Functional connectivity of the hand motor cortex in American Sign Language

Abstract

Broca’s area is considered to be a language planning region of the brain regardless of modality because both speaking and signing evoke activity in the area. However, signed languages involve grammatical facial expressions and mouth movements, so it is possible that the role Broca’s area plays in signing is related to the region being a mouth premotor region. If Broca’s area is a language planning area for signers, they should show a functional connectivity between Broca’s area and the hand motor cortex that would not be present if Broca’s area was a mouth premotor region. We investigated the functional connectivity between the hand motor region and Broca’s area in students in an introductory American Sign Language (ASL) course. We expected to see a greater correlation in the ASL students compared to those who took an introductory Spanish class. Additionally, since some regions of the body-selective visual cortex have been shown to be sensitive to the execution of motor movements, we expected to see a greater correlation between the hand motor region and some of the limb-selective regions in lateral occipitotemporal cortex. Although we did not find a significantly higher correlation between the hand motor cortex and Broca’s area in its entirety, there was a significantly greater correlation between the right hemisphere hand motor cortex and a subregion of Broca’s area in the ASL group. However, we did not find a significant difference in the correlation between the hand motor regions and the “limb crescent” between the ASL and the Spanish groups. These findings contribute to a better understanding of the complex role of classical Broca’s area in both spoken and signed language processing.