Hemispheric asymmetries in arousal affect outcome of the intracarotid amobarbital test.

OBJECTIVE: To evaluate changes in arousal and their impact on memory performance during the intracarotid amobarbital test (IAT). METHODS: Along with memory measures, level of arousal was evaluated through clinical ratings and nonverbal self-ratings in epilepsy patients undergoing IAT before anterior temporal lobectomy. RESULTS: Irrespective of seizure focus, left-sided amobarbital injection resulted in decreased objective and subjective arousal more often than right-side injection. Impaired objective arousal was greater when the left hemisphere was injected second, because of the presumed additive effects of systemic amobarbital residual from the first injection. Decreased objective arousal was related to poorer performance on memory testing following left-hemisphere injection. CONCLUSIONS: The IAT, as practiced in most centers, is biased, so patients with right temporal lobe seizure focus are more likely to "pass" the test, whereas patients with left seizure focus are more likely to "fail" the test. The significant impact of changes in arousal on memory testing needs to be considered when using IAT results to select patients for temporal lobectomy.