Electrophysiological oscillations are assumed to be the core mechanism for large-scale network communication. The specific role of frontal-midline theta oscillations as cognitive control mechanism is under debate. According to the dual mechanisms of control framework, cognitive control processes can be divided into proactive and reactive control. The present study aimed at investigating the role of frontal-midline theta activity by assessing oscillations in two tasks varying in the type of cognitive control needed. More specifically, a delayed match to sample (DMTS) task requiring proactive control and a color Stroop task recruiting reactive control processes were conducted within the same group of participants. Moreover, both tasks contained conditions with low and high need for cognitive control. As expected larger frontal-midline theta activity was found in conditions with high need for cognitive control. However, theta activity was focally activated at frontal sites in the DMTS task whereas it had a broader topographical distribution in the Stroop task, indicating that both proactive and reactive control are reflected in frontal-midline theta activity but reactive control is additionally characterized by a broader theta activation. These findings support the conclusion that frontal-midline theta acts functionally different depending on task requirements.
Frontal‐midline (FM) theta activity (4–8 Hz) is proposed to reflect a mechanism for cognitive control that is needed for working memory retention, manipulation, and interference resolution. Modulation of FM theta activity via neurofeedback training (NFT) demonstrated transfer to some but not all types of cognitive control. Therefore, the present study investigated whether FM theta NFT enhances performance and modulates underlying EEG characteristics in a delayed match to sample (DMTS) task requiring mainly proactive control and a color Stroop task requiring mainly reactive control. Moreover, temporal characteristics of transfer were explored over two posttests. Across seven 30‐min NFT sessions, an FM theta training group exhibited a larger FM theta increase compared to an active control group who upregulated randomly chosen frequency bands. In a posttest performed 13 days after the last training session, the training group showed better retention performance in the DMTS task. Furthermore, manipulation performance was associated with NFT theta increase for the training but not the control group. Contrarily, behavioral group differences and their relation to FM theta change were not significant in the Stroop task, suggesting that NFT is associated with proactive but not reactive control enhancement. Transfer to both tasks at a posttest one day after training was not significant. Behavioral improvements were not accompanied by changes in FM theta activity, indicating no training‐induced modulation of EEG characteristics. Together, these findings suggest that NFT supports transfer to cognitive control that manifests late after training but that other training‐unspecific factors may also contribute to performance enhancement.
In research on visual working memory (WM), a contentiously debated issue concerns whether or not items are stored independently of one another in WM. Here we addressed this issue by exploring the role of the physical context that surrounds a given item in the memory display in the formation of WM representations. In particular, we employed bilateral memory displays that contained two or three lateralized singleton items (together with six or five distractor items), defined either within the same or in different visual feature dimensions. After a variable interval, a retro-cue was presented centrally, requiring participants to discern the presence (vs. the absence) of this item in the previously shown memory array. Our results show that search for targets in visual WM is determined interactively by dimensional context and set size: For larger, but not smaller, set sizes, memory search slowed down when targets were defined across rather than within dimensions. This dimension-specific cost manifested in a stronger contralateral delay activity component, an established neural marker of the access to WM representations. Overall, our findings provide electrophysiological evidence for the hierarchically structured nature of WM representations, and they appear inconsistent with the view that WM items are encoded in isolation.
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