Are volume conduction effects asymmetrical? The tonotopic gradient in macaque A1 is about 1.0 mm/octave (Kosaki et al., 1997; Kusmierek and Rauschecker, 2009; Merzenich and Brugge, 1973), and thus, 6 octaves difference on the tonotopic map is about 6 mm away from a recording site, for example, more than ½ way along the frequency representation in A1, and the attenuation of LFP amplitude at this distance laterally appears to be about the same as at this distance vertically above A1 (Fig. 5). This fits with the observation that neocortical conductivity appears isotropic (Logothetis et al., 2007;Ranck, 1963).
