seen in response maps flanking the primary excitation, sharpening the unit's frequency tuning. The LSO projects bilaterally to the central nucleus of the inferior colliculus (ICC). Ipsilateral projections are primarily inhibitory (glycinergic), and the contralateral projections are excitatory. Additional projection targets include the dorsal and ventral nuclei of the lateral lemniscus (DNLL & VNLL). The GABAergic projections from the DNLL form a major source of GABA in the auditory brainstem, and project bilaterally to the ICC and to the contralateral DNLL. These converging excitatory and inhibitory connections may act to decrease the level dependence of ILD sensitivity in the ICC compared to the LSO. Additional projections form the lateral olivocochlear bundle (LOC), which innervates cochlear inner hair cells. These projections are thought to have a long time constant, and act to normalize the sound level detected by each ear in order to aid in sound localization. Considerable species differences exist: LOC projection neurons are distributed within the LSO in rodents, and surround the LSO in predators (i.e. cat). Medial nucleus of the trapezoid body (MNTB) The MNTB, in the trapezoid body, is composed of mainly neurons with round cell bodies which utilize glycine as a neurotransmitter. The size of the MNTB is reduced in primates. Each MNTB neuron receives a large "calyx" type ending, the calyx of Held arising from the globular bushy cells in the contralateral AVCN. There are two response types found: a ‘chopper type’ similar to spindle cells in the AVCN and a primary type which is similar to those of bushy cells in the AVCN. Periolivary nuclei The SOC is composed of between six and nine periolivary nuclei, depending upon the researcher cited, typically named based upon their location with regard to the primary nuclei. These nuclei surround each of the primary nuclei, and contribute to both the ascending and descending auditory systems. These nuclei also form the source of the olivocochlear bundle, which innervates the cochlea. In the guinea pig, ascending projections to the inferior colliculi are primarily ipsilateral (>80%), with the largest single source coming from the SPON. Also, ventral nuclei (RPO, VMPO, AVPO, & VNTB) are almost entirely ipsilateral, while the remaining nuclei project bilaterally. , *The MSO appears to be smaller and disorganized in mice. Ventral nucleus of the trapezoid body (VNTB) The VNTB is a small nucleus located laterally to the MNTB, and ventral to the MSO. Made up of a