The Gamma Oscillation: Master or Slave?

The idea that gamma enhancement reflects a state of high neuronal excitability and synchrony, critical for active brain operations, sets gamma up as a master'' or executor process that determines whether an input is effectively integrated and an effective output is generated. However, gamma amplitude is often coupled to the phase of lower frequency delta or theta oscillations, which would make gamma a slave'' to lower frequency activity. Gamma enslavement is productive and typical during rhythmic mode brain operations; when a predictable rhythm is in play, low and mid-frequency oscillations can be entrained and their excitability fluctuations of put to work in sensory and motor functions. When there is no task relevant rhythm that the system can entrain to, low frequency oscillations become detrimental to processing. Then, a continuous (vigilance) mode of operation is implemented; the system's sensitivity is maximized by suppressing lower frequency oscillations and exploiting continuous gamma band oscillations. Each mode has costs and benefits, and the brain shifts dynamically between them in accord with task demands.