Abstracts

Rationale: Event-related potentials (ERPs) are averaged electroencephalographic (EEG) responses time-locked to external stimuli or internal events (Naatanen & Kahkonen, 2009). Mismatch negativity (MMN), one of a component of ERP, usually peaks approximately 100-250ms stimulus onset at the fronto-central sites. It has been shown that MMN reflects pre-attentive function and has two generators, one is in the frontal lobe which associates with attention switching and another is in the temporal lobe which associated with sensory memory mechanism. MMN is suitable to examine the existence of dysfunction in the temporal lobe or in the frontal lobe. Miyajima et al. (2011) revealed that both the temporal and frontal cortices contributing to MMN generation were affected in temporal lobe epilepsy (TLE) patients. In order to elucidate whether there are any pre-attentive dysfunctions in frontal lobe epilepsy patients, we performed the same paradigm as Miyajima et al. Methods: We examined seven FLE patients (five female, six right-handed), with a mean age of 35.9 ± 7.4 (22-45 years). The mean age of seizure onset was 14.9 ± 14.7 (6 months-44 years). Six were seizure free for more than one year. Six patients took one or two anti-epileptic drugs (AEDs). One patientsdid not take any AED. Control data was collected from seven age-matched healthy controls (HCs, five females, all right handed). Epileptic foci were on the left for four patients, right in two patients, and unclear for one patient. The stimuli presented were pure-tones (1000 Hz as standard and 1050 Hz as deviant). Numbers of stimuli given were 800 standard and 200 deviant. We evaluated the MMN (deviant minus standard) peak and mean amplitude, and peak latency separately for each subtraction waveforms at Fz, Cz, left, and right mastoids between 100-250 ms stimuli onset. The study was approved by the Ethics Committee at Tokyo Medical and Dental University, and written informed consent was obtained from each participant. There is no conflict of interest. Results: Visual inspection revealed that MMN at Fz was larger in FLE patients than HCs. MMN at the right mastoid was smaller in FLE patients than in HCs, whereas MMN at the left mastoid was similar between FLE patients and HCs. We confirmed that the MMN difference between HC and FLE at fronto-central sites were attributed by the difference of the deviant responses rather than standard responses. Conversely, the amplitude difference between right and left mastoid sites in FLE was due to the small deviant responses at right mastoid site in FLE (Figure1 and 2). Conclusions: In the present study, MMN in the fronto-central region was larger in FLE patients than in HCs. This result might reflect hyper excitability in fronto-central region in FLE. We observed smaller MMN amplitude in the right mastoid than left mastoid in FLE patients. The limitation of this study is that the number of patients was small. A larger number of patients are needed to confirm the present asymmetry at the mastoids.