Spectral and temporal characteristics of activation and suppression of units in the cochlear nuclei of the anaesthetized cat

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Abstract
The responses are described of cochlear nucleus neurons of anaesthetized cats as a function of time in dependence on intensity and frequency of tonal stimuli. Depending on spectral properties three types are distinguished in the group of spontaneously active units: A type (activation only) AS type (activation and suppression) and S type (suppression only). The A(S) neurons have insufficient spontaneous activity to judge presence or absence of suppression. Four temporal patterns of response are distinguished: transient, sustained, build up and complex. Units of the A type display a sustained time course of activation and have properties similar to those of auditory nerve fibres. S type units show sustained suppression. Temporal patterns of activation other than sustained were found only in the AS and A(S) units. The recordings indicate that on suppression and off suppression are present more frequently in VCN neurons than previously found. The suppression phenomena in the DCN are, however, still more wide spread and more dramatic in appearance. In contrast to earlier findings, off suppression was always observed and never seen to extend beyond the on activation band in A neurons. Data from AS neurons indicate that off suppression is neither simply an after effect of high firing rates nor simply a continuation of on suppression. The relations between off suppression and spectral and temporal characteristics of on activation and suppression can be matched with a model featuring overlapping antagonistic inputs and postexcitatory inhibition.