The impact of oscillations on local computation and long-range communication is rendered more complex by the presence of several distinct brain rhythms. In vitro work investigating the local cellular origins of different rhythms shows that application of chemicals and neurotransmitters (i.e., carbachol, kainate, glutamate, etc) to isolated cortical slices reliably evokes electrical activity within a set of distinct modal frequencies [10]. These modal rhythms correspond to band-specific activity observed in vivo, including the traditional delta (1–4 Hz), theta (4–8 Hz), alpha (8–12 Hz), beta (12–30 Hz), and gamma (>30 Hz) bands as well as finer subdivisions within each band [5, 11–15]. Importantly, while different frequencies provide distinct temporal windows for processing (corresponding to the duration required to complete one oscillatory cycle), different rhythms are also associated with different spatial scales and therefore different cell population sizes. For a given spatial 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
