Goal-directed behavior relies on maintaining relevant goals in working memory (WM) and updating them when required. Computational modeling, behavioral, and neuroimaging work has previously identified the processes and brain regions involved in selecting, updating, and maintaining declarative information, such as letters and pictures. However, the neural substrates that underlie the analogous processes that operate on procedural information, namely, task goals, are currently unknown. Forty-three participants were therefore scanned with fMRI while performing a procedural version of the reference-back paradigm that allowed for the decomposition of WM updating processes into gate-opening, gate-closing, task switching, and task cue conflict components. Significant behavioral costs were observed for each of these components, with interactions indicating facilitation between gate-opening and task switching, and a modulation of cue conflict by gate state. In neural terms, opening the gate to procedural WM was associated with activity in medial pFC, posterior parietal cortex (PPC), the basal ganglia (BG), thalamus, and midbrain, but only when the task set needed to be updated. Closing the gate to procedural WM was associated with frontoparietal and BG activity specifically in conditions where conflicting task cues had to be ignored. Task switching was associated with activity in the medial pFC/ACC, PPC, and BG, whereas cue conflict was associated with PPC and BG activity during gate closing but was abolished when the gate was already closed. These results are discussed in relation to declarative WM and to gating models of WM.

Working memory (WM) needs to protect current content from interference and simultaneously be amenable to rapid updating with newly relevant information. An influential model suggests these opposing requirements are met via a BG–thalamus gating mechanism that allows for selective updating of PFC WM representations. A large neuroimaging literature supports the general involvement of PFC, BG, and thalamus, as well as posterior parietal cortex, in WM. However, the specific functional contributions of these regions to key subprocesses of WM updating, namely, gate opening, content substitution, and gate closing, are still unknown, as common WM tasks conflate these processes. We therefore combined fMRI with the reference-back task, specifically designed to tease apart these subprocesses. Participants compared externally presented face stimuli to a reference face held in WM, while alternating between updating and maintaining this reference, resulting in opening versus closing the gate to WM. Gate opening and substitution processes were associated with strong BG, thalamic, and frontoparietal activation, but intriguingly, the same activity profile was observed for sensory cortex supporting task stimulus processing (i.e., the fusiform face area). In contrast, gate closing was not reliably associated with any of these regions. These findings provide new support for the involvement of the BG in gate opening, as suggested by the gating model, but qualify the model's assumptions by demonstrating that gate closing does not seem to depend on the BG and that gate opening also involves task-relevant sensory cortex.

Optimal working memory (WM) functioning depends on a control mechanism that balances between maintenance and updating by closing or opening the gate to WM, respectively. Here, we examined the neural oscillation correlates of WM updating and of the control processes involved in gating. The reference-back paradigm was employed to manipulate gate opening, gate closing, and updating independently and examine how the control functions involved in these processes are mapped to oscillatory EEG activity. The results established that different oscillatory patterns were associated with the control process related to gate opening than in gate closing. During the time of gate closing, a relative increase in theta power was observed over midfrontal electrodes. This theta response is a known EEG signature of cognitive control that is proposed here to reflect reactive conflict resolution, achieved by closing the gate when facing irrelevant information. On the other hand, proactive gate opening in preparation for relevant information was associated with an increase in relative delta power over parietal-occipital electrodes. Finally, WM updating was associated with relative increase in delta power over midfrontal electrodes, suggesting a functional role of delta oscillations in WM updating.