Gesture's neural language: The neurobiology of processing manual gestures and meaning

What are the neural systems that process manual gestures and the meanings they convey? This work includes three studies that were done to address this. In the first study, results indicate that areas of the lateral temporal and inferior frontal cortices exhibit responses to symbolic meaning, independent of whether it is conveyed by the hands (as emblematic gestures) or in spoken language. In contrast, parietal and premotor regions respond to manual actions, regardless of whether they are symbolic emblematic gestures or non-symbolic grasping actions. The results of the second study further implicate the importance of parietal and premotor regions in perceiving hand actions, as extensive responses to a variety of co-speech gestures perceived in a naturally unfolding audiovisual discourse were also found in these areas. Additionally, beyond these more general parietal and premotor responses, the results of this study provide novel evidence that suggests the types of represented semantic content these gestures convey may involve distinct and distributed responses. In the case of gestures that represent physical objects these responses include areas that have prior association with a range of higher-level cognitive processes, such as working memory, visuospatial attention, sensory-motor integration, as well as semantic recognition and selection. In the case of gestures that represent a hand or a foot, both associate responses in areas that are involved in motor behaviors and their perception. In the third study, the functional interconnectivity of neural systems involved in processing natural audiovisual discourse and the gestures performed in that discourse was examined. The results of this study identified densely connected sub-systems that capture the functional anatomy involved in audiovisual discourse and gesture processing in a way that relates the brain's connectivity to task-related impulse responses. Overall, the findings in this work further characterize the prominent parietal-premotor responses in perceiving manual actions, the diverse and distributed ways in which the brain interacts with represented meaning, and the functionally interconnected systems that provide a dynamic neural basis for interpretation.