Abstracts

The value of material-specific memory performance during the intracarotid amobarbitol procedure (IAP) is debatable. If there are material specific memory profiles that occur regardless of seizure laterality, the validity of IAP memory may be affected. The present study examined whether seizure laterality and side of injection had an impact on material specific memory performance during the IAP.
Nineteen intractable epilepsy patients (10 L foci; 9 R foci) underwent IAP as part of surgical planning. The procedure involved initial injection of the hemisphere ipsilateral to the seizure focus followed by the contralateral hemisphere. Patients were presented a unique set of ten stimuli following each injection, including 3 words, 1 arithmetic equation, 3 line drawings of objects, one colored square, and 2 non-verbalizable designs. Patients were asked to identify the correct memory item from an array of five foils 10 minutes post-injection. Memory items were separated into three categories: dually encoded (pictures, color), verbal only (words, equation), and non-verbal (designs).
Total IAP recognition memory performance was significantly better following injection of the hemisphere ipsilateral to the seizure focus ( % correct L focus = 65; R focus = 72) compared to injection of the contralateral hemisphere (% correct L focus = 35; R focus = 46). These findings held for all types of stimuli and for patients with right or left foci, with one exception. Following the left hemisphere injection, there was no significant difference in memory performance between patients who had right or left foci for dually encoded stimuli (L 68% vs. R 58% correct). After the right hemisphere injection, patients exhibited a stratified pattern in which dually encoded stimuli were recalled better than verbal only stimuli (R focus = 83% vs. 75% correct; L focus = 53% vs. 32% correct) which in turn were recalled better than non-verbal stimuli (% correct R focus = 44; L focus = 5). In contrast, no specific memory pattern was seen for the left hemisphere injection (R focus % correct: dually encoded = 58, verbal only = 39, non-verbal = 33; L focus % correct: dually encoded = 68, verbal only = 60, non-verbal = 70).
The study found that inclusion of dually encoded memory stimuli may reduce the validity of the memory portion of the IAP. Our results show that performance on these items following the left hemisphere injection did not significantly differ between patients with right and left seizure foci. Therefore, the validity of the IAP may be improved by including material specific memory items rather than dually encoded stimuli. We also found a clear pattern of memory performance following right hemisphere injection regardless of seizure focus. In contrast, no pattern was seen following left hemisphere injection, confirming previous findings that the right hemisphere may be less discretely organized for memory functioning, and may exhibit more intrinsic plasticity.