The effects of ipsilateral tone burst stimulus level on the discharge patterns of cat lateral superior olivary units.

Discharges were recorded extracellularly from single units localized in the lateral superior olive (LSO) of barbiturate anesthetized cats. The statistical properties of the unit discharges to monaurally presented tone bursts were determined. Increasing the stimulus level of an ipsilaterally presented tone burst produced an increase in the discharge rate and the emergence and growth of a time-locked discharge pattern in the initial portion of the response. The initial time-locked response was transient and was followed by a nontime-locked sustained response. In the sustained portion, increasing stimulus level produced increases in rate and changes in the interspike interval statistics. Average rate and interval statistics were found to be systematically related. LSO units were differentiated on the basis of rate and pattern of their initial discharges into two main types: the fast and slow chopping units. An analysis of the results indicated that some aspects of response type differences may be related to input characteristics rather than to neuron response mechanisms.