Neural mechanisms for serial order in a stereotyped behaviour sequence

Abstract

A single, transient sensory stimulus can evoke a complex behavioural response in which several behavioural units occur in a serially ordered manner. For stereotyped behavioural sequences, two alternative neural mechanisms have been proposed to account for the serial ordering of behavioural units: chain reflexes¹, which depend on peripheral feedback, and central pattern generators², which attribute the sequence to interactions among central neural elements. Although long thought to be mutually exclusive, both alternatives were recently shown to contribute to simple crayfish escape responses^3–5. We now demonstrate that the integration of these simple, serially ordered escape responses into the compound escape sequence of the crayfish is mediated by a third mechanism for serial order, namely the parallel activation by the same sensory stimulus of two separate behavioural units with different intrinsic reaction times.