Dissociation of cortical and single unit activity in spoken and signed languages.

Based on stroke and other lesion data, the cortical organization of sign language has been shown to be in the verbal language-dominant hemisphere. However, finer detail of the cortical organization of sign language is not readily available. Intraoperative cortical mapping of spoken and American Sign Language (ASL) was performed in a hearing patient proficient in ASL undergoing an awake operation for intractable epilepsy. We found the dissociation of essential cortical language sites for spoken and signed languages, the relationship of these sites to the interpretation of ASL, and the importance of the anterior temporal lobe in the language-dominant hemisphere for proper ASL handshapes. Single unit recordings in the anterior temporal lobe, at a site later identified to be important in handshape formation, showed sustained activity during naming with superimposed increases in activity during overt speech.