2000). Involvement of these cortical areas was confirmed by subdural recordings (Ikeda et al. 1992, 1995; Yazawa et al. 2000). In the raw records of MEG signals without high-pass filtering of signals,
we also observed premovement field activities in these cortical regions, but the slow shift (readiness fields) beginning earlier than 1.0 sec before the movement onset was not manifested anywhere over the cortex (Fig. (Fig.1A;1A; see also Fig. Fig.4A).4A). This might be attributable to the spatial orientations of MEG sensors that are Inhibitors,research,lifescience,medical insensitive to a dipole with an intracellular current radial to the brain surface. Shibasaki and Hallett (2006) subdivided the readiness potential into two components. The first is a slow, negative potential preceding Inhibitors,research,lifescience,medical onsets of self-paced movements by 1 ~ 2 sec (e.g., Barrett et al. 1986) covering many regions in each hemisphere, whereas the second one is observed mainly in the sensorimotor region contralateral to the movement and rises more steeply 0.5 sec before the movement onset (e.g., Ikeda et al. 1992). The second component peaking just before the movement onset reflects MF activity Inhibitors,research,lifescience,medical in MEG records (Nagamine et al. 1996). According to this scheme, the MF activity we observed in the high-pass
filtered responses (e.g., Fig. Fig.1A-b)1A-b) may partly involve the early component similar to that recorded in EEG studies, but mainly reflects the spatiotemporal pattern of the latter component over
the sensorimotor Inhibitors,research,lifescience,medical area in the hemisphere contralateral to the movement. Sources composing MRCFs We found all sources of MRCFs to be in close vicinity of the central sulcus in group data (Fig. (Fig.3).3). Among these, the mean source location for the MF (smf) was found to be 7 mm medial to s3b in the postcentral gyrus (Table (Table1).1). It is widely accepted Inhibitors,research,lifescience,medical that MF is generated in the primary motor cortex (area 4) in the anterior bank of the central sulcus (Cheyne and Weinberg 1989; Kristeva et al. 1991; Ball et al. 1999; Cheyne et al. 2006). Of more importance in our findings is that sources of MF and of the subsequent three components (MEFI–MEFIII) are all localized at nearly the same portions of the precentral gyrus where finger and hand motor areas locate (Yousry et al. 1997). The source of MEFI has been proposed to reflect either of two components in the posterior wall of the central 4-Aminobutyrate aminotransferase sulcus or deep in the central sulcus, reflecting activation due to tactile or proprioceptive afferent check details inputs to areas 3b or 3a, respectively (Kristeva-Feige et al. 1995, 1996, 1997; Oishi et al. 2004; Cheyne et al. 2006). However, the removal of cutaneous inputs does not decrease the MEFI response, but rather enhances it (Kristeva-Feige et al. 1996), suggesting that proprioceptive inputs to area 3a also contribute to the generation of MEFI, as supported by later studies (Mima et al.