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 ei ther right (RTLE; n = 28) or left (LTLE; n = 22) temporal lobe epileps y was assessed at baseline, and after left and right intracarotid amob arbital sodium injection. Results: There were no differences between g roups on baseline performance. Performance following injection ipsilat eral to the side of seizure focus was relatively lower for the LTLE as compared with the RTLE group, but this difference did not reach stati stical significance. However, performance following injection contrala teral to the side of seizure focus was significantly lower for the RTL E as compared with the LTLE group. Within-group differences in perform ance after ipsilateral as compared with contralateral injection were s ignificant for the RTLE but not the LTLE group. The difference in inte rhemispheric asymmetry in IAP memory performance between RTLE and LTLE groups was reflected in decreased ability to classify LTLE patients a s compared with RTLE patients about side of seizure onset, using a cli nically applicable decision rule. Conclusions: Recognition memory duri ng the LAP for real objects, simultaneously named and presented visual ly during encoding, is mediated effectively by both the left and right hemisphere when there is no seizure focus present. However, memory ap pears to be more vulnerable to the presence of a seizure focus in the right as compared with the left hemisphere.