The human medial geniculate body.

The medial geniculate body in non-human species is divided into several parts, each with a different structure, physiological organization, and pattern of connections. Which parts of the human medial geniculate body and which types of neurons might be homologous to those of other species is unknown, and the object of the present study. The cytoarchitecture, fiber architecture, and neuronal organization of the adult human medial geniculate body were studied in Nissl, Golgi, and other preparations. Three divisions, comparable to those in other mammals, were described. The ventral division had a bimodal distribution of somatic sizes in Nissl material which, in Golgi impregnations, may correspond, respectively, to a larger neuron with bushy dendrites and a tufted branching pattern, and a smaller stellate cell with a radiating, spherical dendritic field. The large neurons formed clusters surrounded by a particular pattern of neuropil which, together, constituted fibro-dendritic laminae whose long axis was oriented medio-laterally in parallel sheets or rows. The dorsal division was dominated by small and medium-sized somata representing at least three populations of neurons in the Golgi preparations. The large stellate cell had a radiate dendritic field and a dichotomous branching pattern; an equally large neuron with an elongated, multiangular perikaryon and bushy dendritic arbors forming tufts also occurred. Blended among these larger neurons were many smaller cells with tiny, flask-shaped, round, or drumstick-like perikarya, limited dendritic fields and thin dendrites, and poorly developed stellate or bushy dendritic configurations. In the medial division, larger somata were more common than in the other medial geniculate divisions, but small cells were present in considerable numbers. The fiber architecture and the different kinds of neurons distinguished the three major divisions and the nuclei within them. Thus, the ventral nucleus had long fascicles of axons running parallel to the dendrites of bushy neurons, while the marginal and ovoid nuclei had a different organization. The dorsal division had a more diffuse, irregular arrangement of thinner axons interspersed among bundles of coarser fibers, whereas the medial division was traversed by many coarse preterminal axons passing laterally and dorsally from the brachium of the inferior colliculus; these imparted a striated pattern to the neuropil. Regional variation in cytoarchitecture and the fiber plexus defined several nuclei in each subdivision, except in the medial division, where the density of the staining made further subdivision impossible.(ABSTRACT TRUNCATED AT 400 WORDS)