Abstracts

RATIONALE: Material specific memory impairment is often considered a sign of lateralized temporal lobe epilepsy, based largely upon the body of literature reporting material specific memory impairment after temporal lobectomy. However, there is little information about the baseline pattern of memory ability in surgical candidates. The present study sought to establish the baserate and predictors of global memory impairment, defined as poor learning for both verbal and nonverbal information, in epilepsy surgery candidates. METHODS: One-hundred twenty-one patients presenting for possible surgery were administered a battery of neuropsychological tests, including measures of verbal (California Verbal Learning Test) and nonverbal (Rey Complex Figure) memory. Patients were classified as having memory impairment on either test if their performance fell more than one standard deviation below the age corrected mean (<16th percentile). RESULTS: Thirty-six percent (44/121) patients had impaired memory for both verbal and nonverbal information. Twenty-one percent demonstrated normal memory for both verbal and nonverbal information. Only 42% of patients demonstrated selective memory impairment for either verbal (18%) or nonverbal (24%) information. The frequency of selective memory impairment was not significantly different from the frequency of global memory impairment or normal memory (p>.10). Factors associated with global memory impairment include sex, left hemisphere memory on the Wada test, and Full Scale IQ. CONCLUSIONS: Patients presenting for possible surgical treatment of seizures commonly present with global memory impairment. The association with low IQ scores suggests that this may be a function of lower overall cognitive function. However, global memory impairment was more commonly observed in patients that failed the left memory portion of the Wada test, suggesting possible alternative explanations such as the crowding effect. The implications of the present findings for predicting outcome following surgery and the localizing value of material specific memory tests are discussed.