The role of alpha oscillations in distractor inhibition during memory retention.

Only small amounts of visual information, as determined by the capacity of working memory, can be held in an active and accessible state. Thus, it is important to select and maintain information that is relevant while ignoring irrelevant information. However, the underlying neural mechanism of these processes has yet to be identified. One potential candidate are alpha oscillations (8-14 Hz), which have been shown to inhibit stimulus processing in perceptual tasks. During memory maintenance, alpha power increases with set size suggesting that alpha oscillations are involved either in memory maintenance or in the inhibition of task-irrelevant information to protect relevant information from interference. The need for such a protection should increase with the amount of distracting information, but most previous studies did not show any distractors. Therefore, we directly tested whether alpha oscillations are involved in inhibition of distractors during memory maintenance. Participants memorized the orientation of one or two target lines embedded among irrelevant distractors. Distractors were either strong or weak and were present during the retention interval after which participants reported the orientation of probed targets. Computational modeling showed that performance decreased with increasing set size and stronger distraction. Alpha power in the retention interval generally increased with set size, replicating previous studies. However, here stronger distractors reduced alpha power. This finding is in clear contradistinction to previous suggestions, as alpha power decrease indicates higher neuronal excitability. Thus, our data do not support the suggested role of alpha oscillations in inhibition of distraction in working memory.