4.13 - Specialization of the Neocortical Pyramidal Cell during Primate Evolution

Abstract

In a recent series of investigations, dramatic differences in pyramidal cell structure have been demonstrated in the primate neocortex. Initial studies in the cortex of the macaque monkey revealed a remarkable degree of heterogeneity in the structure of pyramidal cells sampled from homologous cortical layers among functionally related cortical areas. For example, there was, on average, a 13-fold difference in the number of spines in the dendritic trees of layer III pyramidal cells involved in visual processing. Moreover, the differences in the complexity of pyramidal cell structure among cortical areas were not random: cells involved in what are generally accepted to be more complex aspects of visual processing had more complex structure. Similar systematic trends in pyramidal cell specialization were found among cortical areas involved in somatosensation, locomotion, emotion, and even in executive cortical functions such as conceptualization, planning, and prioritizing. These studies revealed up to a 16-fold difference in the number of dendritic spines (putative excitatory inputs) in the dendritic trees of pyramidal cells in different cortical areas of the adult macaque monkey brain. Moreover, there are systematic and dramatic differences in the branching structure of pyramidal cells in the macaque cerebral cortex, with neurons in executive cortical areas having significantly more branches than those in sensory or motor cortex.