Functional MRI of language processing: Dependence on input modality and temporal lobe epilepsy

Purpose: Functional magnetic resonance imaging (MRI) using two language-com prehension tasks was evaluated to determine its ability to lateralize langu age processing and identify regions that must be spared in surgery. Methods: Two parallel cognitive language tasks, one using auditory input an d the other visual input. were tested in a group of control subjects and in temporal lobe epilepsy patients who were candidates for surgical intervent ion. The patient studies provide an opportunity to compare functional MRI l anguage localization with that obtained using Wada testing and electrocorti cography. All of the patients in this study underwent all three procedures and a battery of neuropsychological testing. Such studies provide an opport unity not only to validate the fMRI findings but also, by comparing the pat ient results with those obtained in control subjects, to provide insight in to the impact of a pathology such as epilepsy on cortical organization or f unctional patterns of activation. Results: The results reveal both modality-dependent and modality-independen t language-processing patterns for visual versus auditory task presentation . The visual language task activated distinct sites in Broca's area, BA (Br odmann area) 44 that were not activated in the auditory language task. The auditory language task strongly activated contralateral right BA22-21 area (homologous to Wernicke's area on the left). Language lateralization scores were significantly stronger for visual than for auditory task presentation . The conjunction of activation from the two different input modalities (mo dality-independent areas) likely highlights regions that perform more abstr act computations (e.g., syntactic or pragmatic processing) in language proc essing. Modality-specific areas (e.g., right Wernicke, left fusiform gyrus, Broca BA44, supramarginal gyrus), appear to cope with the computations rel evant to making contact with these more abstract dimensions. Patients showe d recruitment of contralateral homologous language areas (p < 0.005) that w as significantly above that found in a normal control group. Extra- and int raoperative cortical stimulations were concordant with the fMRI data in eig ht of 10 cases. The fMR1 lateralization scores were also consistent with th e Wada testing in 8/10 patients. Conclusions: The fMR1 results demonstrate that the epileptic brain may be a progressive model for cortical plasticity.