| This project reexamined the incidence of left and right hemispheric speech, as reflected in Wada testing, and the influence of various factors on that speech representation. Factors studied included seizure laterality, handedness, age at onset, presumed etiology, seizure localization, and gender. A second goal of this study was to compare each factor according to three classification schemes in an attempt to explain inconsistencies found in the literature. Tremendous discrepancies exist in the literature regarding the incidence of left hemisphere speech ranging from as low as 63% to as high as 96% for right handers and from 48% to 75% for left handers. The three classification schemes that were utilized in this study included the five-part UCSF classification scheme, a classification scheme with the greatest proportion assigned to the left language category (e.g., Woods et al., 1988), and a classification scheme with the least proportion assigned to the left language category (e.g., Zatorre, 1989). Archival data were collected from a series of patients evaluated and treated at the Northern California Comprehensive Epilepsy Center at the University of California, San Francisco Medical Center.; Factors found to influence language lateralization were seizure focus and handedness. Left seizure focus and left handedness were more likely to result in a right hemisphere contribution to language than right seizure focus and right handedness. However, in the present study there were a few cases in which patients with right hemisphere lesions who were right handed had speech in their right and left hemispheres (L = R). Age at onset, presumed etiology, seizure localization, and gender were found to have little or no statistically significant influence on language lateralization.; The results of this project suggest that, although the left hemisphere is dominantly responsible for language in the majority of patients, it is not solely responsible for language in many patients. Using more subtle classification criteria may improve the ultimate understanding of the factors responsible for left or right hemisphere speech representation. |
