Functional MRI of phonological and semantic processing in temporal lobe epilepsy

Phonological and semantic aspects of language were examined in patients wit h unilateral temporal lobe epilepsy (TLE) and healthy controls using functi onal MRI, We expected to replicate previous findings in healthy individuals showing relatively greater activation in frontal regions for phonological compared with semantic processing, and greater activation in temporal regio ns for semantic compared with phonological processing. We hypothesized that differences between patients with left TLE and healthy controls would be f ound in the pattern of left temporal cortical activation associated specifi cally with semantic processing. Patients with right TLE were included as a seizure control group. All TLE patients previously showed left hemisphere l anguage dominance on intracarotid sodium amytal studies, Greater blood oxyg en level dependent activation was found during phonological processing comp ared with semantic processing in frontal regions for healthy participants b ut, contrary to expectation, semantic processing did not lead to increased temporal lobe activity relative to phonological processing. Furthermore, no differences between left temporal patients and controls were found specifi cally in left temporal cortex. Rather, patients with left temporal seizure foci showed significantly greater left dorsolateral prefrontal activity com pared with controls, as well as increased signal change in left inferior fr ontal and right middle temporal gyrus, Surprisingly, patients with right, b ut not left, TLE showed poorer performance on the linguistic tasks compared with controls, as well as a decrease in right superior temporal activation . The results converge with studies of dyslexic patients showing increased left frontal activity in the presence of left temporal dysfunction and are suggestive of both inter- and intra-hemispheric functional reorganization o f language representation in left TLE.