Central Pattern Generation

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Central Pattern Generation

• By
• Andrew Zayachkivsky

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Introduction

• Central pattern generators are neuronal circuits
  that when activated can produce rhythmic patterns
  such as walking, breathing, flying, and swimming
  in the absence of sensory or descending inputs
  that carry specific timing information

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CPG History

• 90 Years ago Brown suggested that muscles during
  walking are controlled by neurons that inhibited
  each other
• Spinal reflex dominant theory for years
• First experiments to cut off all sensory feedback
  deafferented locust could generate rhythmic
  flight motor patterns in response to non-rhythmic
  stimulation

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Reflex vs. CPG
Marder and Bucher, 2001
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Fictive Motor Patterns

• Fictive motor patterns motor patterns which
  would drive motor movement if the muscles were
  present
• CPGs can produce patterns without receiving
  extrinsic timing information
• Sometimes neuromodulators supplied by descending
  pathways are needed to activate CPGs

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in Vivo vs. in Vitro

• In many cases in vitro setups generate rhythms
• However, complexity might be lost (breathing,
  coughing, gasping, sighing, vomit uses same
  muscles, but in different sequences).
• Same neurons are involved in several different
  pattern generation circuits

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Crusteacen stomatogastric nervous system
Marder and Bucher, 2001
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Locust CPG
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Intrinsic Properties of CPG neurons
- Endogenous Bursting oscillatory, provide
timing inputs for circuits - Bistable generate
plateau potentials, can be triggered by
depolarizing pulse, terminated by hyperpolarizing
pulse - Posinhibitory rebound happens when neuron
fires right after inhibiton, crucial for
timing of their firing - Spike adaptation
decrease in frequency of firing during a constant
depolarization.
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Mechanisms of CPG production

• Two mechanisms
• - Pacemaker neurons
• - Synaptic connections
• Pacemakers found in rhythmic networks which act
  continuously
• Synaptic connections ex. Reciprocal inhibition
• - used in reciprocal inhibition via. Spike
  adaptation

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Mechanisms of CPG production
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Modulation of CPGs

• Examples of modulation
• -Running, Walking, Swimming styles
• Pathways of modulation in lobster STG
• - Descending fibers from higher centers
• - Fibers ascending from peripheral sens.
  neurons
• - Hormones from neurosecretory structures

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Modulation

• Modulators alter both synaptic strength and
  intrinsic membrane properties
• Change frequency and phasing of the units

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Coupling and Coordination the bigger picture

• One CPG can provide many outputs depending on
  frequency/phase relationships under various
  modulations
• Switches from one CPG to others
• Reconfiguration of same networks

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Stick insect example
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Spinal Cord implications in Humans

• 1st approach enchance regeneration of injured
  areas
• 2nd approach exploiting uninjured portion below
  the lesion
• Treadmill training reconditions CPGs to
  pre-injury levels

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