Mapping the neural substrates of verbal and sign language: A single-case study using direct electrical stimulation

This case report investigates the cortical and subcortical representations of verbal and sign language in a bilingual patient who uses both spoken and signed modalities, assessed intraoperatively during awake surgery. Although spoken language is regularly mapped during awake craniotomies, other language modalities are rarely reported. We performed direct electrical stimulation (DES) during both spoken and sign language tasks in peritumoral regions of the left temporoparietal lobe. The language abilities of the patient were intraoperatively assessed using verbal object naming and sign recognition. Our findings demonstrate that cortical regions, such as the supramarginal gyrus, play a crucial role for both verbal and sign language. However, the specific sites within this region that elicit DES-positive responses differ between the two language modalities. Similarly, subcortical disconnections highlight the overlap between sign and verbal language, particularly in major language pathways, while also emphasizing the specialized role of motor pathways in sign language processing. Clinically, our results emphasize the importance of tailoring DES protocols for intraoperative mapping to individual patient needs, and theoretically, they enhance our understanding of the roles of the supramarginal gyrus and the corticospinal tract in language comprehension.