Second, accumulating evidence suggests that information and processing is integrated across these multiple spatial and temporal scales, and that a hierarchy of mutually-interacting oscillations would be well-positioned to regulate this multi-scale integration [5, 6]. Neuronal oscillations can be viewed as rhythmic changes in cortical excitability [7]. Therefore, brain rhythms affect local computation since neuronal activity associated with stimulus processing differs depending on its timing relative to the phase of ongoing oscillations. If high neuronal excitability is associated with the trough of an LFP oscillation, then stimuli time-locked to the LFP trough may be processed faster or more comprehensively than stimuli time-locked to the peak of the oscillatory waveform [7]. Similarly, long-range communication between areas may also be influenced by oscillatory activity by modulating the effective gain of communication [7–9]. For example, for a given phase difference between two areas, spikes leaving one area will arrive when the other area is maximally excitable, while a shift in the relative phase implies that spikes will arrive when the receiving area is less excitable, making communication less effective.
