To investigate the inter-and intrahemispheric reorganization of the language cortex in left temporal lobe epilepsy (TLE) with left-sided hippocampal sclerosis. A functional magnetic resonance imaging was performed on 13 right-handed patients suffering from medically intractable left TLE, and in 13 sex-and age-matched healthy controls. The activation paradigm used was a silent word generation task. A language laterality index (LI) was calculated from the number of activated voxels in the right and left anterior two-thirds of the hemispheres. Significant differences between the patients and the controls were observed in the activation of the left-sided inferior frontal gyrus. Less consistent findings in this region, as well as the relative protection of Broca's area from the activation, were revealed in the patients. In addition, different patterns of activation were proven in the cerebellum and other cortical as well as subcortical brain structures within both hemispheres. Significant differences were also found in the values of the language LIs between the investigated groups: these values suggested a more bihemispheric language representation in the patients. As anticipated, lateralization of the language functions in the epileptics significantly decreased in connection with an earlier age of initial insult. Our results support the hypothesis of a significant intra-and interhemispheric functional reorganization of language-related neuronal networks in left TLE.

Several functional MR imaging studies evaluating the lateralisation of linguistic functions in patients who underwent Wada testing have been reported. There is extensive variance in the Laterality index (LI) calculation across the studies, and the optimal calculation method remains unclear. We attempted to calculate the LI in different ways in the same subjects, in order to find the LI calculation method with the highest correlation to the Wada test. Fifteen patients (10 females, 5 males) suffering from medically intractable temporal lobe epilepsy (TLE) (12 left, 3 right) were admitted for the study. The patients underwent a standardized bilateral intracarotid short-acting barbiturate test. Language testing included spontaneous speech, oral comprehension, reading, object and picture naming, and repetition. All the tasks were scored separately in order to increase the possibility of correlation between Wada and LI. A silent phonemic verbal fluency task (VFT) was used as a language paradigm for functional measurement. Regions of interest (ROIs), with a known association with language function (Broca's area, the lateral prefrontal cortex, etc.), were defined. First, the LIs were calculated from the ROIs using a previously reported method (simple suprathreshold count). Next, we used several new methods of LI calculation (t-weighting of voxels, methods independent of the choice of the statistical threshold, etc.) The most significant correlation with Wada was proven in the LIs that were evaluated from Broca's area (up to R = 0.94, P = 1 x 10(-7)). However, the new LI calculation methods used in the present study did not produce a statistically significant benefit in comparison to previously reported methods.