A prominent characteristic of cortical activity is the rhythmic and synchronous oscillation of the membrane potential of populations of neurons, a phenomenon that can be detected even with scalp electrodes as a component of the electroencephalogram. Cortical inhibition is an essential element in at least some of the fastest oscillations, occurring in the "beta" and "gamma" frequency range (20–80 Hz) (Atallah and Scanziani, 2009; Cardin et al., 2009; Hasenstaub et al., 2005; Sohal et al., 2009; Traub et al., 1997; Traub et al., 1996; Wang and Buzsaki, 1996). These fast oscillations take place under a variety of behavioral states, either spontaneously or in response to sensory stimuli and are thought to play a role in the transmission of information across cortical areas. Specifically, because excitatory input is more efficient in depolarizing target neurons when they are active synchronously rather than distributed in time (Azouz and Gray, 2000; Pouille and Scanziani, 2001), oscillations enable neurons to cooperate in the depolarization of common downstream targets, and thus in the propagation of neuronal signals. Through this mechanism, gamma oscillations are proposed to contribute to the merging of information processed in distinct cortical regions, for example, by "binding" neuronal ensembles that oscillate in phase.
