TEMPORAL PROCESSING IN THE AUDITORY SYSTEM.

In spite of the fact that the auditory system is the best available acoustic signal processor, so far computational modelling in neuroacoustics has concentrated on the auditory periphery. The first auditory stage, the cochlea, may be considered as filter bank performing a kind of frequency analysis. However, this is only the first step of complex hierarchical processing which finally, at the level of the cortex, leads to perception and recognition of sound signals. On the basis of our neurophysiological investigations, a spiking neural network has been simulated which implements temporal processing in the central auditory system. Essential elements of the first level of this network are coding of amplitude modulations by oscillatory neurons in the ventral cochlear nucleus (VCN) and by integrating neurons in the dorsal nucleus cochlearis (DCN). At the second level undelayed responses from the VCN and delayed responses from the integrated response in the DCN coincide on neurons in the inferior colliculus (IC). Finally, synchronized inhibition originating in the nucleus of the lateral lemniscus (VNLL) provides additional timing and low pass filtering. In the auditory system the result of temporal analysis is represented along a neuronal axis orthogonal to the well-known tonotopic axis. Corresponding evidence comes from different methods of mapping auditory midbrain and cortex in various animal, including man.