THE LINEAR ORGANIZATION OF CELL COLUMNS IN HUMAN AND NONHUMAN ANTHROPOID TPT CORTEX

Neurons in the cerebral cortex are organized horizontally into laminae and vertically into columns and modules. Little is known about the st ructural variation of neuronal organization in the vertical (pia to wh ite matter) dimension. We describe here a new computer-assisted method ology that quantifies the linear arrangement of cells and shows how co rtical columns in a homologous region differ by species and age. Perik arya in eulaminate temporal cortex, Tpt, were segmented from the backg round on the basis of their optical densities and sizes in human, rhes us (Macaca mulatta), and chimpanzee (Pantroglodytes) brains. Within ea ch lamina, the two-dimensional arrays of neurons were divided into rep etitive, objectively defined vertical clusters. Following this, ratios and indices quantified the displacement of perikaryal centroids from the central axis and from the center point in each cell cluster, The e xtremely linear and vertical arrangement of cells in the prelaminated fetal cortical plate served as the template to which the other arrays were compared. In all species, the linear arrangements of perikarya in lamina III, and to a lesser extent, in lamina V, closely resemble tha t of the early fetal template, whereas perikaryal arrangements in laye rs II and IV diverge from the template formation. Corroborating subjec tive visualization, each lamina had its own 'fingerprint'. As expected , cell density is less in the species with larger brains, with most of the differences in density coming from increased spacing between cell ular columns rather than among the cells within columns. Not all aspec ts of perikaryal organization alter when bigger brains are compared wi th smaller ones. Although chimpanzee brains are about four times bigge r than those of rhesus monkeys and human brains are about three times larger than chimpanzee brains, absolute measures of cellular linearity in chimpanzees and rhesus monkeys resemble each other more closely th an the same measures do in humans and chimpanzees. After accounting fo r differences in interval widths, the parameters of linearity sorted o n the basis of brain weight in pyramidal cell layers III and V, but no t in the stellate cell layers II and IV. Human perikarya have the wide st horizontal dispersion and this displacement is most pronounced in l ayer II, least in layer III.