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 p rocessing monaural sounds, because its neurons receive input chiefly f rom the contralateral cochlear nucleus. However, we demonstrate here t hat a region of the VNLL contains a distinct population of neurons tha t process binaural sounds and are sensitive to interaural temporal dis parities (ITDs). Responses of single neurons were recorded from unanes thetized rabbits by using metal electrodes or micropipettes loaded wit h dextran tagged with either biotin or a fluorescent label. Reconstruc tions of recording sites based on a few marks indicated that ITD-sensi tive neurons were located in a medial region of VNLL that has a low de nsity of neurons or in the adjacent reticular formation. In one animal the locations of five ITD-sensitive neurons were marked directly by i njection of dextrans with different tags. All of these neurons lay in the medial region of the VNLL. The ITD-sensitive neurons of the VNLL h ad 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 i n the ITD. The presence of ITD-sensitive neurons in the VNLL that resp onded only at the onset of tones suggests that this center plays a rol e in the localization of transient sounds.