separation, the two-point spatial autocorrelation function is often larger for low-frequency electrical activity than for high-frequency activity [1, 16]. For example, two ECoG electrodes separated by 10 mm will often have highly-correlated theta activity while gamma activity exhibits a lower correlation [17, 18]. This suggests that low frequencies modulate activity over large spatial regions in long temporal windows, while high frequencies modulate activity over small spatial regions and short temporal windows [19]. Therefore, distinct frequency bands appear to parse ongoing neuronal activity into discrete packets, each of which has a characteristic spatial and temporal scale [20, 21]. This parsing does not appear to be a strict binary classification, but is more akin to a statistical weighting or membership within a fuzzy set [22].
