[Clinical application of magnetoencephalography for brain infarction]

Magnetoencephalography (MEG) is a noninvasive functional imaging technique that provides information regarding neuronal activity with high spatial resolution. Analyses of spikes and slow waves in various brain disorder have performed using spontaneous magnetic field, and functional mapping studies have performed using evoked magnetic field. The goal of this study was to determine the characteristics of MEG findings in these two magnetic fields for ischemic stroke patients. In the first examination, we recorded the spontaneous magnetic activity with a 37-channel neuromagnetometer and counted the number of equivalent current dipoles (neuromagnetic sources) which were divided into 6 groups with different frequencies of every 4 Hz. There were much more dipoles below 8 Hz in stroke patients than in normal controls, which tended to distribute in the hypoperfusion area near the infarct. In the second examination, we recorded auditory evoked responses for tone burst stimuli and analyzed the localization of dipoles for the 100-m.sec. component after the onset of the stimuli. The dipoles lay near the Heschl gyrus in most of control group. On the contrary, they often distributed apart from the Heschl gyrus in stroke patients with severely damaged regional oxygen metabolism measured by positron emission tomography, indicating an inappropriate response for auditory stimuli. In conclusion, MEG brought interesting informations for the brain function of stroke patients.