However, the ECD depths of MEF1 indicate that MEF1 responses do not originate from area 3a, which is located deeper than area 3b. Additionally,

area 3a is situated at the bottom of the central sulcus, and the orientation of ECDs generated in 3a is primarily radial toward the brain surface. As radial vectors do not produce an external magnetic field, MEG should be largely blind to generating sources in area 3a (Hari and Forss 1999). Therefore, activities in area 3a may not be recorded even if these areas are activated immediately after movement. On the other hand, Inhibitors,research,lifescience,medical it has been reported that ECD of MEF1 located in the precentral area, regardless of MEF1 responses, is the result of afferent feedback from muscles (Woldag et al. 2003; check details Onishi et al. 2011). It is well Inhibitors,research,lifescience,medical known that the muscle afferents project to areas 3a and 2 (Jones 1983). However, several investigators, using electrocorticography in humans (Goldring and Ratcheson 1972; Papakostopoulos

et al. 1974; Cooper et al. 1975; Lee et al. 1986) or microelectrodes Inhibitors,research,lifescience,medical in monkeys or baboons (Rosen and Asanuma 1972; Wiesendanger 1973; Lucier et al. 1975; Lemon 1979, 1981; Lemon and van der Burg 1979; Fetz et al. 1980) have proposed that the muscle afferents project to the precentral area. Kawamura et al. (1996) reported that ECD of the second peak elicited by median nerve stimulation was medial and superior to that at N20m, on the anterior wall of the central sulcus, “area 4”. The findings of our study and the Inhibitors,research,lifescience,medical above-mentioned studies suggest that the MEF1 response might be originating from area 4. We found two peaks of MEG response associated with passive finger movement from 30–100 msec after movement onset. The peak latency and ECD location of earliest component (PM1) following PM were not significantly different from those of MEF1 following active movement. An fMRI study showed that the activity in area 4 accompanying PM was the same as that accompanying active movement (Terumitsu Inhibitors,research,lifescience,medical et al. 2009). As mentioned above, it has

been reported that neurons in area 4 receive muscle afferent inputs (e.g., Goldring and Ratcheson 1972). Subdural recording has shown that PM can elicit an initial response at 34 msec in the precentral area (Papakostopoulos and et al. 1974; Lee et al. 1986). If a muscle is passively stretched, the afferent input from muscle spindles projects to that area of the cortex that excites cells for contracting the same muscle (e.g., Rosen and Asanuma 1972). Desmedt and Ozaki (1991) reported somatosensory-evoked potentials (SEPs) following PM, and they concluded that the recorded positive response with a mean peak latency of 33 msec at the contralateral precentral site was primarily generated in area 4. Mima et al. (1996) reported SEPs following PM using a unique technique.