Some principles of the auditory preprocessing

Along the whole auditory pathway, an acoustic signal is expressed by a spatiotemporal pattern of the binary neural activity. The author points out several general features of neural auditory preprocessing. On the first level of the auditory system, the amplitude changes of narrowband stimuli are encoded by an instantaneous firing rate in a frequency channel consisting of 30-40 fibres. On the next level, owing to the summation of the inputs received from neighboring frequency channels and to the effect of delayed lateral inhibition, the dynamic range of single units increases considerably. In phasic neurons, enhancement of the amplitude changes due to short-term adaptation effects is observed. The role of delayed inhibition is also considered. Finally, in many tonic neurons of the auditory pathway, long-term adaptation leads to the adjustment of the threshold level to the mean level of the received synaptic input. This effect may play the leading role in the process of small amplitude change enhancement for long-duration stimuli