Influencing factors on interhemispheric language 'shift' and memory asymmetry in temporal lobe epilepsy

ABSTRACT

BACKGROUND AND OBJECTIVES: Interhemispheric memory asymmetry & language 'shift' (right hemisphere restitution of originally left hemisphere functions or vice versa) and its lateralizing value in temporal lobe epilepsy (TLE) have been repeatedly reported. We analyzed the factors influencing the memory asymmetry & language 'shift', which, to our knowledge, has rarely been reported. METHODS: The IAP (Intracarotid Amobarbital Procedure) was performed in 94 patients, who were candidates for temporal lobectomy. We determined language dominance (LD) hemisphere and calculated 'memory asymmetry indexes' (difference of percentage of memory recall between left and right hemisphere). We reviewed sex, history of 'risk factors' (episodes of febrile convulsion, head trauma, or meningoencephalitis during period of infant and early childhood), age of epilepsy-onset, duration of epilepsy, and then correlated each of them with the presence of language shift and the degree of memory asymmetry. RESULTS: Atypical LD (bilateral or right hemisphere LD) was significantly more frequent in left TLE group than in right (left TLE 19%, right 0%, p=0.009). The 'shift' of LD hemisphere was more frequent in patients with 'risk factors' (p=0.04). The 'shift' of LD hemisphere was seen only in patients with duration of epilepsy of > 10 years, but statistically not significant(p=0.07). Interhemispheric memory asymmetry occurred in most patients. The presence of 'risk factors' (p=0.05), duration of epilepsy of 10-20 years (p=0.04), and female sex (p=0.01) were significantly associated with the memory asymmetry in left TLE group. But in right TLE group, the memory asymmetry was not associated with above factors. CONCLUSION: Only in left TLE group, the presence of 'risk factors' and duration of epilepsy influenced both interhemispheric memory asymmetry & language 'shift', whereas sex influenced memory asymmetry only. In right TLE, we failed to find correlation. These results could be explained that in right TLE, memory might be easily or rapidly shifted to the contralateral hemisphere, even in absence of above factors.