Abstracts

Rationale: Cognitive dysfunction in epileptic patients may be connected with the neurophysiological changes related to seizures or antiepileptic drugs (AED). Mismatch negativity (MMN) is a well established objective index of auditory cortex function and widely used to investigate the pathophysiological mechanisms of neuropsychiatric disorders. The aim of this study was to evaluate cognitive dysfunction in patients with temporal lobe epilepsy (TLE) by examing MMN extracted from a pure-tone paradigm. Methods: This study included 13 TLE patients (33.8±11.0 years old, five females) and nine age-matched healthy controls. The laterality of epileptic focus was left in four patients, right in one patient, and unclear or bilateral in the rest. Eight patients had more than 10 seizures a year, while five had been seizure free for the last two years. Twelve patients were under AED treatment (mean 1.8 AEDs). The electroencephalogram was recorded from scalp electrodes including Fz, Cz, Pz, Oz and bilateral mastoids. The stimulus series was composed of 1050 Hz deviant tones (20%) and 1000 Hz standard tones (80%). MMN was measured as a difference waveforms obtained by subtracting the event-related potentials for standard stimuli from those for deviant stimuli. The MMN amplitude and latency were analyzed by repeated measures analysis of variance using Super ANOVA software. Results: In TLE patients, the MMN peak amplitudes at Fz and Cz were higher (P<0.05) than those of controls. Both patients under remission as well as in intractable state showed greater MMN peak amplitude than controls. At the bilateral mastoids patients showed a tendency for small or unclear peak of MMN. There were no singnificant differences in the latency of MMN at Fz and Cz between TLE and control groups. No hemispheric preference for processing was observed. The number of AEDs was negatively correlated with the MMN peak amplitude at Fz and Cz in epileptic patients. Conclusions: The findings demonstrate that TLE patients have impaired pre-attentive processing of pure-tone sounds. Larger peak MMN amplitude at Fz and Cz may reflect the hyper-excitability of the auditory cortex in TLE patients, and thus serve as a marker for cognitive dysfunction. The present results also suggests that AEDs may affect cognitive function.