Volume conduction (Mitzdorf, 1985;Mitzdorf, 1986;Nunez et al., 1991;Schroeder et al., 1995) provides the likely explanation for manifestation of LFPs outside of the activated substrate as observed here and earlier [e.g., (Arezzo et al., 1975; Legatt et al., 1986; Schroeder et al., 1992)], and indeed, for the manifestations of EEG and ERPs at the scalp (Nunez et al., 1991;Vaughan, Jr. and Arezzo, 1988). Our findings confirm that when stimulus strength is in the range of natural events, there is lateral volume conduction of LFPs extending at least 6 mm (see below), as well as vertical volume conduction of LFPs extending from the active tissue literally to the brain surface. Both of these findings are consistent with predictions by prior modeling studies (Tenke et al., 1993; Wang et al., 2005).
