Decoding the status of working memory representations in preparation of visual selection.

Daily life is filled with sequences of multiple tasks, each with their own relevant perceptual input. Working memory needs to dissociate representations that drive attention towards currently relevant information from prospective representations that are needed for future tasks, but that until then should be prevented from guiding attention. Yet, little is known about how the brain initiates and controls such sequential prioritization of selection. In the current study we recorded EEG while subjects remembered a color as the target template for one of two sequential search tasks, thus making it either currently relevant (when it was the target for the first search) or prospectively relevant (when it was the target for the second search) prior to the task sequence. Using time-frequency specific linear classifiers, we were able to predict the priority status (current versus prospective) of the memory representation from multivariate patterns of delta (2-4 Hz) and non-lateralized alpha power (8-14 Hz) during both delay periods. The delta band was only transiently involved when initializing the priority status at the start of the first delay, or when switching priority during the second delay, which we interpret as reflecting the momentary top-down control over prioritization. In contrast, alpha power decoding was based on a more stable pattern of activity that generalized across time both within and between delay periods, which we interpret as reflecting a difference in the prioritized memory representations themselves. Taken together, we reveal the involvement of a complex, distributed and dynamic spatiotemporal landscape of frequency-specific oscillatory activity in controlling prioritization of information within working memory.