Influence of dipole fit time window on the quality of finger motor somatotopy

In the pioneering works [e.g. Foerster 1936, Penfield et al. 1937] hand motor somatotopy was described using electrical stimulation of the brain. Today, techniques like MEG, PET, or FMRI allow to show motor somatotopy noninvasively. While somatosensoric mapping usually allows stable conditions, motor mapping is more difficult due to variabilities in movement execution. Therefore, there was a long debate about finger motor somatotopy organization which requires fine scale localization. However, recent investigations in human subjects achieved with FMRI [Kleinschmidt et al. 1997, Lotze et al. 2000], MEG [Cheyne et al. 1991], and lesion studies [Schieber 1999] indicate that finger motor somatotopy exists, at least concerning the centers of mass of overlapping somatotopic regions. Our group recently described similar findings with MEG [Erdler et al. 1998, 1999]. The goal of the present study was to investigate the quality of dipole solutions for finger motor somatotopy depending on the time window for the dipole fit, and in addition to examine the influence of different filter settings on the localization results.