a t " t h e release o f m o t o r r esponses i n t e g r a t e d a t l o w e r l e v e l s f r o m res t r a i n i n g i n f l u e n c es o f h i g h e r centers, espe-cia l ly t h a t o f t h e c o r t e x , leads t o a b n o r m a lp o s t u r a l r e f l ex a c t i v i t y " ( 1 6 ) .

Based o n a r e f l e x / h i e r a r c h i c a l t h e o r y o fm o t o r c o n t r o l a n d d e v e l o p m e n t , a n u m b e r o fref lex tests have been d eve l oped as pa r t o f thec l in i ca l assessment of pa t i en t s w i t h n e u r o l o gical i m p a i r m e n t s ( 1 7 ) . These r e f l ex assessmentprof i l e s a re used to e s t ima te the l eve lo f n e u r a lm a t u r a t i o n a n d p r e d i c t f u n c t i o n a lab i l i t y. I na d d i t i o n , r e fl e x p r o f i l e s a re u s e d t o d o c u m e n tt h e presence o f p e r s i s t i n g a n d d o m i n a t i n gp r i m i t i v e an d pa t ho l og ica l r e f l exes be l i ev ed

t o b e m a j o r d e t e rr e n t s t o n o r m a l m o t o rc o n t r o l .

A n u m b e r o f t r e a t m e n t a p p r o a ch e s h a v eb e e n d e v e l o p e d w h i c h f o c u s o n e n h a n c i n g o rr e d u c i n g th e efficacy o f reflexes as ani m p o rt a n t step in r e t r a i n i n g m o t o r c o n t r o l . T h eg o a l o f t r ea tm ent is to ach ieve g rea te r fun c

tion t h r o u g h th e m o d i f i c a t i o n of r e f l ex ac t ion .O n e o f t h e d i ff i cu l t i e s in us ing a r e f l ex app r o a c h t o r e t r a i n i n g m o t o r c o n t r o l is t h a tsuc-cessful m o d i f i c a t i o n o f r e f l ex ac t iv i ty i s no t a lways m i r r o r e d i n i m p r o v e m e n t s i n f u n c t i o n a lski l l s . Par t o f the d i f f i c u l t y may he in the issueo f f o c u s i n g t r e a t m e n t o n r e a c ti o n s i n s t e a d o fp r e p a r i n g p a t i e n t s f o r a c t i o n .

Motor Programming Theories

M o r e c u r r e n t th e o r ie s o f m o t o r c o n t r o lh a v e e x p a n d e d o u r u n d e r s t a n d i n g o f t h e

C N S . T h e y h a v e m o v e d aw a yf r o m v i e w s o fthe C N S as a m os t ly r eac t ive sys tem an d haveb e g u n t o e x p l o r e t h e p h y s i o l o g y o f a c t io n sr a t h e r t h a n t h e p h y s i o l o g y o f r e a c t i o n s .

Ref lex theor ies have bee n u se fu l i n exp l a i n i n g c e r t a i n s t er e o t y p e d p a t t e r n s o fm o v em e n t . H o w e v e r , a n i n t e r e s ti n g w a y o fv i e w i n gr e f l exes i s to cons ide r tha t one can remove thes t i m u l u s , or the a ffe ren t i n p u t , a n d s t i l l havea p a t t e r n e d m o t o r response ( 1 8 ) . I f w e r e

m o v e t h e mw e ar e l e f t wp a t t e r n . T h im o r e f l e x i bcause i t cans t i m u l i o r b y

A m o tt r o l has conF o r e x a m p l es t u d i e d th e gt h a t t h e timflight d e p e n de r a t o r. E v e nc u t , t h e n e r verate t h e o u tever, the w i n gges ted tha tabsence o f rw h i l e n o t essea n i m p o r t a n tThese c o n c l uw o r k e x a m i n iresu l t s o f thethe cat , spinaa l o c o m o t o ri n p u t s o r descB y c h a n g i n g t h e s p i n a l c o rw a l k , t r o t , o r gt h a t ref lexes dt r a l p a t t e r n geerate s u c h c ot r o t , a n d g a l l ot h e i m p o r t a n tsensory inpu t st o r ( 2 2 ) .

These exp r o g r a m t h e o rhas been used iresearchers, som i n i n g h o w t hm o t o r p r o g r ac e n t r a l p a t t e r nspecif ic neural w a l k i n g i n t h eresents n e u r a lt y p e d a n d h a r d

B u t the t et o desc r ibe thet h a t represent a


6/16

Chapter O ne T H E O R I E S O F M O T O R C O N T R O L 1 1

of neural

r m a l m o t o r

roaches have

e n h a n c i n g o ra s a n i m p o r -c o n t r o l . T h egreater f u n c -r e f le x a c t i o n ,

a r e f l ex ap -o l i s th at suc-

i s no t a l -in f u n c t i o n a l

:n the issue

n s i n s t e a d o f

Theories

m o t o r c o n t r o lnding o f th efrom v i e w s o fs t em and have - of actionseac t ions .

use fu l in ex -s o f m o v e -

ay of v i e w i n gca n r e m o v e t h e^ a n d s t i l l have4 8 ) . I f w e r e

m o v e t h e m o t o r response f r o m i t s s t i m u l u s ,

we a re l e f tw i t h t h e concept o f a c e n t r a l m o t o rp a t t e r n . T h i s concept o f a m o t o r p a t t e r n i sm or e f l ex ib le t ha n theconcept o f a r e f l ex because i t can e i the r be ac t iva ted bysensorys t i m u l i o r b y c e n t r a l processes.

A m o t o r p r o g r a m t h e o r y o f m o t o r c o nt r o l h a s c o n s i d e r a b l e e x p e r i m e n t a l s u p p o r t .F o r e x a m p l e , e x p e r i m e n t s i n t h e e a r ly1960ss t u d i e d th e grasshopper o r l o c u s t a n d s h o w e dt h a t t h e timing o f t h e a n i m a l ' s w i n g beat i nf l i g h t d e p e n d e d o n a r h y t h m i c p a t t e r n g e ne r a t or . E v e n w h e n t h esensory nerves w e r ec u t , t h e n e r v o u s s y s t e m b y i t s e l f c o u l d g e n

erate t h e o u t p u t w i t h n o sensory i n p u t ; h o wever, t h e w i n g beat w a s s l o w e d ( 2 0 ) . T h i s s u ggested t h a t m o v e m e n t is p o s s i b l e i n t h eabsence o f r e f l e x i v e a c t i o n .Sensory i n p u t ,w h i l e n o t essential i n d r i v i n g m o v e m e n t , h a sa n i m p o r t a n t f u n c t i o n i n m o d u l a t i n g a c t i o n .These c o n c l u si o n s w e r e f u r t h e r s u p p o r t e d b yw o r k e x a m i n i n g l o c o m o t i o n i ncats ( 2 1 ) . T h eresu l t s o f these e x p e r i m e n t s s h o w e d t h a t i nt h e c a t, s p i n a l n e u r a l n e t w o r k s c o u l d p r o d u c ea l o c o m o t o r r h y t h m w i t h o u t e i t h e r sensoryi n p u t s o r d e s c e n d i n g p a t t e r n sf r o m t h e b r a i n .B y c h a n g i n g t h e i n t e n s i t y o f s t i m u l a t i o n t o

t h e s p i n a l c o r d , t h e a n i m a l c o u l d b e m a d e t ow a l k , t r o t , o r g a l l o p . T h u s , i t w a s a g a i n s h o w nt h a t reflexes d o n o t d r i v e a c t i o n , b u t t h a tcen-t r a l p a t t e r n generators b y themselves c a n g e nerate s u c h c o m p l e x m o v e m e n t s as t h e w a l k ,t r o t , a n d g a l l o p . F u r t h e r e x p e r i m e n t s s h o w e dt h e i m p o r t a n t m o d u l a t o r yeffects o f i n c o m i n gsensory i n p u t s o n t h e c e n t r a l p a t t e r ngenera-to r ( 2 2 ) .

These e x p e r i m e n t s l e d t o t h e m o t o rp r o g r a m t h e o r y o f m o t o r c o n t r o l . T h i s t e r mha s been u s e d i n a n u m b e r o f w a y s b y d i f f e r e n tresearchers, so care s h o u l d b e t a k e n i n d e t e rm i n i n g h o w th e t e r m is b e i n g u s e d . T h e t e r mm o t o r p r o g r a m m a y b e u s e d t o i d e n t i f y ac e n t r a l p a t t e r n g e n e r a t o r ( C P G ) , t h a t i s , aspecific n e u r a l c i r c u i t l i k e t h a t f o r g e n e r a t i n gw a l k i n g i n the ca t . I n th i scase t h e t e r m r e presents n e u r a l connections t ha t a re stereo-t y p e d a n d h a r d w i r e d .

B u t t h e t e r m m o t o r p r o g r a m isalso u s e dto describe t h e h i g h e r l e v el m o t o r p r o g r a m st h a t represent actions i n m o r e abstract t e r m s .

A s i g n i f i c a n t a m o u n t o fresearch i n t h e f i e ld

o f p s y c h o l o g y h a s s u p p o r t e d th eexistence o fh i e r a r c h ic a l ly o r g a n i z e d m o t o r p r o g r a m s t h a tstore t h e r u l e s f o r g e n e r a t i n g m o v e m e n t s s ot h a t w e c an p e r f o r m t h etasks w i t h a v a r i e t yo f e f f e c t o r systems.

A C T I V E L EA R N I N G M O D U L E

You can see this for yourself. Trywr i t i ng your s ignature as you normal lyw o u l d on a smal lpiece of paper. Now

wri te i t larger, on a blackboard. Now try itwi th

your other hand. While you may be much moreprof ic ientwith one hand versus the other, youwil lsee elements of your s ignature that are commonto all situations. As shown in Figure 1.7, the rulesfor wr i t i ng your name are stored as a motor program at higher levelswithin the CNS. A s a result,neural commands from these higher centers towri te y o u r name can be sent to various parts of thebody. Yet, elements of the wri t ten signature remain constant regardless of the part of the bodyused to carry out thetask (23).


T h e concept o f c e n t r a l p a t t e r n genera-t o r s e x p a n d e d o u r u n d e r s t a n d i n g o f t h e r o l eo f t h e n e r v o u s s y s t e m i n t h e c o n t r o l o f m o v em e n t . H o w e v e r, w e m u s t b e c a r e f u l t o r e a l i z et h a t t h e c e n t r a l p a t t e r n g e n e r a t o rconcept hasn e v e r been i n t e n d e d t o replace t h e concept o ft h e i m p o r t a n c e o fsensory i n p u t i n c o n t r o l l i n gm o v e m e n t . I t s i m p l y e x p a n d e d o u r u n d e rs t a n d i n g o f t h e f l e x i b i l i t yo f t h e n e r v o u s sys-te m i n c r e a t i n g m o v e m e n t s , t o i n c l u d e i tsab i l i t y t o create m o v e m e n t s i n i s o l a t i o nf r o mfeedback.

A n i m p o r t a n t l i m i t a t i o n o f t h e m o t o rp r o g r a m concept i s t h a t a c e n t r a l m o t o r p r og r a m c a n n o t b e c o n s i d e r e d t o b e t h esole d et e r m i n a n t o f a c t i o n ( 2 3 ) . T w o i d e n t i c a l c o mma nds to the e lbo w f lexors, fo r exa mp le ,w i l lp r o d u c e v e r y d i f f e r e n t m o v e m e n t s d e p e n d i n go n w h e t h e r y o u r a r m i s r e s t i n g a t y o u r s i d e ,o r i f y o u a re h o l d i n g y o u r a r m o u t i n f r o n t o fy o u . T h e forces o f g r a v i t yw i l l a c t d i f f e r e n t l yo n t h e l i m b i n t h e t w o c o n d i t i o n s , a n d t h u s


7/16

12 S ec tio n I T H E O R E T I C A L F R A M E W O R K

Abstractmotor program

Synergy Synergy Synergy

Right handmuscles

Right armmuscles

Left handmuscles

Figure 1. 7 . Levels of control for motor programs and their output systems. Rules for act ion are represented at thehighest level , in abstract motor programs. Low er levels of the hierarchy co ntain information essent ial for effect ing

ac t ion .

m o d i f y t h e m o v e m e n t . I n a d d i t i o n , i f y o u rm usc les a re f a t igu ed , s im i la r ne rvo us sys temc o m m a n d s w i l l give ve ry d i ffe ren t r e su l t s .T h u s , t h e m o t o r p r o g r a m c o n ce p tdoes n o tt ake i n t o a c c o u n t t h e f a c t t h a t t h e n e r v o u ssyst em m u s t t a k e i n t o a c c o u n t b o t h m u s c u l os k e le t a l a n d e n v i r o n m e n t a l v a r i a bl e s i n a c h i evi n g m o v e m e n t c o n t r o l.


M o t o r p r o g r a m t h e o ri e s o f m o t o r c o nt r o l h a v e a l l o w e d c l i n ic i a n s t o m o v e b e y o n d ar e fl e x e x p l a n a t i o n f o r d i s o r d e r e d m o t o r c o nt r o l . E x p la n a t io n s f o r a b n o r m a l m o v e m e n th a v e b e en e x p a n d e d t o i n c l u d e p r o b l e m s r es u l t i n g f r o m a b n o r m a l i t i e s i n c e n t r a l p a t t e r ng e n e r a t o r s , o r i n h i g h e r le v e l m o t o r p r og r a m s .

M r s . J o h n s o n , o u r s t r o k e p a t i e n t , m a yi n d e e d have f l ex or spas t i c ity i n he r a rm sw h i chm ay a ffec t he r a b i l i t y t o m o v e . H o w e v e r , i tw i l l b e i m p o r t a n t t o d e t e r m i n e w h a t l ev el s o fm o t o r p r o g r a m m i n g a r e i n v o l v e d . I f h e rh i g h e r l ev el s o f m o t o r p r o g r a m m i n g a re n o ta ffec ted , she w i l l be ab le to con t in ue to uses u c h p r o g r a m s a s h a n d w r i ti n g , b u t w i l l f i n da l t e rna te e ffec to r s , fo r example , he r unaff e c t e d h a n d , t o c a r r y o u t t h e t as ks . O f c o u r s e ,these less u s e d l o w e r l e v e l s y n e rg y a n d m u sc u l a r systems w i l l have to be t r a ine d to ca r ryo ut these h i g h e r l e v el p r o g r a m s .

I n pa t i en t s w hose h ig her l evel so f m o t o rp r o g r a m m i n g a re a f f e c te d , m o t o r p r o g r a mt h e o r y suggests t h e i m p o r t a n c e o f h e l p i n g p atients r e l e a r n t h e c o r r e c t r u l e s f o r a c t i o n . I na d d i t i o n , t r e a t m e n t s h o u l d fo c u s o n r e t r a i ni ng m o v e m e n t s i m p o r t a n t t o a f u n c t i o n a lt a sk , no t jus t on reeduca t ing spec i f i c musc lesi n i s o l a t i o n .

Systems Theory

E v e n b ef o r e m o t o r p r o g r a mconceptsw e r e d e v e l o p e d , a n o t h e rresearcher, N i c o l a iB e r n s t e i n ( 1 8 9 6 - 1 9 6 6 ) , a Russia n sc ient is t ,w a s l o o k i n g a t t h e n e r v o u s s y s t e m a n d b o d yi n a w h o l e n e w w a y. P re v i o us n e u r o p h y s i o l -o g i s ts h a d f o c u s e dp r i m a r i l y o n n e u r a l c o n t r o laspects o f m o v e m e n t . B e r n s t e in r e c o g n i z e dt h a t y o u c a n n o t u n d e r s t a n d t h e n e u r a l c o n t r o lo f m o v e m e n t w i t h ou t a n u n d e r s t a n d i n g o fthe charac te r i st i c s o f the sys tem yo u a re m ovi n g , a n d t h e e x t e r n a l a n d i n t e r n a lforces a c t i n go n t h e b o d y.

I n de sc r ib ing the cha rac te r i s ti c s o f thesystem b e i n g m o v e d , h e l o o k e d a t t h e w h o l eb o d y as a mechan ica l sys tem,w i t h mass, a n dsub jec t to bo th ex te rna l fo rces ,l i ke g rav i ty,a nd i n t e r n a l f o r c e s , i n c l u d i n g b o t h i ne r t i a la nd m o v e m e n t - d e p e n d e n t f o r c e s .D u r i n g th ecourse o f a n y m o v e m e n t th e a m o u n t so f f o r c ea c t i n g o n t h e b o d y w i l l change a s p o t e n t i a la nd k i n e t i c e n e rg y ch a n g e . H e t h u s s h o w e d


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Chapter One THE ORIE S OF M O T O R C O N T R O L 1 3

concepts

Nicolaiscientist,and bodyphysiol -

c o n t r o lecognizedl con t ro li r . i : n g o fi re mov-

r:es acting

ties ot ther.t wholemass, and

ke grav ity,h iner t ia l

Tu ri ng thes of force potentials showe d

that the same central command could resulti n quite different movements because of thei n t e r p l a y between external forces and variations i n th e i n i t i a l conditions (23). For thesame reasons, different commands coul d resu l t in the same movement .

Bernstein also suggested that control ofintegrated movement was probably d i s t r i bu t e d throughout many interact ing systemsw o r k i n g cooperatively to achieve movement .This gave rise to the concept o f a distributedmodel of motor control.

H o w does Bernstein's approach to mot o r contro l d i ffer f r o m the reflex, hierarchical,or motor program approaches presented previously? Bernstein asked questions about theorganism, in a con tinu ous ly changi ng situation. He found answers that were differentf r o m previous researchers about the naturean d cause of movement , since he asked d i fferent questions , such as: H o w does the bodyas a mechanical system influence the co nt ro lprocess? H o w do the i n i t i a l conditions affectthe properties o f the movemen t?

I n describing the body as a mechanicalsystem, Bernst ein n ot ed that we have man ydegrees of f r eedom tha t need to be cont r o l l e d . For example, we have many joints, all

of which flex or extend and many of whichcan be rotated as w e l l . Thi s complicates mo vement control incredibly. He sa id , "C oo rd in a t i o n of movement is the process o f masteri ng the redundant degrees of freedom of them o v i n g organ ism" (23) . I n other words , i tinvolves converting the body into a controllable system.

As a solution to the degrees of freedomproblem Bernstein hypothesized that hierarchical control exists to simplify the con trol ofthe body's multiple degrees of f reedom. I nt h i s way, the higher levels of the nervous sys

t em activate low er levels. Th e lo we r levels ac-: ate synerg ies, o r groups of muscles that areconstrained to act together as a u n i t . Wea n t h i n k of our movement repertoire likesentences made up of many words. Theletters w i t h i n the words are the muscles;the words themselves are the synergies,and the sentences are the actions t hemselves.

Thus, Bernstein believed that synergiesp l a y an important role in solving the degreesof freedom problem. This is achieved by cons t r a i n i n g certain muscles t o w o r k together asa u n i t . He hypoth esized that th ou gh there arefew synergies, they make possible almost thew h o l e variety o f move ments we kn ow . For example, he considered some simple synergiest o be the locomotor, postural, and respiratorysynergies.


Wha t are the limitatio ns of Bernstein'ssystems approach? As you can see, it is thebroadest o f the approaches we have discussedthus far, and since i t takes i n to account n o to n l y the cont rib utio ns o f the nervous systemt o action, but also the contributions of themuscle and skeletal systems, as w e l l as theforces of gravit y and inert ia, it predicts actualbehavior much better than previous theories.However, as it is presented today, it does n o tfocus as heavily on the interaction of the organism w i t h the environment, as do someother theories of mo to r con tro l.

C L I N I C A LI M P L I C AT I O N S

Th e systems theory has a number of i mplications for therapists. First, it stresses th eimportance of understanding the body as amechanical system. Mo ve me nt is no t solelydetermined by the output of the nervous syst e m , bu t is the o ut pu t o f the nervous systemas filt ered th ro ug h a mechanical system, theb o d y . W h e n w o r k i n g w i t h the patient whohas a cent ral nervous system de fic it, the the rapist must be careful to assess the contr ibution of impairments in the musculoskeletalsystem, as w e l l as the neural system, to overall

loss of motor control .I n our example o f Mr s. Johnson, th e

l o n g - t e r m loss o f m o b i l i t y in her arm and legw i l l pot ent iall y affect the musculoskeletal syst e m . She may show short eni ng o f the elb owflexors and loss of range of motion at the ankle j o in t . These musculoskeletal l imitationsw i l l have a significant effect on her ability torecover motor con t ro l .


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1 4 S ec tio n I T H E O R E T I C A L F R A M E W O R K

T h e systems t h e o r y suggests t h a t assess-m e n t a n d t r e a t m e n t m u s t f o c u s n o t o n l y o n

t h e i m p a i r m e n t s w i t h i n i n d i v i d u a l systemsc o n t r i b u t i n g t o m o t o r c o n t r o l , b u t t h e e f fe c to f i n t e r a c t i n g i m p a i r m e n t s a m o n gm u l t i p l esystems. A g o o d e x a m p le o f t h i s i n M r s .John-s o n i s t h e i n t e r a c t i n g i m p a i r m e n t s i n t h e m u sc u l o s k e l e t a l a n d n e u r o m u s c u l a rsystems t h a tc o n s t r a i n h e r a b i l i t y t o m o v e h e r a r m .

Dynamical Action Theory

T h e d y n a m i c a l a c t i o n t h e o r y a p p r o a c ht o m o t o r c o n t r o l ha s b e g u n t o l o o k a t t h em o v i n g p e r s o n f r o m a n e w p e rs p e ct i v e ( 2 4 -

2 6 ) . T h e p e r s p e c t i v ecomes f r o m t h e b r o a d e rs tudy o f dynamics o r syne rge t i c sw i t h i n t h ep h y s i c a l w o r l d , a n d asks t h e q u e s t io n s : H o wd o t h e p a t t e r n s a n d o rg a n i z a t i o n w e see i n t h ew o r l d come i n t o b e i n g f r o m t he i r o rde r l e s sc o n s t i t u e n t parts? A n d , h o w d o these systemschange ove r time? For exam ple , w e havet h o u s a n d s o f m u s c l e cells i n t h e h e a r t t h a tw o r k t o g e t h e r t o m a k e t h e h e a r tbeat. H o wis th i s sys tem o f thou sand s o fdegrees of f r eed o m (each c e l l w e a d d c o n t r i b u t e s a n e w d egree o f f r e e d o m t o t h esystem) r e d u c e d t o o n eo f f e w degrees o f f r e e d o m , s o t h a t a l l t h ecells

f u n c t i o n as a unit?T h i s p h e n o m e n o n , w h i c h w e se e n o t

o n l y i n h e a r t m u s c l e , b u t i n t h e p a t t e r n s o fc l o u d f o r m a t i o n s a n d t h e p a tt e r n s o f m o v em e n t o f w a t e r as i tgoes f r o m ice to l i q u i d t ob o i l i n g t o e v a p o r a t i o n , i ll u s t r a te s t h e p r i n c i p l eo f self-organization, w h i c h i s a f u n d a m e n t a ld y n a m i c a l systems p r i n c i p l e . I tsays t h at w h e na sys t em o f i n d i v i d u a l par t s comes t o g e t h e r ,i ts elements behave c o l l e c t i v e l y i n a n o r d e r e dw a y . T h e r e i s n o n e e d f o r a " h i g h e r "centeri s s u in g i n s t ru c t i o n s o r c o m m a n d s t oachievec o o r d i n a t e d a c t i o n . T h i s p r i n c i p l e a p p l i e d t om o t o r c o n t r o l suggests t h a t m o v e m e n temerges as a r e s u l t o f i n t e r a c t i n g e l e m e n t s ,w i t h o u t t h e n e e d f o r s p e ci f ic c o m m a n d s , o rm o t o r p r o g r a m s w i t h i n t h e n e r v o u s s y s t e m .

T h e d y n a m i c a l a c t i o n o rsynergetics perspective also t r i e s to find m a t h e m a t i c a l d e s c r i ptions o f these s e l f - o r g a n i z i n gsystems. C r i t i c a lf ea tu res tha t a re exam ined a re w ha t a re ca l l edt h e nonlinear properties o f t h e s y s te m ( 2 7 ) .

W h a t is n o n l i n e a r b e h a v i o r ? I t i s a s i t u a t i o n i nw h i c h , as one pa ra mete r i s a l t e red an dreaches

a c r i t i ca l va lue , t he sys t emgoes i n t o a w h o l en e w b e h a v i o r p a t t e r n . F o r e x a m p l e , as a n a ni m a l w a l k s faster an d fa s te r, t he re i s a po in t a tw h i c h , s u d d e n l y, i t s h i f t s i n t o at r o t . A s t h ean ima l con t inues to move fa s t e r, t he re i s asec-o n d p o i n t at w h i c h i t s hi f t s i n t o a g a l l o p . T h i si s s h o w n i n F i g u r e 1 . 8 .

T h e d y n a m i c a l a c ti o n a p p r o a c h doesn o t seek t o e x p l a i n these sh i f t s i n t e rms o f then e r v o u s s y s t e m c i r c u i t r y, b u t i n s t e a d s i m p l ya t t e m p t s t o describe m a t h e m a t i c a l l y t h e f u n ction o f these systems. T h i s a l lo w s t h e p r e d i ction o f t h e w a y s t h a t a g i v e n s ys t e mw i l l ac t in

d i f f e r e n t s i t u a t i o n s . O n e o f t h e p o i n t s t h a tp r o p o n e n t s o fth i s p e r s p e c t i v e p u tf o r t h i s t ha tm a n y b o d y m o v e m e n t t r a n s i ti o n s m a y b e e xp l a i n a b l e w i t h o u t i n v o k i n g a spec i f ic neu ra lp a t t e r n g e n e r a t o r t o cause t h e t r a n s i t i o n . T h et rans i t ions ins t ead may be due to the osc i l l at o r y o r p e n d u l u m - l i k e p r o p e r t ie s o f t h e l i m b st h e m s e l v e s . T h u s , t h e d y n a m i c a l a c t i o n p e rs p e ct i v e ha s d e e m p h a s i z e d t h e n o t i o n o f c o mm a n d s f r o m t he cen t ra l ne rvous sys t em inc o n t r o l l i n g m o v e m e n t a n d h as s o u g h t p h y s ic a l e x p l a n a t i o n s t h a t m a y c o n t r i b u t e t o m o v em en t cha rac te r i s ti c s a sw e l l ( 2 8 ) .

T h e d y n a m i c a l a c t i o n t h e o r y h a s r ec e n t l y been m o d i f i e d t o i n c o r p o r a t e m a n y o fBernstein's concepts. This has r e su l t ed in theb l e n d i n g o f these t w o t h e o ri e s o f m o t o r c o nt r o l i n t o a d y n a m i c a l systems m o d e l ( 2 4 ) .T h i s m o d e l suggests t h a t m o v e m e n t u n d e rl y i n g ac t ion r e su l t s f r o m t h e i n t e r a c t i o n o fb o t h p h y s ic a l a n d n e u r a l c o m p o n e n t s ( 2 9 ) .


T h i s a p p r o a c h h as a d d e d t o o u r u n d e rs t a n d i n g o f t h e elements c o n t r i b u t i n g t om o v e m e n t i t se l f, a n dserves as a r e m i n d e r t h a tu n d e r s t a n d i n g t h e n e r v o u s s y st e m i n i s o l a t i o nw i l l n o t a l lo w t h e p r e d i c t i o n o f m o v e m e n t .H o w e v e r , a l i m i t a t i o n o f t h i s m o d e l c an b et h e p r e s u m p t i o n t h a t t h e n e r v o u s s y s te m h asa f a i r l y u n i m p o r t a n t r o l e , a n d t h a t th e r e lat ionsh ip be tw een the phys ic a l sys t em of thea n i m a l a n d t h e e n v i r o n m e n t i nw h i c h i t o perates p r i m a r i l y d e t e r m i n e s t h e a n i m a l ' s b e -


10/16

Chapter O n e T H E O R I E S O FM O T O R C O N T R O L 15

a t i o n i n

a wholes an a n -point at

A s t h ets i sec

p. T h i s

; r . doess o r th e

srmplyme runc -e p red ic -

w i l l act i nnts t h a th i s t ha tay be ex- /c n e u r a lt ion . T h ee osc i l l a -t h e l i m b stion per-oo f c o m -ystem i nt p h y s i -t o m o v e -

v has re-m a n y o f

lted i n th eotor c o n -del ( 2 4 ) .t u n d e r -action o fn t s (29 ) .

o u r u n d e r -

nbut ing t om i n d e r t h a ti n i s o l a t i o nm o v e m e n t .d e l c a n b e

svstem hasi : m e r e l a-t em o f theh i c h i t o p -n ima l ' s be -

Velocity

Behavioralstate

Gallop

Trot

Walk

Figure 1 . 8 . A dynamical action model predicts discrete changes in behavior resulting from changes in the lineardynamics of a moving system. Forexample, as velocity increases linearly, a threshold is reached that results in a changein behavioral state of the moving animal from a walk, to a t rot , and a gal lop.

h a v i o r . T h e focus o f t h e d y n a m i c a l a c t i o n t h eo r y i s u sua l ly a t t he l eve l o f th i s in t e r face , no ta t u n d e r s t a n d i n g t h e n e u r a l c o n t r i b u t i o n s t othe sys t em.


O n e o f t h e m a j o r i m p l i c a t i o n s o f t h e d yn a m i c a l a c t i o n t h e o r y is t h e v i e w t h a t m o v em e n t is a n e m e rg e n t p r o p e r t y. T h a t i s , i temerges f r o m t h e i n t e r a c t i o n o fm u l t i p l e e lements t h a t s e l f - o rg a n i z e based o n c e r t a i n d yn a m i c a l p r o p e r t i e s o f t h e elements t h e mselves. T h i s means t ha t sh i f t s o r a l t e ra t ions inm o v e m e n t b e h a v i o r c a n o f t e n b e e x p l a i n e d i nt e r m s o f p h y s i c a l p r i n c i p l e s r a t h e r t h a nnec-essa r ily in t e rm s o f neu ra l s t ruc tu re s .

W h a t a re t h e i m p l i c a t i o n s o f t h i s f o rt r e a t i n g m o t o r d y s c o n t r o l i npatients? I f as c l in i c ia n s w e u n d e r s t o o d m o r e a b o u t th e p h y s

i c a l o r d y n a m i c a l p r o p e r t i e s o f t h e h u m a nb o d y, w e c o u l d m a k e u s e o fthese p r o p e r t i e si n h e l p i n g p a t i e nt s t o re g a i n m o t o r c o n t r o l .F o r e x a m p l e , v e l o c i t y c a n b e a n i m p o r t a n tc o n t r i b u t o r t o t h e d y n a m i c s o f m o v e m e n t .O f t e n , pa t i en t s a re asked t o m o v e s l o w l y i n a ne f f o r t t o mo ve sa fe ly. Ye t , t h i s app roa ch tor e t r a i n i n g f a i l s t o t ake in toaccount t h e i n t e ra c t i o n b e t w e e n speed a n d p h y s i ca l p r o p e r t i e so f t h e b o d y, w h i c h p r o d u c e m o m e n t u m , a n d

t h e r e f o r e c a n h e l p a w e a k p a t i e n t m o v ew i t hgreater ease.

I n o u r ex a m p l e o f M r s .Johnson, m o vi n g s l o w l y m a y n o t b e t h ebest s t r a t e g y f o rg e t t i n g f r o m s i t t o s t a n d , i fweakness is a p r im a r y i m p a i r m e n t . I n s t e a d , t e a c h i n g h e r t o i ncrease t h e speed o f t r u n k m o t i o n m a y a l lo w

h e r t o generate s u ff i ci e nt m o m e n t u m t osuc-ceed i n s t a n d i n g .

Parallel D istribu ted ProcessingTheory

T h e p a r a l l e l d i s t r i b u t e d p r o c e s s i n g( P D P ) t h e o r y o f m o t o r c o n t r o ldescribes h o wthe ne rvous sys t em processes i n f o r m a t i o n fo ra c t i o n . T h i s t h e o r y h a sbeen u s e d t o e x p l a i nh o w we acqu i re new sk i l l s ,since i t makes p r ed i c t i o n s a b o u t t h eprocesses used by the ne rvous sys t em d u r i n g t h e d e v e l o p m e n t o r a c

q u i s i t i o n o f n e w s k il l s ( 3 0 ) .T h e P D P t h e o r y i sconsistent w i t h c u r

r e n t k n o w l e d g e i n n e u r o p h y s i o l o g y t h a t t h ene rvous sys t em operates b o t h t h r o u g h s e r i a lp r o c e s s i n g , t h a t i s , p r o c e s s i n g i n f o r m a t i o nt h r o u g h a s i n g l e p a t h w a y, a n d t h r o u g h p a ra l l e l p r o c e s s i n g , t h a t i s , p r o c e s s i n g i n f o r m ation t h r o u g h m u l t i p l e p a t h w a y s t h a t processt h e same i n f o r m a t i o n s im u l t a ne o u s ly i nd i ff e r e n t w a y s ( 3 1 ) .


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Inputunits

Hidden units

Output units


Figure 1.9. Parallel distributed processingmodel showing three layers , the input , hidden,and output layers , hypothet ical ly equivalent to

sensory, interneuron, and motor uni ts .

Scientists h a v e b e g u n t o m o d e l n e u r a lp r o c e s s i n g u s i n g c o m p u t e r p r o g r a m s .Thesep r o g r a m s h a v e b e e n d e v e l o p e d w i t h soph i st i c a t e d c i r c u i t r y s i m i l a r t o b r a i n n e t w o r k s .T h i s is h ow the m o d e l i n g is d o n e : M o d e l scons i s t o f e lements tha t are h o o k e d t o g e t h e ri n c i r c u i t s . L i k e n e u r o n a lsynapses, each ele-m e n t can be a ffec ted i n a p o s i t i v e or nega t ivew a y b y t h e o t h e r e l em e n t s . A l s o ,l ike n e u r o n a ls y n a p t ic t r a n s m i s s i o n ,each e l e m e n t can haved i f f e r e n t m a g n i t u d e s o f e i the r pos i t iveor n e gat ive effect o n t h e n e x t e l e m e n t . Each e l e m e n tt h e n s u m m a t e s all the i n c o m i n g p o s i t i v e an d

nega t ive i n p u t s . These mo dels have beenm a d e i n t o l a y e re d n e t w o r k s c o n t a i n i n gi n p u te lemen ts , in te rm edia te p rocess ing l aye r sca l l ed h i d d e n layers , an d o u t p u t e l e m e n t s .T h i s is s h o w n i n F i g u r e 1.9. These layers aree q u i v a l e n t t o s e n s o r y n e u r o n s , i n t e r n e u r o n s ,a n d m o t o r n e u ro n s (30).

Just as i n the n e r v o u s s y s t e m , t he eff ic iency o f p e r f o r m a n c e i n th i s sys tem depend so n t w o f ac t o rs .T he f i rs t is the p a t t e r n o f c o nn e c t i o n s b e t w e e n t he l aye r s , and the s e c o n dis the s t r e n g t h of i n d i v i d u a l c o n n e c t i o n s . T heb e a u t y o f t h i s m o d e l is t h a t t h e researcher cand e t e r m i n e the m o s t e f f i c i e n t c o n n e c t i o n s t op e r f o r m a p a r t i c u l a r f u n c t i o n t h r o u g h a t e c hn i q u e ca l l ed back propagation. T h r o u g h t heprocess o f b a c k p r o p a g a t i o n , the m o s t eff ic i e n t o u t p u t f r o m the " m o t o r n e u r o n " l a y e ri s d e t e r m i n e d . I t starts w i t h a r a n d o m set ofi n p u t s to the sys tem. T h e sys tem then ca lculates the d i f f e r e n c e b e t w e e n the des i red an dthe ac tua l ac t iv i ty o f t h e o u t p u t u n i t . T h e d i f

ference b e t w e e n a c tu a l an d des i red ac t iv i ty isca l l ed the error. Th e e r r o r is used t o m o d i f yt h e c o n n e c t i o n s a m o n g t h o s e e l e m e n t s t h a th a v e p r o d u c e d the e r r o r .

T h e process is r u n o v e r an d o v e r , s i mu l a t i n g the r e p e t i t i o n o f a t a s k p e r f o r m e daga in and aga in . W i t h th i s ac t iv i ty, the systemself-corrects u n t i l i t solves the o u t p u t p r o bl e m .

T h e m o d e l has c o r r e c t l y p r e d i c t e d p r ocesses i n b o t h p e r c e p t u a l a n d a c t i o n s y st em s .F o r e x a m p l e , a PD P has been used t o s i m u l a t et h e p r o c e s si n g o fv i sua l s t i m u l i u n d e r l y i n g theab i l i t y t o r e c o g n i z e a n d i d e n t i f y l e t t e r s . In add i t i o n , the models have been used t o p r e d i c th o w we calculate the c o r r e c t j o i n t angles as-soc ia ted w i t h m o v i n g a l i m b t o a p a r t i c u l a rp o s i t i o n i n space (31) .

P D P is s o m e w h a t u n i q u e i n it s e m p h a s iso n e x p l a i n i n g n e u r a l m e c h a n i s m s associatedw i t h m o t o r c o n t r o l . T h i s t h e o r yan d its re-l a t e d m o d e l s are of grea t in te res t r i g h t n o wbecause, t h o u g h t he y are n o t exact repl icas o fthe ne rvous sys tem, they have manyof thep r o p e r t i e s t h a t are also seen i n the n e r v o u ss y s t e m . T h u s , t h e y may h e l p us u n d e r s t a n dh o w the nervous sys tem solves p a r t i c u l a rm o v e m e n t p r o b l e m s .


T h i s t h e o r y is n o t i n t e n d e d t o be an ex-act repl ica o f the ne rvous sys tem, an d t h e r ef o r e m a n y o f i t s f u n c t i o n s , su c h as b a c k p r o pa g a t i o n , do not m i m i c n e r v o u s s y s te m


12/16

Chapter O n e THEORIES O F M O T O R C O N T R O L 1 7

p H O B f o f i n fo rm a t i o n d u r i n g p e r f o r -mamac a n d l e a r n i n g .

v K A L I M P L I C A T I O N S

T l i c P D P t h e o r y is r e l a t i v e l y n e w , a n d. j r i c a l a p p l i c a t i o n s a re r e l a t i v e l y u n -

I W I I L There are several w a ys t h a t P D P m o d -: r r e g r a t e d i n t o c l i n i c a l p r a c ti c e .

: de l co u ld beused t o p r e d i c tmmm anrcrv w i t h i n t h e n e r v o u s system affectsfaaJOL T h e t h e o r y p r e d i c ts t h a tbecause o f3 K a n i a b i l i r v o f p a ra ll el r e d u n d a n t p a t h - B E T Lr r e loss o f j u s t a f e welements w i l l n o t

izz' z ;: r u n c t i o n . H o w e v e r , t h e t h e -

-acx p r e d i c t t h a t once a ce r t a in l ev e l o rstmanwkA i s a t t a i n e d , t h e loss o f a d d i t i o n a l e l-

g r - i f * , w i l l affect t h e capacity o f t h e system H T W I T h i s concept o f a t h r e s h o l d f o r

a r r ~ ; i r . r e seen i n m a n y cases o f p a -n u c 0 ; . F o r e xa m pl e, i nParkinson's disease

. j s a r i r t a l loss o f cells i n t h e basal g a n -- ; i r . r r o m s m a y n o t b e a p p a re n t

murrain a r i l th e n u m b e r o f n e u r o n s l o s tTESkrae* a c r i t i c a l t h r e s h o l d .

H i i h a u l m i p a t h w a y s suggest t he poss i -: . r. e roads t o r e c o v e r y ; t h u s , t h e

re used t o suggest approachesi - i i m i f m o t o r d y s c o n t r o l . I t suggests

Tear. MJUJMJ> m i g h t b e best w h e n r e h a b i l i t a -3D K wammmg. i s a p p l i e d t o m u l t i p l e p a t h w a y s .Wa r cii.~s t M r s . lohnson's r e h a b i l i t a t i o n

- - g r.r . r e l u d e b o t h v o l u n t a r y ' a c t i-: r i - : r r n e m i u s muscle t o h e l p

- : ~ - : : s t r en g th , bu talso p r a c t i c e , a - ro c muscle i n p o s t u r a l a n d l o c o m o t o r

Ti s k Oriented Theories

se last 5 0 years, a t r e m e n d o u s. .- r r : r r i r o n o n t h e basic s t r u c t u r e

n as emerged f r o m neuroscience_ : there is s t i l l t h e r e c o g n i t i o n t h a t

J W WM t a t b u t understand v e r y l i t t l e . T h a trr m u c h a b o u t n e u r a l c i r c u i t r y, b u t

e n e u r o n s operate together- nc : r. ~ . r r Peter Greene ( 3 2 ) , a t h e -

m t s t L Z L a o l o g i s t . suggested t h a t w h a t w a s. d : c m o t o r c o n t r o l w a s a

t h e o r y o f tasks. B y tasks, Greene w a s r e f e r r i n gt o t h e f u n d a m e n t a l p r o b l e m s t h a t t h e C N S

w a s r e q u i r e d t o solve i n o r d e r t o a c c o m p l i s hm o t o r tasks. A c c o r d i n g t o Greene, a n e x a mp l e o f a fu n d a m e n t a ltask i n h e r e n t i n m o t o rc o n t r o l i s t h edegrees o f f r e e d o m p r o b l e m d es c r i b e d b y B e r n s t e i n .

A c c o r d i n g t o Greene, a t h e o r y o f tasksw o u l d h e l p neuroscientists f i n d observableb e h a v i o r s t o measure t ha t a r e r e l evan t t o t hetasks t h e b r a i n i s c a ll e d u p o n t o p e r f o r m .T h u s , a n u n d e r s t a n d i n g o f m o t o r c o n t r o l r eq u i r e s m o r e t h a n a n u n d e r s t a n d i n g o f c ir c u i t s .I t r e q u i re s a n u n d e r s t a n d i n g o f t h e u n d e r l yi n g p r o b l e m s t h e C N S i s r e q u i r e d t osolve i n

o r d e r t o a c c o m p l i s h m o t o rtasks. A t a s k - o r ie n t e d a p p r o a c h t o t h e s t u d y o f m o t o r c o n t r o lw o u l d p r o v i d e t h e basis f o r a m o r e coherentp i c t u r e o f t h e m o t o rsystem. Greene suggestst h a t once t h e essentials o f a task have beeno r g a n i z e d i n t o acoherent p i c t u r e , i t becomespossible t o k n o w less a n d u n d e r s t a n d m o r e .

A n a d a p t a t i o n o f Greene's t h e o r y o ftasks has been e l a b o r a te d b y G o r d o n ( 3 3 ) a n dH o r a k ( 3 4 ) . T h e t a s k - o r i e n t e d a p p r o a c h p r esented b y G o r d o n a n d H o r a k , h o w e v e r , d ef ines task f r o m a m o r e f u n c t i o n a l p e r s p ec t iv e .T h a t i s, w h a t c o n t r o lissues a r e i n h e r e n t i n t h ea c c o m p l i s h m e n t o f f u n c t i o n a ltasks i n m e a ni n g f u l e n v i r o n m e n t s ? T h e t a s k - o r i e n t e d a pp r o a c h i s based o n t h e r e c o g n i t i o n t h a t t h eg o a l o f m o t o r c o n t r o l is t h e c o n t r o l o f m o v em e n t t o a c c o m p l i s h a p a r t i c u l a rtask, n o t t h ee l a b o r a t i o n o f m o v e m e n t f o r t h esake o f m o vi n g alone (except i n u n u s u a l cases such a sdance). T h e t a s k - o r i e n t e d a p p r o a c hassumest h a t c o n t r o l o f m o v e m e n t is o r g a n i z e da r o u n d g o a l - d i r e c t e d f u n c t i o n a l b e h a v i o r ssuch a s w a l k i n g o r t a l k i n g .


A l i m i t a t i o n o f a t a s k - o r i e n t e d t h e o r y o fm o t o r c o n t r o l is a l a c k o fconsistent agree-m e n t a b o u t w h a t t h e fu n d a m e n t a ltasks o f t h eC N S a r e. I n a d d i t i o n ,scientists d o n ' t a l w a y sagree o n w h a t t h e essential elements b e i n gc o n t r o l l e d w i t h i n a task a r e. F o r e x a m p l e ,some scientists s t u d y i n g p o s t u r a l c o n t r o l b el i e v e t h a t c o n t r o l l i n ghead po s i t i o n i s t he e s-


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s e n t ia l g o a l o f t h e p o s t u r a l s y s t em . H o w e v e r ,o t h e r scientists s t u d y i n g p o s t u r a l c o n t r o l b el i e v e t h a t c o n t r o l l i n gcenter o f mass p o s i t i o nto achieve b o d y s t a b i l i t y is t h eessential g o a lo f p o s t u r a l c o n t r o l .

C L I N I C A L I M P L I C A T I O N S

T h e m o s t s i g n i f ic a n t i m p l i c a t i o n o f at a s k - o r i e n t e d t h e o r y o f m o t o r c o n t r o l i s th econcept t h a t m o t o r r e t r a i n i n gneeds t o focuso n essential f u n c t i o n a l tasks. I t suggests t h ei m p o r t a n c e o f u n d e r s t a n d i n g t h e r o l e o f p e r

c e p t u a l , c o g n i t i v e , a n d a c t i o nsystems in acc o m p l i s h i n g these tasks. O n e o f t h e c h a llenges fo r c l in i c i ans i s t o ana lyzeessentialc o m p o n e n t s o f e v e r y d a ytasks we a re ca l l edu p o n t o r e t r a i n . T h i s r e q u i r e s m o r e t h a n a nu n d e r s t a n d i n g o f th e b i o m e c h a n i c a lfeaturesof the t a sk , t ha t i s , t he moto rstrategies usedt o a c c o m p l i s h t h e t a s k . I talso r e q u i r e s u nd e r s t a n d i n g t h e p e r c e p t u a l basis f o r a c t i o n ,a n d t h e c o g n i t i v e c o n t r i b u t i o n s t o a c t i o n .

I n o u r e x a m p l e o f M r s .Johnson, w h a tare the essential tasks t h a t w i l l b e r e t r a i n e dd u r i n g t h e course o f h e r recovery? H o w w i l l

these tasks b e r e t ra i n e d ? H o w m u c h t im ew i l lt h e c l i n i c i a n s p e n d o n r e t r a i n i n g f u n c t i o n , a so p p o s e d t o w o r k i n g o n some o f t h e essentialelements c o n t r i b u t i n g t o f u n c t i o n , s u c h ass t r e n g t h a n d r a n g e o f m o t i o n ? H o w ca n t h ec l i n i c i a n ensure t h a t tasks l e a r n e d i n a c l i n i c a ls e t t i n g w i l l b e r e t a i n e d w h e n M r s .Johnsonfinally r e t u r n s t o h e r o w n home?

Ecological Theory

I n t h e 1960s, i n d e p e n d e n t o f t h e r esearch i n p h y s i o l o g y , a p s y c h o l o g i s t n a m e dJames G i b s o n w a s b e g i n n i n g t o e x p l o r e t h eway i n w h i c h o u r m o t o r systems a l l o w u s t oi n t e r a c t m o s t e f f e c t i v e lyw i t h t h e e n v i r o n m e n ti n o r d e r t o p e r f o r m g o a l - o r i e n t e d b e h a v i o r( 3 5 ) . H i sresearch f o c u s ed o n h o w w edetecti n f o r m a t i o n i n o u r e n v i r o n m e n t t h a t is r e lev a n t t o o u r a c t i o n s , a n d h o w w e u se t h i s i nf o r m a t i o n t o c o n t r o l o u r m o v e m e n t s ( se e F i g .1.10).

T h i s v i e w w a s e x p a n d e d b y t h e s t u d e n t so f G i b s o n ( 3 6 , 3 7 ) a n dbecame k n o w n as the

Figu re 1 .10 . Ecological approach s t resses the interac-t ion between the individu al and the environ men t . Theindividu al act ively explores the environm ent , whi ch inturn supports the individual ' s act ions.

e c o l o g ic a l a p p r o a c h t o m o t o r c o n t r o l . I t s u ggests t h a t m o t o r c o n t r o l e v o l v e d s o t h a t a n im a l s c o u l dcope w i t h t h e e n v i r o n m e n t a r o u n dt h e m , m o v i n g i n i t e f fe c ti v e ly i n o r d e r t ofindf o o d , r u n a w a y from p r e d a t o r s , b u i l d she l t e r,a n d e v en p l a y ( 2 8 ) . W h a t is n e w a b o u t t h i sapproach? I t was r ea l ly the first t ime that re

searchers began f o c u s i n g o n h o w actions aregeared t o t h e e n v i r o n m e n t . A c t i o n s r e q u i r ep e r c e p t u a l i n f o r m a t i o n t h a t isspecific t o a des i re d g o a l - d i r ec t e d a c t i o n p e r f o r m e dw i t h i n aspecific e n v i r o n m e n t . T h e o r g a n i z a t i o n o f a ction is specific t o t h e task a n d t h e e n v i r o nm e n t i n w h i c h t h e task i s b e i n g p e r f o r m e d .

Whereas m a n y p r e v i o u s researchers h a dseen t h e o rg a n i s m a s a s e n s o r y - m o t o r s y s t em ,G i b s o n stressed t ha t i t was no t sensa t ion pe rse t h a t w a s i m p o r t a n t t o t h e a n i m a l , b u t p e rc e p t i o n . S p e c i f i c a ll y, w h a t isneeded i s the perc e p t i o n o f e n v i r o n m e n t a l fa c to r s i m p o r t a n t t o

t h e t as k . H e s t a t e d t h a t p e r c e p t i o nfocuses o nd e t e c ti n g i n f o r m a t i o n i n t h e e n v i r o n m e n tt h a t w i l l s u p p o r t t h e actions necessary t oachieve t h e g o a l . F r o m a n e c o l o g i c a lperspec-tive, i t is i m p o r t a n t t o d e t e r m i n e h o w a n o rg a n i s m detects i n f o r m a t i o n i n t h e e n v i r o nm e n t t h a t i s r e l e v a n t t o a c t i o n , w h a tf o r m t h i si n f o r m a t i o n takes, a n d h o w t h i s i n f o r m a t i o nis u s e d t o m o d i f y a n d c o n t r o l m o v e m e n t ( 2 8 ) .

I n s u m m a r y, t h e e c o l o g i c a l p e r s p e c t iv eh a s b r o a d e n e d o u r u n d e r s t a n d i n g o f n e r v o u s


14/16

Chapter O ne T H E O R I E S O F M O T O R C O N T R O L 1 9

mnction f r o m t h a t o f a s e n s o r y - m o t o r

- - g t o e n v i r o n m e n t a l v a r ia b le s ,K o f a p e r c e p t i o n - a c t i o n s y st e m w h i c h

m r l jres t h e e n v i r o n m e n t t o sa t is f y i t s

^ C 7 A ~ O X S

A d m o u g h t h e e c o l o g i c a l a p p r o a c h h a sm : : i : _ r 1 -mowledge s ign i f i can t l y c on -

- - z i n t e r a c t i o n o f t h e o r g a n i s m a n dt , i t h a s t e n d e d t o g i v eless

t o t h e o r g a n i z a t i o n a n d f u n c t i o n o fs y s t e m , w h i c h l e d t o t h i s i n t e r

s ' t he research emphasis hast h e n e r v o u s sy s t e m t o t h e o rg a n -

n t i n t e r f a c e .

I M P L I C A T I O N S

-. - L :: : D.n t r ibu t ion o f th i s v i e w is inm e i n d i v i d u a l as an ac tive exp lo r e r

: - n m e n t . T h e a c t iv e e x p l o r a t i o n o ftu ( ; - ; m e e n v i r o n m e n t i n w h i c h t h e p e r f o r m e d a l lo w s t h ei n d i v i d u a l t o d e -c - ways to accompl i sh a t a sk .

i s i m p o r t a n t n o t o n l y i n th e w a y

m o v e m e n t s t o a c c o m p l i s h a ta s k,- s _ me way we use ou rsenses d u r i n g

- r m i n t p a r t o f t r e a t m e n t i s h e l p -o h n s o n e x p l o r e t h e p o s s i b i l i t ie s f o r

m m m , i f u n c t i o n a ltask i n m u l t i p l e w a y s .d e v e l o p m u l t i p l e a d a p t i v e s o -

- : _ : : m p d s h i n g atask r e q u i r e s t h a tsent e x p l o r e a r a n g e o f p o s s i b l e w a y s t o-~ . . - - i t a sk , and d i scover th ebest so - f cr t h e m , g i v e n th e p a t i e n t ' s s et o fl i mns.. I n M r s . Johnson's case, t h i s a b i l i t y t o

rjsoorcr a r a n g e o f s o l u t i o n s is h a m -_ r e d u c e d a b i l i t y t o m o v e , i n a c c u r a t e

y m n v . a n d p o s si b l e c o g n i t i v e l i r n i t a -

H T H E O R Y O F M O T O R

C O N T R O L I S B E S T ?

* h k h m o t o r c o n t r o l t h e o r ybest n s m e c u r r e n t th e o r e t i c a l a n d p r a c t i c e

: .-mists? W h i c h is t h e m o s t c o m

p l e te t h e o r y o f m o t o r c o n t r o l , t h e o n e t h a t

r e a l l y p r e d i c t s t h e n a t u r e a n dcause o f m o v em e n t a n d is consistent w i t h o u r c u r r e n tk n o w l e d g e o f b r a i n a n a t o m y a n d p h y s i o l o g y ?

A s y o u n o d o u b t c a n a l r ea d y se e, t h e r ei s n o o n e t h e o r y t h a t ha s i t a l l . W e b e l i e v e t h ebest t h e o r y o f m o t o r c o n t r o l is o n e t h a t c o mbines elements f r o m a l l o f t h e p r e s e n t e d t h eo r i e s. A c o m p r e h e n s i v e , o r i n t e g r a t e d , t h e o r yrecognizes t h e elements o f m o t o r c o n t r o l w ed o k n o w a b o u t a n dleaves r o o m f o r t h e t h i n g sw e d o n ' t . A n y c u r r e n t t h e o r y o f m o t o r c o nt r o l i s in a sense unfinished, since t h e r e m u s ta l w ay s b e r o o m t o r e v is e a n d i n c o r p o r a t e n e w

i n f o r m a t i o n .M a n y p e o p l e have been w o r k i n g t o d e

v e l o p a n i n t e g r a t e d t h e o r y o f m o t o r c o n t r o l( 2 4 , 3 4 , 3 8 ^ 3 ) . I n some cases, as theor i e sa re m o d i f i e d , n e wnames a re app l i ed . As a r esu l t , i t becomes d i f f i c u l t t o d i s t i n g u i s h a m o n ge v o l v i n g t h e o r i e s . F o r e x a m p l e ,systems, d yn a m i c a l , d y n a m i c a l a c t i o n , a n d d y n a m i c a l a ction systems a re a l l t e rm s tha t are o f t e n u sedi n t e r c h a n g e a b l y.

I n p r e v i o u s a r t i c l e s w e ( 4 0 , 4 2 )havec a ll e d t h e t h e o r y o f m o t o r c o n t r o l o n w h i c hw e base o u r research a n d c l i n i c a l p r a c t i c e asystems approach. W e have c o n t i n u e d t o u s et h is n a m e , t h o u g h o u rconcept o f systems t h eo r y d i f f e r s f r o m Bernstein's systems t h e o r ya n d ha s e v o l v e d t o i n c o r p o r a t e m a n y o f t h econcepts p r o p o s e d b y o t h e r t he o r ie s o f m o t o rc o n t r o l . I n t h i s b o o k w ew i l l c o n t i n u e t o r e f ert o o u r t h e o r y o f m o t o r c o n t r o l as asystemsapproach. T h i s a p p r o a c h argues t ha t i t i s c r i ti c al t o r e c o g n i z e t h a t m o v e m e n temergesf r o m a n i n t e r a c t i o n b e t w e e n t h ei n d i v i d u a l ,t h e t as k , a n d t h e e n v i r o n m e n t i n w h i c h t h etask i s b e i n g c a r r i e d o u t . T h u s , m o v e m e n t i sn o t so l e l y t h e r e s u l t o fmuscle-specific m o t o rp r o g r a m s , o r s t e r e o t y p e dreflexes, b u t r e s u l t sf r o m a d y n a m i c i n t e r p l a y b e t w e e n p e r c e p t u a l ,c o g n i t i v e , a n d a c t i o nsystems.

A c t i o n systems a r e d e f i n e d here t o i nc l u d e b o t h t h e n e u r o m u s c u l a raspects a n d t h ep h y s i ca l o r d y n a m i c p r o p e r t i e s o f th e m u s c ul o s k e l e t a l s y s te m i t s e lf . T h e o rg a n i z a t i o n a lp r o p e r t i e s o f t h e s y s t ememerge as a f u n c t i o no f t h e task a n d th e e n v i r o n m e n t i n w h i c h t h etask is p e r f o r m e d .

1


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T h i s t h e o r e t i c a l f r a m e w o r kw i l l be usedt h r o u g h o u t t h i s t ex t , and i s t hebasis f o r c l i ni c a l m e t h o d s f o rassessing a n d t r e a ti n g m o t o rd y s c o n t r o l i n t h e p a t i e n tw i t h n e u r o l o g i c a lp r o b l e m s . We have f o u n d t h e t h e o r y u s e f u l i nh e l p i n g us to generate research questions a n dhypotheses a b o u t t h e n a t u r e a n d cause o fm o v e m e n t .

SUMMARY

1 . The study of motor control is the study of thenature and cause of mov ement . I tdeals withboth s tabi l iz ing the bod y inspace, that is, pos

tural and balance control , and with m o v i n gthe body inspace.2. The specific practices used to assess and treat

the pat ient with mo tor dysco ntrol are determ i n e d by under lyin g assumptions about thenature an d v cause of movement that comefrom specific theories of moto r con t ro l .

3 . A theory of motor con trol is a group ofabstractideas about the nature andcause of movement . Theories prov ide : (a) a f r amework fo rinterpreting behavior ; (b) a guide for c l inicalaction; (c) new ideas; and id) w o r k i n g hypotheses fo r assessment and t reatment .

4 . Rehabi l i ta t ionpractices reflect the theories, or

basic ideas, w e have about the cause and nature of funct ion and dysfunct ion.5. In thischapter w e have reviewed many motor

con t ro l theories that have an impact on ourperspective regardingassessment and treatment , including the reflex theory, hierarchicaltheory, motor pro gram ming theor ies ,systemstheory, dynamical act ion theory, paral le l d istributed processing theo ry, task-oriented theor ies , and ecological theory.

6. In this text we use oursystems theory approach as the foundat ion for many cl inical appl icat ions . According to this theory, movement arises f rom the interaction ofmul t ip l e

processes, including (a) perceptual, cognitive,and motor processes wi th in th e individual ,and (h) interactions between theindividual ,th e task, and the env i ronment .

R E F E R E N C E S

1 . Rosenbaum D . H u m a n m o t o r c o n t r o l . N e wYork: AcademicPress, 1 9 9 1 .

2 . Brooks VB. The neura lbasis of mo to r cont r o l . New York : Oxford Unive r s i tyPress.

1 9 9 0 .3 . Shepard K. Theory : cr i ter ia , importance ar.c

impac t . In : Con tempora rymanagement c :moto r con t ro l p rob lems :proceedings of theI I Step Conference. Alexandr i a , VA: APTA.1991:5-10.

4 . Ro ths t e in JM ,Echternach JL. Hypothesis-or iented a lg or i th m for c l inic ians: a meth odfo r evaluat ion and t reatment planning.PhysTher 1986;66:1388-1394.

5. Sherr in gton, C. The integrat ive act ion of thenervous system. 2nd ed. New Haven:YaleUnivers i ty Press, 1 9 4 7 .

6. Gal l is te l , CR . The organizat ion of act ion: anew synthesis. Hil lsdale , N J: Lawrence Eri -baum, 1980 .

7. Taub E, Berman AJ. Mo vem ent and learningin th e absence o f sensory feedback. I n : Freed-man SJ, ed. The neurophysiology of spatiallvo r i en ted behavio r. Ho me wo od: DorseyPress, 1968: 173-192 .

8. Foerster O . T h e m o t o rcortex in man in thel i gh t o f H u g h l i n g sJackson's doctr ines . In:P a y t o n O D ,H i r t S, New ma n, R, eds.Scientific bases for neurophysiologicapproaches totherapeutic exercise. Philadelphia: FA Davis .1977:13-18.

9. Magn us R A n i m a l posture (Croonian lect u re ) . Proc Roy Soc Lo nd on1925;98:339.

10 . Magnus R Some results of studies in thephysiology of posture .Lancet 1926;2:531-585 .

1 1 . Schaltenbrand G. The deve lopment o f hum an mot i l i t y and motor dis turbances . ArchN e u r o l Pyschiatr 1928;20:720-730.

1 2. Weisz S. Studies i n equ i l i b r ium reaction. JN e r v M e n t D i s 1938;88:150-162.

1 3 . Gesell A, Amat ruda CS . Deve lopmenta l d iagnosis. 2nd ed . New York : Pau l B. Hoeber.1 9 4 7 .

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Reading for MRL Course Theories of Motor Control

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