The morphology of minicolumns

Abstract

The cerebral cortex is composed of minicolumns, which are vertically oriented arrays of neurons. The minicolumns can be demonstrated both physiologically and morphologically. Physiologically, the minicolumns become evident when a recording electrode is advanced through the cortex in a horizontal direction. It is then found that as the electrode is advanced there are shifts in the receptive field properties of neurons. These shifts occur every 50 microns or so, as the electrode moves from one minicolumn to the next one. The anatomical correlates of the minicolumns are neuronal units based on vertically organized groups of pyramidal neurons, whose apical dendrites cluster together as they ascend through the layers of the cortex. The clusters of apical dendrites define the central axes of the three-dimensional minicolumns, which are similar in size to the physiological ones. Recently, digitized images of vertically oriented Nissl stained sections have been used to determine if there are changes in organization of minicolumns in aging and in some behavioral disorders such as autism. In Nissl sections vertically oriented strings of neurons are seen to be separated by clear spaces and it is assumed that these spaces correspond to the locations of the clusters of apical dendrites seen in the three-dimensional reconstructions of minicolumns. By analyzing digitized images of the Nissl stained sections it has been found that there is some disorganization of the minicolumns as a consequence of aging, and that in Alzheimer's disease the minicolumns are almost completely disrupted. In autism the minicolumns are narrower than in control brains, suggesting that the minicolumns are more numerous than normal. Since the minicolumns are generated as the pyramidal neurons migrate into the cortex along radial glia fibers, it is suggested that autistic changes in cerebral cortex must have their origins during development.