Harnessing Visual Imagery and Oculomotor Behaviour to Understand Prospection

Eye movements reinstate remembered locations during episodic simulation

Imagining the future, like recalling the past, relies on the ability to retrieve and imagine a spatial context. Research suggests that eye movements support this process by reactivating spatial contextual details from memory, a process termed gaze reinstatement. While gaze reinstatement has been linked to successful memory retrieval, it remains unclear whether it supports the related process of future simulation. In the present study, we recorded both eye movements and audio while participants described familiar locations from memory and subsequently imagined future events occurring in those locations while either freely moving their eyes or maintaining central fixation. Restricting viewing during simulation significantly reduced self-reported vividness ratings, supporting a critical role for eye movements in simulation. When viewing was unrestricted, participants spontaneously reinstated gaze patterns specific to the simulated location, replicating findings of gaze reinstatement during memory retrieval. Finally, gaze-based location reinstatement was predictive of simulation success, indexed by the number of internal (episodic) details produced, with both measures peaking early and co-varying over time. Together, these findings suggest that the same oculomotor processes that support episodic memory retrieval - that is, gaze-based reinstatement of spatial context - also support episodic simulation.

Brain extended and closed forms glutathione levels decrease with age and extended glutathione is associated with visuospatial memory

During aging, the brain is subject to greater oxidative stress (OS), which is thought to play a critical role in cognitive impairment. Glutathione (GSH), as a major antioxidant in the brain, can be used to combat OS. However, how brain GSH levels vary with age and their associations with cognitive function is unclear. In this study, we combined point-resolved spectroscopy and edited spectroscopy sequences to investigate extended and closed forms GSH levels in the anterior cingulate cortex (ACC), posterior cingulate cortex (PCC), and occipital cortex (OC) of 276 healthy participants (extended form, 166 females, age range 20-70 years) and 15 healthy participants (closed form, 7 females, age range 26-56 years), and examined their relationships with age and cognitive function. The results revealed decreased extended form GSH levels with age in the PCC among 276 participants. Notably, the timecourse of extended form GSH level changes in the PCC and ACC differed between males and females. Additionally, positive correlations were observed between extended form GSH levels in the PCC and OC and visuospatial memory. Additionally, a decreased trend of closed form GSH levels with age was also observed in the PCC among 15 participants. Taken together, these findings enhance our understanding of the brain both closed and extended form GSH time course during normal aging and associations with sex and memory, which is an essential first step for understanding the neurochemical underpinnings of healthy aging.

Scene construction in healthy aging - Exploring the interplay between task complexity and oculomotor behaviour

Mounting evidence indicates a close correspondence between episodic memory, mental imagery, and oculomotor behaviour. It remains unclear, however, how oculomotor variables support endogenously driven forms of mental imagery and how this relationship changes across the adult lifespan. In this study we investigated age-related changes in oculomotor signatures during scene construction and explored how task complexity impacts these processes. Younger and cognitively healthy older participants completed a guided scene construction paradigm where scene complexity was manipulated according to the number of elements to be sequentially integrated. We recorded participants' eye movements and collected subjective ratings regarding their phenomenological experience. Overall, older adults rated their constructions as more vivid and more spatially integrated, while also generating more fixations and saccades relative to the younger group, specifically on control trials. Analyses of participants' total scan paths revealed that, in the early stages of scene construction, oculomotor behaviour changed as a function of task complexity within each group. Following the introduction of a second stimulus, older but not younger adults showed a significant decrease in the production of eye movements. Whether this shift in oculomotor behaviour serves a compensatory function to bolster task performance represents an important question for future research.

The positive dimension of schizotypy is associated with self-report measures of autobiographical memory and future thinking but not experimenter-scored indices

ABSTRACTThe ability to remember our past and to imagine the future are critical to our sense of self. Previous research has indicated that they are disrupted in schizophrenia. However, it is unclear (i) whether this is found when examining experimenter-scored indices of content and/or participants' self-report of phenomenological characteristics, and (ii) how these abilities might be related to symptoms. This study sought to address these questions by taking a dimensional approach and measuring positive and negative schizotypal experiences in healthy people (n = 90). Participants were given cue words. For some, they remembered an event from the past and for others they generated an event in the future. No significant relationships were found with any aspect of schizotypy when participants' descriptions were scored by the experimenter according to a standardised episodic content measure. In contrast, several significant positive correlations were observed for past memory and future thinking when examining the positive dimension of schizotypy and participants' ratings, particularly to sensory characteristics of the experience and mental pre- or reliving. These results indicate enhanced subjective experiences of autobiographical memory and future thinking in those who report delusional and hallucinatory-like occurrences, which might be linked to mental imagery or metacognitive alterations.

Attentional switch to memory: An early and critical phase of the cognitive cascade allowing autobiographical memory retrieval

Remembering and mentally reliving yesterday's lunch is a typical example of episodic autobiographical memory retrieval. In the present review, we reappraised the complex cascade of cognitive processes involved in memory retrieval, by highlighting one particular phase that has received little interest so far: attentional switch to memory (ASM). As attention cannot be simultaneously directed toward external stimuli and internal memories, there has to be an attentional switch from the external to the internal world in order to initiate memory retrieval. We formulated hypotheses and developed hypothetical models of both the cognitive and brain processes that accompany ASM. We suggest that gaze aversion could serve as an objective temporal marker of the point at which people switch their attention to memory, and highlight several fields (neuropsychology, neuroscience, social cognition, comparative psychology) in which ASM markers could be essential. Our review thus provides a new framework for understanding the early stages of autobiographical memory retrieval.

Seeing the future: Connectome strength and network efficiency in visual network predict individual ability of episodic future thinking

Episodic future thinking (EFT) refers to the critical ability that enables people to construct and pre-experience the vivid mental imagery about future events, which impacts on the decision-making for individuals and group. Although EFT is generally believed to have a visual nature by theorists, little neuroscience evidence has been provided to verify this assumption. Here, by employing the approach of connectome-based predictive modeling (CPM) and graph-theoretical analysis, we analyzed resting-state functional brain image from 191 participants to predict their variability of EFT ability (leave-one-out cross-validation), and validated the results by applying different parcellation schemas and feature selection thresholds. At the connectome strength level, CPM-based analysis revealed that EFT ability could be predicted by the connectome strength of visual network. Besides, at the network level, graph-theoretical analysis showed that EFT ability could be predicted by the network efficiency of visual network. Moreover, these findings were replicated using different parcellation schemas and feature selection thresholds. These results robustly and collectively supported that the visual network might be one of the neural substrates underlying EFT ability from a comprehensive perspective of resting-state functional connectivity strength and the neural network. This study provides indications on how the function of visual network supports EFT ability, and enhances our understanding of the EFT ability from a neural basis perspective.

"Look at the future": Maintained fixation impoverishes future thinking

We evaluated the relationship between eye movements and future thinking. More specifically, we evaluated whether maintained fixation could influence cognitive characteristics of future thinking. We invited participants to imagine future events in two conditions: while freely exploring a white wall and while fixating a cross on the wall. Results demonstrated fewer and longer fixations, as well as fewer and shorter saccades during maintained fixation condition than in the free gaze condition. Shorter total amplitude of saccades was also observed during the maintained fixation condition than during the free-gaze condition. Regarding the cognitive characteristics of future thinking, fewer spatiotemporal details and less visual imagery, slower retrieval time, and shorter descriptions were observed for future thinking during maintained fixation than during free-gaze condition. These results demonstrate that maintaining fixation results in an effortful construction of future scenarios. We suggest that maintained fixation limits the cognitive resources that are required for future thinking.

Functional Coupling between the Fronto-Parietal Network and Default Mode Network Is Associated with Balanced Time Perspective

Balanced time perspective refers to the ability to flexibly switch between different temporal foci in an adaptive manner according to the current context. Functional connectivity within the default mode network (DMN) has been suggested to support balanced time perspective. The coupling between the DMN and fronto-parietal network (FPN) may drive many important expressions of internally directed cognition. However, it remains unclear whether balanced time perspective is supported by the interaction between the FPN and DMN. To examine these issues, we recruited 91 participants (52 males with mean age of 19.6, and 39 females with mean age of 20.0) to undergo resting-state brain imaging scan and to complete a questionnaire measuring balanced time perspective. Seed-based voxel-wise functional connectivity analyses implicated midline DMN regions including the anterior medial prefrontal cortex (amPFC) and posterior cingulate cortex (PCC) along with the anterior cingulate cortex (ACC), precuneus, and cerebellum in supporting a balanced time perspective. More importantly, functional connectivity between the right amPFC and right dorsal lateral prefrontal cortex (DLPFC) in the FPN was found to associate with balanced time perspective. Our findings suggest the importance of coordinated brain activity in supporting a balanced time perspective.

Unrestricted eye movements strengthen effective connectivity from hippocampal to oculomotor regions during scene construction

Scene construction is a key component of memory recall, navigation, and future imagining, and relies on the medial temporal lobes (MTL). A parallel body of work suggests that eye movements may enable the imagination and construction of scenes, even in the absence of external visual input. There are vast structural and functional connections between regions of the MTL and those of the oculomotor system. However, the directionality of connections between the MTL and oculomotor control regions, and how it relates to scene construction, has not been studied directly in human neuroimaging. In the current study, we used dynamic causal modeling (DCM) to interrogate effective connectivity between the MTL and oculomotor regions using a scene construction task in which participants' eye movements were either restricted (fixed-viewing) or unrestricted (free-viewing). By omitting external visual input, and by contrasting free- versus fixed- viewing, the directionality of neural connectivity during scene construction could be determined. As opposed to when eye movements were restricted, allowing free-viewing during construction of scenes strengthened top-down connections from the MTL to the frontal eye fields, and to lower-level cortical visual processing regions, suppressed bottom-up connections along the visual stream, and enhanced vividness of the constructed scenes. Taken together, these findings provide novel, non-invasive evidence for the underlying, directional, connectivity between the MTL memory system and oculomotor system associated with constructing vivid mental representations of scenes.

Schema-related eye movements support episodic simulation

Recent work indicates that eye movements support the retrieval of episodic memories by reactivating the spatiotemporal context in which they were encoded. Although similar mechanisms have been thought to support simulation of future episodes, there is currently no evidence favoring this proposal. In the present study, we investigated the role of eye movements in episodic simulation by comparing the gaze patterns of individual participants imagining future scene and event scenarios to across-participant gaze templates for those same scenarios, reflecting their shared features (i.e., schemas). Our results provide novel evidence that eye movements during episodic simulation in the face of distracting visual noise are (1) schema-specific and (2) predictive of simulation success. Together, these findings suggest that eye movements support episodic simulation via reinstatement of scene and event schemas, and more broadly, that interactions between the memory and oculomotor effector systems may underlie critical cognitive processes including constructive episodic simulation.

Rethinking the distinction between episodic and semantic memory: Insights from the past, present, and future

On the 50th anniversary of Tulving's introduction of the celebrated distinction between episodic and semantic memory, it seems more than fitting to revisit his proposal in light of recent conceptual and methodological advances in the field. This Special Issue of Memory & Cognition brings together researchers doing cutting-edge work at the intersection between episodic and semantic memory to showcase studies directly probing this psychological distinction, as well as articles that seek to provide conceptual and theoretical accounts to understand their interaction. The 14 articles presented here highlight the need to critically examine the way in which we conceptualize not only the relationship between episodic and semantic memory, but also the interplay between declarative and non-declarative memory, and the myriad implications of such conceptual changes. In many ways, we suggest this Special Issue might serve as a call to action for our field, inspiring future work to challenge pre-existing conceptions and stimulate new directions in this fast-moving field.

Putting the Pieces Together: Mental Construction of Semantically Congruent and Incongruent Scenes in Dementia

Scene construction refers to the process by which humans generate richly detailed and spatially cohesive scenes in the mind’s eye. The cognitive processes that underwrite this capacity remain unclear, particularly when the envisaged scene calls for the integration of various types of contextual information. Here, we explored social and non-social forms of scene construction in Alzheimer’s disease (AD; n = 11) and the behavioural variant of frontotemporal dementia (bvFTD; n = 15) relative to healthy older control participants (n = 16) using a novel adaptation of the scene construction task. Participants mentally constructed detailed scenes in response to scene–object cues that varied in terms of their sociality (social; non-social) and congruence (congruent; incongruent). A significant group × sociality × congruence interaction was found whereby performance on the incongruent social scene condition was significantly disrupted in both patient groups relative to controls. Moreover, bvFTD patients produced significantly less contextual detail in social relative to non-social incongruent scenes. Construction of social and non-social incongruent scenes in the patient groups combined was significantly associated with independent measures of semantic processing and visuospatial memory. Our findings demonstrate the influence of schema-incongruency on scene construction performance and reinforce the importance of episodic–semantic interactions during novel event construction.

Subjective Time in Dementia: A Critical Review

The capacity for subjective time in humans encompasses the perception of time's unfolding from moment to moment, as well as the ability to traverse larger temporal expanses of past- and future-oriented thought via mental time travel. Disruption in time perception can result in maladaptive outcomes-from the innocuous lapse in timing that leads to a burnt piece of toast, to the grievous miscalculation that produces a traffic accident-while disruption to mental time travel can impact core functions from planning appointments to making long-term decisions. Mounting evidence suggests that disturbances to both time perception and mental time travel are prominent in dementia syndromes. Given that such disruptions can have severe consequences for independent functioning in everyday life, here we aim to provide a comprehensive exposition of subjective timing dysfunction in dementia, with a view to informing the management of such disturbances. We consider the neurocognitive mechanisms underpinning changes to both time perception and mental time travel across different dementia disorders. Moreover, we explicate the functional implications of altered subjective timing by reference to two key and representative adaptive capacities: prospective memory and intertemporal decision-making. Overall, our review sheds light on the transdiagnostic implications of subjective timing disturbances in dementia and highlights the high variability in performance across clinical syndromes and functional domains.

Mental imagery-based episodic simulation amplifies motivation and behavioural engagement in planned reward activities

Preliminary evidence suggests mental imagery-based episodic simulation of planned reward activities may amplify motivation and promote greater behavioural engagement, particularly for activities with high motivational barriers (Renner, Murphy, Ji, Manly, & Holmes, 2019). This study conducted a conceptual replication and extension of Renner et al. (2019). N = 81 first-year university students self-selected and scheduled two reward activities (one hedonic, one mastery) for the following week before being randomly allocated to either an Imagery-Experiential elaboration condition (n = 27), a Verbal-Reasoning elaboration condition (n = 28), or a Scheduling-only Control condition (n = 26). Following the lab session, all participants received standardized daily prompts to complete daily activity diaries online for seven days. The Imagery-Experiential condition reported greater increases in anticipatory pleasure (state mood), anticipated pleasure, and self-reported motivation compared to the Scheduling-only Control condition, and greater increases in anticipatory pleasure (state mood), but not anticipated pleasure or motivation, relative to the Verbal-Reasoning condition. Consistent with Renner et al. (2019), the Imagery-Experiential condition, but not the Verbal-Reasoning condition, reported more frequent engagement in high motivational barrier activities than the Scheduling-only Control condition. Exploratory mediational analyses suggested that mental imagery may exert unique motivational impacts via its impact on anticipatory pleasure (state mood), although indirect effects were only observed for self-reported motivation change in the lab, with real world behavioural effects falling short of statistical significance.

The distinct and overlapping brain networks supporting semantic and spatial constructive scene processing

Scene imagery features prominently when we recall autobiographical memories, imagine the future and navigate around in the world. Consequently, in this study we sought to better understand how scene representations are supported by the brain. Processing scenes involves a variety of cognitive processes that in the real world are highly interactive. Here, however, our goal was to separate semantic and spatial constructive scene processes in order to identify the brain areas that were distinct to each process, those they had in common, and the connectivity between regions. To this end, participants searched for either semantic or spatial constructive impossibilities in scenes during functional MRI. We focussed our analyses on only those scenes that were possible, thus removing any error detection that would evoke reactions such as surprise or novelty. Importantly, we also counterbalanced possible scenes across participants, enabling us to examine brain activity and connectivity for the same possible scene images under two different conditions. We found that participants adopted different cognitive strategies, which were reflected in distinct oculomotor behaviour, for each condition. These were in turn associated with increased engagement of lateral temporal and parietal cortices for semantic scene processing, the hippocampus for spatial constructive scene processing, and increased activation of the ventromedial prefrontal cortex (vmPFC) that was common to both. Connectivity analyses showed that the vmPFC switched between semantic and spatial constructive brain networks depending on the task at hand. These findings further highlight the well-known semantic functions of lateral temporal areas, while providing additional support for the previously-asserted contribution of the hippocampus to scene construction, and recent suggestions that the vmPFC may play a key role in orchestrating scene processing.