The intercollicular area of the inferior colliculus

To study the somatosensory input to the inferior colliculus, lesions were made in the dorsal column nuclei of the hedgehog, tree shrew, slow loris, marmoset and African green monkey, and spinal cord of the hedgehog, tree shrew and slow loris. The degenerating fibers stained with silver impregnation methods. The dorsal column system projects primarily to an area lateral to the central nucleus of the inferior colliculus, whereas the spinotectal projection is primarily to the medial region in the hedgehog and medial and dorsal regions in the tree shrew and slow loris. Both fiber systems are quantitatively quite constant in the various species. It is apparent from published data on a variety of mammals that the central nucleus is primarily part of the auditory system in which the intercollicular area is involved only indirectly via projections from the central nucleus and auditory cortex. In nonmammalian vertebrates, the data available suggest that there is a comparable area in the mesencephalon that is involved with somatosensory as well as auditory sensation. Since low frequency stimulation, generally characterized as vibration, stimulates both modalities, the intercollicular area may be the input side of a mechanism for alterting the animal to vibratory stimuli.