It has been further shown that great apes have a much more flexible and much less context-dependent gestural, compared with vocal, system of communication, and are able to adjust their gestural behaviours to the responses and the attentional state of the recipient. It is well known that chimpanzees produce intentional manual gestures to communicate with social partners in various social contexts, such as play, threat, greeting, invitation for grooming, shared excitation, reassurance-seeking after stress and food begging. īecause chimpanzees ( Pan troglodytes) are our closest phylogenetic relatives, this species may be a relevant model for investigating the potential precursors of left hemisphere specialization for language in humans. These collective findings raise important questions regarding the role of gestures in the origin of language in humans. ![]() Finally, functional brain imaging studies have shown a ‘speech-like’ activation of Broca's area in the left hemisphere for sign production in deaf individuals. Furthermore, evidence of links between speech and gesture production in humans is consistent with the notion of a single integrated communication system within the left cerebral hemisphere for both vocal and gestural communication. Interestingly, signing, pointing or symbolic actions-abilities that might play an active role in the development of children's communicative skills -elicit a stronger degree of right-handedness than non-communicative manual actions in young children, potentially indicating a greater involvement of the left hemisphere for communicative signalling. Right-hand dominance in humans (almost 90% are right-handed ) is not only associated with manipulation, but also with communicative gestures, including signing in deaf people, manual movements when people are talking and pointing gestures by infants. An alternative model claims that handedness for gestural communication may constitute a better predictor of hemispheric specialization for language. Left lateralization for language has been historically linked to right-handedness for manipulative actions, but 70 per cent of left-handed humans also show a similar left lateralization, suggesting that the direction of handedness for manipulation is not a perfect predictor of hemispheric lateralization for language. The PT and IFG overlap with Wernicke's and Broca's areas therefore, these anatomical asymmetries may correspond to the functional dominance of the left hemisphere for language. Leftward size asymmetries have been reported, particularly among right-handed individuals for the planum temporale (PT), but such a leftward bias is not entirely consistent across studies for the inferior frontal gyrus (IFG), which includes Brodmann's cytoarchitectonic areas 44 and 45. Most language functions involve a greater activation of the left hemisphere, including Wernicke's and Broca's areas, two key regions of the language cortical network involved in the comprehension and production of signals within the temporal and the frontal cortex, respectively. Hemispheric specialization of the brain and right-handedness has historically been considered a specific trait of human evolution. The results are consistent with the view that gestural communication in the common ancestor may have been a precursor of language and its cerebral substrates in modern humans. ![]() The direction of hand preference (right- versus left-handed subjects) for clapping explained a significant portion of variability in asymmetries of the PT and IFG. When considering the entire sample, there was a predominance of right-handedness for clapping and the distribution of right- and left-handed individuals did not differ between the two facilities. Using computer manual tracing of regions of interest, we measured the neuroanatomical asymmetries for the homologues of key language areas, including the inferior frontal gyrus (IFG) and planum temporale (PT). The preferred hand for clapping was defined as the one in the upper position when the two hands came together. In the present study, we examined (i) hand preference for a communicative gesture (clapping in 94 captive chimpanzees from two research facilities) and (ii) the in vivo magnetic resonance imaging brain scans of 40 of these individuals. Whether lateralization of communicative signalling in non-human primates might constitute prerequisites of hemispheric specialization for language is unclear.
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