title: Detecting functional asymmetries through the dipole moment of magnetoencephalography.
abstract: To assess the accuracy of magnetoencephalography (MEG) as a tool for quantitative detection of neuronal activity, the dipole moment was estimated at N20m of somatosensory evoked fields (SEFs) produced by median nerve stimulation. Neurologically stable patients were examined twice within 2 weeks. Since the estimated moment values of the two examinations should be essentially the same, we assessed the margin of error for our measurement system. The results showed that a change of more than 5.2 nAm is statistically significant (p=0.05; n=91). The patients were classified as without or with functional asymmetries by measuring the conventional cerebral blood flow (CBF) with single photon emission CT (SPECT), and the dipole moment difference between hemispheres was measured. Hemispheric moment differences were statistically larger for the group with CBF laterality, indicating consistency between conventional CBF results and the moment measurements as a group. Moreover, MEG was able to detect more functional asymmetries than CBF study. The dipole moment provided a reliable quantitative index of cortical response to somatosensory stimulus, and the moment measurement thus holds promise as a clinical tool for direct quantification of cortical response.
authors.affiliation: Department of Geriatrics and Neurology, Osaka City University Medical School, Osaka, Japan. tsuyoshi822@usa.net
authors.forename: Tsuyoshi
authors.initials: T
authors.lastname: Tsutada
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Ikeda
authors.forename: Naohiro
authors.initials: N
authors.lastname: Tsuyuguchi
authors.forename: Hideji
authors.initials: H
authors.lastname: Hattori
authors.forename: Masahiro
authors.initials: M
authors.lastname: Shimogawara
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Shimada
authors.forename: Takami
authors.initials: T
authors.lastname: Miki
mesh_terms: D000328:Adult; D000368:Aged; D001921:Brain / Q000000981:diagnostic imaging / Q000503:physiopathology*; D002560:Cerebrovascular Circulation; D004292:Dominance, Cerebral; D004558:Electric Stimulation; D005073:Evoked Potentials, Somatosensory; D005260:Female; D006801:Humans; D015225:Magnetoencephalography; D008297:Male; D008475:Median Nerve / Q000503:physiopathology; D008875:Middle Aged; D015899:Tomography, Emission-Computed, Single-Photon