A cytoarchitectonic and histochemical study of nucleus basalis and associated cell groups in the normal human brain

Several recent studies have reported loss of neurons in the nucleus basalis in Alzheimer's disease. However, few detailed studies of the normal distribution of these neurons in the human brain have appeared. We have used Nissl staining and acetylcholinesterase histochemical staining of the human basal forebrain, alone or in combination to identify the organization of the nucleus basalis and associated cell groups, (or collectively, the magnocellular basal nucleus) in the normal human brain. The magnocellular basal nucleus includes a series of clusters of neurons and scattered perikarya extending from the medial septum and diagonal band nucleus rostrally, through the substantia innominata to the furthest caudal extent of the globus pallidus. This distribution is similar to that which has been described in the monkey. Furthermore, acetylcholinesterase-positive fibers in the human brain are seen in the two major pathways that have been identified as carrying magnocellular basal nucleus axons to the cerebral cortex in other species. These observations suggest that the topographic organization of the magnocellular basal projection to cerebral cortex in other species probably exists in man as well. It will therefore be important in future studies of the fate of these neurons in neurological degenerative diseases to assess the loss of neurons in the different components of the magnocellular basal nucleus in relation to the clinical evidence for dysfunction in the cortical areas which they innervate.