Abstracts

Rationale: Patients undergoing the intracarotid amobarbital (Wada) procedure sometimes exhibit recognition memory problems which appear to reflect deficits involving contextual learning or confidence in explicit recall. With contextual errors, the patient indicates that he or she has been shown the object before but at a different time and/or location (e.g., “You’ve shown me that shoe yesterday in my home”). With explicit recall problems, the patient recalls seeing the same type of object but not that specific one (e.g., “You’ve shown me that object, but it was a different color.” or “You’ve shown me a watch, but it wasn’t that one”). In the current study, we explored the frequency of both types of errors and examined whether they were more common following either right or left cerebral hemisphere injections. Methods: Video recordings of 79 consecutive participants who underwent a Wada procedure as a part of their pre-operative neurosurgical evaluation were included. Patients who were unable to complete the Wada procedure in its entirety or for whom English was a second language were excluded from the study. The number of patients who committed spontaneous contextual and/or explicit recall errors during the memory recognition portion of each Wada injection was recorded. The two kinds of errors delineated were: (1) contextual (i.e., the patient recognizes the object but insists that they were shown it at another time or place) and (2) failure of explicit recall (i.e., the patient recognizes that they have seen the specific type of object, but insists it was not the one you are showing them now). Differences in error patterns following the right or left hemisphere injections were investigated using 2x2 chi-square analyses. Results: Contextual errors were made by 36.7% (n=29) of all patients undergoing the Wada, while explicit recall errors were made by only 13.9% (n=11) of the sample. There was no significant difference between the likelihood of contextual based errors between the left and right injections (χ2 = 1.00, p = n.s.). However, of those patients who made explicit recall errors, most (82%) occurred following the right injection (χ2 = 5.18, p < .025). Conclusions: Our findings suggest that contextual errors were not lateralized to a single hemisphere, while explicit recall errors were more frequently observed following the right injection. A possible explanation is that the visual attributes of the object were not encoded along with the verbal label of the object when the non-dominant hemisphere was sedated. These results are discussed in light of existing research examining contextual/source memory, explicit recall vs. a feeling of knowing, and metamemory.