Within Working Memory Research Articles

Mental programming of spatial sequences in working memory in the macaque frontal cortex.

How the brain mentally sorts a series of items in a specific order within working memory (WM) remains largely unknown. We investigated mental sorting using high-throughput electrophysiological recordings in the frontal cortex of macaque monkeys, who memorized and sorted spatial sequences in forward or backward orders according to visual cues. We discovered that items at each ordinal rank in WM were encoded in separate rank-WM subspaces and then, depending on cues, were maintained or reordered between the subspaces, accompanied by two extra temporary subspaces in two operation steps. Furthermore, the cue activity served as an indexical signal to trigger sorting processes. Thus, we propose a complete conceptual framework, where the neural landscape transitions in frontal neural states underlie the symbolic system for mental programming of sequence WM.

Attentional flexibility and prioritization improves long-term memory

Recent evidence suggests the focus of attention (FoA) is a flexible resource within working memory (WM) used to temporarily maintain some information in a highly accessible state. This flexibility comes at the expense of other representations, demonstrating a resource trade-off in WM maintenance. The present experiments evaluate how flexibility within the FoA impacts long-term memory (LTM) for semantically meaningful information. A WM probe-recognition task was used in which two items were presented in black and a single item was presented in red. To encourage the prioritization and uninterrupted preferential maintenance of specific items, a process we call online refreshing, the red item was associated with a greater point-reward value than were the black items. This WM task was followed by a surprise delayed LTM test. In Experiment 1, the FoA flexibly adjusted to maintain non-recent semantic information with evidence for a resource trade-off across list positions. Flexibility also directly improved LTM. In Experiment 2, reward value was equated across red and black items to evaluate whether an alternative explanation, distinctiveness of encoding, could account for the LTM findings. When reward value was equated, the cued item did not encourage flexible orienting of the FoA toward non-recent items and there was no benefit of the distinct red item on LTM performance. While supportive of past research, these data further demonstrate that semantic information can be flexibly prioritized at the expense of other list positions and that this is directly tied to improvements in LTM.

Baseline-dependent effect of dopamine\u2019s precursor L-tyrosine on working memory gating but not updating

Adaptive goal-directed behavior requires a dynamic balance between maintenance and updating within working memory (WM). This balance is controlled by an input-gating mechanism implemented by dopamine in the basal ganglia. Given that dopaminergic manipulations can modulate performance on WM-related tasks, it is important to gain mechanistic insight into whether such manipulations differentially affect updating (i.e., encoding and removal) and the closely-related gate opening/closing processes that respectively enable/prevent updating. To clarify this issue, 2.0 g of dopamine’s precursor L-tyrosine was administered to healthy young adults (N = 45) in a double-blind, placebo-controlled, within-subjects study. WM processes were empirically distinguished using the reference-back paradigm, which isolates performance related to updating, gate opening, and gate closing. L-tyrosine had a selective, baseline-dependent effect only on gate opening, which was evidenced by markedly reduced variance across subjects in gate opening performance in the L-tyrosine compared with the placebo condition, whereas the whole-sample average performance did not differ between conditions. This indicates a pattern of results whereby low-performing subjects improved, whereas high-performing subjects were impaired on L-tyrosine. Importantly, this inverted U-shaped pattern was not explained by regression to the mean. These results are consistent with an inverted-U relationship between dopamine and WM, and they indicate that updating and gating are differentially affected by a dopaminergic manipulation. This highlights the importance of distinguishing these processes when studying WM, for example, in the context of WM deficits in disorders with a dopaminergic pathophysiology.

Behavioral measures of attention and cognitive control during a new auditory working memory paradigm

Proactive control is the ability to manipulate and maintain goal-relevant information within working memory (WM), allowing individuals to selectively attend to important information while inhibiting irrelevant distractions. Deficits in proactive control may cause multiple cognitive impairments seen in schizophrenia. However, studies of cognitive control have largely relied on visual tasks, even though the functional deficits in schizophrenia are more frequent and severe in the auditory domain (i.e., hallucinations). Hence, we developed an auditory analogue of a visual ignore/suppress paradigm. Healthy adults (N = 40) listened to a series of four letters (600-ms stimulus onset asynchrony) presented alternately to each ear, followed by a 3.2-s maintenance interval and a probe. Participants were directed either to selectively ignore (I) the to-be-presented letters at one ear, to suppress (S) letters already presented to one ear, or to remember (R) all presented letters. The critical cue was provided either before (I) or after (S) the encoding series, or simultaneously with the probe (R). The probes were encoding items presented to either the attended/not suppressed ear (“valid”) or the ignored/suppressed ear (“lure”), or were not presented (“control”). Replicating prior findings during visual ignore/suppress tasks, response sensitivity and latency revealed poorer performance for lure than for control trials, particularly during the suppress condition. Shorter suppress than remember latencies suggested a behavioral advantage when discarding encoded items from WM. The paradigm-related internal consistencies and 1-week test–retest reliabilities (n = 38) were good to excellent. Our findings validate these auditory WM tasks as a reliable manipulation of proactive control and set the stage for studies with schizophrenia patients who experience auditory hallucinations.

The role of medial prefrontal cortex in the working memory maintenance of one\u2019s own emotional responses

The role of medial prefrontal cortex (MPFC) in maintaining emotional information within working memory (WM) remains insufficiently investigated – with some studies suggesting this process activates MPFC and others suggesting its activity is suppressed. To reconcile these different results, we asked 26 healthy participants to complete a WM task involving the maintenance of emotional content (EWM), visual content (VWM), or no content (“rest”) after exposure to emotion-provoking images. We also assessed individual differences in emotional awareness (EA). We observed that dorsal MPFC was more active during EWM than VWM; further, relative to the rest condition, both of these WM conditions involved suppression of ventral MPFC. We also observed that the dorsal anterior cingulate subregion of dorsal MPFC was positively associated with EA. We discuss how these results may be able to reconcile the findings of previous EWM studies, and extend understanding of the relationship between MPFC, EA, and WM.

Intertemporal Decision-Making Involves Prefrontal Control Mechanisms Associated with Working Memory.

Intertemporal decision-making involves simultaneous evaluation of both the magnitude and delay to reward, which may require the integrated representation and comparison of these dimensions within working memory (WM). In the current study, neural activation associated with intertemporal decision-making was directly compared with WM load-related activation. During functional magnetic resonance imaging, participants performed an intermixed series of WM trials and intertemporal decision-making trials both varying in load, with the latter in terms of choice difficulty, via options tailored to each participant's subjective value function for delayed rewards. The right anterior prefrontal cortex (aPFC) and dorsolateral prefrontal cortex (dlPFC) showed activity modulation by choice difficulty within WM-related brain regions. In aPFC, these 2 effects (WM, choice difficulty) correlated across individuals. In dlPFC, activation increased with choice difficulty primarily in patient (self-controlled) individuals, and moreover was strongest when the delayed reward was chosen on the most difficult trials. Finally, the choice-difficulty effects in dlPFC and aPFC were correlated across individuals, suggesting a functional relationship between the 2 regions. Together, these results suggest a more precise account of the relationship between WM and intertemporal decision-making that is specifically tied to choice difficulty, and involves the coordinated activation of a lateral PFC circuit supporting successful self-control.

The short- and long-term consequences of directed forgetting in a working memory task

Directed forgetting requires the voluntary control of memory. Whereas many studies have examined directed forgetting in long-term memory (LTM), the mechanisms and effects of directed forgetting within working memory (WM) are less well understood. The current study tests how directed forgetting instructions delivered in a WM task influence veridical memory, as well as false memory, over the short and long term. In a modified item recognition task Experiment 1 tested WM only and demonstrated that directed forgetting reduces false recognition errors and semantic interference. Experiment 2 replicated these WM effects and used a surprise LTM recognition test to assess the long-term effects of directed forgetting in WM. Long-term veridical memory for to-be-remembered lists was better than memory for to-be-forgotten lists—the directed forgetting effect. Moreover, fewer false memories emerged for to-be-forgotten information than for to-be-remembered information in LTM as well. These results indicate that directed forgetting during WM reduces semantic processing of to-be-forgotten lists over the short and long term. Implications for theories of false memory and the mechanisms of directed forgetting within working memory are discussed.

Looking Inward

Selective attention plays a fundamental role in emotion regulation. To date, research has examined individuals’ use of selective attention to regulate emotional responses during stimulus presentation. In the present study, we examined whether selective attention can be used to regulate emotional responses during a poststimulus period when representations are active within working memory (WM). On each trial, participants viewed either a negative or a neutral image. After the offset of the image, they maintained a representation of it in WM and were cued to focus their attention on either neutral or arousing aspects of that representation. Results showed that, relative to focusing on an arousing portion of a negative-image representation within WM, focusing on a neutral portion of the representation reduced both self-reported negative emotion and the late positive potential, a robust neural measure of emotional reactivity. These data suggest that selective attention can alter emotional responses arising from affective representations active within WM.

Internally generated and directly cued task sets: an investigation with fMRI

It is widely acknowledged that the prefrontal cortex (PFC) plays a major role for goal-directed behaviour. In this context it is usually necessary to coordinate environmental information and internally represented intentions. Such goal-directed “endogenous control processes” can be investigated with the task-switching paradigm in which participants are required to alternate between different tasks. In the present study, we aimed at investigating different degrees of endogenous control by introducing two cue types with varying directness of the cue-task association. The “transition cues” informed the participants about repeating or switching the task but not about the task identity. Contrary to that, the “task cues” were directly associated with the upcoming task set. Since the transition cues are not directly associated with the task set they should require a higher demand of endogenous control than the task cues. The comparison of both cue types revealed frontolateral as well as frontomedian activations for the transition cue. We assume that the frontolateral activation reflects the coordination of information within working memory (WM) and the frontomedian cortex reflects the higher demand for endogenous control. Furthermore, regions of interest (ROIs) analyses indicate an important role for anterior regions along the left inferior frontal sulcus and frontomedian wall. This is suggested to reflect a functional gradient in anterior–posterior direction which is linked to the relative degree of required endogenous control.

Executive functions and updating of the contents of working memory in unipolar depression

Background: Depression is characterized by cognitive impairments, including executive dysfunctions. These executive deficits could reflect impairments of more basic executive processes, such as updating, set shifting and inhibition. While shifting and inhibition impairments are often reported, studies on depression have been somewhat obscure about specific deficits of the updating process. The main goal of that study was to assess the updating process in young in-patients with depression. Methods: We used a verbal n-back task to assess updating process. Load and mental manipulation within working memory (WM) were incremented by using three different levels of complexity (1,2,3-back). Neuropsychological tests and an attentional task (0-back) were also administered to subjects. Twenty-two individuals meeting DSM-IV criteria for Major Unipolar Depression and 22 healthy control subjects, matched on age, verbal IQ and education, were included in the study. Results: Subjects with depression showed significant deficits at the n-back task compared to control subjects. They were normal in tasks assessing the short-term maintenance in WM and attention. This suggests that depressed patients exhibit impairment in the updating process. Depressed patients also showed set shifting and inhibition deficits. Only the n-back task was correlated with the number of hospitalizations and the longitudinal course of the illness. Conclusions: Our results suggest that young depressed in-patients have widespread executive dysfunctions, including updating, shifting and inhibition processes. We also found a correlation between a longitudinal measure of depression severity and an updating task performance. We suggest that using multiple executive tasks gives the opportunity to distinguish the specific influence of various executive processes on clinical dimensions in depression.