Abstracts

RATIONALE:Correct memory responses and false positive errors (FPE) on the Wada were examined to address the following questions: Is there a difference in FPE rate between hemispheres? Does side injected 1st effect rate of FPE after 2nd injection? Is there a material X hemisphere FPE interaction? Can one FPE adjustment formula be applied? METHODS:The Wada was administered to 35 consecutive, left hemisphere dominant, TLE patients, excluding S's with significant cross-filling. Epileptogenic zone determined first injection side. Language was assessed before memory stimulus presentation. Stimuli consisted of 3 printed words, 3 nameable objects, and 3 irregular abstract designs. On recognition testing, true stimuli were embedded in fixed order among 6 similar foils. Wada scores were compared to pre-surgical neuropsychological scores. Analysis: paired t-test, ANOVA, ANCOVA, Pearson's r. RESULTS: When left was injected 1st there were more word FPE's than on the right (p=.034), but no effect for objects or designs. More recognition FPE's occur after 2nd injection than the 1st (p<.05), but there was no material or hemisphere difference. Recognition FPE rate was material dependent (designs>words>objects) (p<.005). More objects were recognized than designs (p<.05), but objects=words, designs=words. California Verbal Learning Test FPE's predict Wada word FPE's (r=0.483, p<.003). All Wada FPE's are independent of PIQ, but higher VIQ predicts fewer word and design FPE's. CONCLUSIONS: Words and abstract designs give unique lateralizing data, and probably require a different FPE correction formula to reflect the difference between mean word versus design recognition FPE rates. Our design did not allow randomization of side of 1st injection, but the increased word FPE's when the left side was injected first was statistically controlled by the "true recognition" covariate. Relation between CVLT and Wada word FPE's may reflect an amytal disinhibition effect. Absent adoption of a uniform Wada, false positive adjustment, and interpretation should be informed by knowledge of the complex interaction of variables particular to each center's protocol.