Material specific memory changes following anterior temporal lobectomy as predicted by the intracarotid amobarbital test

Temporal Lobe Epilepsy often remains refractory to drug therapy, at which time anterior temporal lobectomy (ATL) may be considered. Left anterior temporal lobectomy (LATL) has been shown to produce deficits in verbal memory, while right anterior temporal lobectomy (RATL) produces deficits in visuospatial memory. The Intracarotid Amobarbital Test (IAT) provides a unique opportunity to assess each hemisphere's contribution to memory function through the production of a reversible lesion. The IAT has been used routinely to predict global memory deficit following unilateral ATL. However, greater predictive power may be obtained by examining the relationship between material-specific components of IAT memory and post-surgical memory. This study tested the hypothesis that unilateral material-specific memory scores on the IAT can predict material-specific memory deficits following unilateral ATL, with both verbal and visuospatial memory. 70 left hemisphere language dominant patients undergoing ATL (42 RATL; 28 LATL) completed the California Verbal Learning Test and the Graduate Hospital Facial Memory Test pre- and post-operatively. IAT material-specific difference scores and absolute hemisphere scores were used to predict post-operative neuropsychological changes. Results indicated reliable changes in verbal and visuospatial memory following unilateral ATL. In the verbal domain, LATL patients declined post-operatively, while the RATL patients improved. In the visuospatial domain, RATL patients declined postoperatively, while LATL patients improved. The IAT total memory asymmetry score and verbal memory asymmetry score significantly predicted changes in verbal memory following ATL, even after controlling for the variance associated with WAIS-R FSIQ, education, and age at first neurological risk for epilepsy. A larger asymmetry between left and right injection memory scores was associated with less of a decline on verbal memory measures post-operatively. Additionally, IAT memory performance following the ipsilateral injection, relying primarily on the non-epileptic hemisphere, predicted changes in verbal memory following ATL. Better performance using the non-epileptic hemisphere was associated with less of a decline on the verbal memory measures post-operatively, providing evidence for the hippocampal reserve theory of memory in ATL. Interestingly, IAT performance does not significantly contribute to the prediction of changes in visuospatial memory following ATL.