Gesture handedness predicts asymmetry in the chimpanzee inferior frontal gyrus

Abstract

Neuroanatomical asymmetries have been identified in chimpanzee frontal and temporal lobes including regions believed to be homologous to human Broca's and Wernicke's areas. This study examined whether or not neuroanatomical asymmetries in chimpanzees are associated with hand use during gestural communication. Analyses revealed that those chimpanzees that reliably employ their right hand for manual gestures have larger inferior frontal gyri in the left hemisphere than those apes that do not show consistent hand use for gestures. These findings are the first to provide a direct link between neuroanatomical asymmetries and the production of lateralized communicative behavior in non-human primates.

The neural and cognitive correlates of aimed throwing in chimpanzees: a magnetic resonance image and behavioural study on a unique form of social tool use

“…The association between hand preferences for throwing and asymmetries within the IFG and KNOB are also consistent with previous studies showing that handedness for other forms of tool use, such as simulated termite-fishing and nutcracking, is linked to lateralization in the cortical language area homologues of chimpanzees [33,44]. It should also be noted that asymmetries in hand use for manual gestures are associated with asymmetries within the IFG [45] Thus, the results reported here are consistent with the evolutionary hypothesis that throwing may have served as a preadaptation for the neural adaptation of motor programmes necessary for complex motor actions, including language and speech [11].…”

The sound of one-hand clapping: handedness and perisylvian neural correlates of a communicative gesture in chimpanzees

“…These neuroanatomical correlates of an auditory communicative gesture are congruent with previous studies in chimpanzees showing that hand preference for human-directed food-begging gestures predicts variation of the neuroanatomical asymmetry in the IFG [66] and of the grey matter asymmetries in the PT [67]. In contrast, it has been previously reported that handedness for non-communicative motor actions (bimanual coordinated task and unimanual reaching) does not significantly correlate with the IFG and PT homologues [66,80]. Thus, these findings support the notion that the gestural communication system in chimpanzees might involve a common cerebral substrate with human language and could have been the precursor of the cerebral substrate for language in the common ancestor of humans and chimpanzees at least 5-7 Myr ago.…”

“…The full details of the procedure of image collection are provided in the electronic supplementary material (point 1; see also [66]). …”

“…Interestingly, according to different assessment methods (i.e. region-of-interest manual tracing of brain imaging scans [64][65][66][67], voxelbased morphometry [68] and post-mortem morphological analyses of the PT tissues [69]), investigations of neuroanatomical asymmetries in great apes-and chimpanzees specifically-have reported leftward biases for both the IFG and PT (considered as the homologue regions that overlap Broca's and Wernicke's areas in humans [70]). Leftward bias has been confirmed at microcellular level by cytoarchitectonic studies for Brodmann's area 22 (which makes up part of the PT) [71], but not for Brodmann's areas 44 and 45 (i.e.…”

“…There is one previous study in captive chimpanzees that reported neuroanatomical correlates between asymmetries in the IFG but not the PT with hand preferences for human-directed food-begging gestures (i.e. extended arm towards humans) [66]. Here, we focused on clapping gestures because they have several unique features in terms of social cognition and handedness that make them particularly interesting for this research topic.…”