Using memories to understand others: the role of episodic memory in theory of mind impairment in Alzheimer disease

Targeting vulnerable microcircuits in the ventral hippocampus of male transgenic mice to rescue Alzheimer-like social memory loss

BACKGROUND

Episodic memory loss is a prominent clinical manifestation of Alzheimer's disease (AD), which is closely related to tau pathology and hippocampal impairment. Due to the heterogeneity of brain neurons, the specific roles of different brain neurons in terms of their sensitivity to tau accumulation and their contribution to AD-like social memory loss remain unclear. Therefore, further investigation is necessary.

METHODS

We investigated the effects of AD-like tau pathology by Tandem mass tag proteomic and phosphoproteomic analysis, social behavioural tests, hippocampal electrophysiology, immunofluorescence staining and in vivo optical fibre recording of GCaMP6f and iGABASnFR. Additionally, we utilized optogenetics and administered ursolic acid (UA) via oral gavage to examine the effects of these agents on social memory in mice.

RESULTS

The results of proteomic and phosphoproteomic analyses revealed the characteristics of ventral hippocampal CA1 (vCA1) under both physiological conditions and AD-like tau pathology. As tau progressively accumulated, vCA1, especially its excitatory and parvalbumin (PV) neurons, were fully filled with mislocated and phosphorylated tau (p-Tau). This finding was not observed for dorsal hippocampal CA1 (dCA1). The overexpression of human tau (hTau) in excitatory and PV neurons mimicked AD-like tau accumulation, significantly inhibited neuronal excitability and suppressed distinct discrimination-associated firings of these neurons within vCA1. Photoactivating excitatory and PV neurons in vCA1 at specific rhythms and time windows efficiently ameliorated tau-impaired social memory. Notably, 1 month of UA administration efficiently decreased tau accumulation via autophagy in a transcription factor EB (TFEB)-dependent manner and restored the vCA1 microcircuit to ameliorate tau-impaired social memory.

CONCLUSION

This study elucidated distinct protein and phosphoprotein networks between dCA1 and vCA1 and highlighted the susceptibility of the vCA1 microcircuit to AD-like tau accumulation. Notably, our novel findings regarding the efficacy of UA in reducing tau load and targeting the vCA1 microcircuit may provide a promising strategy for treating AD in the future.

The role of cognitive estimation in understanding the mental states of others

Previous studies have emphasized the critical role of the prefrontal cortex in cognitive estimation and theory of mind, however, none of them has questioned the possible role of cognitive estimation processes in understanding the mental states of others. In this study, we compared 30 patients with focal prefrontal cortex damage and 30 control subjects matched by gender, age, and education level on their performances on a cognitive estimation task and two tasks assessing theory of mind: the "Faux-Pas" task and the Reading the Mind in the Eyes task. The results showed that patients were significantly impaired compared with control subjects on both abilities of cognitive estimation and theory of mind. Moreover, regression analyses showed that performance on theory of mind was predicted by the scores on cognitive estimation. Finally, using voxel-based lesion analysis, we identified a partially common bilaterally distributed prefrontal network involved in both these domains centred within the ventral and dorsomedial areas with extension to the dorsolateral prefrontal cortex.

Increased Functional Connectivity Involving the Parahippocampal Gyrus in Patients with Schizophrenia during Theory of Mind Processing: A Psychophysiological Interaction Study

BACKGROUND

Theory of Mind (ToM) is an ability to infer the mental state of others, which plays an important role during social events. Previous studies have shown that ToM deficits exist frequently in schizophrenia, which may result from abnormal activity in brain regions related to sociality. However, the interactions between brain regions during ToM processing in schizophrenia are still unclear. Therefore, in this study, we investigated functional connectivity during ToM processing in patients with schizophrenia, using functional magnetic resonance imaging (fMRI).

METHODS

A total of 36 patients with schizophrenia and 33 healthy controls were recruited to complete a ToM task from the Human Connectome Project (HCP) during fMRI scanning. Psychophysiological interaction (PPI) analysis was applied to explore functional connectivity.

RESULTS

Patients with schizophrenia were less accurate than healthy controls in judging social stimuli from non-social stimuli (Z = 2.31, p = 0.021), and displayed increased activity in the right inferior frontal gyrus and increased functional connectivity between the bilateral middle temporal gyrus and the ipsilateral parahippocampal gyrus during ToM processing (AlphaSim corrected p < 0.05).

CONCLUSIONS

Here, we showed that the brain regions related to sociality interact more with the parahippocampal gyrus in patients with schizophrenia during ToM processing, which may reflect a possible compensatory pathway of ToM deficits in schizophrenia. Our study provides a new idea for ToM deficits in schizophrenia, which could be helpful to better understand social cognition of schizophrenia.

Association of cognitive flexibility with neural activation during the theory of mind processing

Theory of mind (ToM), which is the ability to infer and reason about others' mental states, plays a key role in successful social interactions. Previous studies have shown that cognitive flexibility (CF), which refers to the ability to adequately switch between different perspectives, is linked to ToM performance in a variety of experimental tasks. However, the mechanisms of the association between CF and ToM is still largely unknown. Here, we investigated the relation of CF with neural activity during ToM processing in 26 healthy male adults using a functional magnetic resonance imaging task of moving shapes in social patterns. The CF abilities were estimated using the self-report Cognitive Flexibility Scale. Diverse brain areas, including the middle frontal gyrus (MFG), inferior frontal gyrus, amygdala, precuneus, and temporoparietal junction (TPJ), were activated during ToM processing. In these areas, individual differences in CF abilities were associated with the strength of neural activity in the right MFG and TPJ. These findings highlight the notion that cognitive ability to switch between different perspectives according to a changing environment is crucial for the attribution of mental state to others, and suggest that the right MFG and TPJ are deserving of further examination for the development of new therapies to improve social cognition in clinical populations.

EEG and fMRI evidence for autobiographical memory reactivation in empathy

Empathy relies on the ability to mirror and to explicitly infer others' inner states. Theoretical accounts suggest that memories play a role in empathy, but direct evidence of reactivation of autobiographical memories (AM) in empathy is yet to be shown. We addressed this question in two experiments. In Experiment 1, electrophysiological activity (EEG) was recorded from 28 participants. Participants performed an empathy task in which targets for empathy were depicted in contexts for which participants either did or did not have an AM, followed by a task that explicitly required memory retrieval of the AM and non‐AM contexts. The retrieval task was implemented to extract the neural fingerprints of AM and non‐AM contexts, which were then used to probe data from the empathy task. An EEG pattern classifier was trained and tested across tasks and showed evidence for AM reactivation when participants were preparing their judgement in the empathy task. Participants self‐reported higher empathy for people depicted in situations they had experienced themselves as compared to situations they had not experienced. A second independent fMRI experiment replicated this behavioural finding and showed increased activation for AM compared to non‐AM in the brain networks underlying empathy: precuneus, posterior parietal cortex, superior and inferior parietal lobule, and superior frontal gyrus. Together, our study reports behavioural, electrophysiological, and fMRI evidence that robustly supports AM reactivation in empathy.

Social and Neurocognitive Deficits in Remitted Patients with Schizophrenia, Schizoaffective and Bipolar Disorder

This study assesses the empathy level, cognitive performance and emotion recognition skills of remitted patients with schizophrenia, schizoaffective disorder and bipolar disorder, and also explores the relationship between impairments in the mentioned domains. The study was performed on 77 subjects divided into two groups: PAT sample (N = 37) included remitted patients with either schizophrenia, schizoaffective or bipolar disorder who were compared with healthy control subjects from the HC sample (N = 40). Along with sociodemographic and clinical data, empathy levels (using EQ (Empathy Quotient) scale), the ability to recognize another person’s emotional state (using RMET (Reading the Mind in the Eyes Test)), and cognitive performance (using MoCA (Montreal Cognitive Assessment) Scale) were investigated. The intensity of the psychiatric symptoms was measured with BPRS-E (Brief Psychiatric Rating Scale—Expanded). The remitted patients had lower EQ (p = 0.02) and RMET (p < 0.0001) scores than the healthy subjects. In the PAT group, RMET scores were positively correlated with MoCA total scores. Both EQ and RMET scores were negatively correlated with BPRS-E total scores. Psychiatric disorder was a significant predictor for deficits in emotion recognition. There were no significant differences in RMET, EQ and MoCA scores between patients with respect to diagnosis, the type of antipsychotic or the associated medication. In both samples, females had higher empathy levels (p = 0.04) and better emotion recognition abilities (p = 0.04) than males. Patients with schizophrenia, schizoaffective or bipolar disorder, currently in remission, displayed lower empathy levels and poorer emotion recognition skills than healthy subjects. Poor emotion recognition skills were associated with symptom severity and impairments in global cognition.

Partner-Specific Communication Deficits in Individuals With Alzheimer's Disease

Purpose Speakers adjust referential expressions to the listeners' knowledge while communicating, a phenomenon called "audience design." While individuals with Alzheimer's disease (AD) show difficulties in discourse production, it is unclear whether they exhibit preserved partner-specific audience design. The current study examined if individuals with AD demonstrate partner-specific audience design skills. Method Ten adults with mild-to-moderate AD and 12 healthy older adults performed a referential communication task with two experimenters (E1 and E2). At first, E1 and participants completed an image-sorting task, allowing them to establish shared labels. Then, during testing, both experimenters were present in the room, and participants described images to either E1 or E2 (randomly alternating). Analyses focused on the number of words participants used to describe each image and whether they reused shared labels. Results During testing, participants in both groups produced shorter descriptions when describing familiar images versus new images, demonstrating their ability to learn novel knowledge. When they described familiar images, healthy older adults modified their expressions depending on the current partner's knowledge, producing shorter expressions and more established labels for the knowledgeable partner (E1) versus the naïve partner (E2), but individuals with AD were less likely to do so. Conclusions The current study revealed that both individuals with AD and the control participants were able to acquire novel knowledge, but individuals with AD tended not to flexibly adjust expressions depending on the partner's knowledge state. Conversational inefficiency and difficulties observed in AD may, in part, stem from disrupted audience design skills.

Sally-Anne test and regional cerebral blood flow in Alzheimer's disease dementia

AIM

It was recently reported that theory of mind is disturbed in mild Alzheimer's disease dementia (ADD). Some studies have reported reduced scores of ADD patients on false belief tests, even on first-order false belief tests. However, few studies have pursued the neural substrate of false belief tests in patients with ADD in a real-world setting.

METHODS

Sixty-three patients with ADD from outpatient units took the Sally-Anne test and underwent brain single-photon emission computed tomography. Of these patients, 29 answered the Sally-Anne test correctly (successful group) and 34 incorrectly (unsuccessful group). We compared the regional cerebral blood flow between the successful and unsuccessful groups.

RESULTS

A comparison of the two groups showed a significantly lower uptake in the bilateral posterior cingulate gyrus in the unsuccessful group than in the successful group.

CONCLUSIONS

The posterior cingulate gyrus is known to be particularly activated when individuals remember personal events and infer the mental states of others. We suppose that memory or mentalization in the posterior cingulate gyrus-or both-is essential for patients with ADD to be able to pass the Sally-Anne test.

A Brain-Inspired Model of Theory of Mind

Theory of mind (ToM) is the ability to attribute mental states to oneself and others, and to understand that others have beliefs that are different from one's own. Although functional neuroimaging techniques have been widely used to establish the neural correlates implicated in ToM, the specific mechanisms are still not clear. We make our efforts to integrate and adopt existing biological findings of ToM, bridging the gap through computational modeling, to build a brain-inspired computational model for ToM. We propose a Brain-inspired Model of Theory of Mind (Brain-ToM model), and the model is applied to a humanoid robot to challenge the false belief tasks, two classical tasks designed to understand the mechanisms of ToM from Cognitive Psychology. With this model, the robot can learn to understand object permanence and visual access from self-experience, then uses these learned experience to reason about other's belief. We computationally validated that the self-experience, maturation of correlate brain areas (e.g., calculation capability) and their connections (e.g., inhibitory control) are essential for ToM, and they have shown their influences on the performance of the participant robot in false-belief task. The theoretic modeling and experimental validations indicate that the model is biologically plausible, and computationally feasible as a foundation for robot theory of mind.

Neurocognitive mechanisms of theory of mind impairment in neurodegeneration: a transdiagnostic approach

Much of human interaction is predicated upon our innate capacity to infer the thoughts, beliefs, emotions, and perspectives of others, in short, to possess a "theory of mind" (ToM). While the term has evolved considerably since its inception, ToM encompasses our unique ability to apprehend the mental states of others, enabling us to anticipate and predict subsequent behavior. From a developmental perspective, ToM has been a topic of keen research interest, with numerous studies seeking to explicate the origins of this fundamental capacity and its disruption in developmental disorders such as autism. The study of ToM at the opposite end of the lifespan, however, is paradoxically new born, emerging as a topic of interest in its own right comparatively recently. Here, we consider the unique insights afforded by studying ToM capacity in neurodegenerative disorders. Arguing from a novel, transdiagnostic perspective, we consider how ToM vulnerability reflects the progressive degradation of neural circuits specialized for an array of higher-order cognitive processes. This mechanistic approach enables us to consider the common and unique neurocognitive mechanisms that underpin ToM dysfunction across neurodegenerative disorders and for the first time examine its relation to behavioral disturbances across social, intimate, legal, and criminal settings. As such, we aim to provide a comprehensive overview of ToM research in neurodegeneration, the resultant challenges for family members, clinicians, and the legal profession, and future directions worthy of exploration.

The Relationship Between Social Cognition and Awareness in Alzheimer Disease

A large body of evidence highlights the social cognitive impairment in neurodegenerative diseases such Alzheimer disease (AD). This study investigated the relationship among social and emotional functioning (SEF), awareness of disease, and other clinical aspects in people with AD (PwAD). A consecutive series of 50 people with mild to moderate AD and their 50 family caregivers were assessed. There was a significant difference between self-rated SEF and informant-rated SEF. In 56% of PwAD, self-rated SEF is lower than informant-rated SEF. People with AD mostly presented with mildly impaired awareness of the disease (56%), 20% had moderately impaired awareness of the disease, and 6% were unaware of the disease. The multivariate linear regression showed that informant-rated SEF was related to the social functioning, and relationships, domains of awareness of disease, and the PwAD informant-rated quality of life. The relationship between SEF and awareness of social functioning and relationship domain shows that they are comprised of judgments related to perceptions about oneself, values, and beliefs qualitatively different from awareness of memory or functionality, which can be directly observed.

Making sense of self in Alzheimer's disease: reflective function and memory

OBJECTIVE

The current investigation examined the relationship between cognitive impairment and sense of self in Alzheimer's disease (AD).

METHOD

Forty-nine participants with dementia associated with AD were recruited through memory clinics in Victoria, Australia. The 26 participants of the healthy control sample were recruited from a retirement village. Self was measured via the Reflective Self-Function Scale - a theory of mind indicator that provides personal and social self-reflection scores. Cognitive assessment included measures of new learning, executive function, and speed of information processing.

RESULTS

A reduction in sense of self in mild AD was demonstrated in both personal and social domains, as compared to healthy adults of a similar age. With a focus on specific cognitive impairment relationships, new learning was found to predict personal self-reflection, whereas speed of information processing predicted social self-reflection capacity.

CONCLUSION

Findings suggest that deficits in new learning ability contribute to a reduced ability of people with early AD to understand their mental world and interpret thoughts, feelings, and beliefs about themselves. This impaired capacity to self-reflect will be intrusive in daily activities that require monitoring of current self-performance. Furthermore, with reduced speed of information processing found to impact on ability to reflect on social relations, individuals with AD are placed at risk of reduced ability to understand their social world, including communicating and interacting with others. Notwithstanding the overall group findings, individual variability was evident which reinforces the need for person-centred care in dementia.

Are Deficits in Social Cognition Linked to Autobiographical Memory in Patients with Alzheimer’s Disease?

Abstract. We investigated theory of mind (ToM) deficits in Alzheimer‘s disease (AD) and its possible connection to autobiographical memory (ABM). Patients and matched controls were evaluated and compared using a video-based ToM test, an autobiographical fluency task, and a neuropsychological test battery. We found that ToM deficits were positively associated with semantic ABM in the clinical group, whereas a positive relationship appeared between ToM and episodic ABM in controls. We hypothesize that this reflects the course of the disease as well as that semantic ABM is used for ToM processing, being still accessible in AD. Furthermore, we assume that it is also less efficient, which in turn leads to a specific deficit profile of social cognition.

Mental State Inferences Abilities Contribution to Verbal Irony Comprehension in Older Adults with Mild Cognitive Impairment

OBJECTIVE

The present study examined mentalizing capacities as well as the relative implication of mentalizing in the comprehension of ironic and sincere assertions among 30 older adults with mild cognitive impairment (MCI) and 30 healthy control (HC) subjects.

METHOD

Subjects were administered a task evaluating mentalizing by means of short stories. A verbal irony comprehension task, in which participants had to identify ironic or sincere statements within short stories, was also administered; the design of the task allowed uniform implication of mentalizing across the conditions.

RESULTS

Findings indicated that participants with MCI have second-order mentalizing difficulties compared to HC subjects. Moreover, MCI participants were impaired compared to the HC group in identifying ironic or sincere stories, both requiring mental inference capacities.

CONCLUSION

This study suggests that, in individuals with MCI, difficulties in the comprehension of ironic and sincere assertions are closely related to second-order mentalizing deficits. These findings support previous data suggesting a strong relationship between irony comprehension and mentalizing.

Detecting early egocentric and allocentric impairments deficits in Alzheimer's disease: an experimental study with virtual reality

Several studies have pointed out that egocentric and allocentric spatial impairments are one of the earliest manifestations of Alzheimer's Disease (AD). It is less clear how a break in the continuous interaction between these two representations may be a crucial marker to detect patients who are at risk to develop dementia. The main objective of this study is to compare the performances of participants suffering from amnestic mild cognitive impairment (aMCI group), patients with AD (AD group) and a control group (CG), using a virtual reality (VR)-based procedure for assessing the abilities in encoding, storing and syncing different spatial representations. In the first task, participants were required to indicate on a real map the position of the object they had memorized, while in the second task they were invited to retrieve its position from an empty version of the same virtual room, starting from a different position. The entire procedure was repeated across three different trials, depending on the object location in the encoding phase. Our finding showed that aMCI patients performed significantly more poorly in the third trial of the first task, showing a deficit in the ability to encode and store an allocentric viewpoint independent representation. On the other hand, AD patients performed significantly more poorly when compared to the CG in the second task, indicating a specific impairment in storing an allocentric viewpoint independent representation and then syncing it with the allocentric viewpoint dependent representation. Furthermore, data suggested that these impairments are not a product of generalized cognitive decline or of general decay in spatial abilities, but instead may reflect a selective deficit in the spatial organization Overall, these findings provide an initial insight into the cognitive underpinnings of amnestic impairment in aMCI and AD patient exploiting the potentiality of VR.

Theory of mind and cognitive processes in aging and Alzheimer type dementia: a systematic review

OBJECTIVES

Theory of mind (ToM) performance in aging and dementia of the Alzheimer type (DAT) has been a growing interest of researchers and recently, theoretical trends in ToM development have led to a focus on determining the cognitive skills involved in ToM performance. The aim of the present review is to answer three main questions: How is ToM assessed in aging and DAT? How does ToM performance evolve in aging and DAT? Do cognitive processes influence ToM performance in aging and DAT?

METHOD

A systematic review was conducted to provide a targeted overview of recent studies relating ToM performance with cognitive processes in aging and DAT.

RESULTS

RESULTS suggest a decrease in ToM performance, more pronounced in complex ToM tasks. Moreover, the review points up the strong involvement of executive functions, especially inhibition, and reasoning skills in ToM task achievement.

CONCLUSION

Current data suggest that the structure of ToM tasks itself could lead to poor performance, especially in populations with reduced cognitive abilities.

Social influence on associative learning: double dissociation in high-functioning autism, early-stage behavioural variant frontotemporal dementia and Alzheimer's disease

INTRODUCTION

Most of our learning activity takes place in a social context. I examined how social interactions influence associative learning in neurodegenerative diseases and atypical neurodevelopmental conditions primarily characterised by social cognitive and memory dysfunctions.

METHODS

Participants were individuals with high-functioning autism (HFA, n = 18), early-stage behavioural variant frontotemporal dementia (bvFTD, n = 16) and Alzheimer's disease (AD, n = 20). The leading symptoms in HFA and bvFTD were social and behavioural dysfunctions, whereas AD was characterised by memory deficits. Participants received three versions of a paired associates learning task. In the game with boxes test, objects were hidden in six candy boxes placed in different locations on the computer screen. In the game with faces, each box was labelled by a photo of a person. In the real-life version of the game, participants played with real persons.

RESULTS

Individuals with HFA and bvFTD performed well in the computer games, but failed on the task including real persons. In contrast, in patients with early-stage AD, social interactions boosted paired associates learning up to the level of healthy control volunteers. Worse performance in the real life game was associated with less successful recognition of complex emotions and mental states in the Reading the Mind in the Eyes Test. Spatial span did not affect the results.

CONCLUSIONS

When social cognition is impaired, but memory systems are less compromised (HFA and bvFTD), real-life interactions disrupt associative learning; when disease process impairs memory systems but social cognition is relatively intact (early-stage AD), social interactions have a beneficial effect on learning and memory.

The default network and self-generated thought: component processes, dynamic control, and clinical relevance

Though only a decade has elapsed since the default network (DN) was first defined as a large-scale brain system, recent years have brought great insight into the network's adaptive functions. A growing theme highlights the DN as playing a key role in internally directed or self-generated thought. Here, we synthesize recent findings from cognitive science, neuroscience, and clinical psychology to focus attention on two emerging topics as current and future directions surrounding the DN. First, we present evidence that self-generated thought is a multifaceted construct whose component processes are supported by different subsystems within the network. Second, we highlight the dynamic nature of the DN, emphasizing its interaction with executive control systems when regulating aspects of internal thought. We conclude by discussing clinical implications of disruptions to the integrity of the network, and consider disorders when thought content becomes polarized or network interactions become disrupted or imbalanced.