Excitatory/inhibitory interaction in the LSO revealed by point process modeling.

We studied lateral superior olivary (LSO) unit responses to binaural tone-bursts using a general point process approach. We show that inhibition of the ipsilaterally elicited response by contralateral stimulation cannot be modeled simply as a reduction of the ipsilateral input. Statistical analyses reveal that inhibition operates by scaling the intensity of the point process describing the ipsilateral response. In some cases the scaling process has secondary effects: Binaurally elicited discharges produce bimodal interspike interval histograms from units that produce unimodal interval histograms under monaural stimulation. We present a specific point process model that describes the scaling process and successfully replicates the observed responses to monaural and binaural stimulation of the three types of LSO units: slow choppers, fast choppers, and bimodal units. We interpret scaling as a shunting inhibitory process in these LSO neurons. By relating scaling magnitude to interaural level difference, we demonstrate the spatial sensitivity of LSO units.