Given its established role in action value coding, the BG is again an a priori candidate for this function. We recently found evidence consistent with this hypothesis [50••]. We analyzed trials of our reorderable working memory task where context appeared in the middle position, between the presentation of the two lower-level items. When this ‘context middle’ stimulus rendered the preceding lower-level item irrelevant, we observed a large benefit to behavioral performance PCI 32765 when sufficient time followed presentation of the context. This benefit was much larger than that seen in any
other condition — as though subjects required time to reallocate working memory capacity occupied by the irrelevant item. This result parallels others (see [50••]) demonstrating a sluggish time course for WM reallocation, with irrelevant information impacting behavior even 1.5 s later. We predicted that this slowing could occur because to-be-removed items were nonetheless predicted to have utility, even though they were specified as irrelevant by the contextual stimulus. To test this counterintuitive prediction, we adapted a simple reinforcement learning model to track the likelihood that each item, regardless of the context in which it was presented, would in fact be associated with the correct answer. Learning rates in this model were fit to reaction
times in our behavioral task, and from this, we predicted a function of trial-to-trial predicted utility of irrelevant check details items. This timecourse correlated with activation in ventral striatum in a separate fMRI experiment. By contrast, the Coproporphyrinogen III oxidase model-based estimates of the utility of relevant items were tracked by recruitment in frontal, not striatal regions ( Figure 3c,d). These results motivate the inclusion of BG-mediated mechanisms in models of WM reallocation [51] and
other WM control processes. They also reaffirm the dichotomous stability vs. flexibility functions sometimes ascribed to frontal vs. striatal regions in the service of working memory, as well as the opposing actions of dopamine on these two areas. One intriguing possibility consistent with these results is that BG-mediated gating mechanisms might be capable of ‘vetoing’ the clearance of information from working memory, analogous to the motoric preservation induced by stimulation of the ventral striatum [52]. Working memory contends with the complexity of the real world via a set of control processes that select what items to maintain, which maintained items to use, and the priority of items within memory. Many of these demands are analogous to those faced in movement selection by the motor system. Accordingly, fronto-striatal mechanisms for motor selection might be elaborated in more rostral frontostriatal circuits and used for more abstract working memory operations. This long-held hypothesis has now been subjected to empirical tests.