The neurology of American Sign Language, which originated from French signing about 200 years ago, is reviewed by a pediatric neurologist in the UK. Sign language has its primary site of organization in the dominant hemisphere. Neuroimaging studies have shown the right cerebral hemisphere is also involved in prosodic functions and in the encoding of objects. Studies of congenital and acquired deafness and dysphasia contribute to our knowledge of cerebral localization, especially since the advent of functional MRI and PET. Broca’s area of the dominant hemisphere is specialized for sign production, and the non-dominant hemisphere is involved with visual-spatial functions and processing of signing, but an interplay between both hemispheres is important in the development of sign language. In childhood epileptic aphasia (Landau-Kleffner syndrome) sign language may provide an alternative means of communication, and it does not impair the acquisition of spoken speech. The importance of sign language in the deaf is shown in the book Seeing Voices (Sacks O, 1991). Cochlear implants may increase in use in the future, but sign language remains the mainstay of communication among the deaf. 
COMMENT. Sign language comprising gestures executed in space and dependent on visual spatial orientation might be thought to involve chiefly the non-dominant right cerebral hemisphere. Both hemispheres contribute to sign language but the dominant hemisphere is the primary site of organization.