Effects of anomalous language representation on neuropsychological performance in temporal lobe epilepsy

Objective: To examine the effects of anomalous language representation (i.e ., mixed- and right-cerebral dominant on neuropsychological performance. Ba ckground: Right cerebral language dominance resulting from early cerebral i njury is associated with relatively preserved language function with decrea sed visuospatial ability. However, previous reports of this phenomenon have examined patients with relatively large cerebral injuries (e.g., infantile hemiplegia) or limited sample sizes. Methods: A total of 561 patients with complex partial seizures of left temporal lobe origin were studied. Patien ts were classified into left (n = 455), bilateral (n = 58), and right (n = 48) language dominant groups based on Wada testing. Results: Right language dominant patients performed more poorly on multiple tests of visuospatial function, including Performance IQ (PIQ), than did left language patients. No significant group differences were detected for measures of language or general verbal function. The effects of bilateral language on PIQ differed according to handedness. Lowered PIQ was present in the bilateral nondextra l group but not for bilateral dextral patients, and this pattern was observ ed with other visuospatial measures. Conclusions: In patients with relative ly small lesions restricted to the left mesial temporal lobe, a shift in la nguage dominance to the right hemisphere is associated with decreased visuo spatial functions but preserved verbal abilities. Nondextral patients with bilateral language representation also displayed decreased visuospatial per formance, although dextral patients with bilateral language did not.