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 may 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., Seven patients with left temporal TLE secondary to hippocampal sclerosis confirmed by video-EEG monitoring were recruited. Ten 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 then performed a group analysis comparing fMRI activation patterns for concrete and abstract nouns. We also measured subjects[apos] reaction times to in making the lexical decision., Patients with left TLE showed significantly slower reaction times for abstract stimuli (p = 0.2) versus controls. Furthermore, patients with left TLE showed significantly reduced superior and middle temporal gyrus activation compared to controls for abstract stimuli. In contrast, no significant differences were seen between reaction times or patterns of activation between patients and controls for concrete stimuli., These findings suggest that patients with left TLE may show some degree of interhemispheric reorganization for the processing of abstract semantic information. This reorganization, however, was not complete as patients[apos] reaction times for abstract stimuli were slower than normal controls., (Supported by Canadian Institutes of Health Resarch, Alberta Heritage Foundation for Medical Research.)