Abstracts

Rationale: The nociferous cortex hypothesis suggests that improvements in extratemporal functioning following anterior temporal resection (ATL) results from the cessation of abnormal electrophysiological activity propagating from temporal to extratemporal regions. Specifically, improved executive functioning (i.e., verbal fluency and problem solving) is hypothesized to result from reduced disruption to dorsolateral prefrontal cortex (DLPFC). Given reports of improved performance on executive measures, we hypothesized that patients who underwent ATL would also show improved use of verbal learning strategies.Methods: Subjects were 68 temporal lobe epilepsy (TLE) patients, who underwent ATL (45 left, 23 right) and pre and postoperative neuropsychological evaluation, including verbal fluency (FAS) and verbal learning (California Verbal Learning Test; CVLT): total words recalled, long-delay free recall, semantic clustering, serial clustering, perseverations, intrusions, recognition hits, and false positives. Repeated measures, multivariate, 2-way (Group x Time) ANOVAs were used to compare pre- and post-operative performances in left and right TLE patients. Regression analyses were used to determine which factors most contributed to long-delay free recall.Results: Both groups showed improved verbal fluency (p<.001). On the CVLT, left ATL patients declined significantly in both total words recalled (n=36, p<.001) and long delay free recall (n=37, p<.02). Additional CVLT scores tapping executive functioning were available for a subset of patients (19 left, 7 right). Neither semantic nor serial clustering scores improved significantly for left ATL patients (both p>.05). In fact, semantic clustering scores tended to decline postoperatively (p=.059). Further, left ATL patients also showed significant postoperative increases in number of intrusive (p<.05) and false positive (p<.01) errors. Interestingly, though, left ATL patients had significantly fewer perseverative errors (p<.05). Right ATL patients exhibited no significant CVLT changes (all p>.05). Finally, regression analyses showed that 65% of the variance of postoperative long delay free recall scores was accounted for by total initial learning across trials (F=106.83, p<.001). Conclusions: Despite improvement on select measures of executive functioning (i.e., fluency), we found no postoperative improvement in verbal learning strategies following left or right ATL. Rather, left ATL patients declined on measures of strategic organization (semantic clustering) and discrimination between list and non-list items (false positive errors), and demonstrated a greater propensity to confabulate (intrusions), despite expected practice effect gains. Regression analyses showed that initial learning is a strong predictor of long-term recall. Our results suggest that reductions in long-term recall following left ATL might be due, in part, to poor mnemonic strategizing during initial learning. Additionally, it appears that only certain aspects of executive functioning improve following ATL.