Abstracts

Rationale: Many previous studies have characterized verbal and visual memory changes that result from unilateral anterior temporal lobectomy (ATL), yet few studies have characterized the change in rate of information acquisition (e.g., slope) across repeated learning trials and the shape of the learning function following surgery. The present study examined change in spatial and verbal learning characteristics from before to after ATL, as well as the effects of side of surgery and poor post-surgical seizure control on learning.Methods: We compared the performance of 36 patients who underwent left ATL with 42 patients who underwent right ATL on the 8-trial Nonverbal Selective Reminding Test and 12-trial Verbal Selective Reminding Test. Repeated measure ANOVA and growth curve analysis were the primary statistical procedures used. Results: Consistent with previous research, left ATL patients had significant declines in verbal memory (Hotelling’s Trace F[1,76] = 17.0, p < 0.01) and right ATL patients had significant declines in spatial memory (Hotelling’s Trace F[1,76] = 6.4, p < 0.01). Growth curve analyses indicated that the best-fitting model depicting the shape of the learning function was curvilinear (i.e., quadratic or decelerating) for spatial learning (χ2 value = 1059.7, 5 df, p < 0.0001) and verbal learning (χ2 value = 2100.9, 6 df, p <0.001) both before and after surgery. Both side of surgery and poor seizure outcome independently influenced learning abilities in the best fitting models. For side of surgery, the slope of the verbal learning function was significantly reduced across trials only after left ATL. For seizure outcome, the slope of the spatial and verbal learning functions was reduced after surgery in individuals with a poor outcome compared to individuals with a good outcome, regardless of side of surgery. Even though the slope of the functions were drastically reduced for spatial and verbal learning, the shape of the learning functions were not flat (i.e., they were curvilinear) suggesting that rehabilitation intervention strategies could be designed using repeated learning trials to address memory difficulties after ATL.Conclusions: Results call into question the use of indices that quantify learning slope based on a simple linear function model. Varying rates of poor seizure outcome reported in previous studies may partly explain why researchers report nonverbal memory impairments after left ATL and verbal memory impairments after right ATL.