The intricate folding pattern of the human cerebellar cortex is seen all over the cerebellum, in “old” (for example the vermis) as well as in “new” (for example the cerebellar hemispheres) regions of the cerebellum (macaque monkey cerebellar cortex is well-illustrated in Angevine, 1961). Figure 1 illustrates the folding pattern of cerebellar cortex in four different species, rat (Figure 1A), cat (Figure 1B), macaque monkey (Figure 1C), and human (Figure 1D). While the basic laminar organization and cell types of the cerebellar cortex are similar across species, the surface area of cerebellar cortex increases dramatically (illustrations in Sultan and Braitenberg, 1993) and the folding pattern becomes much more intricate. It is also apparent, if less striking, from those pictures that there is a parallel expansion of the cerebellum, especially of the cerebellar hemispheres (see additional images from the studies of Voogd and Glickstein, 1998b MacLeod et al., 2003 Sultan and Glickstein, 2007 Glickstein et al., 2009a and the inset in Figure 1D). It is obvious from a glance at pictures of the brains of different species that the human brain is distinguished by a highly expanded and intricately folded cerebral cortex (for a collection of images of the brains of humans and many other species see ). We suggest that uniquely human motor and cognitive abilities derive from changes at all levels of the central nervous system, including the cerebellum and brainstem, and not just the cerebral cortex. Two aspects of human cortical organization, individual differences and left–right asymmetry, are also seen in the brainstem (principal nucleus of the inferior olive) and the cerebellum (the dentate nucleus). We found that there are major differences in the human brainstem, ranging from relatively subtle differences in the neurochemical organization of structures found in each of the species studied to the emergence of altogether new structures in the human brainstem. We have also compared the neurochemical organization of the human brainstem to that of several other species including the chimpanzee, macaque and squirrel monkey, cat, and rodent, again using Nissl staining and immunohistochemistry. We studied human cases from the Witelson Normal Brain Collection, analyzing Nissl sections and sections processed for immunohistochemistry for multiple markers including the calcium-binding proteins calbindin, calretinin, and parvalbumin, non-phosphorylated neurofilament protein, and the synthetic enzyme for nitric oxide, nitric oxide synthase. We have examined the cytoarchitectonic and neurochemical organization of the human medulla and pons. We have asked if there are accompanying changes in the organization of pre-cerebellar brainstem structures. There is a parallel expansion of the cerebellum, which is interconnected with the cerebral cortex. The cerebral cortex is greatly expanded in the human brain. Department of Physiology and Biophysics, School of Medicine and Biomedical Sciences, University at Buffalo, Buffalo, NY, USA.
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