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BS-2066 Lecture 15: Pattern generationand neuromodulation
Volko Straub Room: MSB 332
email: [email protected]
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Overview
Mammalian locomotion and sensory feedback
Locomotion control Some general principles
Adapting neuronal controllers to specific needs
How hardwired are CPGs? Some lessons from the
stomatogastric system in lobsters
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Models for stepping CPG
basic rhythm is transformedby pre-motor interneurons
also strongly affected bysensory feedback from
primary afferentsdeafferentiation of hind limbcauses impairment ofstepping movements
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Role of sensory feedback
fictive steppingrhythm can be
entrained tofrequency of artificialhip movements
hip position isimportant for stance-swing transition
spinal cat walks ontreadmill
ipsilateral leg issupported byexperimenter, whilst
contralateral leg steps ipsilateral leg onlysteps when leg isextended backwards
Timing of steps is crucially dependent on sensory afferent inputs
CPG is responsible for generation of muscle synergies for the stance andswing phase
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Sensory feedback is shaped by CPG activity
Ia afferent fibres carry information from muscle stretch receptors (e.g.
knee jerk reflex)
passive movement ofankle joint activates Iaafferent fibres ingastrocnemius muscle
same Ia afferent fibres are notactivated during anklemovements in swing phase,but are active during stance
phase
stretch reflexes are active to counteract passive movement oflimb/muscle
stretch reflexes are suppressed during active movement when their
action would counteract the desired movement
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Hierarchy of locomotion control
1. Basic pattern/rhythm isgenerated by central patterngenerator
2. Higher motor centres controldrive for motor activity, etc.
3. Sensory feedback/posturalreflexes shape basic pattern
4. Higher motor centres receiveand integrate feedback fromCPG and sensory inputs
Central
PatternGenerator
HigherControl
EffectorOrgans
Environment
Central Feedback(Efference Copy)
ReflexFeedback
Sensory Input/Environmental
Feedback
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Adapting CPGs to different needs
Altering excitability of CPGs:
can alter direction of wave propagation in oscillator chain e.g. swimming in lamprey and tadpole forward and backward
swimming
Altering phase relationship between CPGs:
does alter overall pattern of motor activity e.g. locomotion in mammals walk, trot, pace, gallop
Sensory feedback:
shapes motor pattern, helps to adjust motor pattern to external
conditions e.g. stepping in mammals, locust flight
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One CPG Multiple patterns?
Cat stepping and scratching
use same muscles motor patterns have many features in common
flexor extensor
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One CPG One behaviour? Motor systems can be used for multiple behaviours
e.g. cat: walking, scratching
CPG 1 CPG 2
Behaviour 1 Behaviour 2
motor system
separate CPGs forspecific behaviours
CPG
Behaviour 1 Behaviour 2
motor system
single CPG that canbe re-configured for
specific behaviours
or
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The stomatogastric system in crustaceansA model for network reconfiguration
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The stomatogastric system An overview
pylorus
gastric millcardiacsac
stomatogastric ganglion (STG) ~30 neurons controls gastric mill and pyloruscommissural ganglia (CoG) ~400 neuronsesophageal ganglion (OG) ~18 neurons
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Pyloric and gastric mill CPGs
stomatogastric CPGs consist
of motor neurons rhythm generation is due to
combination of endogenousbursting properties andnetwork interactions
Pyloric CPG Gastric mill CPG
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Extensive synaptic interactions exist betweenpyloric and gastric mill CPGs
provisional network diagram showing connections between the two CPGs
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Pyloric and gastric mill rhythm rhythm generation in pyloric and gastric mill CPG appears to be
independent of each other
cycle periods: pyloric rhythm: ~1 s gastric mill rhythm: 5-10 s
pyloricrhythm
ga
stricmillrhythm
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Neuron switching between CPGs
Lateral posterior gastric (LPG) and lateral gastric (LG) neurons can
switch between pyloric rhythm and gastric mill rhythm neurons can entrain and reset both rhythms neurons actively takepart in generation of both rhythms (activity is not just entrained to therhythm)
gastric mill
inactive
gastric mill
active
pdn: pyloric dilator nervePD: pyloric dilator neuronDG: dorsal gastric neuron
gastric mill
inactive
gastric mill
active
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Modulatory factors in stomatogastric ganglion stomatogastric ganglion is located in dorsal artery anterior to heart
exposed to multitude of neurohormones secreted by pericardial organ into
the blood stream also receives large number of inputs from descending neuromodulatory
neurons and ascending sensory neurons
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Amines reconfigure pyloric CPGDopamineControl
OctopamineSerotonin
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Fusion of pyloric and gastric mill CPGs
pyloric suppressor (PS) neurons: pairof modulatory neurons located in
inferior ventricular nerve (ivn) neurons project to stomatogastric
ganglion activity leads to temporary fusion of
pyloric and gastric mill rhythm andgeneration of new rhythm
control 5s after PS stimulation 190s after PS stimulation
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Fusion of pyloric and gastric mill CPGs
fused CPG has
different cycle toindividual CPGs
CPG fusion altersphase relationshipbetween neurons
Conclusion: PS activity leadsto complete reconfiguration ofpyloric and gastric mill CPGs
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re-configuration of pyloric andgastric mill networks by pyloricsuppressor neuron also affectsoesophageal networks
not all elements of original
networks participate in new
network
Fusion of pyloric and gastric mill CPGs
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Summary
CPGs are not hardwired
single CPG can control multiple behaviours
various mechanisms have evolved to adapt CPGs to changingdemands:
modulation of CPG excitability
altering phase relationship between neurons and oscillators sensory feedback
modulation of connections within a CPG
switching neurons between CPGs
re-configuration of CPGs
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Lab Practical 3 Motor Pattern Generation Friday, 9th December + 16th December
Aim: Analyse a neuronal network that controlsswim pattern generation in a computer-simulated fish
preparation: read document Preparation for Lab Practical 3
available on Blackboard
revise lectures on motor pattern generation, inparticular experimental methods foridentification of CPG interneurons, e.g.activation and suppression experiments,resetting experiments
bring a copy of the document Lab Practical 3
Manual (available on Blackboard) to the lab
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40v(.5)cell1.soma.v(.5)
Left flexor motor neuron
Right flexor motor neuron