Abstract

The sensitivity to interaural intensity differences (IIDs) of acoustically responsive neurons was examined in multiple microelectrode penetrations along the rostro-caudal axis of deep superior colliculus (SC) in anesthetized cats. The most rostrally located neurons were unresponsive to monaural stimulation but were strongly excited binaurally. IID sensitivity functions for these “predominantly binaural” (PB) neurons were sharply peaked with maximum response at or near zero IID. Caudal to the PB cell area, most neurons were excited by contralateral stimulation and inhibited by ipsilateral stimulation (EI cells). All EI cells were maximally excited over a range of IIDs favoring the contralateral ear and were totally inhibited over a range favoring the ipsilateral ear. The position of the cutoff between excitatory and inhibitory regions was located near zero IID (corresponding to the median plane) for the most rostrally located EI neurons and was shifted progressively to IIDs favoring the contralateral ear (corresponding to increasing contralateral azimuths) for more caudally located EI neurons. The consequence of this topography is that IID, and hence azimuthal location, is represented by the extent of deep SC activated.

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