Abstract
We carried out a three-dimensional vector measurement of a somatosensory evoked field (SEF) with an electric stimulus to the right thumb, using three-dimensional second-order gradiometers connected to 39-channel SQUIDs, which can detect magnetic components perpendicular to the scalp (Br) and tangential to the scalp (BΘ, Bφ) simultaneously. A dynamic singular value decomposition method, with a time window and shift time, was applied to spatio-temporal magnetic data. First, averaging of the SEF data with a dynamic SVD was done with each trigger for stimulation. Second, dynamic SVD was applied to SEF data, having two frequencies ranges (1-80 Hz and 15-80 Hz), and with a time window of 10 ms and which was shifted every 1 ms in analysis. Two dominant singular values were obtained for the contralateral magnetic component in 90 to 110ms. Source localization of SI and SII activity with a ECD method showed dominant GOF (goodness of fitness) around 90ms. We concluded that the proposed dynamic SVD method, with a time window and shift time, is useful for reducing noise component in SEF data and discriminating multiple sources overlapping in time.
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