Alpha Power Gates Relevant Information during Working Memory Updating

Abstract

Human working memory (WM) is inherently limited, so we must filter out irrelevant information in our environment or our mind while retaining limited important relevant contents. Previous work suggests that neural oscillations in the alpha band (8 -14 Hz) play an important role in inhibiting incoming distracting information during attention and selective encoding tasks. However, whether alpha power is involved in inhibiting no-longer-relevant content or in representing relevant WM content is still debated. To clarify this issue, we manipulated the amount of relevant/irrelevant information using a task requiring spatial WM updating while measuring neural oscillatory activity via EEG and localized current sources across the scalp using a surface Laplacian transform. An initial memory set of two, four, or six spatial locations was to be memorized over a delay until an updating cue was presented indicating that only one or three locations remained relevant for a subsequent recognition test. Alpha amplitude varied with memory maintenance and updating demands among a cluster of left frontocentral electrodes. Greater postcue alpha power was associated with the high relevant load conditions (six and four dots cued to reduce to three relevant) relative to the lower load conditions (four and two dots reduced to one). Across subjects, this difference in alpha power was correlated with condition differences in performance accuracy. In contrast, no significant effects of irrelevant load were observed. These findings demonstrate that, during WM updating, alpha power reflects maintenance of relevant memory contents rather than suppression of no-longer-relevant memory traces.

The role of alpha oscillations in deriving and maintaining spatial relations in working memory

“…After the cue that indicated what information was to be derived and maintained during Delay 2 there was a rapid decline in alpha power for both trial types. This decline could indicate a return to baseline or represent the decrease in WM load resulting from the conversion of the WM information from two locations to either one horizontal line or one spatial relationship, which would be consistent with studies that show that alpha power is modulated with WM load (Jensen et al, 2002; Manza, Hau, & Leung, 2014). Approximately 500ms after the cue, however, the alpha power for the Relation trials increased while the power for the Location trials did not.…”

Neural oscillatory correlates of duration maintenance in working memory

“…It is still debated whether alpha oscillation is related to successful maintenance of item information Palva and Palva, 2007;Hsieh et al, 2011;Johnson et al, 2011), or whether it reflects inhibition of task-irrelevant information (Jokisch and Jensen, 2007;Klimesch et al, 2007;Tuladhar et al, 2007;Manza et al, 2014). Our study provided three pieces of evidence to support the maintenance rather than inhibition.…”

“…As previously stated, we hypothesized that different internal representations would be retained in WM for durations below and above about 3 s. We inferred that if alpha oscillation is related to successful maintenance of item information (Palva and Palva, 2007;Hsieh et al, 2011;Johnson et al, 2011), then the alpha band activity would reflect different internal representations of durations below and above about 3 s retained in WM. If alpha oscillation reflects inhibition of task-irrelevant information (Jokisch and Jensen, 2007;Klimesch et al, 2007;Tuladhar et al, 2007;Manza et al, 2014), and there is no relationship between alpha band activity and internal representation of duration retained in WM, we would observe no significant alpha band difference between durations above and below about 3 s.…”

“…However, the precise role of the alpha band in WM is still under debate. Some scholars have proposed that oscillatory alpha activity reflects the inhibition of cortical areas representing task-irrelevant information (Jokisch and Jensen, 2007;Klimesch et al, 2007;Tuladhar et al, 2007;Manza et al, 2014), while others have suggested that alpha oscillation is related to successful maintenance of item information Palva and Palva, 2007;Hsieh et al, 2011;Johnson et al, 2011). Duration maintenance in WM has received much less attention compared with non-temporal stimulus properties, and the relationship between neural oscillation and duration maintenance in WM has yet to be identified.…”

Impaired Suppression of Delay-Period Alpha and Beta Is Associated With Impaired Working Memory in Schizophrenia

“…Interestingly, some studies have reported alpha enhancement (29) or attenuated suppression (30) in healthy individuals during the maintenance period with increased WM load. Though the precise reason for these seemingly inconsistent findings is not yet clear, one speculation is that alpha enhancement represents active suppression of distractor encoding, which was a feature of both of these previous studies (29; 30). Future investigations will be critical for examining conditions under which alpha is suppressed and enhanced to facilitate WM storage.…”