Asymmetries in the effect of side of seizure onset on recognition memory following intracarotid amobarbital injection

Purpose: To assess interhemispheric differences in recognition memory for objects during the intracarotid amobarbital sodium procedure (IAP). Methods: The recognition memory for real objects of patients with either right (RTLE; n = 28) or left (LTLE; n = 22) temporal lobe epilepsy was assessed at baseline, and after left and right intracarotid amobarbital sodium injection. Results: There were no differences between groups on baseline performance. Performance following injection ipsilateral to the side of seizure focus was relatively lower for the LTLE as compared with the RTLE group, but this difference did not reach statistical significance. However, performance following injection contralateral to the side of seizure focus was significantly lower for the RTLE as compared with the LTLE group. Within-group differences in performance after ipsilateral as compared with contralateral injection were significant for the RTLE but not the LTLE group. The difference in interhemispheric asymmetry in IAP memory performance between RTLE and LTLE groups was reflected in decreased ability to classify LTLE patients as compared with RTLE patients about side of seizure onset, using a clinically applicable decision rule. Conclusions: Recognition memory during the LAP for real objects, simultaneously named and presented visually during encoding, is mediated effectively by both the left and right hemisphere when there is no seizure focus present. However, memory appears to be more vulnerable to the presence of a seizure focus in the right as compared with the left hemisphere.