Detecting functional asymmetries through the dipole moment of magnetoencephalography

Tsutada, Tsuyoshi; Ikeda, Hitoshi; Tsuyuguchi, Naohiro; Hattori, Hideji; Shimogawara, Masahiro; Shimada, Hiroyuki; Miki, Takami

« Previous Next »Journal of the Neurological Sciences
Volume 198, Issue 1 , Pages 51-61, 15 June 2002

Detecting functional asymmetries through the dipole moment of magnetoencephalography

Tsuyoshi Tsutada
- Corresponding author. Tel.: +81-6-6645-3889; fax: +81-6-6646-5599
- Department of Geriatrics and Neurology, Osaka City University Medical School, 1-5-7 Asahimachi, Abeno-ku, Osaka 545-8586, Japan
Hitoshi Ikeda
- Department of Neurology, Osaka City General Hospital, Osaka, Japan
Naohiro Tsuyuguchi
- Department of Neurosurgery, Osaka City University Medical School, Osaka, Japan
Hideji Hattori
- Department of Pediatrics, Osaka City University Medical School, Osaka, Japan
Masahiro Shimogawara
- Kanazawa Institute of Technology, Kanazawa, Japan
Hiroyuki Shimada
- Department of Geriatrics and Neurology, Osaka City University Medical School, 1-5-7 Asahimachi, Abeno-ku, Osaka 545-8586, Japan
Takami Miki
- Department of Geriatrics and Neurology, Osaka City University Medical School, 1-5-7 Asahimachi, Abeno-ku, Osaka 545-8586, Japan

Received 8 June 2001; received in revised form 11 January 2002; accepted 11 March 2002.

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.

Keywords: Magnetoencephalography, Dipole moment, Somatosensory evoked field, Functional asymmetries, Threshold of muscle twitch, Cerebral blood flow, Quantification of neuronal activity