Abstracts

Rationale: The conventional epileptic spike is defined as being 14 - 70 milliseconds in duration (14 – 70 Hz). Noticeably, the brain signals that have been typically used for clinical management of epilepsy in the past are limited to this low frequency range (< 100 Hz). Recent reports have indicated that the brain generates high-frequency signals up to1500 Hz [1]. Our previous magnetoencephalography (MEG) study [2] has demonstrated that the epileptic brain is associated with abnormal high-frequency neuromagnetic signals and MEG can non-invasively record them. This study was to volumetrically estimate the high-frequency neuromagnetic abnormality in epilepsy by comparing high-frequency default mode of the normal brain and the epileptic brain. Methods: Six normal volunteers and six patients were studied with a 275-Channel MEG system. Spontaneous neuromagnetic brain activation was recorded without any task. The subjects were asked to close their eyes during the recording. Real-time head localization system was used to monitor the head motion. The sampling rate of MEG data acquisition was 4000 Hz; the length of each epoch of the recorded MEG data was 120 seconds. At least two epochs of MEG data were recorded for each subject. MEG data were transformed from time-domain to frequency domain and then accumulated as one accumulated spectrogram. Focal increases of spectral power were identified in color coded spectrogram. The baseline neuromagnetic activation of the brain was volumetrically reconstructed with synthetic aperture magnetometry and then co-registered with individual magnetic resonance imaging. Results: The preliminary data from the normal subjects have shown that the default activation in 20-100 Hz were mainly around the left and right sensorimotor areas; the default activation in 100-200 Hz were around the middle of the brain; and the strong default activation in 200-300 Hz and 300-400 Hz were around left-median frontal and right –median parietal regions (see Figure 1). The default activation in epilepsy patients was clearly different from the normal default activation of the brain (see Figure 2). All patients showed clear focal increase of spectral power around the lesions detected by MRI. Conclusions: The results of this study have showed clearly that epilepsy is associated with high-frequency neuromagnetic abnormality and MEG can noninvasive record it. We consider that volumetric reconstruction of high-frequency neuromagnetic activation has the potential to be a new powerful tool for clinical management of epilepsy.