Adapting to changing memory retrieval demands: evidence from event-related potentials

Cognitive control depletion reduces pre-stimulus and recollection-related measures of strategic retrieval

Background: The ability to strategically retrieve task-relevant information from episodic memory is thought to rely on goal-directed executive processes, and there is evidence that neural correlates of strategic retrieval are sensitive to reserves of cognitive control. The present study extended this work, exploring the role of cognitive control in the flexible orienting of strategic retrieval processes across alternating retrieval goals.

Method: Pre-stimulus cues directed participants to endorse memory targets from one of two encoding contexts, with the target encoding context alternating every two trials. Items from the nontarget encoding context were rejected alongside new items. One group of participants completed a Stroop task prior to the memory test in order to deplete their reserves of cognitive control, while a second group performed a control task. Event-related potentials (ERPs) were recorded throughout the memory task, and time-locked to both pre-stimulus cues and memory probes.

Results: Control participants’ pre-stimulus ERPs showed sustained divergences at frontal electrode sites according to retrieval goal. This effect was evident on the first trial of each memory task, and linked with the initiation of goal-specific retrieval orientations. Control participants also showed enhanced ERP correlates of recollection (the ‘left parietal effect’) for correctly classified targets relative to nontargets on the second trial of each memory task, indexing strategic retrieval of task-relevant information. Both the pre-stimulus index of retrieval orientation and the target/nontarget left parietal effect were significantly attenuated in participants that completed the Stroop task.

Conclusions: The reduction of pre-stimulus and stimulus-locked ERP effects following the Stroop task indicates that available reserves of cognitive control play an important role in both proactive and recollection-related aspects of strategic retrieval.

Cognitive control depletion reduces pre-stimulus and recollection-related measures of strategic retrieval

Background: The ability to strategically retrieve task-relevant information from episodic memory is thought to rely on goal-directed executive processes, and there is evidence that neural correlates of strategic retrieval are sensitive to reserves of cognitive control. The present study extended this work, exploring the role of cognitive control in the flexible orienting of strategic retrieval processes across alternating retrieval goals. Method: Pre-stimulus cues directed participants to endorse memory targets from one of two encoding contexts, with the target encoding context alternating every two trials. Items from the nontarget encoding context were rejected alongside new items. One group of participants completed a Stroop task prior to the memory test in order to deplete their reserves of cognitive control, while a second group performed a control task. Event-related potentials (ERPs) were recorded throughout the memory task, and time-locked to both pre-stimulus cues and memory probes. Results: Control participants’ pre-stimulus ERPs showed sustained divergences at frontal electrode sites according to retrieval goal. This effect was evident on the first trial of each memory task, and linked with the initiation of goal-specific retrieval orientations. Control participants also showed enhanced ERP correlates of recollection (the ‘left parietal effect’) for correctly classified targets relative to nontargets on the second trial of each memory task, indexing strategic retrieval of task-relevant information. Both the pre-stimulus index of retrieval orientation and the target/nontarget left parietal effect were significantly attenuated in participants that completed the Stroop task. Conclusions: The reduction of pre-stimulus and stimulus-locked ERP effects following the Stroop task indicates that available reserves of cognitive control play an important role in both proactive and recollection-related aspects of strategic retrieval.

Direct electrophysiological evidence for the maintenance of retrieval orientations and the role of cognitive control

Retrieval orientations are memory states that bias retrieval towards specific memory contents. Many neuroimaging studies have examined the influence of retrieval orientations on stimulus processing, but very little direct evidence exists regarding the ongoing maintenance of orientations themselves. Participants completed two memory tasks with different retrieval goals. ERPs were time-locked to a pre-stimulus fixation asterisk and contrasted according to retrieval goals. Pre-stimulus ERPs elicited during the two retrieval tasks diverged at frontal electrode sites. These differences onset early and were sustained throughout the fixation-stimulus interval. The functional and spatiotemporal characteristics of this ERP effect comprise the first direct electrophysiological evidence of the ongoing maintenance of retrieval orientations throughout a task. Moreover, this effect was eliminated in participants who performed a stroop task prior to the memory tests, indicating that reserves of cognitive control play an important role in the maintenance of retrieval orientations throughout memory tasks.

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Pre-stimulus fixation-locked ERPs differed during recognition according to retrieval goal.

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It is proposed that this preparatory effect is a correlate of retrieval orientation maintenance.

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The preparatory effect was eliminated in participants who first completed a stroop task.

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Cognitive control reserves therefore appear to influence retrieval orientation maintenance.

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Elimination of the preparatory effect was associated with enhanced post-retrieval monitoring.

Reflections of Oneself: Neurocognitive Evidence for Dissociable Forms of Self-Referential Recollection

Research links the medial prefrontal cortex (mPFC) with a number of social cognitive processes that involve reflecting on oneself and other people. Here, we investigated how mPFC might support the ability to recollect information about oneself and others relating to previous experiences. Participants judged whether they had previously related stimuli conceptually to themselves or someone else, or whether they or another agent had performed actions. We uncovered a functional distinction between dorsal and ventral mPFC subregions based on information retrieved from episodic long-term memory. The dorsal mPFC was generally activated when participants attempted to retrieve social information about themselves and others, regardless of whether this information concerned the conceptual or agentic self or other. In contrast, a role was discerned for ventral mPFC during conceptual but not agentic self-referential recollection, indicating specific involvement in retrieving memories related to self-concept rather than bodily self. A subsequent recognition test for new items that had been presented during the recollection task found that conceptual and agentic recollection attempts resulted in differential incidental encoding of new information. Thus, we reveal converging fMRI and behavioral evidence for distinct neurocognitive forms of self-referential recollection, highlighting that conceptual and bodily aspects of self-reflection can be dissociated.

Electrophysiological insights into control over recollection

Electrophysiological correlates of successful episodic retrieval were measured in an experiment where participants switched frequently between two different episodic retrieval conditions. They completed three trials of each condition before switching to the other condition. The key contrasts were between neural indices of successful retrieval that were separated according to the number of successive trials of the same condition that had been completed. An electrophysiological correlate of recollection--the left-parietal event-related potential (ERP) old/new effect--was smaller on the first and second trial than on the third successive trial that participants completed for each condition. This ERP old/new effect is assumed to index the extent to which recollection has occurred, and this outcome suggests that control over recovery of task-relevant episodic content is compromised when additional cognitive demands are imposed around the time of retrieval.

The control of long-term memory: brain systems and cognitive processes

This paper provides a selective review of controlled memory retrieval, i.e., processes, that operate on long-term stored information in the service of current goals and task demands. Binding mechanisms that combine fragments of long-term stored information in response to a retrieval cue, are central for the understanding of the interaction between a retrieval cue and memory-stored information. The paper summarizes empirical evidence showing that ERP slow waves are highly sensitive to the initiation and maintenance of retrieval orientations. It is argued that similar mechanisms of controlled memory retrieval operate in the service of successful remembering and the suppression of unwanted memories (forgetting). The mechanisms can be grouped into two classes: those that enhance retrieval cue processing (cue bias) and those that directly act on memory representations and modulate their accessibility (target bias). From a neuroanatomical point of view, the former class of processes reflects selection mechanisms for internal actions that rely on the integrity of the prefrontal cortex (PFC), whereas the second class of processes can be identified with selective attention mechanisms for which the posterior parietal cortex (PPC) plays an important role.