Abstracts

The Wada procedure is a standard part of the pre-surgical evaluation at most epilepsy centers, although surveys of these institutions have found considerable variability in how memory is assessed during this procedure. Patients are asked to remember real objects, visual representations of real objects and geometric designs that may or may not be easy to describe verbally, and words, phrases, and other verbally mediated information. There is a large body of research that demonstrates that the left hemisphere is more adept at learning verbal information and the right hemisphere may be more adept at learning nonverbal information. At our institution, patients are asked to remember a combination of verbal and nonverbal stimuli. We hypothesized that the type of stimuli shown to patients may influence overall memory performance and the discrepancies seen between the hemispheres, important factors when deciding whether to proceed with surgery.
Records of Wada procedures completed at our institution since 1995 were reviewed. Included patients had records of successful injections of both hemispheres and exposure to our normal Wada battery. When two injections were completed to a single side, due to either over- or under-sedation, the second injection of that side was included for analysis. A typical Wada procedure consisted of injecting 125 mg of amobarbital into the side of the suspected focus, exposure to a colored shape, two words, two line drawings, a nursery rhyme, a short phrase, and a math problem while sedated, and then a minimum of 45 minutes before injecting the contralateral hemisphere and testing with an alternate set of items.
13 patients had initial right and 16 had initial left side injections. Repeated measures ANOVA found no significant main effects of the suspected focus or side of injection on total recall, recall of verbal material, or recall of nonverbal material. There was a significant interaction between the suspected focus and side of injection (i.e., patients recalled more overall and more of the verbal stimuli and nonverbal stimuli when their suspected focus side was injected).
Patients demonstrated significantly better memory performance following injection of the hemisphere with the suspected focus. There was no significant difference in memory for verbal vs. nonverbal stimuli based on the hemisphere injected or the suspected focus. It does not appear that the type of stimuli chosen increases or decreases the likelihood that a patient will show the desired direction of discrepancy or be more likely to demonstrate adequate unilateral memory abilities.