1 JHU BME 580.422 Biological Systems II Adaptation of Visuomotor Maps Disorders of parietal cortex Reza Shadmehr.

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JHU BME 580.422 Biological Systems II

Adaptation of Visuomotor Maps

Disorders of parietal cortex

Reza Shadmehr

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xh

Proprioceptive state of the body: arm, head, and eye positions

xt

xa q fq

hand location in fixation coordinates

Target location in fixation coordinates

q

Displacement vector in fixation coordinates

Displacement vector in proprioceptive coordinates

Force (motor output)

Schematic of the computations involved in reaching

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1 1 2 1 2

1 1 2 1 2

1

2

1 2

1 2

1 1 2 1 2 2 1 2

1 1 2 1 2 2

cos( ) cos( )

sin( ) sin( )

sin( ) sin( ) sin( )

cos( ) cos( ) co

x

y

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a t h

x x

y y

p l q l q q

p l q l q q

q

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dp dp

dq dqdJ

dp dpd

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l q l q q l

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s( )

a

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d

d

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4

A

C

B0.5 sec

PPC cell

Control Task

Delay Task

Delay Task

D

F

E

0.5 sec

Somatosensory cortex cell

Control Task

Delay Task

Delay Task

PPC neurons encode target of intended movement during the delay period

Crammond and Kalaska 1989

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PPC neurons encode target of intended movement even after it disappears

Kalaska JF Can J Physiol Pharmacol 1996

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…left of fixation

Delayed pointingDelayed pointing with intervening saccade

Activation area when the remembered target is to the right of fixation

Human PPC neurons code for target location in fixation centered coordinates

Medendorp et al. 2003

Left cortex Right cortex

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Deltoid muscle

Primary motor

cortex cell

Posterior parietal cortex

cell (area 5)

Opposing load No load Assisting load

500 ms

10

0 im

p/s

PPC neurons encode target location and not the forces necessary to reach that target

Kalaska JF (1988)

Kal

aska

et a

l. J

Neu

rosc

i 198

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Experiment: rotate each eye by 180o. After 4-5 months, no sign of adaptation.

“When the piece of meat was moved back and forth in the water several centimeters above and a little to one side of the animals, they tilted their heads downward on that side and began to move toward the bottom of the aquarium. Even though the newts happened to be resting on the bottom when the lure was thus waved above them, they cocked their heads down under them and began pushing about among the pebbles of the bottom with the nose and forefeet. If the lure was placed below the animals, the head and forebody were tilted upward and the newts started toward the surface.”

Newts show an inability to adapt to radical changes in the optics of vision

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A

B

Day 3 Day 34

La

ten

cy (

s)

Pre- Days of reversing Post-

C

Primates adapt to radical changes in optics of vision

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xee

xtxdv

1

2

c1

c2

target

camera

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A B

Wedge prisms: rapid adaptation and equally rapid de-adaptation indicates short-term changes in existing networks

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With extensive training, throwing with wedge prisms can become a skill.

This indicates formation of a new

map for the prism and the ability to switch

on context.

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Model Copy

Patients with lesion in the right hemisphere may exhibit neglect of the left visual space

Marshall JC & Halligan PW (1995) Nature 373:521

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Committeri, G. et al. Brain 2007 130:431-441

Neglect of the extra-personal and personal space

Test for neglect of extra-personal space: Line bisection test, figure copying, reading a sentence.

Test for neglect of personal space: use a comb, use a razor to shave the face, use a lipstick.

Neglect of extra-personal space: lesion of the right frontal lobe, ventral premotor cortex

Neglect of personal space: lesion of the right inferior parietal cortex

STG: superior temporal gyrus

MFG: medial frontal gyrus

WM: white mater

SMG: supramarginal gyrus

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Prism glasses produce after affects that improves the sense of “straight ahead” in neglect patients

Rossetti Y. et al. (1998) Nature 395:166

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Prisms Controls

original

pre-

post-

late

Prism glasses produce after affects that reduce the neglect observed in PPC lesions

Rossetti Y. et al. (1998) Nature 395:166

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Apraxia

Apraxia is an inability to perform skilled movements, particularly tool use, in the absence of elementary motor deficits (weakness, normal posture or tone).

It is most commonly associated with damage to the parietal cortical areas of the left hemisphere.

When the patient is asked to demonstrate use of a screwdriver, the patient may position his hand as if holding a pen. When given a partially driven nail into a piece of wood, and a collection of tools, they may select a scissor to drive the nail rather than a hammer.

In performing a task that requires a sequence of actions, these patients may have difficulty in putting the acts in the proper order. For example, demonstrate how to prepare a letter and envelope for mailing.

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Understanding actions of others: the mirror neuron system

Social skills and theory of mind: the awareness that other people have beliefs and desires as we do, but different from our own, and that these beliefs and desires guides their actions. By observing their actions, we can guess their goals and intentions.

19 Fogassi et al. (2005) Science 308:662-667.

D

20 Fogassi et al. (2005) Science 308:662-667.

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Actions are planned in fixation centered coordinates:Position of the hand and the target are represented in terms of their

location with respect to the fixation.

Neurons combine proprioceptive information with visual information using a gain field.

Movements are planned in terms of goals, not in terms of detailed forces.

Lesion of the right parietal cortex can result in neglect. Lesion of the left parietal cortex can result in apraxia.

Mirror neurons might provide a mechanism through which we understand the intention of others.

Summary of the posterior parietal cortex