Sustained alpha oscillations serve attentional prioritization in working memory, not maintenance

Recent theory on the neural basis of working memory (WM) has attributed an important role to "activity-silent" mechanisms, suggesting that sustained neural activity might not be essential in the retention of information. This idea has been challenged by reports of ongoing neural activity in the alpha band during WM maintenance, however. The precise role of these alpha oscillations is unclear: Do they reflect attentional prioritization of stored information, or do they serve as a general maintenance mechanism, for instance to periodically refresh synaptic traces? To address this, we designed a visual WM task involving two memory items, one of which was prioritized for recall. The task included both a short (1 s) and a long (3 s) delay intervals between encoding and retrieval. The long delay was implemented to provide a more decisive test of WM maintenance, providing a point in time when any initially silent synaptic traces would likely need to be refreshed as well. Time-resolved decoding analyses revealed that both prioritized and deprioritized items were initially decodable following stimulus presentation. However, only the prioritized item exhibited sustained decodability throughout the delay, particularly in the long delay condition, where it transitioned into a stable coding scheme. This prolonged representation was selectively supported by induced alpha power, which reliably tracked the prioritized item, but not the deprioritized one. Impulse-based decoding further confirmed this asymmetry, highlighting a selective reactivation of the deprioritized item only upon contextual relevance. Together, these findings suggest that sustained alpha-band activity reflects attentional prioritization, rather than general memory maintenance. Unattended, non-prioritized items appear to transition into an activity-silent state, consistent with models of synaptic storage in WM.