Neurons sensitive to interaural temporal disparities in the medial part of the ventral nucleus of the lateral lemniscus.

The ventral nucleus of the lateral lemniscus (VNLL) is implicated in processing monaural sounds, because its neurons receive input chiefly from the contralateral cochlear nucleus. However, we demonstrate here that a region of the VNLL contains a distinct population of neurons that process binaural sounds and are sensitive to interaural temporal disparities (ITDs). Responses of single neurons were recorded from unanesthetized rabbits by using metal electrodes or micropipettes loaded with dextran tagged with either biotin or a fluorescent label. Reconstructions of recording sites based on a few marks indicated that ITD-sensitive neurons were located in a medial region of VNLL that has a low density of neurons or in the adjacent reticular formation. In one animal the locations of five ITD-sensitive neurons were marked directly by injection of dextrans with different tags. All of these neurons lay in the medial region of the VNLL. The ITD-sensitive neurons of the VNLL had characteristic responses. Most neurons responded only at the onset of contralaterally or binaurally presented tones; many did not respond to ipsilateral stimulation alone and did not follow dynamic changes in the ITD. The presence of ITD-sensitive neurons in the VNLL that responded only at the onset of tones suggests that this center plays a role in the localization of transient sounds.