Recollection Accuracy Research Articles

Electrically stimulating prefrontal cortex at retrieval improves recollection accuracy

Neuroimaging and brain damage studies suggest that dorsolateral prefrontal cortex (dlPFC) is involved in the cognitive control of episodic recollection. If dlPFC is causally involved in retrieval, then transcranial direct current stimulation (tDCS) of this brain region should increase recollection accuracy, especially when recollection is difficult and requires cognitive control. Here, we report the first brain stimulation experiment to directly test this hypothesis. We administered tDCS to dlPFC immediately after studying to-be-learned material but just prior to recollection testing, thereby targeting retrieval processes. We found that stimulation of dlPFC significantly increased recollection accuracy, relative to a no-stimulation sham condition and also relative to active stimulation of a comparison region in left parietal cortex. There was no significant difference in the size of this increase between hemispheres. Moreover, these dlPFC stimulation effects were behaviorally selective, increasing accuracy only when participants needed to recollect difficult information. Electrically stimulating dlPFC allowed people to more accurately recollect specific details of their experiences, demonstrating a causal role of dlPFC in the retrieval of episodic memories.

Recollection-related increases in functional connectivity predict individual differences in memory accuracy.

Recollection involves retrieving specific contextual details about a prior event. Functional neuroimaging studies have identified several brain regions that are consistently more active during successful versus failed recollection-the "core recollection network." In the present study, we investigated whether these regions demonstrate recollection-related increases not only in activity but also in functional connectivity in healthy human adults. We used fMRI to compare time-series correlations during successful versus unsuccessful recollection in three separate experiments, each using a different operational definition of recollection. Across experiments, a broadly distributed set of regions consistently exhibited recollection-related increases in connectivity with different members of the core recollection network. Regions that demonstrated this effect included both recollection-sensitive regions and areas where activity did not vary as a function of recollection success. In addition, in all three experiments the magnitude of connectivity increases correlated across individuals with recollection accuracy in areas diffusely distributed throughout the brain. These findings suggest that enhanced functional interactions between distributed brain regions are a signature of successful recollection. In addition, these findings demonstrate that examining dynamic modulations in functional connectivity during episodic retrieval will likely provide valuable insight into neural mechanisms underlying individual differences in memory performance.

Continuous theta burst stimulation of angular gyrus reduces subjective recollection.

The contribution of lateral parietal regions such as the angular gyrus to human episodic memory has been the subject of much debate following widespread observations of left parietal activity in healthy volunteers during functional neuroimaging studies of memory retrieval. Patients with lateral parietal lesions are not amnesic, but recent evidence indicates that their memory abilities may not be entirely preserved. Whereas recollection appears intact when objective measures such as source accuracy are used, patients often exhibit reduced subjective confidence in their accurate recollections. When asked to recall autobiographical memories, they may produce spontaneous narratives that lack richness and specificity, but can remember specific details when prompted. Two distinct theoretical accounts have been proposed to explain these results: that the patients have a deficit in the bottom-up capturing of attention by retrieval output, or that they have an impairment in the subjective experience of recollection. The present study aimed to differentiate between these accounts using continuous theta burst stimulation (cTBS) in healthy participants to disrupt function of specific left parietal subregions, including angular gyrus. Inconsistent with predictions of the attentional theory, angular gyrus cTBS did not result in greater impairment of free recall than cued recall. Supporting predictions of the subjective recollection account, temporary disruption of angular gyrus was associated with highly accurate source recollection accuracy but a selective reduction in participants’ rated source confidence. The findings are consistent with a role for angular gyrus in the integration of memory features into a conscious representation that enables the subjective experience of remembering.

Amphetamine Fails to Alter Cued Recollection of Emotional Images: Study of Encoding, Retrieval, and State-Dependency

Stimulant drugs facilitate both encoding and retrieval of salient information in laboratory animals, but less is known about their effects on memory for emotionally salient visual images in humans. The current study investigated dextroamphetamine (AMP) effects on memory for emotional pictures in healthy humans, by administering the drug only at encoding, only at retrieval, or at both encoding and retrieval. During the encoding session, all participants viewed standardized positive, neutral, and negative pictures from the International Affective Picture System (IAPS). 48 hours later they attended a retrieval session testing their cued recollection of these stimuli. Participants were randomly assigned to one of four conditions (N = 20 each): condition AP (20 mg AMP at encoding and placebo (PL) at retrieval); condition PA (PL at encoding and AMP at retrieval); condition AA (AMP at encoding and retrieval); or condition PP (PL at encoding and retrieval). Amphetamine produced its expected effects on physiological and subjective measures, and negative pictures were recollected more frequently than neutral pictures. However, contrary to hypotheses, AMP did not affect recollection for positive, negative, or neutral stimuli, whether it was administered at encoding, retrieval, or at both encoding and retrieval. Moreover, recollection accuracy was not state-dependent. Considered in light of other recent drug studies in humans, this study highlights the sensitivity of drug effects to memory testing conditions and suggests future strategies for translating preclinical findings to human behavioral laboratories.

Age-related differences in the neural correlates mediating false recollection

The current study investigated the effects of aging on the neural basis underlying true and false recollection. Although older adults, compared with younger adults, exhibited equivalent rates of true recollection, age differences in true recollection showed a pattern of activity commonly found among previous memory studies (e.g., age-related decreases in occipital and increases in prefrontal cortices), suggesting reduced retrieval of perceptual details associated with encoding items and a greater reliance on top-down compensatory processing. With regard to false recollection, older adults exhibited significantly greater false recollection yet did not exhibit increased neural processing. They did exhibit decreased activity in prefrontal, parahippocampal gyrus, and occipitoparietal cortex, suggesting a reduced reliance on reconstruction processes mediating false recollection in young. An individual differences analysis in older adults found false recollection rates predicted activity in several regions. including bilateral middle/superior temporal gyrus. Taken together, these results indicate that increases in false recollection in aging may be mediated by reduced access to encoding-related details as well as reliance on semantic gist and familiarity-related neural activity.

How does Encoding Context Affect Memory in Younger and Older Adults?

How does encoding context affect memory? Participants studied visually presented words viewed concurrently with a rich (intact face) or weak (scrambled face) image as context and subsequently made "Remember", "Know", or "New" judgements to words presented alone. In Experiment 1a, younger, but not older, adults showed higher recollection accuracy to words from rich- than from weak-context encoding trials. The age-related deficit in recollection occurred, in Experiment 1b, even when encoding and retrieval time was doubled in older adults, suggesting that insufficient processing time cannot account for this age-related deficit. In Experiment 1c, dividing attention in young, during encoding, reduced overall memory, though the recollection boost from rich encoding contexts remained, suggesting that reduced attention resources cannot explain this age-related deficit. Experiment 2 showed that an own-age bias, to face images as context, could not explain the age-related differences either. Results suggest that age deficits in recollection stem from a lack of spontaneous binding, or elaboration, of context to target information during encoding.

Alzheimer's disease can spare local metacognition despite global anosognosia: Revisiting the confidence–accuracy relationship in episodic memory

Alzheimer's disease (AD) can impair metacognition in addition to more basic cognitive functions like memory. However, while global metacognitive inaccuracies are well documented (i.e., low deficit awareness, or anosognosia), the evidence is mixed regarding the effects of AD on local or task-based metacognitive judgments. Here we investigated local metacognition with respect to the confidence–accuracy relationship in episodic memory (i.e., metamemory). AD and control participants studied pictures of common objects and their verbal labels, and then took forced-choice picture recollection tests using the verbal labels as retrieval cues. We found that item-based confidence judgments discriminated between accurate and inaccurate recollection responses in both groups, implicating relatively spared metamemory in AD. By contrast, there was evidence for global metacognitive deficiencies, as AD participants underestimated the severity of their everyday problems compared to an informant's assessment. Within the AD group, individual differences in global metacognition were related to recollection accuracy, and global metacognition for everyday memory problems was related to task-based metacognitive accuracy. These findings suggest that AD can spare the confidence–accuracy relationship in recollection tasks, and that global and local metacognition measures tap overlapping neuropsychological processes.

The role of phantom recollection in false recall

Although high levels of phantom recollection (illusory vivid experience of the prior "presentation" of unpresented items) have been found for false recognition, little is known about phantom recollection in recall. We examined this issue with Deese/Roediger-McDermott lists using two paradigms: repeated recall and conjoint recall. High levels of phantom recollection were observed with both standard behavioral measures and the parameters of fuzzy-trace theory's dual-recall model. In addition, phantom recollection and the true recollection that accompanies presented items appear to involve different retrieval processes, because they were dissociated by manipulations such as number of recall tests and list strength.

True and phantom recollection: An fMRI investigation of similar and distinct neural correlates and connectivity

Although research suggests that most false memories are mediated by a sense of familiarity, behavioral evidence indicates that some are characterized by retrieval of item-specific details associated with recollection. However, neuroimaging studies have yet to isolate and analyze the neural correlates of false (or phantom) recollection, focusing instead on general recognition processes. In doing so, results are mixed with respect to the role of the medial temporal lobes (MTL) in distinguishing between true and false retrieval. The present study sought to investigate the neural basis of true and phantom recollection and clarify the role of the MTL in dissociating between the two processes. Results showed that true and phantom recollection were associated with a largely overlapping retrieval network including activity in bilateral anterior parahippocampal gyrus, fusiform gyrus, anterior cingulate cortex, and right superior parietal cortex. However, connectivity analyses using two common MTL seeds revealed a more inferior network (fusiform gyrus, hippocampus, middle temporal gyrus) associated with true recollection and a more superior network (superior parietal, superior frontal gyrus, posterior cingulate cortex) associated with false recollection. Finally, direct comparisons between true and phantom recollection showed greater activity in right hippocampus and early visual cortex for true recollection, whereas no region exhibited greater activity for false recollection. Results indicate that while both true and phantom recollection show similar patterns of activation, there are also distinctions in the neural networks contributing to the two recollection processes. Moreover, results conclude that within the MTL, the hippocampus proper can distinguish between true and phantom recollection.

Elevated false recollection of emotional pictures in young and older adults.

Current theories predict opposing effects of emotionally arousing information on false memory. If emotion enhances true recollection, then false recollection might be lower for emotional than for neutral pictures. However, if emotion enhances conceptual relatedness, then false recollection might increase for nonstudied but emotionally related pictures. We contrasted these 2 factors in young and older adults, using the International Affective Pictures Systems set (Lang, Bradley, & Cuthbert, 2005). Although both age groups used recollection in our task, false recollection was greatest for emotional pictures, supporting a conceptual relatedness account. Finally, even after accuracy differences were controlled, age was related to high-confidence false recollection of emotional pictures.

Neural correlates of false memory disqualification by true recollection of feedback

Event-related potentials associated with disqualifying false memories were recorded in a novel false memory paradigm in which participants were given feedback during an initial recognition test, followed by a surprise retest where true recollection of feedback could be used to disqualify previous errors. Two spatiotemporally distinct components emerged: a parietal left-lateralized positivity indexing the recollection of feedback (500-900 ms), which was subsequently joined by a bilateral frontocentral positivity (700-900 ms) associated with rejection of the erroneous response and/or switching to the correct response. This latter effect seems to be distinct from the more anterior and later right frontal positivity typically associated with postretrieval monitoring.

Effects of DHEA administration on episodic memory, cortisol and mood in healthy young men: a double-blind, placebo-controlled study

Dehydroepiandrosterone (DHEA) has been reported to enhance cognition in rodents, although there are inconsistent findings in humans. The aim of this study was to investigate the effects of DHEA administration in healthy young men on episodic memory and its neural correlates utilising an event-related potential (ERP) technique. Twenty-four healthy young men were treated with a 7-day course of oral DHEA (150 mg b.d.) or placebo in a double blind, random, crossover and balanced order design. Subjective mood and memory were measured using visual analogue scales (VASs). Cortisol concentrations were measured in saliva samples. ERPs were recorded during retrieval in an episodic memory test. Low-resolution brain electromagnetic tomography (LORETA) was used to identify brain regions involved in the cognitive task. DHEA administration led to a reduction in evening cortisol concentrations and improved VAS mood and memory. Recollection accuracy in the episodic memory test was significantly improved following DHEA administration. LORETA revealed significant hippocampal activation associated with successful episodic memory retrieval following placebo. DHEA modified ERPs associated with retrieval and led to a trend towards an early differential activation of the anterior cingulate cortex (ACC). DHEA treatment improved memory recollection and mood and decreased trough cortisol levels. The effect of DHEA appears to be via neuronal recruitment of the steroid sensitive ACC that may be involved in pre-hippocampal memory processing. These findings are distinctive, being the first to show such beneficial effects of DHEA on memory in healthy young men.

Phantom recall

Phantom recollection (illusory vivid experience of the “presentation” of unpresented items) occurs at high levels in certain types of false recognition, but it is not yet known whether it occurs at high levels in false recall. A nonintrospective methodology based on fuzzy-trace theory’s dual-retrieval model of recall was used to estimate this hallucinatory phenomenology directly from free-recall data. To generate convergent evidence, the methodology was implemented in two distinct paradigms (repeated recall and conjoint recall) using Deese/Roediger/McDermott lists. With both paradigms, levels of phantom recollection were high and were usually equal to or greater than corresponding levels of true recollection (for presented material). Measurements of phantom recollection and true recollection were singly and doubly dissociated by a series of theory-driven manipulations (list blocking, strength of false-memory illusions, repetition, and study-test delay), suggesting that the two phenomenologies are by-products of different retrieval processes.