Mind-Wandering in People with Hippocampal Damage

Hippocampal sharp-wave ripples correlate with periods of naturally occurring self-generated thoughts in humans

Core features of human cognition highlight the importance of the capacity to focus on information distinct from events in the here and now, such as mind wandering. However, the brain mechanisms that underpin these self-generated states remain unclear. An emerging hypothesis is that self-generated states depend on the process of memory replay, which is linked to sharp-wave ripples (SWRs), which are transient high-frequency oscillations originating in the hippocampus. Local field potentials were recorded from the hippocampus of 10 patients with epilepsy for up to 15 days, and experience sampling was used to describe their association with ongoing thought patterns. The SWR rates were higher during extended periods of time when participants' ongoing thoughts were more vivid, less desirable, had more imaginable properties, and exhibited fewer correlations with an external task. These data suggest a role for SWR in the patterns of ongoing thoughts that humans experience in daily life.

Elucidating the difference between mind-wandering and day-dreaming terms

Self-generated thoughts have been widely investigated in recent years, while the terms "mind-wandering" and "day-dreaming" are usually used interchangeably. But are these terms equivalent? To test this, online study participants were presented with situations of a protagonist engaged in self-generated thoughts. The scenarios differed with regard to type of situation, the activity in which the protagonist was engaged in, and the properties of the self-generated thoughts. Two different groups evaluated the same situations; one group evaluated the extent to which the protagonist mind-wandered and another the extent to which the protagonist day-dreamt. Our key findings were that the situations were perceived differently with regard to mind-wandering and day-dreaming, depending on whether self-generated thoughts occurred when the protagonist was busy with another activity and the type of self-generated thoughts. In particular, while planning, worrying, and ruminating thoughts were perceived more as mind-wandering in situations involving another activity/task, the situations without another activity/task involving recalling past events and fantasizing thoughts were perceived more as day-dreaming. In the additional experiment, we investigated laypeople's reasons for classifying the situation as mind-wandering or day-dreaming. Our results altogether indicate that mind-wandering and day-dreaming might not be fully equivalent terms.

Differential effects of bilateral hippocampal CA3 damage on the implicit learning and recognition of complex event sequences

Learning regularities in the environment is a fundament of human cognition, which is supported by a network of brain regions that include the hippocampus. In two experiments, we assessed the effects of selective bilateral damage to human hippocampal subregion CA3, which was associated with autobiographical episodic amnesia extending ~50 years prior to the damage, on the ability to recognize complex, deterministic event sequences presented either in a spatial or a non-spatial configuration. In contrast to findings from related paradigms, modalities, and homologue species, hippocampal damage did not preclude recognition memory for an event sequence studied and tested at four spatial locations, whereas recognition memory for an event sequence presented at a single location was at chance. In two additional experiments, recognition memory for novel single-items was intact, whereas the ability to recognize novel single-items in a different location from that presented at study was at chance. The results are at variance with a general role of the hippocampus in the learning and recognition of complex event sequences based on non-adjacent spatial and temporal dependencies. We discuss the impact of the results on established theoretical accounts of the hippocampal contributions to implicit sequence learning and episodic memory.

Two models of mind blanking

Mind blanking is a mental state in which attention does not bring any perceptual input into conscious awareness. As this state is still largely unexplored, we suggest that a comprehensive understanding of mind blanking can be achieved through a multifaceted approach combining self-assessment methods, neuroimaging and neuromodulation. In this article, we explain how electroencephalography and transcranial magnetic stimulation could be combined to help determine whether mind blanking is associated with a lack of mental content or a lack of linguistically or conceptually determinable mental content. We also question whether mind blanking occurs spontaneously or intentionally and whether these two forms are instantiated by the same or different neural correlates.

A generative model of memory construction and consolidation

Episodic memories are (re)constructed, share neural substrates with imagination, combine unique features with schema-based predictions and show schema-based distortions that increase with consolidation. Here we present a computational model in which hippocampal replay (from an autoassociative network) trains generative models (variational autoencoders) to (re)create sensory experiences from latent variable representations in entorhinal, medial prefrontal and anterolateral temporal cortices via the hippocampal formation. Simulations show effects of memory age and hippocampal lesions in agreement with previous models, but also provide mechanisms for semantic memory, imagination, episodic future thinking, relational inference and schema-based distortions including boundary extension. The model explains how unique sensory and predictable conceptual elements of memories are stored and reconstructed by efficiently combining both hippocampal and neocortical systems, optimizing the use of limited hippocampal storage for new and unusual information. Overall, we believe hippocampal replay training generative models provides a comprehensive account of memory construction, imagination and consolidation.

Individual variability in neural representations of mind-wandering

Mind-wandering is a frequent, daily mental activity, experienced in unique ways in each person. Yet neuroimaging evidence relating mind-wandering to brain activity, for example in the default mode network (DMN), has relied on population-rather than individual-based inferences due to limited within-individual sampling. Here, three densely-sampled individuals each reported hundreds of mind-wandering episodes while undergoing multi-session functional magnetic resonance imaging. We found reliable associations between mind-wandering and DMN activation when estimating brain networks within individuals using precision functional mapping. However, the timing of spontaneous DMN activity relative to subjective reports, and the networks beyond DMN that were activated and deactivated during mind-wandering, were distinct across individuals. Connectome-based predictive modeling further revealed idiosyncratic, whole-brain functional connectivity patterns that consistently predicted mind-wandering within individuals but did not fully generalize across individuals. Predictive models of mind-wandering and attention that were derived from larger-scale neuroimaging datasets largely failed when applied to densely-sampled individuals, further highlighting the need for personalized models. Our work offers novel evidence for both conserved and variable neural representations of self-reported mind-wandering in different individuals. The previously-unrecognized inter-individual variations reported here underscore the broader scientific value and potential clinical utility of idiographic approaches to brain-experience associations.

A spontaneous neural replay account for involuntary autobiographical memories and déjà vu experiences

Barzykowski and Moulin argue both involuntary autobiographical memories and déjà vu experiences rely on the same involuntary memory retrieval processes but their underlying neurological basis remains unclear. We propose spontaneous neural replay in the default mode network (DMN) and hippocampus as the basis for involuntary autobiographical memories, whereas for déjà vu experiences such transient activation is limited to the DMN.

Recent advances in the neuroscience of spontaneous and off-task thought: implications for mental health

People spend a remarkable 30-50% of awake life thinking about something other than what they are currently doing. These experiences of being "off-task" can be described as spontaneous thought when mental dynamics are relatively flexible. Here we review recent neuroscience developments in this area and consider implications for mental wellbeing and illness. We provide updated overviews of the roles of the default mode network and large-scale network dynamics, and we discuss emerging candidate mechanisms involving hippocampal memory (sharp-wave ripples, replay) and neuromodulatory (noradrenergic and serotonergic) systems. We explore how distinct brain states can be associated with or give rise to adaptive and maladaptive forms of thought linked to distinguishable mental health outcomes. We conclude by outlining new directions in the neuroscience of spontaneous and off-task thought that may clarify mechanisms, lead to personalized biomarkers, and facilitate therapy developments toward the goals of better understanding and improving mental health.

Alzheimer's Disease and Its Possible Evolutionary Origin: Hypothesis

The enormous, 2-3-million-year evolutionary expansion of hominin neocortices to the current enormity enabled humans to take over the planet. However, there appears to have been a glitch, and it occurred without a compensatory expansion of the entorhinal cortical (EC) gateway to the hippocampal memory-encoding system needed to manage the processing of the increasing volume of neocortical data converging on it. The resulting age-dependent connectopathic glitch was unnoticed by the early short-lived populations. It has now surfaced as Alzheimer's disease (AD) in today's long-lived populations. With advancing age, processing of the converging neocortical data by the neurons of the relatively small lateral entorhinal cortex (LEC) inflicts persistent strain and high energy costs on these cells. This may result in their hyper-release of harmless Aβ_1-42 monomers into the interstitial fluid, where they seed the formation of toxic amyloid-β oligomers (AβOs) that initiate AD. At the core of connectopathic AD are the postsynaptic cellular prion protein (PrPC). Electrostatic binding of the negatively charged AβOs to the positively charged N-terminus of PrPC induces hyperphosphorylation of tau that destroys synapses. The spread of these accumulating AβOs from ground zero is supported by Aβ's own production mediated by target cells' Ca2+-sensing receptors (CaSRs). These data suggest that an early administration of a strongly positively charged, AβOs-interacting peptide or protein, plus an inhibitor of CaSR, might be an effective AD-arresting therapeutic combination.

Memory reactivations during sleep: a neural basis of dream experiences?

Newly encoded memory traces are spontaneously reactivated during sleep. Since their discovery in the 1990s, these memory reactivations have been discussed as a potential neural basis for dream experiences. New results from animal and human research, as well as from the rapidly growing field of sleep and dream engineering, provide essential insights into this question, and reveal both strong parallels and disparities between the two phenomena. We suggest that, although memory reactivations may contribute to subjective experiences across different states of consciousness, they are not likely to be the primary neural basis of dreaming. We identify important limitations in current research paradigms and suggest novel strategies to address this question empirically.

Computational constraints on the associative recall of spatial scenes

We consider a model of associative storage and retrieval of compositional memories in an extended cortical network. Our model network is comprised of Potts units, which represent patches of cortex, interacting through long-range connections. The critical assumption is that a memory, for example of a spatial view, is composed of a limited number of items, each of which has a pre-established representation: storing a new memory only involves acquiring the connections, if novel, among the participating items. The model is shown to have a much lower storage capacity than when it stores simple unitary representations. It is also shown that an input from the hippocampus facilitates associative retrieval. When it is absent, it is advantageous to cue rare rather than frequent items. The implications of these results for emerging trends in empirical research are discussed.

Mental navigation and the neural mechanisms of insight

How do new ideas come about? The central hypothesis presented here states that insights might happen during mental navigation and correspond to rapid plasticity at the cellular level. We highlight the differences between neocortical and hippocampal mechanisms of insight. We argue that the suddenness of insight can be related to the sudden emergence of place fields in the hippocampus. According to our hypothesis, insights are supported by a state of mind-wandering that can be tied to the process of combining knowledge pieces during sharp-wave ripples (SWRs). Our framework connects the dots between research on creativity, mental navigation, and specific synaptic plasticity mechanisms in the hippocampus.

Coexistence of thought types as an attentional state during a sustained attention task

Some studies have asked participants about attentional state on a scale from on-task to off-task, which set the middle option as attention focused on both, including the possibility of the coexistence of thoughts. In addition, studies using multidimensional probes explicitly assumed coexistence within spontaneous thoughts and task-focus dimensions. Although several studies have assumed the coexistence of some thought dimensions, none has explored whether these are different types of thoughts (task-focus, mind-wandering, task-related, external stimuli-related). To examine whether this coexistence of thought types occurred, we used thought probes to determine the degree of immersion in each. The participants responded to probes presented at random during a sustained attention task. The results revealed a mixture of thought types in many self-reports. In addition, the state of attentional allocation behind self-reports was estimated using the hidden Markov model. We observed the following attentional states: task-focused, task-unrelated, task-related, external stimuli-focused, and task-focused-but also focused on other thoughts. These results suggest that individuals can simultaneously allocate attention to thought types and discriminate between reporting. In some cases, probe options should also be considered for this coexistence. We also examined the relationship between self-reports and behavioral indexes, and discussed the necessity of separately measuring the degree of immersion for each thought type.

Adding the neuro to cognition: from food storing to nest building

Typically, investigations of animal cognition couple careful experimental manipulations with examination of the animal's behavioural responses. Sometimes those questions have included attempts to describe the neural underpinnings of the behavioural outputs. Over the past 25 years, behaviours that involve spatial learning and memory (such as navigation and food storing) has been one context in which such dual or correlated investigations have been both accessible and productive. Here I review some of that work and where it has led. Because of the wealth of data and insights gained from that work and song learning before it, it seems that it might also be useful to try to add some neurobiology to other systems in animal cognition. I finish then, with a description of recent work on the cognition and neurobiology of avian nest building. It is still relatively early days but asking questions about the cognition of nest building has already shown both neural correlates of nest building and that learning and memory play a much greater role in this behaviour than previously considered. While it is not yet clear how putting these components together will be synergistic, the examples of song learning and food storing provide encouragement. Perhaps this might be true for other behaviours too?

Simulating the situated-self drives hippocampo-cortical engagement during inner narration of events

We often use inner narration when thinking about past and future events. The present paradigm explicitly addresses the influence of the language used in inner narration on the hippocampus-dependent event construction process. We assessed the language context effect during the inner narration of different event types: past, future, daydream, and self-unrelated fictitious events. The language context was assessed via a fluent bilingual population who used inner narration, either in their first language (L1) or second language (L2). Not all inner narration of events elicited hippocampo-cortical activity. In fact, only the angular gyrus and precuneus-retrosplenial cortex were activated by inner narration across all event types. More precisely, only inner narration of events which entailed the simulation of bodily self-location in space (whether or not they were time-marked: past, future, daydream) depended on the hippocampo-cortical system, while inner narration of events that did not entail bodily self-location (self-unrelated fictitious) did not. The language context of the narration influenced the bilinguals' hippocampo-cortical system by enhancing the co-activation of semantic areas with the hippocampus for inner narration of events in the L2. Overall, this study highlights 2 important characteristics of hippocampo-cortical-dependent inner narration of events: The core episodic hippocampal system is activated for inner narration of events simulating self-location in space (regardless of time-marking), and the inner language used for narration (L1 or L2) mediates hippocampal functional connectivity.

Like a rolling stone: Psychotherapy without (episodic) memory

People with profound amnesia still retain the capacity to learn about the emotional value of experiences, which is crucial in developing and sustaining interpersonal relationships. In a 2017 paper, we demonstrated for the first time (with patient JL) that transferential feelings develop across the therapeutic process, despite profound episodic memory impairment after medial temporal lesions. This paper reports a second case (GA) of a profoundly amnesic patient in psychotherapy, this time after lesions to the anterior fornix. The work with GA opens issues such as the differences and similarities to the previous case, counter-transference phenomena, and the effects of hyperphagia. The findings make it clear that many phenomena are common to both GA and JL, such as forgetfulness, various types of repetition, the importance of the therapeutic alliance, and the ability to make therapeutic gain. However, there were differences between the cases, for example as regards confabulation, which may relate to either pre-morbid personality or lesion site. The paper also discusses the way in which patients of this type bear the very status of psychotherapeutic work with profoundly amnesic patients. Where others have seen barriers and in principle problems in working with such patients, we see many opportunities.

Episodic Memory and Recollection Network Disruptions Following Chemotherapy Treatment in Breast Cancer Survivors: A Review of Neuroimaging Findings

Simple Summary

Memory disturbances are amongst the most common and disruptive symptoms of chemotherapy-related cognitive impairment. Chemotherapy treatments commonly cause neurotoxicity within the hippocampus, creating a vulnerability to memory impairment. Most clinical assessments of long-term memory in breast cancer survivors assess basic verbal and visual memory processing, and do not capture the complexities of everyday event memories, including episodic and autobiographical memory. This review focuses on structural and functional neuroimaging studies identifying disruptions in the hippocampus and recollection network, and related episodic memory impairments in chemotherapy-treated breast cancer survivors. We argue for the need to better characterize memory dysfunction following chemotherapy treatments. Given the importance of episodic and autobiographical memory to a person’s personal history and quality of life, an under-appreciation of how this memory domain is impacted by standard cancer treatments potentially diminishes the negative experiences of breast cancer survivors, and neglects cognitive problems that could benefit from intervention strategies.

Abstract

Long-term memory disturbances are amongst the most common and disruptive cognitive symptoms experienced by breast cancer survivors following chemotherapy. To date, most clinical assessments of long-term memory dysfunction in breast cancer survivors have utilized basic verbal and visual memory tasks that do not capture the complexities of everyday event memories. Complex event memories, including episodic memory and autobiographical memory, critically rely on hippocampal processing for encoding and retrieval. Systemic chemotherapy treatments used in breast cancer commonly cause neurotoxicity within the hippocampus, thereby creating a vulnerability to memory impairment. We review structural and functional neuroimaging studies that have identified disruptions in the recollection network and related episodic memory impairments in chemotherapy-treated breast cancer survivors, and argue for the need to better characterize hippocampally mediated memory dysfunction following chemotherapy treatments. Given the importance of autobiographical memory for a person’s sense of identity, ability to plan for the future, and general functioning, under-appreciation of how this type of memory is impacted by cancer treatment can lead to overlooking or minimizing the negative experiences of breast cancer survivors, and neglecting a cognitive domain that may benefit from intervention strategies.

Grey Matter Volume Reductions of the Left Hippocampus and Amygdala in PTSD: A Coordinate-Based Meta-Analysis of Magnetic Resonance Imaging Studies

INTRODUCTION

In recent years, research on posttraumatic stress disorder (PTSD) focused on the description of different biological correlates of illness. Morphological changes of different brain regions were involved in PTSD neurophysiopathology, being related to trauma or considered a resilience biomarker. In this meta-analysis, we aimed to investigate the grey matter changes reported in magnetic resonance imaging (MRI) studies on patients who have developed PTSD compared to exposed subjects who did not show a clinical PTSD onset.

METHODS

We meta-analysed eight peer-reviewed MRI studies conducted on trauma-exposed patients and reported results corrected for false positives. We then conducted global and intergroup comparisons from neuroimaging data of two cohorts of included subjects. The included studies were conducted on 250 subjects, including 122 patients with PTSD and 128 non-PTSD subjects exposed to trauma.

RESULTS

Applying a family-wise error correction, PTSD subjects compared to trauma-exposed non-PTSD individuals showed a significant volume reduction of a large left-sided grey matter cluster extended from the parahippocampal gyrus to the uncus, including the amygdala.

CONCLUSIONS

These volumetric reductions are a major structural correlate of PTSD and can be related to the expression of symptoms. Future studies might consider these and other neural PTSD correlates, which may lead to the development of clinical applications for affected patients.

The Algorithms of Mindfulness

This paper analyzes notions and models of optimized cognition emerging at the intersections of psychology, neuroscience, and computing. What I somewhat polemically call the algorithms of mindfulness describes an ideal that determines algorithmic techniques of the self, geared at emotional resilience and creative cognition. A reframing of rest, exemplified in corporate mindfulness programs and the design of experimental artificial neural networks sits at the heart of this process. Mindfulness trainings provide cues as to this reframing, for they detail each in their own way how intermittent periods of rest are to be recruited to augment our cognitive capacities and combat the effects of stress and information overload. They typically rely on and co-opt neuroscience knowledge about what the brains of North Americans and Europeans do when we rest. Current designs for artificial neural networks draw on the same neuroscience research and incorporate coarse principles of cognition in brains to make machine learning systems more resilient and creative. These algorithmic techniques are primarily conceived to prevent psychopathologies where stress is considered the driving force of success. Against this backdrop, I ask how machine learning systems could be employed to unsettle the concept of pathological cognition itself.

Mind-wandering: mechanistic insights from lesion, tDCS, and iEEG

Cognitive neuroscience has witnessed a surge of interest in investigating the neural correlates of the mind when it drifts away from an ongoing task and the external environment. To that end, functional neuroimaging research has consistently implicated the default mode network (DMN) and frontoparietal control network (FPCN) in mind-wandering. Yet, it remains unknown which subregions within these networks are necessary and how they facilitate mind-wandering. In this review, we synthesize evidence from lesion, transcranial direct current stimulation (tDCS), and intracranial electroencephalogram (iEEG) studies demonstrating the causal relevance of brain regions, and providing insights into the neuronal mechanism underlying mind-wandering. We propose that the integration of complementary approaches is the optimal strategy to establish a comprehensive understanding of the neural basis of mind-wandering.

Lower cortical volume is associated with poor sleep quality after traumatic brain injury

Traumatic brain injury (TBI) is known to be associated with poor sleep. In this report, we aimed to identify associations between differences in cortical volume and sleep quality post-TBI. MRI anatomical scans from 88 cases with TBI were analyzed in this report. Subjective sleep quality was assessed using the Pittsburgh Sleep Quality Index (PSQI). Voxel Based Morphometry (VBM), was used to obtain statistical maps of the association between PSQI and cortical volume in gray matter and white matter voxels. Higher PSQI total scores (poor sleep quality) were strongly associated with smaller gray matter volume in the cerebellum. White matter volume was not associated with total PSQI. The sleep disturbance subcomponent showed a significant association with gray and white matter volumes in the cerebellum. Although not significant, cortical areas such as the cingulate and medial frontal regions were associated with sleep quality. The cerebellum with higher contribution to motor and autonomic systems was associated strongly with poor sleep quality. Additionally, regions that play critical roles in inhibitory brain function and suppress mind wandering (i.e., default mode network including medial frontal and cingulate regions) were associated (although to a lesser extent) with sleep. Our findings suggest that poor sleep quality following TBI is significantly associated with lower cerebellar volume, with trending relationships in regions associated with inhibitory function.

Prefrontal contributions to the stability and variability of thought and conscious experience

The human prefrontal cortex is a structurally and functionally heterogenous brain region, including multiple subregions that have been linked to different large-scale brain networks. It contributes to a broad range of mental phenomena, from goal-directed thought and executive functions to mind-wandering and psychedelic experience. Here we review what is known about the functions of different prefrontal subregions and their affiliations with large-scale brain networks to examine how they may differentially contribute to the diversity of mental phenomena associated with prefrontal function. An important dimension that distinguishes across different kinds of conscious experience is the stability or variability of mental states across time. This dimension is a central feature of two recently introduced theoretical frameworks-the dynamic framework of thought (DFT) and the relaxed beliefs under psychedelics (REBUS) model-that treat neurocognitive dynamics as central to understanding and distinguishing between different mental phenomena. Here, we bring these two frameworks together to provide a synthesis of how prefrontal subregions may differentially contribute to the stability and variability of thought and conscious experience. We close by considering future directions for this work.

Neuropsychological features of mind wandering in left-, right- and extra temporal lobe epilepsy

PURPOSE

Mind wandering, i.e. mental time-travelling and imagery unrelated to the current situation has recently been related to mesial temporal lobe (memory) function. In this regard we evaluated as to whether parameters of mind wandering are related to material specific memory in patients with a left-, right-, or extra- temporal lobe epilepsy.

METHODS

In this prospective controlled study we analyzed mind wandering, material specific memory, and executive functions in 29 right-handed patients with right-, left-, or extra-temporal lobe epilepsies. Mind wandering was assessed with a sustained attention to response task containing embedded inquiries on mind wandering. In addition, verbal list learning and memory (VLMT), design list learning (DCS-R), and executive function (EpiTrack) were assessed.

RESULTS

In patients with right temporal lobe epilepsy, the propensity to mind wander was positively related to verbal memory performance, while in left temporal lobe epilepsy, the propensity and future related mind wandering were positively correlated to the performance in visual/figural memory. Generally, the propensity of MW was related to executive function as well.

CONCLUSION

The results suggest that mind wandering in lateralized temporal lobe epilepsy appears to be non-specifically driven by executive function and specifically by the mode and functionality of the memory system of the non-epileptic hemisphere. Repeated assessments would be required to discern as to how much such patterns depend on lesions versus epileptic dysfunction and whether they change with successful medical or surgical treatment.

Mind wandering and depression: A status report

While many clinical studies and overviews on the contribution of rumination to depression exist, relatively little information regarding the role of mind wandering (MW) in general is available. Therefore, it remains an open question whether patterns of MW are altered in depression and, if so, how these alterations are related to rumination. Here, we review and discuss studies investigating MW in cohorts, showing either a clinically significant depression or with clinically significant disorders accompanied by depressive symptoms. These studies yield first tentative insights into major issues. However, further investigations are required, specifically studies which: i) compare patients with a primary diagnosis of major depression with healthy and appropriately matched controls, ii) implement measures of both MW and rumination, iii) are based on experience sampling (in combination with other key approaches), iv) compare experience sampling during daily life, resting state and attentional tasks, v) explore possible biases in the assessment of MW, vi) acquire data not only related to the propensity and contents of MW, but also regarding meta-awareness and intentionality.

The Hippocampal Horizon: Constructing and Segmenting Experience for Episodic Memory

How do we recollect specific events that have occurred during continuous ongoing experience? There is converging evidence from non-human animals that spatially modulated cellular activity of the hippocampal formation supports the construction of ongoing events. On the other hand, recent human oriented event cognition models have outlined that our experience is segmented into discrete units, and that such segmentation can operate on shorter or longer timescales. Here, we describe a unification of how these dynamic physiological mechanisms of the hippocampus relate to ongoing externally and internally driven event segmentation, facilitating the demarcation of specific moments during experience. Our cross-species interdisciplinary approach offers a novel perspective in the way we construct and remember specific events, leading to the generation of many new hypotheses for future research.

Navigating through the ebbs and flows of language

Is progress in understanding the neural basis for spatial navigation relevant to the human language faculty? Not so much at the shortest scale, where movement is continuous, a recent study in the space of vowels suggests. At a much larger scale, however, that of the verbalization of run-away thoughts, a rich phenomenology appears to involve critical contributions by some of the brain structures also involved in spatial cognition. Their interactions may have to be approached with models operating at an integrated cortical level and allowing for the compositionality of multiple local attractor states. A useful window on the latching dynamics enabled by cortico-cortical interactions may be offered by altered states of consciousness. As an example, psychedelic states have been reported to alter the graph properties of functional connectivity in the cortex so as to facilitate wide-ranging trips.

Biopsychosocial Functions of Human Walking and Adherence to Behaviourally Demanding Belief Systems: A Narrative Review

Human walking is a socially embedded and shaped biological adaptation: it frees our hands, makes our minds mobile, and is deeply health promoting. Yet, today, physical inactivity is an unsolved, major public health problem. However, globally, tens of millions of people annually undertake ancient, significant and enduring traditions of physiologically and psychologically arduous walks (pilgrimages) of days-to-weeks extent. Pilgrim walking is a significant human activity requiring weighty commitments of time, action and belief, as well as community support. Paradoxically, human walking is most studied on treadmills, not ‘in the wild’, while mechanistically vital, treadmill studies of walking cannot, in principle, address why humans walk extraordinary distances together to demonstrate their adherence to a behaviourally demanding belief system.

Pilgrim walkers provide a rich ‘living laboratory’ bridging humanistic inquiries, to progressive theoretical and empirical investigations of human walking arising from a behaviourally demanding belief system. Pilgrims vary demographically and undertake arduous journeys on precisely mapped routes of tracked, titrated doses and durations on terrain of varying difficulty, allowing investigations from molecular to cultural levels of analysis. Using the reciprocal perspectives of ‘inside→out’ (where processes within brain and body initiate, support and entrain movement) and ‘outside→in’ (where processes in the world beyond brain and body drive activity within brain and body), we examine how pilgrim walking might shape personal, social and transcendental processes, revealing potential mechanisms supporting the body and brain in motion, to how pilgrim walking might offer policy solutions for physical inactivity.

Episodic-semantic interactions in spontaneous thought

The distinction between a semantic memory system, encompassing conceptual knowledge, and an episodic memory system, characterized by specific episodes, is one of the most important theoretical proposals in cognitive science. However, the distinction between systems has rarely been discussed in relation to spontaneous thought that comes to mind with reduced cognitive effort and intentionality. In this review, we propose that the growing research on spontaneous thought can contribute to current discussions on the interaction between the episodic and semantic systems. Firstly, we review research that shows that, as in deliberate retrieval, spontaneous thoughts are influenced by both episodic and semantic memory, as reflected by the mix of semantic and episodic elements in descriptions of spontaneous thoughts, as well as semantic priming effects in spontaneous thoughts. We integrate the current evidence based on the interplay between cues and semantic activation. Namely, we suggest that cues are key to access episodic memory and modulate the frequency of spontaneous thought, while semantic activation modulates the content of spontaneous thought. Secondly, we propose that spontaneous retrieval is a privileged area to explore the question of functional independence between systems, because it provides direct access to the episodic system. We review the evidence for spontaneous thought in semantic dementia, which suggests that episodic and semantic systems are functionally independent. We acknowledge the scarcity of evidence and suggest that future studies examine the contents of spontaneous thought descriptions and their neural correlates to test the functional relationship and inform the interaction between episodic and semantic systems.

Prediction of stimulus-independent and task-unrelated thought from functional brain networks

Neural substrates of “mind wandering” have been widely reported, yet experiments have varied in their contexts and their definitions of this psychological phenomenon, limiting generalizability. We aimed to develop and test the generalizability, specificity, and clinical relevance of a functional brain network-based marker for a well-defined feature of mind wandering—stimulus-independent, task-unrelated thought (SITUT). Combining functional MRI (fMRI) with online experience sampling in healthy adults, we defined a connectome-wide model of inter-regional coupling—dominated by default-frontoparietal control subnetwork interactions—that predicted trial-by-trial SITUT fluctuations within novel individuals. Model predictions generalized in an independent sample of adults with attention-deficit/hyperactivity disorder (ADHD). In three additional resting-state fMRI studies (total n = 1115), including healthy individuals and individuals with ADHD, we demonstrated further prediction of SITUT (at modest effect sizes) defined using multiple trait-level and in-scanner measures. Our findings suggest that SITUT is represented within a common pattern of brain network interactions across time scales and contexts.

People spend much of their daily lives thinking about things that are unrelated to their immediate environment. Using fMRI, Kucyi et al. show that occurrence of these “stimulus-independent” thoughts can be predicted from a complex pattern of coordinated activity between distinct parts of the brain.

Characterising the hippocampal response to perception, construction and complexity

The precise role played by the hippocampus in supporting cognitive functions such as episodic memory and future thinking is debated, but there is general agreement that it involves constructing representations comprised of numerous elements. Visual scenes have been deployed extensively in cognitive neuroscience because they are paradigmatic multi-element stimuli. However, questions remain about the specificity and nature of the hippocampal response to scenes. Here, we devised a paradigm in which we had participants search pairs of images for either colour or layout differences, thought to be associated with perceptual or spatial constructive processes respectively. Importantly, images depicted either naturalistic scenes or phase-scrambled versions of the same scenes, and were either simple or complex. Using this paradigm during functional MRI scanning, we addressed three questions: 1. Is the hippocampus recruited specifically during scene processing? 2. If the hippocampus is more active in response to scenes, does searching for colour or layout differences influence its activation? 3. Does the complexity of the scenes affect its response? We found that, compared to phase-scrambled versions of the scenes, the hippocampus was more responsive to scene stimuli. Moreover, a clear anatomical distinction was evident, with colour detection in scenes engaging the posterior hippocampus whereas layout detection in scenes recruited the anterior hippocampus. The complexity of the scenes did not influence hippocampal activity. These findings seem to align with perspectives that propose the hippocampus is especially attuned to scenes, and its involvement occurs irrespective of the cognitive process or the complexity of the scenes.

Lesion network mapping demonstrates that mind-wandering is associated with the default mode network

Functional neuroimaging research has consistently associated brain structures within the default mode network (DMN) and frontoparietal network (FPN) with mind-wandering. Targeted lesion research has documented impairments in mind-wandering after damage to the medial prefrontal cortex (mPFC) and hippocampal regions associated with the DMN. However, no lesion studies to date have applied lesion network mapping to identify common networks associated with deficits in mind-wandering. In lesion network mapping, resting-state functional connectivity data from healthy participants are used to infer which brain regions are functionally connected to each lesion location from a sample with brain injury. In the current study, we conducted a lesion network mapping analysis to test the hypothesis that lesions affecting the DMN and FPN would be associated with diminished mind-wandering. We assessed mind-wandering frequency on the Imaginal Processes Inventory (IPI) in participants with brain injury (n = 29) and healthy comparison participants without brain injury (n = 19). Lesion network mapping analyses showed the strongest association of reduced mind-wandering with the left inferior parietal lobule within the DMN. In addition, traditional lesion symptom mapping results revealed that reduced mind-wandering was associated with lesions of the dorsal, ventral, and anterior sectors of mPFC, parietal lobule, and inferior frontal gyrus in the DMN (p < 0.05 uncorrected). These findings provide novel lesion support for the role of the DMN in mind-wandering and contribute to a burgeoning literature on the neural correlates of spontaneous cognition.

Neuromodulation of the mind-wandering brain state: the interaction between neuromodulatory tone, sharp wave-ripples and spontaneous thought

Mind-wandering has become a captivating topic for cognitive neuroscientists. By now, it is reasonably well described in terms of its phenomenology and the large-scale neural networks that support it. However, we know very little about what neurobiological mechanisms trigger a mind-wandering episode and sustain the mind-wandering brain state. Here, we focus on the role of ascending neuromodulatory systems (i.e. acetylcholine, noradrenaline, serotonin and dopamine) in shaping mind-wandering. We advance the hypothesis that the hippocampal sharp wave-ripple (SWR) is a compelling candidate for a brain state that can trigger mind-wandering episodes. This hippocampal rhythm, which occurs spontaneously in quiescent behavioural states, is capable of propagating widespread activity in the default network and is functionally associated with recollective, associative, imagination and simulation processes. The occurrence of the SWR is heavily dependent on hippocampal neuromodulatory tone. We describe how the interplay of neuromodulators may promote the hippocampal SWR and trigger mind-wandering episodes. We then identify the global neuromodulatory signatures that shape the evolution of the mind-wandering brain state. Under our proposed framework, mind-wandering emerges due to the interplay between neuromodulatory systems that influence the transitions between brain states, which either facilitate, or impede, a wandering mind. This article is part of the theme issue 'Offline perception: voluntary and spontaneous perceptual experiences without matching external stimulation'.

Reduced past-oriented mind wandering in left compared to right medial temporal lobe epilepsy

Mind wandering refers to a shift of attention away from a task at hand to task-unrelated thoughts. Several groups have shown increased activation of the left medial temporal lobe (MTL) before and during spontaneous thoughts suggesting that the left MTL may play a crucial role in mind wandering. Due to its relevance for long-term memory, we further hypothesized that the left MTL is particularly involved in mind wandering towards the past. Accordingly, we predicted a reduced propensity to mind wander and less past-oriented mind wandering in patients with left MTL epilepsies. To this end, we experimentally investigated mind wandering in 89 in-patients undergoing diagnostic evaluation of their putative epileptic disorder. Patients performed a sustained attention to response task with embedded experience sampling probes aiming to assess occurrence, meta-awareness and temporal orientation (past/present/future) of mind-wandering episodes. We did not find significant differences in the propensity to mind wander between patient subgroups. However, the left MTL epilepsy subgroup showed significantly reduced past-oriented mind wandering compared to right MTL epilepsies, as well as a trend towards diminished past-oriented mind wandering compared to idiopathic epilepsies. Possibly due to compensatory mechanisms, the right MTL epilepsy subgroup showed significantly increased past-oriented mind wandering compared to extratemporal epilepsies and patients with syncopes. These behavioural findings point to a rejection of the hypothesis that the amount of time engaged in mind wandering crucially depends on the left MTL. However, our data do support the idea that the left MTL is particularly involved in mind wandering towards the past.

Mental transportation mediates nostalgia's psychological benefits

Nostalgizing confers social, existential, and self-oriented psychological benefits or functions. But how does the experience of nostalgia conduce to these functions? We propose that it does so, in part, through mental transportation, which involves mentally leaving one's current space and transporting oneself into a past event. We addressed the role of mental transportation in one daily diary study and two experiments (N = 514). By assessing daily experiences of nostalgia in Study 1, we found that, on days in which participants felt more nostalgic, they were more likely to experience mental transportation. Following a narrative induction of nostalgia, we assessed mental transportation (Studies 2 and 3) and the three putative nostalgia functions: social, existential, self-oriented (Study 3). Nostalgic (vs. control) participants reported greater mental transportation (Studies 2 and 3), which in turn was associated with stronger functions (Study 3). The findings portray mental transportation as a key mechanism underlying the psychological benefits of nostalgia.

Jacques PL. The effects of aging and an episodic specificity induction on spontaneous task-unrelated thought

When voluntarily describing their past or future, older adults typically show a reduction in episodic specificity (e.g., including fewer details reflecting a specific event, time and/or place). However, aging has less impact on other types of tasks that place minimal demands on strategic retrieval such as spontaneous thoughts. In the current study, we investigated age-related differences in the episodic specificity of spontaneous thoughts using experimenter-based coding of thought descriptions. Additionally, we tested whether an episodic specificity induction, which increases episodic detail during deliberate retrieval of events in young and older adults, has the same effect under spontaneous retrieval. Twenty-four younger and 24 healthy older adults performed two counterbalanced sessions including a video, the episodic specificity or control induction, and a vigilance task. In the episodic specificity induction, participants recalled the details of the video while in the control they solved math exercises. The impact of this manipulation on the episodic specificity of spontaneous thoughts was assessed in the subsequent vigilance task, in which participants were randomly stopped to describe their thoughts and classify them as deliberate/spontaneous. We found no differences in episodic specificity between age groups in spontaneous thoughts, supporting the prediction that automatic retrieval attenuates the episodic specificity decrease in aging. The lack of age differences was present regardless of the induction, showing no interactions. For the induction, we also found no main effect, indicating that automatic retrieval bypasses event construction and accesses pre-stored events. Overall, our evidence suggests that spontaneous retrieval is a promising strategy to support episodic specificity in aging.

Neurocognitive patterns dissociating semantic processing from executive control are linked to more detailed off-task mental time travel

Features of ongoing experience are common across individuals and cultures. However, certain people express specific patterns of thought to a greater extent than others. Contemporary psychological theory assumes that individual differences in thought patterns occur because different types of experience depend on the expression of different neurocognitive processes. Consequently, individual variation in the underlying neurocognitive architecture is hypothesised to determine the ease with which certain thought patterns are generated or maintained. Our study (N = 178) tested this hypothesis using multivariate pattern analysis to infer shared variance among measures of cognitive function and neural organisation and examined whether these latent variables explained reports of the patterns of on-going thoughts people experienced in the lab. We found that relatively better performance on tasks relying primarily on semantic knowledge, rather than executive control, was linked to a neural functional organisation associated, via meta-analysis, with task labels related to semantic associations (sentence processing, reading and verbal semantics). Variability of this functional mode predicted significant individual variation in the types of thoughts that individuals experienced in the laboratory: neurocognitive patterns linked to better performance at tasks that required guidance from semantic representation, rather than those dependent on executive control, were associated with patterns of thought characterised by greater subjective detail and a focus on time periods other than the here and now. These relationships were consistent across different days and did not vary with level of task demands, indicating they are relatively stable features of an individual’s cognitive profile. Together these data confirm that individual variation in aspects of ongoing experience can be inferred from hidden neurocognitive architecture and demonstrate that performance trade-offs between executive control and long-term semantic knowledge are linked to a person’s tendency to imagine situations that transcend the here and now.

Dreaming with hippocampal damage

The hippocampus is linked with both sleep and memory, but there is debate about whether a salient aspect of sleep - dreaming - requires its input. To address this question, we investigated if human patients with focal bilateral hippocampal damage and amnesia engaged in dreaming. We employed a provoked awakening protocol where participants were woken up at various points throughout the night, including during non-rapid eye movement and rapid eye movement sleep, to report their thoughts in that moment. Despite being roused a similar number of times, dream frequency was reduced in the patients compared to control participants, and the few dreams they reported were less episodic-like in nature and lacked content. These results suggest that hippocampal integrity may be necessary for typical dreaming to occur, and aligns dreaming with other hippocampal-dependent processes such as episodic memory that are central to supporting our mental life.

A role for the ventromedial prefrontal cortex in self-generated episodic social cognition

The human mind is equally fluent in thoughts that involve self-generated mental content as it is with information in the immediate environment. Previous research has shown that neural systems linked to executive control (i.e. the dorsolateral prefrontal cortex) are recruited when perceptual and self-generated thoughts are balanced in line with the demands imposed by the external world. Contemporary theories (Smallwood and Schooler, 2015) assume that differentiable processes are important for self-generated mental content than for its regulation. The current study used functional magnetic resonance imaging in combination with multidimensional experience sampling to address this possibility. We used a task with minimal demands to maximise our power at identifying correlates of self-generated states. Principal component analysis showed consistent patterns of self-generated thought when participants performed the task in either the lab or in the scanner (ICC ranged from 0.68 to 0.86). In a whole brain analyses we found that neural activity in the ventromedial prefrontal cortex (vMPFC) increases when participants are engaged in experiences which emphasise episodic and socio-cognitive features. Our study suggests that neural activity in the vMPFC is linked to patterns of ongoing thought, particularly those with episodic or social features.

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We identified neural regions associated with patterns of self-generated thought.

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Ventromedial prefrontal cortex (vMPFC) activity during episodic social cognition.

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VMPFC may play a role in episodic and social features of self-generated thought.

Pattern similarity and connectivity of hippocampal-neocortical regions support empathy for pain

Empathy is thought to engage mental simulation, which in turn is known to rely on hippocampal-neocortical processing. Here, we tested how hippocampal-neocortical pattern similarity and connectivity contributed to pain empathy. Using this approach, we analyzed a data set of 102 human participants who underwent functional MRI while painful and non-painful electrical stimulation was delivered to themselves or to a confederate. As hypothesized, results revealed increased pattern similarity between first-hand pain and pain empathy (compared to non-painful control conditions) within the hippocampus, retrosplenial cortex, the temporo-parietal junction and anterior insula. While representations in these regions were unaffected by confederate similarity, pattern similarity in the dorsal medial prefrontal cortex was increased the more dissimilar the other individual was perceived. Hippocampal-neocortical connectivity during first-hand pain and pain empathy engaged largely distinct but neighboring primary motor regions, and empathy-related hippocampal coupling with the fusiform gyrus positively scaled with trait measures of perspective taking. These findings suggest that shared representations and mental simulation might contribute to pain empathy via hippocampal-neocortical pattern similarity and connectivity, partially affected by personality traits and the similarity of the observed individual.

Manipulating the temporal locus and content of mind-wandering

The human brain has a tendency to drift into the realm of internally-generated thoughts that are unbound by space and time. The term mind-wandering (MW) is often used describe such thoughts when they are perceptually decoupled. Evidence suggests that exposure to forward and backward illusory motion skews the temporal orientation of MW thoughts to either the future or past respectively. However, little is known about the impact of this manipulation on other features of MW. Here, using a novel experimental paradigm, we first confirmed that our illusory motion method facilitated the generation of MW thoughts congruent with the direction of motion. We then conducted content analyses which revealed that goal orientation and temporal distance were also significantly affected by the direction of illusory motion. We conclude that illusory motion may be an effective means of assaying MW and could help to elucidate this ubiquitous, and likely critical, component of cognition.

Deficits in Spontaneous Cognition as an Early Marker of Alzheimer's Disease

In the absence of a pharmacological cure, finding the most sensitive early cognitive markers of Alzheimer's disease (AD) is becoming increasingly important. In this article we review evidence showing that brain mechanisms of spontaneous, but stimulus-dependent, cognition overlap with key hubs of the default mode network (DMN) that become compromised by amyloid pathology years before the clinical symptoms of AD. This leads to the formulation of a novel hypothesis which predicts that spontaneous, but stimulus-dependent, conscious retrieval processes, that are generally intact in healthy aging, will be particularly compromised in people at the earliest stages of AD. Initial evidence for this hypothesis is presented across diverse experimental paradigms (e.g., prospective memory, mind-wandering), and new avenues for research in this area are outlined.

Sleeping with Hippocampal Damage

The hippocampus plays a critical role in sleep-related memory processes [1-3], but it is unclear which specific sleep features are dependent upon this brain structure. The examination of sleep physiology in patients with focal bilateral hippocampal damage and amnesia could supply important evidence regarding these links. However, there is a dearth of such studies, despite these patients providing compelling insights into awake cognition [4, 5]. Here, we sought to identify the contribution of the hippocampus to the sleep phenotype by characterizing sleep via comprehensive qualitative and quantitative analyses in memory-impaired patients with selective bilateral hippocampal damage and matched control participants using in-home polysomnography on 4 nights. We found that, compared to control participants, patients had significantly reduced slow-wave sleep-likely due to decreased density of slow waves-as well as slow-wave activity. In contrast, slow and fast spindles were indistinguishable from those of control participants. Moreover, patients expressed slow oscillations (SOs), and SO-fast spindle coupling was observed. However, on closer scrutiny, we noted that the timing of spindles within the SO cycle was delayed in the patients. The shift of patients' spindles into the later phase of the up-state within the SO cycle may indicate a mismatch in timing across the SO-spindle-ripple events that are associated with memory consolidation [6, 7]. The substantial effect of selective bilateral hippocampal damage on large-scale oscillatory activity in the cortex suggests that, as with awake cognition, the hippocampus plays a significant role in sleep physiology, which may, in turn, be necessary for efficacious episodic memory.

Constant Sub-second Cycling between Representations of Possible Futures in the Hippocampus

Cognitive faculties such as imagination, planning, and decision-making entail the ability to represent hypothetical experience. Crucially, animal behavior in natural settings implies that the brain can represent hypothetical future experience not only quickly but also constantly over time, as external events continually unfold. To determine how this is possible, we recorded neural activity in the hippocampus of rats navigating a maze with multiple spatial paths. We found neural activity encoding two possible future scenarios (two upcoming maze paths) in constant alternation at 8 Hz: one scenario per ∼125-ms cycle. Further, we found that the underlying dynamics of cycling (both inter- and intra-cycle dynamics) generalized across qualitatively different representational correlates (location and direction). Notably, cycling occurred across moving behaviors, including during running. These findings identify a general dynamic process capable of quickly and continually representing hypothetical experience, including that of multiple possible futures.

Human hippocampal CA3 damage disrupts both recent and remote episodic memories

Neocortical-hippocampal interactions support new episodic (event) memories, but there is conflicting evidence about the dependence of remote episodic memories on the hippocampus. In line with systems consolidation and computational theories of episodic memory, evidence from model organisms suggests that the cornu ammonis 3 (CA3) hippocampal subfield supports recent, but not remote, episodic retrieval. In this study, we demonstrated that recent and remote memories were susceptible to a loss of episodic detail in human participants with focal bilateral damage to CA3. Graph theoretic analyses of 7.0-Tesla resting-state fMRI data revealed that CA3 damage disrupted functional integration across the medial temporal lobe (MTL) subsystem of the default network. The loss of functional integration in MTL subsystem regions was predictive of autobiographical episodic retrieval performance. We conclude that human CA3 is necessary for the retrieval of episodic memories long after their initial acquisition and functional integration of the default network is important for autobiographical episodic memory performance.

Mind wandering as data augmentation: How mental travel supports abstraction

Gilead et al. state that abstraction supports mental travel, and that mental travel critically relies on abstraction. I propose an important addition to this theoretical framework, namely that mental travel might also support abstraction. Specifically, I argue that spontaneous mental travel (mind wandering), much like data augmentation in machine learning, provides variability in mental content and context necessary for abstraction.

Neural Bases of Cognitive Impairments in Post-Traumatic Stress Disorders: A Mini-Review of Functional Magnetic Resonance Imaging Findings

INTRODUCTION

Post-Traumatic Stress Disorder (PTSD) is often associated with impairments in emotional and cognitive domains. Contrarily to the emotional sphere, neural basis underpinnings to cognitive impairments are still not well known.

METHODS

We performed a bibliographic search on PUBMED of all the studies investigating the cognitive impairments in PTSD individuals. We considered only studies that applied cognitive tasks using a functional Magnetic Resonance Imaging technique. The inclusion criteria were met by nine studies.

RESULTS

Overall, PTSD individuals reported significant impairments in the dorsolateral prefrontal cortex, anterior cingulate cortex, inferior frontal gyrus, insula, inferior temporal cortex, supplement motor area, and Default Mode Network (DMN). Moreover, abnormal activity was reported in subcortical structures (e.g. hippocampus, amygdala, thalamus) and in the cerebellum.

LIMITATIONS

Cognitive functioning was assessed using different cognitive tasks. Potential confounding factors such as age, sex, symptoms intensity, and comorbidities might have influenced the results.

CONCLUSION

So far, the evidence reported that PTSD is characterized by cognitive impairments in several domains, such as attention, memory and autonomic arousal, which may be due to selective dysfunctions in brain regions that are part of cortical networks, the limbic system and DMN. However, further studies are needed in order to better assess the role of cognitive impairments in PTSD and to develop more targeted therapeutic approaches.

Scene construction impairments in frontotemporal dementia: Evidence for a primary hippocampal contribution

The capacity to generate naturalistic three-dimensional and spatially coherent representations of the world, i.e., scene construction, is posited to lie at the heart of a wide range of complex cognitive endeavours. Clinical populations with selective damage to key nodes of a putative scene construction network of the brain have provided important insights regarding the contribution of medial temporal and prefrontal regions in this regard. Here, we explored the capacity for atemporal scene construction, and its associated neural substrates, in the behavioural-variant of frontotemporal dementia (bvFTD); a neurodegenerative brain disorder in which atrophy systematically erodes medial and lateral prefrontal cortices with variable medial temporal lobe involvement. Nineteen bvFTD patients were compared to 18 typical Alzheimer's Disease (AD), and 25 healthy older Control participants on a scene construction task. Relative to Controls, both patient groups displayed marked impairments in generating contextually detailed and spatially coherent scenes, with bvFTD indistinguishable from AD patients across the majority of task metrics. Voxel-based morphometry, based on structural brain MRI, revealed divergent neural substrates of scene construction performance in each patient group. Despite widespread medial and lateral prefrontal atrophy, the capacity to generate richly detailed and spatially coherent scenes in bvFTD was found to rely predominantly upon the integrity of right medial temporal structures, including the hippocampus and parahippocampal gyrus. Scene construction impairments in AD, by contrast, hinged upon the integrity of posterior parietal brain regions. Our findings in bvFTD resonate with a large body of work implicating the right hippocampus in the construction of spatially integrated scene imagery. How these impairments relate to changes in autobiographical memory and prospection in bvFTD will be an important question for future studies to address.