Interhemispheric Reorganization of Memory Function Assessed by Wada Test in Patients with Mesial Temporal Lobe Epilepsy

ABSTRACT

BACKGROUND: We investigate an interhemispheric reorganization of memory functions using Wada test in patients with unilateral mesial temporal lobe epilepsy (MTLE). METHODS: We included 70 patients with unilateral MTLE and 37 with neocortical epilepsy (NE). The Wada memory stimuli were composed of 10 items. Scores for each injection were calculated with 1 and 0.5 points assigned for each correct free recall and recognition, respectively. A cut-off asymmetry score for lateralization of memory deficit was defined as 2 points. We statistically analyzed the proportion of memory asymmetry and the average memory score according to the type of epilepsy and the lateralization of seizure focus. RESULTS: The lateralizations of memory deficit determined by Wada memory asymmetry were evenly distributed in the left MTLE (n=34): left in 12 (36%), right in 11 (32%), and undetermined in 11 (32%). However, most (92%) of the right MTLE (n=36) were correctly lateralized to the side of seizure focus. More than 90% of patients with NE were lateralized to right hemisphere regardless of the seizure laterality. The average total (left plus right) memory score were not significantly different between each group. However, right memory score in left MTLE or left memory score in right MTLE were significantly higher than those in NE. The earlier age at seizure onset and the longer duration of epilepsy were observed in patients with left MTLE who had ipsilateral memory deficit comparing to those who had contralateral memory deficit. CONCLUSIONS: A pure interhemispheric reorganization of memory functions could occur in some patients with MTLE. It may be influenced by age at the onset of a seizure and the duration of epilepsy.