The basic subdivision of the inferior colliculus (IC) in mammals into three main parts — the central nucleus, the pericentral nucleus and the external nucleus (Fig. 1) is known since the pioneering work of Ramon y Cajal (1911). Recent anatomical and electrophysiological studies, beginning with the work of Rose et al. (1963) up to the more recent results by Aitkin et al. (1975) have demonstrated that these three nuclei may have a different function. For example Aitkin et al. (1978) demonstrated that the external nucleus of the IC has an extensive somatosensory input and that neurones in this part of the IC may belong to a system which integrates the information about the space parameters impinging upon different sensory organs. Major interest has been concentrated, however, upon the morphology and function of the central nucleus of the IC. This essentially oval nucleus, which forms the central part of the IC, consists of two subdivisions which have been found to be similar in many species of mammals — the smaller dorsomedial division, consisting mainly of large cells, receiving fibres from the auditory cortex and the larger ventrolateral division, which has a pronounced laminar arrangement of cell dendrites and axons (Morest 1964, Rockel and Jones 1973, Fitzpatrick 1975).