Magnetoencephalography (MEG)


Magnetoencephalography (MEG) is one of the recent noninvasive techniques for investigating human neuronal activities. MEG measures magnetic fields outside the skull, which is produced by electric current flow in the neural activities. MEG is especially good at tracing for sources in the cerebral cortex with millisecond range temporal resolution. The University of Tokyo Hospital has introduced a bland-new whole-head MEG system, VectorviewTM systems (Neuromag, LTD., Helsinki, Finland) in March 2000. With the systems, our laboratory is devoted to investigate such higher brain functions as image or language processing. As language studies, we have lately examined the reading process of Japanese phonograms. An ongoing study is concerning visual processing of printed words.

MEG system that can detect magnetic signals reflecting neuronal activities not only in the cerebral cortex but also in the deep portion of the brain such as in the hippocampus. Applications of this system to the measurements of higher brain functions and the diagnosis for brain surgery, etc. are also within the scope of this project.

Meg responses from musicians who had absolute pitch and from non-musicians were measured while they received different auditory stimuli. The parameters of single equivalent current dipoles (ECDs) were calculated for the N1m responses occurring in the auditory cortex. The location of the ECD for the noise burst was significantly posterior to the ECDs for the tones in the two hemispheres of the musicians, but not for those of the non-musicians. Further, in the left hemisphere the ECDs for the musicians were significantly posterior to those for the non-musicians. These results suggest distinct neural activities in the auditory cortex of musicians, which may be the result of cortical plasticity produced by training and/or an inherent cortical structural specificity.