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Among the rhythms of the brain, oscillations in the beta frequency range (∼13–30 Hz) have been considered the most enigmatic. Traditionally associated with sensorimotor functions, beta oscillations have recently become more broadly implicated in top-down processing, long-range communication, and preservation of the current brain state. Here, we extend and refine these views based on accumulating new findings of content-specific beta-synchronization during endogenous information processing in working memory (WM) and decision making. We characterize such content-specific beta activity as short-lived, flexible network dynamics supporting the endogenous (re)activation of cortical representations. Specifically, we suggest that beta-mediated ensemble formation within and between cortical areas may awake, rather than merely preserve, an endogenous cognitive set in the service of current task demands. This proposal accommodates key aspects of content-specific beta modulations in monkeys and humans, integrates with timely computational models, and outlines a functional role for beta that fits its transient temporal characteristics.

Prior studies, mostly using intentional learning, suggest that power increases in theta and gamma oscillations and power decreases in alpha and beta oscillations are positively related to later remembering. Using incidental learning, this study investigated whether these brain oscillatory subsequent memory effects can be differentiated by encoding task. One group of subjects studied material performing a semantic (deep) encoding task, whereas the other group studied the same material performing a nonsemantic (shallow) encoding task. Successful encoding in the semantic task was related to power decreases in the alpha (8-12 Hz) and beta (12-20 Hz) frequency band, and a power increase in the gamma band (55-70 Hz). In the shallow task, successful encoding was related to a power decrease in the alpha band and a power increase in the theta frequency band (4-7 Hz). A direct comparison of results between the 2 encoding tasks revealed that semantic subsequent memory effects were specifically reflected by power decreases in the beta (0.5-1.5 s) and the alpha frequency band (0.5-1.0 s), whereas nonsemantic subsequent memory effects were specifically reflected by a power increase in the theta frequency band (0.5-1.0 s).

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