Chemoarchitectonic Indicators of Functional Asymmetries in Human Brain Language Area Homologs.

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This new approach will characterize the evolutionary substrate of human brain language area homologues in primates. The prevailing current paradigm is based on the premise that these left-hemisphere-lateralized areas of the cerebral cortex are unique to humans and are not functionally active in non-human primate communication. This governing principle is based largely on a strict concept of the singular nature of human cognition and communication. However, compelling anatomic and brain-chemistry-based evidence has supported an alternate hypothesis: that these lateralized regions, in at least anthropoid primates, manifest a long-lived functional identity. The validity of this novel premise will be tested by rigorous quantitative analysis of hemispheric asymmetries in selected modulatory chemical systems via use of cutting-edge immunocytochemistry and stereology techniques. It is proposed that interhemispheric asymmetries, demonstrated within these neurochemical systems, will serve as powerful indicators of lateralized communication-related functions in primate brain language areas. Although non-human primates such as Old World monkeys share some anatomic components of human brain language areas it is unclear to what functional level and how far the evolutionary history of these features extends. These compelling questions are to be considered within a multidisciplinary framework of neurobiology and anthropology with integration of conjoint functional imaging and molecular biology projects in humans, great apes and Old World monkeys. Development of a profound non-human primate model of volitional communication/language is a key long-term goal.