Representation of sound onsets in the auditory system

Sound onsets constitute particularly salient and behaviorally relevant transients and elicit vigorous responses from most auditory neurons. Here I show that response latency, precision of response timing, and response magnitude depend on dynamic properties of the stimulus envelope at onset. The joint consideration of these response parameters, and of the stimulus and neuronal properties on which they depend, suggests a point-by-point sampling, or tracking, mechanism for the onset envelope. This mechanism is characterized by an automatically adjusted sampling rate and precision of spike timing, so that it should be rather robust against changes in the dynamics of the envelope, brought about for example by changes in a signal's sound pressure level. There will be a one-to-one relationship between stimulus onset and the evoked spatiotemporal response pattern. That pattern involves both the tonotopic and the isofrequency axes of cortical maps. Such a mechanism could provide a temporal resolution of the time course of the onset envelope which is likely orders of magnitude higher than that inferred from the phase-locking capabilities of neurons in cortical fields to periodic signals and could contribute to the instantaneous coding of transients.