Neural underpinning of communicative gestures in left-handers

Abstract

One of the most left-lateralized functions in the human brain is the control of complex manual skills, such as common gestures that can be used instead of speech. Most of the contemporary neuroimaging research on their two particular categories – conventionalized “communicative” gestures, and tool use pantomimes – often utilized in neuropsychology to test the preserved cognitive functions in patients with brain injuries, focused on right-handers using their dominant hands. Counter to neuropsychological reports, neuroimaging data most often suggest that a common left-lateralized neural substrate underlies both gesture categories. This paper, based on the results from functional magnetic resonance imaging (fMRI), contains a description of the neural underpinning of their planning and control in left-handers. The main goal of the presented research was to verify a hypothesis that even in subjects preferring their left hands, the higher-order control of manual skills is lateralized similarly to right-handers, irrespective of the gesture and hand used. Group data support this notion, suggesting at the same time that particularly during the control of the right hand, the representations of the two gesture categories are less lateralized (i.e., they are localized more symmetrically in both hemispheres). Another novel aspect of this work is the preliminary assessment of the issue whether the observed lateralization of functions, or its absence in some individuals, is accompanied by any structural asymmetries. It turns out that this is the case but in a rather unexpected brain region, the insular cortex.