  Being permanently confronted with an uncertain world, brains have faced
evolutionary pressure to represent this uncertainty in order to respond
appropriately. Often, this requires visiting multiple interpretations of the
available information or multiple solutions to an encountered problem. This
gives rise to the so-called mixing problem: since all of these "valid" states
represent powerful attractors, but between themselves can be very dissimilar,
switching between such states can be difficult. We propose that cortical
oscillations can be effectively used to overcome this challenge. By acting as
an effective temperature, background spiking activity modulates exploration.
Rhythmic changes induced by cortical oscillations can then be interpreted as a
form of simulated tempering. We provide a rigorous mathematical discussion of
this link and study some of its phenomenological implications in computer
simulations. This identifies a new computational role of cortical oscillations
and connects them to various phenomena in the brain, such as sampling-based
probabilistic inference, memory replay, multisensory cue combination, and place
cell flickering.
