Abstracts

In normal readers, different semantic classes of nouns (e.g. concrete versus abstract) are processed in different cortical regions. Specifically, concrete words preferentially activate left basal temporal cortex and abstract words preferentially activate the left inferior frontal cortex. Previous functional MRI (fMRI) studies have shown interhemispheric reorganization of semantic representation in patients with temporal lobe epilepsy (TLE). However, the degree of reorganization specific to concrete versus abstract nouns was not explored. To this end, we used fMRI to determine whether patients with TLE show differential representation of semantic information for the different noun classes, potentially causing reorganization that is selective to the concrete noun class. Three patients with left temporal TLE confirmed by video-EEG monitoring were recruited. Three age and gender-matched controls were also studied. All subjects were right handed, had English as their native language, and completed secondary school. Event-related fMRI was performed at 3 Tesla during a lexical decision task, involving semantic class stimuli manipulation (e.g. concrete versus abstract nouns). The concrete noun stimuli used in this task were taken from Billingsley et al. (Brain 124, 1218-1227, 2001). Abstract noun stimuli were selected and matched to the concrete nouns on printed frequency, length, and orthographic neighborhood size. Word stimuli were all pilot tested for concreteness using 20 control subjects. We compared fMRI activation patterns and laterality indices in patients with left TLE to the control participants. Patients with left TLE showed right lateralization with significant activation in the right superior and middle temporal gyri for the concrete stimuli condition and no significant activity in left temporal regions, ipsilateral to the seizure focus. Control subjects, however, showed left temporal activation and lateralization. No differences were seen between patients and controls for the abstract stimuli condition. These preliminary findings suggest that patients with left TLE may show some degree of interhemispheric reorganization for the processing of concrete semantic information. (Supported by Canadian Institutes for Health Research and Alberta Heritage Foundation for Medical Research.)