Abstracts

Semantic Memory (SM) is impaired in neurodegenerative diseases (e.g., AD, FTD) or structural lesions affecting the lateral temporal cortex bilaterally (e.g., Herpes Encephalitis). The effect of unilateral lesions is less understood. Prior studies reported deficits in pre- as well as postsurgical temporal lobe epilepsy (TLE) patients. These deficits have been suggested to be highly specific to the clinical difficulties experienced by TLE patients.
Our goal is to study SM in patients before and after anterior temporal lobectomy (ATL) to determine the effect of seizure laterality and the impact of surgery. Our specific aims are to investigate whether deficits in SM after ATL are related to the surgery or the TLE, to assess the magnitude of possible effects, and to determine whether dominant ATL represents a higher risk. We use 4 tests of semantic knowledge for 48 items. They test the ability to name an item when provided with either a picture or a description (confrontation naming, auditory naming), to provide a definition of the item, and to generate exemplars from a category (category fluency). We have cross-sectionally examined 14 pre-ATL and 18 post-ATL patients, and 8 controls. A prospective study arm is comparing performance before and after ATL in individual patients. Both dominant and non-dominant TLE patients were impaired compared to controls, but the deficit in dominant TLE patients was more severe (ANCOVA IQ covariate, p[lt]0.05). Interestingly, surgical patients did significantly or marginally worse than presurgical patients on both naming tasks, but they performed better on the definitions task (p[lt]0.05). Surgical patients supplied more information about the items defined, whereas error rates were similar. Category fluency was also better in the ATL group. Overall performance remains impaired for TLE patients regardless of surgical status in reference to controls. This cross-sectional study found that SM was impaired before and after ATL, suggesting that ATL does not substantially alter SM. However, our prospective study will provide firmer conclusions regarding the impact of ATL on SM. SM was more impaired in dominant TLE. Postsurgical patients performed worse on confrontation naming but better on the definitions task; the latter is likely to be due to a nonspecific effect of improved fluency (less AEDs and less seizures) since error rates did not differ. (Supported by the Epilepsy Foundation through the generous support of the Roger F. and Edna F. Evans Fund.)