Abstracts

Rationale: We have demonstrated that temporal lobe epilepsy (TLE) patients undergoing MRI-guided stereotactic laser ablation of the hippocampus avoid the significant deficits in object recognition and category-specific naming that occur following standard surgical approaches (including selective amygdalohippocampectomy). Given the presumed importance of the hippocampus in episodic memory, we predicted that deficits would occur in this cognitive domain. However, we hypothesized deficits would be less severe following laser ablation than after standard approaches, as this technique preserves more brain regions and interconnections. Methods: We present pre and postsurgical neuropsychological data for 7 patients undergoing hippocampal laser ablation at Emory University who have reached 6-month follow-up (5 left and 2 right resections). Chi square analyses were used to compare these patients to a comparable group of TLE patients who underwent either a standard or selective surgical approach (n=9; 4 left/5 right) on two clinical episodic memory measures. This included tasks of visual (recall of simple geometric figures) and verbal (list learning) memory. Data for the standard resection group was from their one-year follow-up, as we added the 6-month assessment after starting the laser ablation study. This methodological issue should have increased the likelihood of finding deficits in the laser ablation group due, as these subjects will have experienced a shorter recovery period. Results: Only one of the 7 laser ablation patients experienced significant decline on either of the episodic memory tasks, while 9 of 10 patients undergoing standard resection procedures experienced a significant decline on one or both tasks. This outcome was significantly worse for the standard resection group ( 2=9.75, p<.002). Significant change on these measures was defined as an improvement or decline of 1 or more standard deviations based on normative data. The sole laser ablation patient experiencing decline exhibited decreases on the verbal memory task. This was a patient with left language dominance who underwent right hippocampal ablation but is now presenting with seizures from the left TL region. Thus, the declines may be related to multiple seizure onset regions rather than a result of surgery. Six of 7 laser ablation patients demonstrated significant improvement on one or more memory measure, while 4 of 10 standard resection patients demonstrated a similar improvement ( 2=5.76, p<.02). Conclusions: Results suggest that TLE patients undergoing laser ablation to control seizures experience a better outcome on episodic memory measures than do TLE patients undergoing standard resections. Additionally, the selective unilateral damage to the hippocampus does not appear to produce memory decline on the examined tasks suggesting that memory decline requires broader damage to mesial TL structures or that epilepsy patients are able to reorganize memory functions more efficiently if structural damage is more selective.