Neuroanatomical and neurochemical correlates of cerebral dominance: A minireview

The authors review the evidence suggesting that anatomical asymmetries may be, in part at least, responsible for the remarkable functional differences existing between the two halves of the human brain. In particular, they stress the presence in the posterior part of the sylvian fissure of clear neuroanatomical asymmetries (such as the greater size on the left of the 'plenum temporale' and the greater extent on the same side of the cytoarchitectonic 'Tpt' area) which could represent the structural substrate for the left hemisphere dominance for language. At the same time the authors suggest that, in addition to the anatomical data, neurochemical asymmetries could also account for the striking functional differences existing between right and left hemisphere. Results recently obtained by the authors have shown in fact that: in the posterior part of the first temporal gyrus the ChAT activity (which is a selective marker of the cholinergic system) is consistently higher on the left than on the right side of the brain; the prevalence of enzymatic activity on the left side is not equally distributed across the 6 cortical layers, but is significant only at the level of layers II and IV, which contain the highest number of nervous endings. Some implications of these findings are briefly discussed.