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BS-2066 Lecture 15: Pattern generationand neuromodulation

Volko Straub Room: MSB 332

email: vs64@le.ac.uk

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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