Journal of Neurological Sciences [Turkish] 20:(3)#28;140-150, 2003
نویسندگان
چکیده
This review attempts to formulate a new hypothesis on the neuronal organization of human cerebral asymmetries. In short, we claim that left-right differences of diverse functions are constituted by two different mechanisms. One are neuroanatomical asymmetries of different cortical and subcortical areas. It is assumed that these features develop according to principles laid down in early ontogeny and are established by tight interactions between genetic and epigenetic constraints. We suppose that neuroanatomical asymmetries do not change importantly in adults and thus represent an invariant feature over time. The second mechanism is constituted by dynamic factors that are capable to importantly alter the balance between the hemispheres. As outlined below, we suppose that commissural interactions, which can be asymmetrical by themselves, mediate this effect. In addition, since the efficiency of synaptic transmission at commissural synapses can be altered by gonadal steroids, interhemispheric interactions are sexdependent and change in women over the menstrual cycle, thereby leading to alterations of functional hemispheric asymmetries. Thus, the degree of lateralization of diverse human functions is equal to the net result of the two factors, a time-invariant and a time-variant one.
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