The posterior field P of cat auditory cortex: coding of envelope transients.
The posterior field (P) of the cat auditory cortex contains a very high proportion of neurons whose responses change non-monotonically with the sound pressure level (SPL) of tonal stimuli, leading to circumscribed frequency-SPL response areas, and it has therefore been suggested that field P may be specialized for processing of sound intensity. We demonstrate here a great diversity of response areas in field P. Furthermore, by varying tone SPL and rise time, we show that, as in primary auditory cortex (AI), the onset response of a field P neuron is better described as a function of the instantaneous peak pressure (envelope) at the time of response generation than of the steady-state SPL of the stimulus. Such responses could be used to track transients or represent envelopes in more general terms, rather than to code SPL. Compared with AI, field P neurons have relatively long minimum latencies along with a large jitter in spike timing. Tracking would therefore be most effective for slowly varying envelopes, and one function of the inhibition that generates non-monotonicity in field P may be to suppress temporally sluggish responses to rapid transients, such as the onsets of high-SPL, short rise time tones. Field P may thus be specialized for coding slowly varying signals.
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Department of Psychology, Monash University, Clayton, Victoria, Australia. peter.heil@sci.monash.edu.au
Irvine
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D000161:Acoustic Stimulation; D000200:Action Potentials / Q000502:physiology; D000818:Animals; D001303:Auditory Cortex / Q000166:cytology* / Q000502:physiology*; D001309:Auditory Threshold / Q000502:physiology; D002415:Cats; D005260:Female; D008297:Male; D009475:Neurons, Afferent / Q000502:physiology*; D011930:Reaction Time / Q000502:physiology