Central Pattern Generators

Abstract Essential behaviours such as walking or breathing are rhythmic, that is, characterised by repetitive activation of muscles in a specific temporal sequence. A basic version of the underlying neural activity is generated in the central nervous system by networks called central pattern generators (CPGs). CPGs can produce these patterns even in the absence of inputs that carry specific timing information. The core rhythmic activity can be based on intrinsic oscillatory properties of pacemaker neurons or emerge from the synaptic connectivity of nonoscillatory neurons. In both cases, other neurons are recruited into this rhythmic activity to generate a whole pattern. Neuronal and synaptic properties underlying the precise temporal patterning of sequential bursting activity are shaped by neuromodulators to generate different versions of motor patterns. The circuitry controlling rhythmic behaviours of a whole animal is organised in modules that control different body parts and can be coordinated in different ways to generate different behaviours. Key Concepts Essentially all rhythmic motor behaviours are based on CPGs. CPGs can produce patterned activity in the absence of patterned input. Rhythm generation can be based on intrinsically rhythmic neurons or network interactions. The speed, strength and specific temporal sequence in which CPG neurons fire arise from complex interactions of synaptic and intrinsic neuronal properties governed by diverse types of ion channels. CPG activity is modified by sensory feedback to adapt the motor pattern to changing environmental parameters. CPGs can be activated and reshaped by neuromodulators that adjust neuronal excitability by modifying or suppressing existing ionic currents or adding new currents and changing the properties of synapses. Neuromodulation provides flexibility of motor pattern generation to adjust output to changing behavioural demands. The central networks controlling rhythmic behaviours are inherently modular and allow different coordination of body parts for different behaviours or different versions of the same behaviour.