Several reports (Leopold et al., 2003; Maier et al. 2010) predict that lower frequency signals should spread farther than higher frequency signals. Figure 6 shows how LFPs in a number of different frequency bands spread over distance. We split LFP signals in the range of 1~256 Hz into 5 frequency bands (FB1-5), for the same data set as that used for Figure 5. The spatial spreads of signal was similar across bands (Fig. 6A). Confidence intervals (bootstrap, 95%) indicated that the amplitudes of low FB attenuated to zero level (asterisks). However, this result was attributable to variability in the phase of signals and mean phase across penetration sites for each FB. First, at all depths, we checked the bias of the signal phases among penetration sites. At most of recording depths, where the amplitudes of signals were at zero level, phases of corresponding signals were random (Rayleigh test, p>10−3). Thus, amplitudes of signals were variably positive or negative in different penetration sites, and they cancelled one another when combined. Second, at a fixed timing (24 ms), not all FB signals
