ENTORHINAL CORTEX MODULES OF THE HUMAN BRAIN

Much is known about modular organization in the cerebral cortex, but t his knowledge is skewed markedly toward primary sensory areas, and in fact, it has been difficult to demonstrate elsewhere. In this report, we test the hypothesis that a unique form of modules exists in the ent orhinal area of the human cortex (Brodmann's area 28). We examined thi s issue using classic cyto- and myeloarchitectonic stains, immunolabel ing for various neurochemicals, and histochemistry for certain enzymes . The findings reveal that the entorhinal cortex in the human is forme d by a mosaic of cellular aggregates whose most conspicuous elements a re the cell islands of layer II and myelinated fibers around the cell islands, the disposition of glutamic acid decarboxylase-positive neuro ns and processes, cytochrome oxidase staining, and the pattern of chol inergic afferent fibers. The neuropathology of Alzheimer's disease cas es highlights the modules, but inversely so, by destroying their featu res. The findings are of interest because 1) anatomically defined modu les are shown. to be present in areas other than the sensory and motor cortices, 2) the modules are morphological entities likely to reflect functions of the entorhinal cortex, and 3) the destruction of entorhi nal cortex modules may account disproportionately for the severity of memory impairments in Alzheimer's disease. (C) 1996 Wiley-Liss, Inc.