Subdivisions of the medial geniculate body in the tree shrew (Tupaia glis)

The medial geniculate body of the tree shrew has 3 major divisions which can be identified on the basis of cytoarchitecture. Each of these major divisions can be subdivided further. The present paper describes these divisions and compares them in terms of their patterns of afferent and efferent connections. In particular, anterograde degeneration and autoradiographic techniques are used to demonstrate that the dorsal and medial divisions receive projections from the deep layers of the superior colliculus and from the tegmentum. Results are also presented which indicate that the dorsal division projects to a non-primary cortical area adjacent to primary auditory cortex. Evidence is discussed which suggests that large sectors of what we have called the medial geniculate body constitute subdivisions of the auditory thalamus.