The inhibition of cat lateral superior olive unit excitatory responses to binaural tone bursts. I. The transient chopper response.

1. The temporal properties of lateral superior olivary (LSO) unit discharges to binaural tone bursts were studied to determine the general time course and statistical properties of these discharges and to provide a basis for extending a point process model of LSO unit monaural discharges to describe their binaural discharges. Single-unit activity was recorded extracellularly from the LSO of the anesthetized cat. The initial transient and the gross temporal features of LSO unit discharges to binaural simultaneous tone bursts are examined in this paper. 2. The poststimulus time (PST) histograms generated by LSO unit discharges to monaural and binaural tone bursts illustrated that the ipsilaterally elicited tone-burst discharges were most strongly inhibited during the initial segment of the binaural response and that the degree of inhibition decreased (i.e., discharge rate increased) as the poststimulus onset time increased. Hence, the contralateral inhibitory effect "adapts" in a manner similar to the ipsilaterally elicited discharges. 3. When the interaural level difference was decreased, the degree of discharge inhibition increased: the period of maximal inhibition spread to shorter and longer poststimulus onset times as the contralateral latency decreased and as the contralateral response magnitude increased. The latency of the inhibitory effect could decrease sufficiently to result in the suppression of the first spike of the ipsilateral discharge. Also, when the binaural stimulus was of sufficient intensity, an increase in spike output, the OFF discharge, was often observed during the last 1-10 ms of the response. 4. It was concluded that the initial and general time course of the binaural response could serve as cues of binaural stimulus level, interaural level differences, and interaural time-of-arrival differences of high-frequency stimuli. The binaural response could be discriminated from a monaural response of similar discharge rate as the former either occurred with shorter latency or, when the first spike was suppressed, with much longer and/or more variable latency than the latter. The gross temporal differences between the monaural and binaural responses could be accounted for in terms of differences in certain gross temporal features (e.g., latency and adaptation) of the ipsilateral and contralateral responses. 5. The effect of stimulating the contralateral ear was not limited to the inhibition of discharges. The timing of a discharge to an ipsilateral stimulus could be perturbed (lengthened) by a contralateral stimulus at levels below that which suppressed the discharge.(ABSTRACT TRUNCATED AT 400 WORDS)