Dynamic predictions: Oscillations and synchrony in top-down processing

Classical theories of sensory processing view the brain as a passive, stimu lus-driven device. By contrast, more recent approaches emphasize the constr uctive nature of perception, viewing it as an active and highly selective p rocess. Indeed, there is ample evidence that the processing of stimuli is c ontrolled by top-down influences that strongly shape the intrinsic dynamics of thalamocortical networks and constantly create predictions about forthc oming sensory events. We discuss recent experiments indicating that such pr edictions might be embodied in the temporal structure of both stimulus-evok ed and ongoing activity, and that synchronous oscillations are particularly important in this process. Coherence among subthreshold membrane potential fluctuations could be exploited to express selective functional relationsh ips during states of expectancy or attention, and these dynamic patterns co uld allow the grouping and selection of distributed neuronal responses for further processing.