Signy Sheldon

The role of the hippocampus in memory and mental construction.

Much has been learned about the processes that support the remembrance of past autobiographical episodes and their importance for a number of cognitive tasks. This work has focused on hippocampal contributions to constructing coherent mental representations of scenarios for these tasks, which has opened up new questions about the underlying hippocampal mechanisms. We propose a new framework to answer these questions, which incorporates task demands that prompt hippocampal contributions to mental construction, the online formation of such mental representations, and how these demands relate to the functional organization of the hippocampus. Synthesizing findings from autobiographical memory research, our framework suggests that the interaction of two task characteristics influences the recruitment of the hippocampus: (1) the degree of task open‐endedness (quantified by the presence/absence of a retrieval framework) and (2) the degree to which the integration of perceptual details is required. These characteristics inform the relative weighting of anterior and posterior hippocampal involvement, following an organizational model in which the anterior and posterior hippocampus support constructions on the basis of conceptual and perceptual representations, respectively. The anticipated outcome of our framework is a refined understanding of hippocampal contributions to memory and to the host of related cognitive functions.

Intrinsic medial temporal lobe connectivity relates to individual differences in episodic autobiographical remembering.

People vary in how they remember the past: some recall richly detailed episodes; others more readily access the semantic features of events. The neural correlates of such trait-like differences in episodic and semantic remembering are unknown. We found that self-reported individual differences in how one recalls the past were related to predictable intrinsic connectivity patterns of the medial temporal lobe (MTL) memory system. A pattern of MTL connectivity to posterior brain regions supporting visual-perceptual processing (occipital/parietal cortices) was related to the endorsement of episodic memory-based remembering (recalling spatiotemporal event information), whereas MTL connectivity to inferior and middle prefrontal cortical regions was related to the endorsement of semantic memory-based remembering (recalling facts). These findings suggest that the tendency to engage in episodic autobiographical remembering is associated with accessing and constructing detailed images of a past event in memory, while the tendency to engage in semantic autobiographical remembering is associated with organizing and integrating higher-order conceptual information. More broadly, these findings suggest that differences in how people naturally use memory are instantiated though distinct patterns of MTL functional connectivity.

The medial temporal lobes distinguish between within‐item and item‐context relations during autobiographical memory retrieval

During autobiographical memory retrieval, the medial temporal lobes (MTL) relate together multiple event elements, including object (within‐item relations) and context (item‐context relations) information, to create a cohesive memory. There is consistent support for a functional specialization within the MTL according to these relational processes, much of which comes from recognition memory experiments. In this study, we compared brain activation patterns associated with retrieving within‐item relations (i.e., associating conceptual and sensory‐perceptual object features) and item‐context relations (i.e., spatial relations among objects) with respect to naturalistic autobiographical retrieval. We developed a novel paradigm that cued participants to retrieve information about past autobiographical events, non‐episodic within‐item relations, and non‐episodic item‐context relations with the perceptuomotor aspects of retrieval equated across these conditions. We used multivariate analysis techniques to extract common and distinct patterns of activity among these conditions within the MTL and across the whole brain, both in terms of spatial and temporal patterns of activity. The anterior MTL (perirhinal cortex and anterior hippocampus) was preferentially recruited for generating within‐item relations later in retrieval whereas the posterior MTL (posterior parahippocampal cortex and posterior hippocampus) was preferentially recruited for generating item‐context relations across the retrieval phase. These findings provide novel evidence for functional specialization within the MTL with respect to naturalistic memory retrieval.

Ill-defined problem solving in amnestic mild cognitive impairment: Linking episodic memory to effective solution generation

It is well accepted that the medial temporal lobes (MTL), and the hippocampus specifically, support episodic memory processes. Emerging evidence suggests that these processes also support the ability to effectively solve ill-defined problems which are those that do not have a set routine or solution. To test the relation between episodic memory and problem solving, we examined the ability of individuals with single domain amnestic mild cognitive impairment (aMCI), a condition characterized by episodic memory impairment, to solve ill-defined social problems. Participants with aMCI and age and education matched controls were given a battery of tests that included standardized neuropsychological measures, the Autobiographical Interview (Levine et al., 2002) that scored for episodic content in descriptions of past personal events, and a measure of ill-defined social problem solving. Corroborating previous findings, the aMCI group generated less episodically rich narratives when describing past events. Individuals with aMCI also generated less effective solutions when solving ill-defined problems compared to the control participants. Correlation analyses demonstrated that the ability to recall episodic elements from autobiographical memories was positively related to the ability to effectively solve ill-defined problems. The ability to solve these ill-defined problems was related to measures of activities of daily living. In conjunction with previous reports, the results of the present study point to a new functional role of episodic memory in ill-defined goal-directed behavior and other non-memory tasks that require flexible thinking. Our findings also have implications for the cognitive and behavioural profile of aMCI by suggesting that the ability to effectively solve ill-defined problems is related to sustained functional independence.

What versus where: Investigating how autobiographical memory retrieval differs when accessed with thematic versus spatial information

Autobiographical memory research has investigated how cueing distinct aspects of a past event can trigger different recollective experiences. This research has stimulated theories about how autobiographical knowledge is accessed and organized. Here, we test the idea that thematic information organizes multiple autobiographical events whereas spatial information organizes individual past episodes by investigating how retrieval guided by these two forms of information differs. We used a novel autobiographical fluency task in which participants accessed multiple memory exemplars to event theme and spatial (location) cues followed by a narrative description task in which they described the memories generated to these cues. Participants recalled significantly more memory exemplars to event theme than to spatial cues; however, spatial cues prompted faster access to past memories. Results from the narrative description task revealed that memories retrieved via event theme cues compared to spatial cues had a higher number of overall details, but those recalled to the spatial cues were recollected with a greater concentration on episodic details than those retrieved via event theme cues. These results provide evidence that thematic information organizes and integrates multiple memories whereas spatial information prompts the retrieval of specific episodic content from a past event.

Individual differences in visual imagery determine how event information is remembered

ABSTRACT Individuals differ in how they mentally imagine past events. When reminiscing about a past experience, some individuals remember the event accompanied by rich visual images, while others will remember it with few of these images. In spite of the implications that these differences in the use of imagery have to the understanding of human memory, few studies have taken them into consideration. We examined how imagery interference affecting event memory retrieval was differently modulated by spatial and object imagery ability. We presented participants with a series of video-clips depicting complex events. Participants subsequently answered true/false questions related to event, spatial, or feature details contained in the videos, while simultaneously viewing stimuli that interfered with visual imagery processes (dynamic visual noise; DVN) or a control grey screen. The impact of DVN on memory accuracy was related to individual differences in spatial imagery ability. Individuals high in spatial imagery were less accurate at recalling details from the videos when simultaneously viewing the DVN stimuli compared to those low in spatial imagery ability. This finding held for questions related to the event and spatial details but not feature details. This study advocates for the inclusion of individual differences when studying memory processes.

The Ventromedial Frontal Lobe Contributes to Forming Effective Solutions to Real-world Problems.

Although the ventromedial frontal lobe (VMF) has been implicated in several complex cognitive tasks such as decision-making and problem solving, the processes for which this region is critical remain unclear. Laboratory studies have largely focused on how the VMF contributes to decision-making when outcomes or options are provided, but in the real world generating appropriate options is likely a crucial and rate-limiting initial step. Here, we determined how VMF damage affected the option generation phase of naturalistic problem solving. A group of patients with VMF damage and two controls groups—age-matched healthy participants and patients with frontal damage sparing VMF—were asked to generate as many options as possible to five scenarios depicting open-ended, real-world problems (e.g., having lunch at a restaurant and forgetting your wallet at home). Both the number of options and the effectiveness of each option generated were examined. Damage to VMF led to a significant reduction in both the number of options produced across all problem-solving scenarios and the ability to generate effective options, most notably for scenarios that were social in nature. We discuss these findings in terms of the mechanisms by which the VMF may contribute to option generation, focusing on proposals suggesting this region is important for integrating subjective value and retrieving schematic representations.

The cognitive tools that support mentally constructing event and scene representations

ABSTRACT Constructing mental representations is critical for many cognitive tasks, yet it is unclear if forming different representations relies on distinct cognitive processes. We tested how episodic memory contributes to constructing scene and event-based mental scenarios as well as the effects of two types of imagery ability (object and spatial imagery) on this contribution. Forty participants were given a series of scenario cues that were classified as scenes (e.g., a beach) or events (e.g., a family meal) by independent raters. To these cues, the participants described the details of the associated mental representation. They also rated the representation for vividness, sense of presence, and if forming the representation stimulated the retrieval of an autobiographical memory. The resulting descriptions were then scored for number of contained episodic and non-episodic details. We found participants generated more details – particularly episodic – for event than scene representations. Interestingly, episodic detail generation was predicted by subjective ratings for the scene and not event representations. Other rating differences were that scenes were experienced with a greater sense of presence and events were more likely to trigger autobiographical memory retrieval. Finally, we found dissociation in how object and spatial imagery ability related to event representations. For these representations, generating episodic and non-episodic details related to object and spatial imagery, respectively. These findings indicate how the nature of a representation directs contributions from episodic memory and are affected by imagery ability.

The medial temporal lobe functional connectivity patterns associated with forming different mental representations

The medial temporal lobes (MTL), and more specifically the hippocampus, are critical for forming mental representations of past experiences—autobiographical memories—and for forming other “nonexperienced” types of mental representations, such as imagined scenarios. How the MTL coordinate with other brain areas to create these different types of representations is not well understood. To address this issue, we performed a task‐based functional connectivity analysis on a previously published dataset in which fMRI data were collected as participants created different types of mental representations under three conditions. One condition required forming and relating together details from a past event (autobiographical task), another required forming and relating together details of a spatial context (spatial task) and another condition required relating together conceptual/perceptual features of an object (conceptual task). We contrasted the connectivity patterns associated with a functionally defined region in the parahippocampal cortex (PHC) and anatomically defined anterior and posterior hippocampal segments across these tasks. Examining PHC connectivity patterns revealed that the PHC seed was distinctly connected to other MTL structures during the autobiographical task, to posterior parietal regions during the spatial task and to a distributed network of regions for the conceptual task. Examining hippocampal connectivity patterns revealed that the anterior hippocampus was preferentially connected to regions of default mode network during the autobiographical task and to areas implicated in semantic processing for the conceptual task whereas the posterior hippocampus was preferentially connected to medial‐posterior regions of the brain during the spatial task. We interpret our findings as evidence that there are MTL‐guided networks for forming distinct types of mental representations that align with functional distinctions within the hippocampus.

More than a feeling: Emotional cues impact the access and experience of autobiographical memories

Remembering is impacted by several factors of retrieval, including the emotional content of a memory cue. Here we tested how musical retrieval cues that differed on two dimensions of emotion—valence (positive and negative) and arousal (high and low)—impacted the following aspects of autobiographical memory recall: the response time to access a past personal event, the experience of remembering (ratings of memory vividness), the emotional content of a cued memory (ratings of event arousal and valence), and the type of event recalled (ratings of event energy, socialness, and uniqueness). We further explored how cue presentation affected autobiographical memory retrieval by administering cues of similar arousal and valence levels in a blocked fashion to one half of the tested participants, and randomly to the other half. We report three main findings. First, memories were accessed most quickly in response to musical cues that were highly arousing and positive in emotion. Second, we observed a relation between a cue and the elicited memory’s emotional valence but not arousal; however, both the cue valence and arousal related to the nature of the recalled event. Specifically, high cue arousal led to lower memory vividness and uniqueness ratings, but cues with both high arousal and positive valence were associated with memories rated as more social and energetic. Finally, cue presentation impacted both how quickly and specifically memories were accessed and how cue valence affected the memory vividness ratings. The implications of these findings for views of how emotion directs the access to memories and the experience of remembering are discussed.