Neuromagnetic response of bilateral somatosensory area to stimulus repetition frequencies with a 3-D MEG measurement

Magnetoencephalogram (MEG) measurement of the magnetic field perpendicular to the scalp is widely used for research on brain function. Few reports showed phase lag characteristic of neuromagnetic responses to stimulus repetition frequencies (SRF) with SEF data of upper and lower extremities. However, phase lag characteristic with SEF data measured in contralateral hemisphere to stimulation was reported. An aim of this study is to discuss the phase lag characteristic of the neuromagnetic responses with the SRFs obtained from both ipsilateral and contralateral somatosensory area using a 3-D MEG measurement using a 3-D second-order gradiometers connected to 39-channel SQUIDs. To obtain the phase lag characteristic to the SRF, the delay time of a component synchronous with the SRFs (1.99 to 27.02 Hz) were calculated by the convolution of the SEFs and reference signal, having the same frequency as the SRFs. The phase lag characteristic to the SRF in the contralateral hemisphere was linear in the ranges below 8 Hz and above 8 Hz in all magnetic components. The phase lag characteristic of the ipsilateral hemisphere was linear only below 8 Hz in three magnetic components. These were tested for significance of the linear regression slope. Above the SRFs of 8 Hz in ipsilateral hemisphere, however, the linear regression slope was of no significance. It was found that the result of ipsilateral hemisphere was caused by SII activity. And it was also found that the result of contralateral hemisphere was caused by the activation of somatosensory area including both the SI activity and the SII activity.