Reorganized cerebral metabolic interactions in temporal lobe epilepsy

Patients with left temporal lobe epilepsy demonstrate language impairments that are not well understood. To explore abnormal patterns of brain functio nal connections with respect to language processing, we applied a principal component analysis to resting regional cerebral metabolic data obtained wi th positron emission tomography in patients with right- and left-sided temp oral lobe epilepsy and controls. Two principal components were expressed di fferentially among the groups. One principal component comprised a pattern of metabolic interactions involving left inferior frontal and left superior temporal regions-corresponding to Broca's and Wernicke's areas, respective ly-and right mesial temporal cortex and right thalamus. Functional coupling s between these brain regions were abnormally enhanced in the left-sided ep ilepsy patients. The right thalamic-left superior temporal coupling was als o abnormally enhanced in the right-sided epilepsy patients, but differentia lly from that in the left-sided patients. The other principal component was characterized by a pattern of metabolic interactions involving right and l eft mid prefrontal and right superior temporal cortex. Although both the ri ght- and left-sided epilepsy patients showed decreased functional couplings between left mid prefrontal and the other brain regions, a weaker right-le ft mid prefrontal coupling in the left-sided epilepsy patients best disting uished them from the right-sided patients. The two mutually independent, ab normal metabolic patterns each predicted verbal intelligence deficits in th e patients. The findings suggest a site-dependent reorganization of two ind ependent, language-subserving pathways in temporal lobe epilepsy. (C) 1999 Elsevier Science Ltd. All rights reserved.