rhythmic CPG circuits

rhythmic motor patterns

• a repeating, time-structured movements, e.g. swimming, walking, breathing

• consists of alternative phases, e.g. left-right, flexor-extensor

• continues once started without patterned sensory input

• typically generated by CPG circuits

central pattern generators (CPGs)

• neural circuits that can produce rhythmic motor output without requiring patterned sensory input

• output consists of alternating rhythmic neural activity - bursts of APs rather than single spikes

• once initiated, rhythmic activity can persist for multiple cycles without patterned input

  • though sensory feedback often shapes stability and timing

• rhythmic activity reflects underlying oscillatory dynamics that can arise from different circuit configurations

intrinsic bursting

intrinsic neuronal properties alone can generate oscillatory bursting

• no synaptic input required

• bursts persist when neuron is isolated

• oscillations generated by ion channels alone

membrane conductance

changing ion channel activity modifies intrinsic bursting properties

• slow depolarising current sustains bursts via plateau potentials

• repolarising current terminates bursts and sets rhythm timing

clione swimming

rhythmic DV wing movements for swimming

• pacemaker driven

• identifiable neurons show intrinsic bursting that contributes to rhythm generation

• pacemaker rhythm emerges from inhibitory coupling

• out of phase activity

mammalian breathing

2-phases, inspiration and expiration

• ~1,000-3,000 neurons provide rhythmic drive to inspiratory motor neurons

• recurrent excitatory coupling within a subset of neurons

• excitatory coupling- in-phase activity during inspiration

• inspiration terminated due to spike freq adaptation and synaptic depression

network driven rhythms

rhythmic activity can emerge from circuit interactions, even when individual neurons are not intrinsically rhythmic

• reciprocal inhibition (out of phase)

• reciprocal excitation (in phase)

tritonia swimming

rhythm emerges from distributed network interactions involving both excitation and inhibition

• synaptic depression sets the timing window in which PIR can trigger the next burst

lymnaea feeding

activated by a command-like interneuron, slow oscillator, which engages the network through reciprocal excitatory connections

• three phase rhythm

• rhythm emerges from circuit interactions

• inhibitory connection supress neurons associated with other phases to ensure clean sequencing

arthropod digestion

two phase rhythm in two main functional regions

• controlled by ~30 neurons in the stomatogastric ganglion

lobster stomatogastric (STG)

network and pacemaker driven, generated rhythmic motor output for digestion

• three phase rhythm

• network driven CPG with pacemaker kernel

• some intrinsically bursting neurons, some conditionally bursting neurons

half centre organisation

reciprocal inhibition forms a simple oscillating network

coordinating multiple CPGs

locomotion can be generated by multiple CPGs, each organised as a half-centre oscillator

lamprey swimming

spinal CPG controlling axial swimming through left right alternation. spinal cord contains repeating segmental oscillators along the rostral caudal axis

within each segment - 2 neuronal populations mutually inhibit each other, producing alternating activity

between segments - excitatory intersegmental coupling links oscillator, generating a travelling wave of muscle contraction

mammalian walking

• locomotion is generated by multiple coordinated CPG models distributed along the spinal cord

• each limb is organised around flexor extensor HCOs

• half centres interact ipsilaterally (coordination within a limb) and contralaterally (coordination between limbs)