The Neural Basis of Recollection Rejection: Increases in Hippocampal-Prefrontal Connectivity in the Absence of a Shared Recall-to-Reject and Target Recollection Network

Memory Abilities Are Selectively Related to Food Label and Numeracy Nutrition Skills

OBJECTIVE

We investigated the relationship between nutrition literacy, diet quality, carotenoid status, and cognition.

METHODS

Adults aged 37.5 ± 17.0 years (n = 52) completed the 42-item Nutrition Literacy Assessment Instrument (NLit). The Dietary History Questionnaire III was analyzed to determine the Healthy Eating Index. Skin carotenoids were assessed as a diet quality biomarker. Selective attention, relational memory, and pattern separation abilities were assessed using the flanker, spatial reconstruction, and mnemonic similarity tasks, respectively. Statistical adjustments included age, sex, education, and body mass index.

RESULTS

No correlations were observed for NLit scores and NLit subscales with Healthy Eating Index and skin carotenoid status. However, the NLit's food label and numeracy subscale was related to greater pattern separation abilities (ρ = 0.33, r2 = 0.11, P = 0.03).

CONCLUSIONS AND IMPLICATIONS

Comprehension of food labels and numeracy information was associated with memory abilities. Future work is needed to test whether targeting working memory and attentional processes during memory retrieval in larger samples may facilitate the acquisition of nutrition knowledge.

Prefrontal cortex-mediated inhibition supports face recognition

Inhibitory processes are thought to be important for memory function. A recent behavioral study that employed a face recognition paradigm reported that participants made fewer "old" responses to highly similar faces than less similar faces, providing evidence that memory for faces may rely on related-item inhibition. However, these results could also be explained by a non-inhibitory recall-to-reject process. The current study sought to use fMRI connectivity analysis to distinguish between these hypotheses. Although both hypotheses predict correct rejection of highly similar faces will produce activity in the prefrontal cortex, the inhibition hypothesis predicts negative connectivity between the prefrontal cortex and regions associated with memory retrieval and face processing, whereas the recall-to-reject hypothesis predicts positive connectivity between these regions. During the study phase, participants were presented with male and female faces. During the test phase, they viewed old faces, related face morphs (20-80% similar to old faces), and new faces, and made "old"-"new" judgements. Correct rejection of highly similar face morphs was associated with increased activity in the right lateral prefrontal cortex and negative connectivity between this region and regions associated with face processing and memory retrieval. These results indicate that prefrontal cortex-mediated memory inhibition supports face recognition.

Neural correlates of paired associate recollection: A neuroimaging meta-analysis

Functional neuroimaging data on paired associate recollection have expanded over the years, raising the need for an integrative understanding of the literature. The present study performed a quantitative meta-analysis of the data to fulfill that need. The meta-analysis focused on the three most widely used types of activation contrast: Hit > Miss, Intact > Rearranged, and Memory > Perception. The major results were as follows. First, the Hit > Miss contrast mainly involved regions in the default mode network (DMN)/medial temporal lobe (MTL), likely reflecting a greater amount of retrieved information during the Hit than Miss trials. Second, the Intact > Rearranged contrast mainly involved regions in the DMN/MTL, supporting the view that rejecting recombination foils is based on familiarity with the component parts in the absence of recollection. Third, the Memory > Perception contrast primarily involved regions in the frontoparietal control network, likely reflecting the greater demands on controlled processing during Memory than Perception conditions. Fourth, the subcortical clusters included the amygdala, caudate nucleus/putamen, and mediodorsal thalamus regions, suggesting that these regions are components of the neural circuits supporting associative recollection. Finally, comparisons with previous meta-analyses suggested that associative recollection involves the DMN regions more strongly than source recollection but less strongly than subjective recollection. In conclusion, this study contributes uniquely to the growing literature on paired associate recollection by clarifying the convergent findings and differences among studies.

Intrinsic functional connectivity in the default mode network predicts mnemonic discrimination: A connectome-based modeling approach

The ability to distinguish existing memories from similar perceptual experiences is a core feature of episodic memory. This ability is often examined using the mnemonic similarity task in which people discriminate memories of studied objects from perceptually similar lures. Studies of the neural basis of such mnemonic discrimination have mostly focused on hippocampal function and connectivity. However, default mode network (DMN) connectivity may also support such discrimination, given that the DMN includes the hippocampus, and its connectivity supports many aspects of episodic memory. Here, we used connectome-based predictive modeling to identify associations between intrinsic DMN connectivity and mnemonic discrimination. We leveraged a wide range of abilities across healthy younger and older adults to facilitate this predictive approach. Resting-state functional connectivity in the DMN predicted mnemonic discrimination outside the MRI scanner, especially among prefrontal and temporal regions and including several hippocampal regions. This predictive relationship was stronger for younger than older adults, primarily for temporal-prefrontal connectivity. The novel associations established here are consistent with mounting evidence that broader cortical networks including the hippocampus support mnemonic discrimination. They also suggest that age-related network disruptions undermine the extent that the DMN supports this ability. This study provides the first indication of how intrinsic functional properties of the DMN support mnemonic discrimination.

How recent learning shapes the brain: Memory-dependent functional reconfiguration of brain circuits

The process of storing recently encoded episodic mnestic traces so that they are available for subsequent retrieval is accompanied by specific brain functional connectivity (FC) changes. In this fMRI study, we examined the early processing of memories in twenty-eight healthy participants performing an episodic memory task interposed between two resting state sessions. Memory performance was assessed through a forced-choice recognition test after the scanning sessions. We investigated resting state system configuration changes via Independent Component Analysis by cross-modeling baseline resting state spatial maps onto the post-encoding resting state, and post-encoding resting state spatial maps onto baseline. We identified both persistent and plastic components of the overall brain functional configuration between baseline and post-encoding. While FC patterns within executive, default mode, and cerebellar circuits persisted from baseline to post-encoding, FC within the visual circuit changed. A significant session × performance interaction characterized medial temporal lobe and prefrontal cortex FC with the visual circuit, as well as thalamic FC within the executive control system. Findings reveal early-stage FC changes at the system-level subsequent to a learning experience and associated with inter-individual variation in memory performance.

Pattern separation beyond the hippocampus: A high-resolution whole-brain investigation of mnemonic discrimination in healthy adults

Episodic memory depends on the computational process of pattern separation in order to establish distinct memory representations of similar episodes. Studies of pattern separation in humans rely on mnemonic discrimination tasks, which have been shown to tax hippocampal-dependent pattern separation. Although previous neuroimaging research has focused on hippocampal processing, little is known about how other brain regions, known to be involved in recognition memory performance, are involved in mnemonic discrimination tasks. Conversely, neuroimaging studies of pattern separation with whole-brain coverage lack spatial resolution to localize activation to hippocampal subfields. In this study, 48 healthy young adult participants underwent whole-brain high-resolution functional MRI (fMRI) scanning while completing a mnemonic discrimination task. A priori region-of-interest analyses revealed activation patterns consistent with pattern separation in distinct hippocampal subregions, particularly in the subiculum. Connectivity analyses revealed a network of cortical regions consistent with the memory retrieval network where fMRI activation was correlated with hippocampal activation. An exploratory whole-brain analysis revealed widespread activation differentially associated with performance of the mnemonic discrimination task. Taken together, these results suggest that a network of brain regions contribute to mnemonic discrimination performance, with the hippocampus and parahippocampal cortex as a hub in the network displaying clear signals consistent with pattern separation and regions such as the dorsal medial prefrontal cortex particularly important for successful lure discrimination.

Tracking prototype and exemplar representations in the brain across learning

There is a long-standing debate about whether categories are represented by individual category members (exemplars) or by the central tendency abstracted from individual members (prototypes). Neuroimaging studies have shown neural evidence for either exemplar representations or prototype representations, but not both. Presently, we asked whether it is possible for multiple types of category representations to exist within a single task. We designed a categorization task to promote both exemplar and prototype representations and tracked their formation across learning. We found only prototype correlates during the final test. However, interim tests interspersed throughout learning showed prototype and exemplar representations across distinct brain regions that aligned with previous studies: prototypes in ventromedial prefrontal cortex and anterior hippocampus and exemplars in inferior frontal gyrus and lateral parietal cortex. These findings indicate that, under the right circumstances, individuals may form representations at multiple levels of specificity, potentially facilitating a broad range of future decisions.

Saccade-induced retrieval enhancement and the recovery of perceptual item-specific information

Saccade-induced retrieval enhancement (SIRE) effects refer to the finding that memory can be enhanced when a short period of saccadic eye movements takes place prior to retrieval. Previous published work testifies to this eye movement advantage, but no work has yet examined if SIRE effects can be found when retrieval demands are high as a result of testing non-studied memoranda that are identical in name/conceptual codes, similar in perceptual features, but differ in terms of perceptual-item-specific information. The results indicate SIRE effects can be found under such conditions and are independent of encoding orientation (intentional vs. incidental). More particularly, SIRE effects manifested themselves in terms of the retrieval of item-specific detail and recollection (vs. familiarity). In terms of the latter, recollection but not familiarity was enhanced by eye movements. These findings are considered in the context of extant theories of SIRE and related research.

Differential activation of the medial temporal lobe during item and associative memory across time

Studies have shown that the hippocampus plays a crucial role in associative memory. One central issue is whether the involvement of the hippocampus in associative memory remains stable or declines with the passage of time. In the majority of studies, memory performance declines with delay, confounding attempts at interpreting differences in hippocampal activation over time. To address this issue, we tried to equate behavioral performance as much as possible across time for memory of items and associations separately. After encoding words and word pairs, participants were tested for item and associative memories at four time intervals: 20-min, 1-day, 1-week, and 1-month. The results revealed that MTL activation differed over time for associative and item memories. For associative memory, the activation of the anterior hippocampus decreased from 20-min to 1-day then remained stable, whereas in the posterior hippocampus, the activation was comparable for different time intervals when old pairs were correctly retrieved. The hippocampal activation also remained stable when recombined pairs were correctly rejected. As this condition controls for familiarity of the individual items, correct performance depends only on associative memory. For item memory, hippocampal activation declined progressively from 20-min to 1-week and remained stable afterwards. By contrast, the activation in the perirhinal/entorhinal cortex increased over time irrespective of item and associative memories. Drawing on Tulving's distinction between recollection and familiarity, we interpret this pattern of results in accordance with Trace Transformation Theory, which states that as memories are transformed with time and experience, the neural structures mediating item and associative memories will vary according to the underlying representations to which the memories have been transformed.

The inhibition process underlying correct rejection of lures under different attentional states: an event-related potential study

This study explored the effects of different attentional states on correct rejection of lures (CRL) by studying event-related potentials. Healthy college students were recruited to complete a study-test task. Results showed that CRL processing was regulated by participants' attentional states. Under focused attention, CRL was confirmed using subsequent diagnostic monitoring. Under distracted attention, lures were identified using early-familiarity processing; in addition, subsequent processes of CRL under distracted attention might reflect subjects' confidence in making rejection judgments. Time-frequency results indicated that a top-down inhibition process from the frontal cortex to the hippocampus supported by theta oscillation might play an important role in CRL. These findings provide new inspiration and directions for future research on CRL neural mechanisms.

Differential Functional Connectivity along the Long Axis of the Hippocampus Aligns with Differential Role in Memory Specificity and Generalization

The hippocampus contributes to both remembering specific events and generalization across events. Recent work suggests that information may be represented along the longitudinal axis of the hippocampus at varied levels of specificity: detailed representations in the posterior hippocampus and generalized representations in the anterior hippocampus. Similar distinctions are thought to exist within neocortex, with lateral prefrontal and lateral parietal regions supporting memory specificity and ventromedial prefrontal and lateral temporal cortices supporting generalized memory. Here, we tested whether functional connectivity of anterior and posterior hippocampus with cortical memory regions is consistent with these proposed dissociations. We predicted greater connectivity of anterior hippocampus with putative generalization regions and posterior hippocampus with putative memory specificity regions. Furthermore, we tested whether differences in connectivity are stable under varying levels of task engagement. Participants learned to categorize a set of stimuli outside the scanner, followed by an fMRI session that included a rest scan, passive viewing runs, and category generalization task runs. Analyses revealed stronger connectivity of ventromedial pFC to anterior hippocampus and of angular gyrus and inferior frontal gyrus to posterior hippocampus. These differences remained relatively stable across the three phases (rest, passive viewing, category generalization). Whole-brain analyses further revealed widespread cortical connectivity with both anterior and posterior hippocampus, with relatively little overlap. These results contribute to our understanding of functional organization along the long axis of the hippocampus and suggest that distinct hippocampal-cortical connections are one mechanism by which the hippocampus represents both individual experiences and generalized knowledge.

Neural evidence for age-related differences in representational quality and strategic retrieval processes

Mounting behavioral evidence suggests that declines in both representational quality and controlled retrieval processes contribute to episodic memory decline with age. The present study sought neural evidence for age-related change in these factors by measuring neural differentiation during encoding of paired associates and changes in regional blood oxygenation level-dependent activity and functional connectivity during retrieval conditions that placed low (intact pairs) and high (recombined pairs) demands on controlled retrieval processes. Pattern similarity analysis revealed age-related declines in the differentiation of stimulus representations at encoding, manifesting as both reduced pattern similarity between closely related events and increased pattern similarity between distinct events. During retrieval, both groups increased recruitment of areas within the core recollection network when endorsing studied pairs, including the hippocampus and angular gyrus. In contrast, only younger adults increased recruitment of, and hippocampal connectivity with, lateral prefrontal regions during correct rejections of recombined pairs. These results provide evidence for age-related changes in representational quality and in the neural mechanisms supporting memory retrieval under conditions of high, but not low, control demand.

Exploring the neurocognitive basis of episodic recollection in autism

Increasing evidence indicates that the subjective experience of recollection is diminished in autism spectrum disorder (ASD) compared to neurotypical individuals. The neurocognitive basis of this difference in how past events are re-experienced has been debated and various theoretical accounts have been proposed to date. Although each existing theory may capture particular features of memory in ASD, recent research questions whether any of these explanations are alone sufficient or indeed fully supported. This review first briefly considers the cognitive neuroscience of how episodic recollection operates in the neurotypical population, informing predictions about the encoding and retrieval mechanisms that might function atypically in ASD. We then review existing research on recollection in ASD, which has often not distinguished between different theoretical explanations. Recent evidence suggests a distinct difficulty engaging recollective retrieval processes, specifically the ability to consciously reconstruct and monitor a past experience, which is likely underpinned by altered functional interactions between neurocognitive systems rather than brain region-specific or process-specific dysfunction. This integrative approach serves to highlight how memory research in ASD may enhance our understanding of memory processes and networks in the typical brain. We make suggestions for future research that are important for further specifying the neurocognitive basis of episodic recollection in ASD and linking such difficulties to social developmental and educational outcomes.

Sensory Representations Supporting Memory Specificity: Age Effects on Behavioral and Neural Discriminability

Older adults' difficulty in distinguishing between old and new information contributes to memory decline, which may occur because older adults are less likely than young adults to retrieve specific sensory details necessary to distinguish between similar items. In male and female human subjects, the present study measured the extent of age differences in the specificity of memory representations using a false memory paradigm in which studied items were linked to retrieval items at multiple levels of similarity. Older adults showed poorer behavioral discrimination than young adults, driven primarily by false recognition of lures that differed from targets only in perceptual details. Patterns of activation across several regions within ventral visual cortex could be used to distinguish between targets and lures when they differed in both perceptual details and a semantic label. However, of ventral visual regions, only signals in the midline occipital cortex could be used to distinguish targets from lures when they differed only in perceptual details. Although there was an overall age deficit for this neural discrimination in this region, the positive relationship between neural and behavioral discriminability did not differ across age groups. In contrast, age moderated the relationship between neural and behavioral discriminability in lateral occipital and fusiform cortices, suggesting that activation patterns within these regions represent different types of information in each age group. Therefore, the quality of perceptual signals is a key contributor to memory discrimination across age groups, with evidence that age differences in the nature of representations emerges outside early visual cortex.SIGNIFICANCE STATEMENT Age-related memory decline is due in part to older adults' difficulties in discriminating between old and new information. We tested whether this deficit arises from lack of specificity in the sensory representations underlying older adults' recognition judgments. Using pattern classification analyses in ventral visual cortices, we found that signals in a region early in the visual stream could distinguish between targets and lures at the highest level of similarity. The discriminability of targets and lures in this region was positively related to behavioral discriminability across age groups despite an overall age deficit in classification accuracy. Together, results showed that older adults' memory deficits are related to reduced discriminability of cognitive processes (old/new recognition) in portions of visual cortex.

Reduced Hippocampal Functional Connectivity During Episodic Memory Retrieval in Autism

Increasing recent research has sought to understand the recollection impairments experienced by individuals with autism spectrum disorder (ASD). Here, we tested whether these memory deficits reflect a reduction in the probability of retrieval success or in the precision of memory representations. We also used functional magnetic resonance imaging (fMRI) to study the neural mechanisms underlying memory encoding and retrieval in ASD, focusing particularly on the functional connectivity of core episodic memory networks. Adults with ASD and typical control participants completed a memory task that involved studying visual displays and subsequently using a continuous dial to recreate their appearance. The ASD group exhibited reduced retrieval success, but there was no evidence of a difference in retrieval precision. fMRI data revealed similar patterns of brain activity and functional connectivity during memory encoding in the 2 groups, though encoding-related lateral frontal activity predicted subsequent retrieval success only in the control group. During memory retrieval, the ASD group exhibited attenuated lateral frontal activity and substantially reduced hippocampal connectivity, particularly between hippocampus and regions of the fronto-parietal control network. These findings demonstrate notable differences in brain function during episodic memory retrieval in ASD and highlight the importance of functional connectivity to understanding recollection-related retrieval deficits in this population.

Modulation of target recollection and recollection rejection networks due to retrieval facilitation and interference

To better understand neural recollection processing, we induced interference in target recollection by presenting related lures before their respective targets and facilitated recollection rejection of lures by presenting targets before their related lures. Target recollection following interference recruited visual and prefrontal cortices, showing that these regions support recollection when related information has disrupted target representations. Recollection rejection following target presentation recruited angular gyrus, indicating that this region supports recollection rejection when target representations are strong and highly accessible. Thus, recollection networks are sensitive to the accessibility of target representations that are affected by the presentation of related information during retrieval.

Search and recovery of autobiographical and laboratory memories: Shared and distinct neural components

Functional neuroimaging evidence suggests that there are differences in the neural correlates of episodic memory for laboratory stimuli (laboratory memory) and for events from one's own life (autobiographical memory). However, this evidence is scarce and often confounded with differences in memory testing procedures. Here, we directly compared the neural mechanisms underlying the search and recovery of autobiographical and laboratory memories while minimizing testing differences. Before scanning, participants completed a laboratory memory encoding task in which they studied four-word "chains" spread across three word pairs. During scanning, participants completed a laboratory memory retrieval task, in which they recalled the word chains, and an autobiographical memory retrieval task, in which they recalled specific personal events associated with word cues. Importantly, response times were similar in the two tasks, allowing for a direct comparison of the activation time courses. We found that during memory search (searching for the memory target), similar brain regions were activated during both the autobiographical and laboratory tasks, whereas during memory recovery (accessing the memory traces; i.e., ecphory), clear differences emerged: regions of the default mode network (DMN) were activated greater during autobiographical than laboratory memory, whereas the bilateral superior parietal lobules were activated greater during laboratory than autobiographical memory. Also, multivariate functional connectivity analyses revealed that regardless of memory stage, the DMN and ventral attention network exhibited a more integrated topology in the functional network underlying autobiographical (vs. laboratory) memory retrieval, whereas the fronto-parietal task control network exhibited a more integrated topology in the functional network underlying laboratory (vs. autobiographical) memory retrieval. These findings further characterize the shared and distinct neural components underlying autobiographical and laboratory memories, and suggest that differences in autobiographical vs. laboratory memory brain activation previously reported in the literature reflect memory recovery rather than search differences.

Declines in representational quality and strategic retrieval processes contribute to age-related increases in false recognition

In a Yes/No object recognition memory test with similar lures, older adults typically exhibit elevated rates of false recognition. However, the contributions of impaired retrieval, relative to reduced availability of target details, are difficult to disentangle using such a test. The present investigation sought to decouple these factors by comparing performance on a Yes/No (YN) test to that on a Forced Choice (FC) test, which minimizes demands on strategic retrieval processes, enabling a more direct measure of the availability of object details. Older adults exhibited increased lure false recognition across test formats (Experiment 1), suggesting a decline in the availability of object details contributes to deficits in performance. Manipulating interference by varying the number of objects studied selectively enhanced performance in the FC test, resulting in matched performance across groups, whereas age differences in YN performance persisted (Experiment 2), indicating an additional contribution of impaired strategic retrieval. Consistent with differential sensitivity of test format to strategic retrieval and the quality of stimulus representations among older adults, variability in the quality of object representations, measured using a perceptual discrimination task, was selectively related to FC performance. In contrast, variability in memory control processes, as measured with tests of recall and executive function, was related to performance across test formats. These results suggest that both declines in the availability of object details and impaired retrieval of object details contribute to elevated rates of lure false recognition with age, and highlight the utility of test format for dissociating these factors in memory-impaired populations.

Elucidating the neural correlates of related false memories using a systematic measure of perceptual relatedness

Previous memory research has exploited the perceptual similarities between lures and targets in order to evoke false memories. Nevertheless, while some studies have attempted to use lures that are objectively more similar than others, no study has systematically controlled for perceptual overlap between target and lure items and its role in accounting for false alarm rates or the neural processes underlying such perceptual false memories. The current study looked to fill this gap in the literature by using a face-morphing program to systematically control for the amount of perceptual overlap between lures and targets. Our results converge with previous studies in finding a pattern of differences between true and false memories. Most importantly, expanding upon this work, parametric analyses showed false memory activity increases with respect to the similarity between lures and targets within bilateral middle temporal gyri and right medial prefrontal cortex (mPFC). Moreover, this pattern of activation was unique to false memories and could not be accounted for by relatedness alone. Connectivity analyses further find that activity in the mPFC and left middle temporal gyrus co-vary, suggestive of gist-based monitoring within the context of false memories. Interestingly, neither the MTL nor the fusiform face area exhibited modulation as a function of target-lure relatedness. Overall, these results provide insight into the processes underlying false memories and further enhance our understanding of the role perceptual similarity plays in supporting false memories.