The riddle of the right hemisphere's contribution to the recovery of language

Although it is generally acknowledged that the right hemisphere plays some role in the recovery of language in aphasic patients, the exact nature of this role is still controversial. According to the model of right hemisphere language proposed by Zaidel, the right hemisphere should selectively contribute to the recovery of language comprehension (and in particular of lexical comprehension) but not to the recovery of language production. According to the model of right hemisphere language proposed by Gazzaniga, on the contrary, no language function is selectively supported by the right hemisphere, but the contribution of this hemisphere to the recovery of language varies widely from one individual to another. The aim of this paper is to try and clarify this problem, starting from the basic clinical observations which have given a preliminary shape to the whole issue, and passing then to a survey of results obtained following more recent and specific lines of research. The following conclusions are reached: (1) although the right hemisphere plays (at least in some patients) a definite role in the recovery from aphasia, a greater role is usually played by the undamaged areas of the left hemisphere; (2) the right hemisphere's contribution to the recovery of language seems to concern more the receptive than the expressive components of speech; and (3) the extent of the right hemisphere's contribution varies widely from one individual to another, probably due to individual differences in the hemispheric representation of language.