Abstracts

Rationale: The mismatch negativity (MMN) is one of the most intensely investigated components of event-related potentials (ERPs). It is thought to reflect a pre-attentive auditory discrimination process and intentional switching. It has been argued that MMN has at least two main sources: the first source is located in the bilateral auditory cortex and underlies pre-perceptual sound change detection in the auditory cortex. This likely triggers the second source, the frontal-cortex MMN generator, which is associated with the initiation of the attention switch to sound change. Recently, there are many MMN reports in temporal lobe epilepsy (TLE) which demonstrated the enhanced amplitudes and prolonged latencies. Conversely, there are no MMN reports in frontal lobe epilepsy (FLE) As long as we searched. The aim of this study was to examine cognitive function in patients with FLE using duration MMN. Methods: We examined 15 FLE patients (seven females). The mean age was 36.6 ± 9.9 (range 22-53 years). The mean age at epilepsy onset was 13.7 ± 7.8 (8 months to 32 years). Nine of 15 patients had been seizure free for more than 41 months. Two patients did not take AED. Four patients took 1 AED, seven patients took 2 AEDs, and two patients took >3 AEDs. Control data were collected from 15 age-matched healthy subjects (nine females, all right handed). The stimuli were 1000 Hz pure tones differing in duration, such that standard stimuli had a duration of 100 ms and the deviant stimuli were 150 ms long. The MMN was recorded from the four midline (Fz, Cz, Pz, Oz) sites and bilateral mastoid electrodes. The participants were instructed to watch silent cartoons during the recording session and to ignore sounds heard through their earphones. Data analysis focused on a 600 ms time window ranging from 100 ms pre-stimulus to 500 ms post-stimulus onset. At least 100 responses to deviant stimuli were analyzed for each participant. We evaluated the mean MMN amplitude and peak latency at each electrode between 190 and 340 ms, and ERP parameters were compared by a one-way ANOVA. The study was approved by the Ethics Committee of the Tokyo Medical and Dental University. Written informed consent was obtained from all the participants after a thorough description of the study. Results: Although the FLE patients appeared to show smaller MMN amplitudes than the controls (HC -0.66 ± 0.89 vs., FLE= -0.24 ± -0.88 micro-volts), there was no significant difference in the mean amplitude or peak latency at Fz (HC 247 ± 29 vs. FLE= 227 ± -30 vs., ms). Conclusions: We have previously demonstrated an impairment of pre-attentive processing in TLE patients. This study showed that FLE patients had a similar waveform compared to controls. The results suggest that FLE patients did not have impairments of auditory cognitive processing. Therefore, the temporal lobe, rather than the frontal lobe, may be the responsible MMN generator. Larger studies with more subjects will be necessary to investigate the MMN in FLE.