Abstracts

RATIONALE: The incidence of atypical (right, bilateral) speech in the general population has been difficult to determine because a definitive test such as the intracarotid amobarbital procedure (IAP) cannot be accomplished with normal persons due to the risks involved. An estimation of atypical speech can be obtained, however, by studying people who had completely normal developmental histories but who had a specific neurological event in adulthood (trauma or cerebral infection) and who subsequently developed epilepsy. METHODS: 836 patients with valid IAPs were examined for this study. Of these, exactly 50 people were found who had totally normal neurological histories through age 15 and who later had either head trauma or cerebral infection as a preceeding event and highly probable cause of their epilepy. RESULTS: The IAP showed that speech was associated with the left hemisphere and left hemisphere only in all 50 cases with completely normal neurological histories. In no instance was there a questionable or doubtful case regarding speech lateralization. In contrast, with the unselected group of 836 patients with valid IAPs, in 85.4% speech was on the left, in 7.9% speech was on the right, and in 6.7% was speech bilaterally represented. The difference between the groups was statistically significant (Fisher's Exact=.0001). Of the 50 cases with normal histories, 47 (94%) were right handed (they wrote with their right hands) and 3 (6%) were left handed (wrote with left hands) which was different than for the entire group (80.7% right handed; 19.3% left handed; Fisher's Eact=.0147). CONCLUSIONS: Atypical speech lateralization is rare in the general population unless there is a positive neurological history. Our large sample with IAPs never revealed such a case. However, our sample of cases with normal neurological histories is too small to permit a definitive statement that such cases do not exist. It can be said that atypical speech lateralization is routinely associated with an abnormal developmental neurological history. In contrast, left handedness does appear in the context of a normal neurological history even though it is not common. (Supported in part by NIH Grant NS 01910).