Monaural and binaural processing in the ventral nucleus of the lateral lemniscus: a major source of inhibition to the inferior colliculus

The ventral nucleus of the lateral lemniscus (VNLL) is a major source of input to the inferior colliculus. This paper reviews recent studies of neural responses in the VNLL of the unanesthetized rabbit. The VNLL has generally been viewed as a monaural nucleus, with its neurons responding primarily to stimulation of the contralateral ear. In the rabbit, the VNLL is divided into a medial division (VNLLm) comprising neurons intercalated in the medial limb of the lemniscus, a compact lateral division (VNLLl), and a dorsal division. The VNLLm contains an abundance of neurons sensitive to interaural temporal disparities (ITDs), one of the major binaural cues for sound localization. These neurons respond only at the onset of tones, and therefore appear to encode the ITDs of transients. Even in the VNLLl, many neurons are sensitive to binaural stimulation. The VNLLl contains a variety of neurons with different discharge patterns, the two most common of which are sustained and onset. The discharge patterns, frequency-tuning and dynamic ranges of VNLLl neurons indicate that this division is able to supply the inferior colliculus with a variety of inputs, each serving a different function in the analysis of sound.