The Role of the Frontal Lobes in Speech & Language as Suggested by the Aftereffects of Hemispherectomy, Ablation, Vascular Lesions, and Tumors and by blood Flow and Direct Stimulation Studies

Many reputable texts and experts have yet to view the Supplementary Motor Area as integral to language. Evidence from a number of sources, including blood flow studies, cerebrovascular accident infarctions, tumors, ablations, hemispherectomies, etc., has been reviewed to show that the SMA is crucial to most speech and language tasks. The fact that unilateral lesioning of the SMA results in only transient speech deficits led many to conclude that it played no role in speech. Evidence presented herein indicates that the reason for the transiency of the deficits lies in the fact that the motor programming system is a dynamic, equipotential BILATERAL system. If either SMA is lesioned, the other can assume full control of both sides of the body with the only deficit being in fine, rapidly alternating movements involving both hands. The boundaries of the SMA have not been clearly delineated. The findings of this review suggest that two distinct areas be investigated. The first one and the one limited to Brodmann\u27s area #6,is active during motor programming. The second area, sometimes comprising the anterior part of Brodmann\u27s #6,area #8 and part of #9,appears to be involved in the initiation and formulation of thoughts and actions. Injury to this area results in verbal fluency deficits and long lasting deficits in writing and spontaneous speech formulation. Taken together, the findings of this review underscore the role of the Supplementary Motor Area in speech, but primarily in motor programming. The evidence suggests that the source of the creative speech impulse, the highest level of language abstraction, appears to involve areas of the frontal lobe anterior to the SMA (possibly areas #8 & #9). Though the data suggests bilateral equipotentiality for the motor programming functions of the SMA, such would not appear to be the case for the Prefrontal Language Area (PLA) since lesions to this area in the left hemisphere often result in permanent deficits in speech fluency, writing, and spontaneous speech