Cytoarchitectonics of the human nucleus accumbens.

More than 400 publications per year deal with the Nucleus accumbens, however its morphological substrate and anatomical borders appear arbitrary. With a modified Nissi-technique applied to complete sets of thick serial, frontoparallel sections, it became possible to characterize the human Nucleus accumbens. In two series a clear delineation of its borders is documented. Along its rostro-caudal axis, the Nucleus accumbens shows morphological differences: the rostral Nucleus accumbens exhibits a higher cell-density and basophilia than Nucleus caudatus and Putamen; in caudal planes, the Nucleus accumbens dissolves into cell-clusters. A hitherto unrecognized supracommissural part of the Nucleus accumbens dorsal to the Commissura anterior is contiguous to the medial and lateral parts of the Nucleus interstitialis striae terminalis. The thickness of the hemispheric slices (approximately 600 micrometers) facilitated the topographical unravelling of the surrounding cell-islands. In accordance with Sanides (1957) these islands were referred to as Insulae terminales. Based on their topography and cellular structure, they were termed insulae terminales subputaminales (ltsp), Insulae terminales nuclei accumbentis (Itna), Insulae terminales supracommissurales (Itsc) and Insulae terminales olfactoriae mediales et laterales (Itom, Itol). The Insulae terminales form an almost complete envelope around the human Nucleus accumbens and could correspond to the neurochemically defined accumbal shell-region of the rat. Marked differences between medial and lateral insulae terminales olfactoriae permit a clear delineation between the human Nucleus accumbens and the lateral, rudimentary Tuberculum olfactorium: the basis for modifying the concept of a ventral striatum in man.