Inhibitory deterioration may contribute to hallucinations in Alzheimer's disease

The Difference in Cognitive Profiles Between Patients With Alzheimer Dementia With and Without Psychosis: A Rapid Review

BACKGROUND

Psychosis in Alzheimer disease (AD) is a major burden for patients and their family. Identifying the characteristics of delusions and hallucinations in the AD population is key to understanding the interconnection between the psychiatric and cognitive symptoms in neurocognitive disorders. The aim of this study is to compare the cognitive profiles of AD patients with and without psychosis.

METHODS

We conducted a rapid review to explore the relationship between psychotic symptoms and cognitive performances in patients with AD. We used MEDLINE, Embase, and PsychINFO literature databases between January 2015 and January 2023. This rapid review was guided by the Cochrane Rapid Reviews Methods Group.

RESULTS

We identified 2909 records from the initial searches. After reviewing the titles, abstracts, and full texts, we selected 8 cross-sectional and 5 cohort studies for the qualitative analysis. Among them, 6 studies were included in the final quantitative analysis. Most studies suggested a correlation between general cognitive decline and the risk of presenting psychotic symptoms. Three studies found an association between hallucinations and deficits in the visuocognitive domains (visuospatial, visuoperceptual, and visuoconstructive skills). Two studies found a relationship between psychotic symptoms and executive dysfunction. Two studies also found a correlation between psychotic symptoms and language. Our results are in line with previous data in the literature, especially regarding the outcome of psychosis on executive function and visuocognitive abilities.

CONCLUSIONS

There appears to be an association between cognitive deficits and psychotic symptoms in AD, but the direction of causality is still unclear, and further studies using longitudinal designs would give more insight into the pathophysiological process of psychosis in AD.

On hallucinations and memory: the relationship between hallucinations and autobiographical overgenerality in Alzheimer's Disease

OBJECTIVES

Alzheimer's disease (AD) has been associated with autobiographical overgenerality (i.e. a tendency of patients to retrieve general rather than specific personal memories). AD has also been associated with hallucinations. We investigated the relationship between autobiographical overgenerality and hallucinations in AD.

METHODS

We invited 28 patients with mild AD to retrieve autobiographical memories, and we also evaluated the occurrence of hallucinations in these patients.

RESULTS

Analysis demonstrated significant correlations between hallucinations and autobiographical overgenerality in the patients.

CONCLUSION

AD patients who are distressed by hallucinations may demonstrate autobiographical overgenerality as a strategy to avoid retrieving distressing information that may be related with hallucinations. However, hallucinations as observed in our study can be attributed to other factors such as the general cognitive decline in AD.

Limited awareness of hallucinations in patients with Alzheimer's disease

INTRODUCTION

We investigated the degree of cognitive insight in patients with Alzheimer's Disease (AD) regarding their hallucinations, aiming to elucidate the subjective experiences and perceptions associated with this phenomenon.

METHODS

Using a cross-sectional design, we invited both AD patients (n = 31) and their informants to evaluate the occurrence of hallucinations. Degree of cognitive insight was based upon the discrepancy between the patients' and informants' evaluations.

RESULTS

Analysis demonstrated that AD patients rated the occurrence of hallucinations lower than their informants, indicating that patients tended to underestimate the frequency of their hallucinations. The discrepancy between the ratings of patients and informants was negatively correlated with cognitive functioning, suggesting that a greater discrepancy (indicating poorer insight) was associated with lower cognitive functioning in patients.

DISCUSSION

Our findings highlight the deficits in insight into hallucinations among AD patients, specifically indicating that AD patients have limited awareness of their own hallucinations. Furthermore, our findings support the idea that deficits in insight into hallucinations are associated with the progression of AD.

Neuropsychiatric and cognitive features of major depressive disorder in aging, based on the data from the US National Alzheimer's Coordinating Center (NACC)

OBJECTIVE

The diagnosis of Major Depressive Disorder (MDD) is based on the DSM-V criteria and is established by a clinician. This allows quantifying depression based on clinical criteria. As such, MDD differs from other types of depressions that are measured by subjective scales. Here, we evaluated the MDD risk factor on other neuropsychiatric symptoms (NPS) as well as MDD association with cognitive performance in Alzheimer's disease (AD), Mild Cognitive Impairment (MCI) and Healthy Controls (HC).

METHODS

Data of 208 patients with AD, 291 patients with MCI and 647 HC were extracted from the National Alzheimer's Coordinating Center database. All participants included in this study were assessed by a physician for the MDD criteria, underwent an NPS evaluation using the NeuroPsychiatric Inventory, and a comprehensive cognitive assessment. Participants were classified as being with and without MDD. We performed logistic regression and MANCOVA models respectively with NPS and cognitive performance as variables of interest and MDD as fixed factors within each group. The MANCOVA was controlled for the effects of age, sex, and education.

RESULTS

MDD increased the risk for psychotic, affective and behavioral NPS in MCI, as well as affective and behavioral NPS in HC and AD. Also, MCI with MDD had lower performance on selective attention and mental flexibility.

CONCLUSIONS

MDD seems to increase the probability of a prevalence of NPS in all groups (HC, MCI and AD). Longitudinal data processing would help to understand the neuropsychiatric evolution of elderly subjects with MDD.

The Effect of Agomelatine in Behavioral and Psychological Symptoms of Dementia

OBJECTIVE

Moderate and severe behavioral and psychological symptoms of dementia (BPSD) often need medical treatment to improve symptoms. Agomelatine is a selective melatonergic (MT1/MT2) agonist that has normalizing effects on disturbed circadian rhythms and disrupted sleep-wake cycles. Its activity of 5HT-2C receptor antagonism is associated with lessening depression and anxiety and increasing slow-wave sleep. Based on past clinical records and current findings it suggests that agomelatine can improve BPSD for patients. This retrospective cohort study was designed to compare the BPSD before and after using agomelatine.

METHODS

Records of dementia cases who had ever received agomelatine treatment for BPSD in a general hospital setting during the past 2.5 years were identified and reviewed. Scores from before and after 3 months of treatment with agomelatine were collected for Neuropsychiatric Inventory (NPI), Brief Psychiatric Rating Scale (BPRS), and Clinical Global Impression (CGI) to compare and analyze the difference of psychological and behavioral symptoms pre- and post-agomelatine used.

RESULTS

Records of 144 cases of dementia with BPSD who had ever used agomelatine from January 2015 to June 2017 were collected. All of the 112 cases had BPRS and CGI scores, of which 75 cases had additional NPI scores. Among these 112 cases, the BPRS and CGI scores were significantly improved in all types of dementia. NPI scores indicated that the use of agomelatine alleviated obvious symptoms and decreased overall distress, especially in the depression/poor mood, anxiety, and sleep/night behavior.

CONCLUSION

It is consistent with an effective result of agomelatine in improving BPSD.

A Multimodal Neuroimaging and Neuropsychological Study of Visual Hallucinations in Alzheimer’s Disease

Background: Hallucinations in Alzheimer’s disease (AD) have been linked to more severe cognitive and functional decline. However, research on visual hallucinations (VH), the most common type of hallucinations in AD, is limited. Objective: To investigate the cognitive and cerebral macrostructural and metabolic features associated with VH in AD. Methods: Twenty-four AD patients with VH, 24 with no VH (NVH), and 24 cognitively normal (CN) matched controls were selected from the Alzheimer’s Disease Neuroimaging Initiative (ADNI) database. Differences in regional gray matter (GM) volumes and cognitive performance were investigated with whole brain voxel-based morphometry analyses of MRI structural brain scans, and analyses of neuropsychological tests. Glucose metabolic changes were explored in a subsample of patients who had FDG-PET scans available. Results: More severe visuoconstructive and attentional deficits were found in AD VH compared with NVH. GM atrophy and hypometabolism were detected in occipital and temporal areas in VH patients in comparison with CN. On the other hand, NVH patients had atrophy and hypometabolism mainly in temporal areas. No differences in GM volume and glucose metabolism were found in the direct comparison between AD VH and NVH. Conclusion: In addition to the pattern of brain abnormalities typical of AD, occipital alterations were observed in patients with VH compared with CN. More severe visuoconstructive and attentional deficits were found in AD VH when directly compared with NVH, and might contribute to the emergence of VH in AD.

The fabricated past: intentionally fabricated autobiographical memories in Alzheimer's disease

OBJECTIVE

We investigated intentionally fabricated autobiographical memories in Alzheimer's Disease (AD).

METHOD

We invited AD patients and control participants to construct real events as well as fabricated events describing fictitious personal events that occurred in the past.

RESULTS

Results demonstrated slower retrieval time for intentionally fabricated memories than for real ones in both AD patients and control participants. The analysis also showed similar vividness for intentionally fabricated memories and real ones in AD patients but lower vividness for intentionally fabricated memories than for real ones in control participants.

CONCLUSIONS

The slow retrieval time of intentionally fabricated memories may be attributed to the cognitive effort required to retrieve elements from autobiographical memory and edit them to construct a new memory. We suggest that the vividness of intentionally fabricated memories observed in AD may induce confusion with real memories. In addition to the experimental approach of our study, we offer a theoretical rationale for intentionally fabricated autobiographical memories by situating them in the wider context of different facets of false memories in AD (e.g. confabulations, source monitoring errors).

Hallucinations and Covid-19: Increased Occurrence of Hallucinations in Patients with Alzheimer's Disease During Lockdown

We investigated the effects of lockdown, as implemented by retirement homes to cope with the spread of Covid-19, on hallucinatory experiences in patients with Alzheimer's disease (AD). The study included 47 patients with AD living in retirement homes and who were already experiencing hallucinations prior to the lockdown. We invited caregivers to rate hallucinatory experiences in these patients during the lockdown, and compared this rating with that provided by the same caregivers prior to the lockdown. Results demonstrated increased hallucinatory experiences in patients with AD during the lockdown, compared with before the lockdown. The decrease in social and physical activities during the lockdown, and especially, the physical separation of residents from family members, might have led to decreased sensory stimulation and increased loneliness, and consequently, to the hallucinatory experiences in patients with AD living in retirement homes during the lockdown. While the restrictive measures were necessary to cope with the spread of Covid-19, these measures have increased hallucinations in patients with AD living in retirement homes, at least in those who were already experiencing hallucinations prior to the lockdown.

Repeated recall on source misattribution in Alzheimer's disease

We assessed the effect of repeated recall on item memory and source monitoring in Alzheimer's disease (AD). AD patients and controls were instructed to either look at or imagine items. They then had to either retrieve the items without indicating their source in three consecutive free recall tests, or to remember the source of the retrieved items in three consecutive source tests. Results showed a significant increase in item memory across all three free recall tests and all three source monitoring tests in control participants, but not in AD patients. More source misattributions were observed in AD patients and controls in the third source test than in the first and second tests. The absence of beneficial effect of repeated recall on item memory in AD patients may be attributed to compromise in memory consolidation processes, while the increase in source misattributions due to repetitions may be attributed to the inflation effect.

Hallucinations and Delusions Signal Alzheimer's Associated Cognitive Dysfunction More Strongly Compared to Other Neuropsychiatric Symptoms

OBJECTIVES

Neuropsychiatric symptoms (NPS) are common among individuals with dementia of the Alzheimer's type (DAT). We sought to characterize which NPS more purely relate to cognitive dysfunction in DAT, relative to other NPS.

METHOD

Demographic, neurocognitive, neuroimaging, and NPS data were mined from the Alzheimer's Disease Neuroimaging Initiative database (n = 906). Using factor analysis, we analyzed the degree to which individual NPS were associated with DAT-associated cognitive dysfunction. We also employed item response theory to graphically depict the ability of individual NPS to index DAT-associated cognitive dysfunction across a continuum ranging from cognitively normal to mild DAT.

RESULTS

Psychotic symptoms (hallucinations and delusions) were more strongly related to the continuum of DAT-associated cognitive dysfunction than other NPS, with the strength of the relationship peaking at high levels of disease severity. Psychotic symptoms also negatively correlated with brain volume and did not relate to the presence of vision problems. Aberrant motor behavior and apathy had relatively smaller associations with DAT-associated cognitive dysfunction, while other NPS showed minimal associations.

DISCUSSION

Psychotic symptoms most strongly indexed DAT-associated cognitive dysfunction, whereas other NPS, such as depression and anxiety, were not as precisely related to the DAT-associated cognitive dysfunction.

Olfactory hallucinations in Alzheimer's disease

We assessed the frequency, duration, and degree of unpleasantness of olfactory hallucinations in Alzheimer's disease (AD). Informants of 31 AD patients were invited to rate the frequency, duration, and degree of unpleasantness of olfactory, auditory, and visual hallucinations. Analysis demonstrated little occurrence of olfactory hallucinations compared with auditory or visual hallucinations. Results also demonstrated that olfactory hallucinations span from a few seconds to one minute, a duration that was similar to that of auditory and visual hallucinations. Olfactory hallucinations were rated as unpleasant compared with auditory or visual hallucinations. Finally, olfactory hallucinations were significantly correlated with depression. Our findings demonstrate little occurrence of olfactory hallucinations but that when they occur, they are experienced as relatively unpleasant in AD patients. Our findings also demonstrate a relationship between olfactory hallucinations and psychiatric characteristics (i.e., depression) in AD.

Hallucinations and source monitoring in Alzheimer's disease

INTRODUCTION

the source monitoring account has been widely investigated for hallucinations in schizophrenia. According to this account, hallucinations are inner events that are misattributed to another source. Our paper investigated this account for Alzheimer's disease.

METHOD

we investigated hallucination experiences in participants with Alzheimer's disease and age-matched healthy controls, as well as their source monitoring ability. The assessment of source monitoring included three conditions. In the first condition, participants had to remember whether objects were previously manipulated by themselves or by the experimenter (i.e. reality monitoring). In the second condition, they had to remember whether objects were previously manipulated by a black or white experimenter-gloved hand (i.e. external monitoring). In the third condition, participants had to remember whether they had previously manipulated objects or had imagined having done so (i.e. internal monitoring).

RESULTS

relative to healthy control participants, participants with Alzheimer's disease experienced hallucinations more often and lower hits on source monitoring. Interestingly, significant correlations were only observed between hallucinations and the internal monitoring condition in participants with Alzheimer's disease.

DISCUSSION

hallucinations in Alzheimer's disease seem to be related to the processes of making judgments about the (internal) context in which an event has occurred.

Hallucinations in a Patient with Alzheimer's Disease During the COVID-19 Crisis: A Case Study

While social distancing may be deemed necessary in order to avoid COVID-19 infections, the lockdown may impact mental health of patients with Alzheimer’s disease (AD). We present a case study involving hallucinations in a patient with AD who lives in a nursing home during the COVID-19 crisis. We compared this patient’s hallucination scores before and during the lockdown. We observed increased hallucinations during, compared to before, the lockdown. These increased hallucinations can be attributed to a number of elements such as the decreased in daily activities, social distancing, lack of physical contact with family members, and loneliness during the lockdown.

A look into hallucinations: the relationship between visual imagery and hallucinations in Alzheimer's disease

Introduction: We investigated the relationship between visual hallucinations and vividness of visual imagery in patients with Alzheimer's disease (AD). Method: We recruited 28 patients with AD and 30 healthy control participants, matched for age and education. We evaluated proneness towards hallucinations with the Launay-Slade Hallucinations Scale, which includes items assessing visual and auditory hallucinations. We also evaluated vividness of visual imagery with the Vividness of Visual Imagery Questionnaire on which participants had to imagine four images (i.e., imagining the face of a friend, the rising sun, a familiar shop-front, and a country scene) and report the vividness of the images they generated. Results: Analysis demonstrated significant positive correlations between visual hallucinations and vividness of visual imagery in AD patients, however, no significant correlations were observed between auditory hallucinations and vividness of visual imagery in these participants. No significant correlations were observed between hallucinations and vividness of visual imagery in healthy control participants, probably due to the lack of hallucinations in these participants. Discussion: These results demonstrate a selective relationship between the occurrence of visual (but not auditory) hallucinations and the ability to generate vivid visual images in AD.

Hallucinations in Alzheimer's disease: failure to suppress irrelevant memories

INTRODUCTION

Research with patients with schizophrenia suggests that inhibitory dysfunction leads to the emergence of redundant or irrelevant information from long-term memory into awareness, and that this process may be involved in generating hallucinations. We investigated whether inhibitory dysfunction in Alzheimer's disease (AD) leads to hallucinations.

METHOD

AD participants and healthy matched controls were assessed with a hallucinations scale and a directed forgetting task. On the directed forgetting task, they were asked to retain a list of 10 words (i.e., List 1). Thereafter, half of the participants were asked to forget this list whereas the other half were asked to retain the list in memory. After the List 1 presentation, all participants were asked to retain another list of 10 words and, successively, were asked to remember all of the words from both lists, regardless of the previous forget or remember instruction.

RESULTS

Relative to healthy matched controls, AD participants showed difficulties in suppressing the words from List 1. AD participants also showed more hallucinatory experiences than healthy matched controls. Interestingly, a significant correlation was observed between the score on the hallucinations measure and difficulties in suppressing List 1 in AD participants.

DISCUSSION

Hallucinations in AD may, at least in part, be related to difficulties in suppressing memory representations, such that unwanted or repetitive thoughts intrude into consciousness.

Clinical correlates of saccadic eye movement in antipsychotic-naïve schizophrenia

Some aspects of saccadic performance have been found to be abnormal in chronic schizophrenia. The majority of this research has, however, been performed on patients treated with long-term antipsychotic medication. Very few studies have examined saccadic performance in antipsychotic-naïve/free patients. There are also very few studies describing the relationship between saccadic performance and clinical symptoms, particularly in antipsychotic free patients. In this study, we compared pro and antisaccade performance in a large sample of antipsychotic-naïve/free schizophrenia patients (N = 45) with healthy controls (N = 57). Clinical symptoms were assessed using Scale for Assessment of Positive Symptoms (SAPS) and Negative Symptoms (SANS). In the antisaccade task, patients made significantly more errors, and their correct antisaccades had smaller amplitudes in comparison to healthy controls. Higher error rates were associated with increased severity of hallucinations. In the prosaccade task, patients had less accurate final eye positions, and made saccades with slower latency and reduced amplitude compared to the healthy controls. These observations in schizophrenia patients without the potential confounds of antipsychotic treatment suggest intrinsic link between saccadic deficits and schizophrenia pathogenesis. The relationship between antisaccade errors and hallucination severity supports the potential link between hallucinations and deficits in inhibitory control.

Clinical and neurocognitive aspects of hallucinations in Alzheimer's disease

Due to their prevalence, hallucinations are considered as one of the most frequent psychotic symptoms in Alzheimer's disease (AD). These psychotic manifestations reduce patients' well-being, increase the burden of caregivers, contribute to early institutionalization, and are related with the course of cognitive decline in AD. Considering their consequences, we provide a comprehensive account of the current state of knowledge about the prevalence and characteristics of hallucinations in AD. We propose a comprehensive and testable theoretical model about hallucinations in AD: the ALZHA (ALZheimer and HAllucinations) model. In this model, neurological, genetic, cognitive, affective, and iatrogenic factors associated with hallucinations in AD are highlighted. According to the ALZHA model, hallucinations in AD first involve trait markers (i.e., cognitive deficits, neurological deficits, genetic predisposition and/or sensory deficits) to which state markers that may trigger these experiences are added (e.g., psychological distress and/or iatrogenic factors). Finally, we provide recommendations for assessment and management of these psychotic manifestations in AD, with the aim to benefit patients, caregivers, and health professionals.

Visual hallucinations in Alzheimer's disease is significantly associated with clinical diagnostic features of dementia with Lewy bodies

Visual hallucinations (VHs) are among the most striking features of dementia with Lewy bodies (DLB). Given that Lewy body pathology is frequently observed in the brains of patients with AD, we aimed to study factors associated with VHs in AD and examine their association with DLB features. This cross-sectional study enrolled a consecutive series of AD patients who visited the dementia clinic of a regional hospital. Clinically diagnosed possible or probable DLB cases were excluded. VH frequency and associated factors including age, sex, education, disease severity, DLB features, vascular risk factors, cognitive function, and neuropsychiatric symptoms were compared between AD patients with VHs (VH+) and those without VHs (VH−). Among a total of 295 patients analyzed, 42 (14.2%) had VHs. After adjusting for age, sex, and disease severity, DLB features including fluctuations in cognition scores, rapid-eye-movement behavioral disorder (RBD), and severe neuroleptic sensitivity were more frequent in the VH+ group. Furthermore, depression score, total Neuropsychiatric Inventory (NPI) score, and total caregiver burden score as assessed by the NPI were higher in the VH+ group. Among neuropsychiatric symptoms, delusions, hallucinations in the non-visual domains, anxiety, and disinhibition were more frequent in the VH+ group. Conversely, none of the vascular risk factors (VRFs) or cognitive domains of the Cognitive Abilities Screening Instrument (CASI) was associated with VHs in AD. In summary, VHs, albeit occurring at a low rate, had a high impact on AD. Diagnostic features of DLB, including fluctuations, RBD, and severe neuroleptic sensitivity were significantly associated with VHs in AD. AD patients with VHs tended to have more severe neuropsychiatric symptoms and greater caregiver burden.

Hallucinations in Healthy Older Adults: An Overview of the Literature and Perspectives for Future Research

KEY POINTS

➢ Studies suggest a substantial minority of healthy older adults have hallucinatory experiences, in line with existing evidence on hallucinations in other age groups, though it is still unclear if hallucination prevalence increases or declines with age in older cohorts.

➢ Stigma attached to both hallucinations and ageing leads to considerable under-reporting of these experiences in healthy older adults and may negatively bias how professionals, family members, and the public respond.

➢ Why and when hallucinations in healthy older adults remit, persist, or progress to other clinical disorders remains poorly understood.

➢ Current evidence points to a range of factors associated with hallucinations in older adults including decline in sensory or cognitive functioning, poor sleep, and psychosocial stressors (e.g., social isolation, loneliness, and bereavement), highlighting the need for accurate assessment and tailored interventions.

Hallucinations, though common in youth and younger adults, are not the preserve of these age groups. Accumulating evidence shows that hallucinatory experiences are also present at surprisingly high rates in healthy older adults in the general community. Furthermore, stigma and misunderstanding of hallucinations, together with ageism, may lead to under-reporting of these experiences by older adults, and misdiagnosis or mismanagement by health and mental health practitioners. Consequently, improved public and professional knowledge is needed about the nature and significance of hallucinations with advancing age. The purpose of this review is to provide a comprehensive overview, and critical analysis, of research on the prevalence, psychosocial, and neurobiological factors associated with hallucinations in people aged 60 years and over. To the best of our knowledge, this is the first review of its kind in the literature. The evidence supports a dynamic conceptualization of hallucinations, in which the emergence of hallucinations is viewed as a balance between the sensory, cognitive, or social impairments accompanying advancing age and the degree to which compensatory processes elicited by these impairments are successful. We briefly summarize the implications of the literature for aged care services and interventions, and stress that far more studies are needed in this important field of research.

Hallucinations, loneliness, and social isolation in Alzheimer's disease

INTRODUCTION

Cognitive and functional compromise, as frequently observed in Alzheimer's disease (AD), hinders communication and social interactions. One consequence of this hindrance may be a feeling of loneliness. Moreover, emptiness and boredom, as observed in social isolation and loneliness, may thus be compensated for by creating imagined stimuli. Conditions of loneliness may be viewed as potentially generating hallucinatory experiences. To assess this assumption, the present study explored the relationship between social isolation, loneliness, and hallucinations in a sample of 22 mild AD participants and 24 elderly, healthy controls.

METHODS

Participants were assessed using the Launay-Slade Hallucination Scale, the UCLA Loneliness Scale, and a scale exploring contact with others and social participation.

RESULTS

More hallucinatory experiences, social isolation, and loneliness were found in the AD group than in the healthy control group. Moreover, significant correlations were observed between hallucinations and loneliness and between hallucinations and social isolation in both groups. Finally, hallucinations were predicted by social isolation.

DISCUSSION

Hallucinations may constitute a compensatory mechanism that aims to fulfil communication needs in lonely, elderly participants. Hallucinations may also be regarded as experiences that allow certain participants to escape the cycle of boredom, emptiness, and affective deprivation caused by social isolation.

Are Hallucinations Due to an Imbalance Between Excitatory and Inhibitory Influences on the Brain?

This review from the International Consortium on Hallucinations Research intends to question the pertinence of the excitatory-to-inhibitory (E/I) imbalance hypothesis as a model for hallucinations. A large number of studies suggest that subtle impairments of the E/I balance are involved in neurological and psychiatric conditions, such as schizophrenia. Emerging evidence also points to a role of the E/I balance in maintaining stable perceptual representations, suggesting it may be a plausible model for hallucinations. In support, hallucinations have been linked to inhibitory deficits as shown with impairment of gamma-aminobutyric acid transmission, N-methyl-d-aspartate receptor plasticity, reductions in gamma-frequency oscillations, hyperactivity in sensory cortices, and cognitive inhibition deficits. However, the mechanisms by which E/I dysfunctions at the cellular level might relate to clinical symptoms and cognitive deficits remain unclear. Given recent data advances in the field of clinical neuroscience, it is now possible to conduct a synthesis of available data specifically related to hallucinations. These findings are integrated with the latest computational frameworks of hallucinations, and recommendations for future research are provided.

Impaired Reality Testing in Mice Lacking Phospholipase Cβ1: Observed by Persistent Representation-Mediated Taste Aversion

Hallucinations and delusions are the most prominent symptoms of schizophrenia and characterized by impaired reality testing. Representation-mediated taste aversion (RMTA) has been proposed as a potential behavioral assessment of reality testing and has been applied to a neurodevelopmental rat model of schizophrenia. However, the theory underlying this approach has not been generalized yet with any demonstration of impaired reality testing in other animal models of schizophrenia, such as genetically-modified mice. We devised a RMTA procedure for mice that combines a Pavlovian association protocol pairing odor conditioned stimulus (CS) with sugar reward unconditioned stimulus (US), and a conditioned taste aversion (CTA) method. In this RMTA paradigm, we compared performances of wild-type (PLCβ1+/+) mice and phospholipase C β1 knock-out (PLCβ1-/-) mice which are known as one of the genetic models for schizophrenia. With a minimal amount of initial odor-sugar associative training, both PLCβ1+/+ and PLCβ1-/- mice were able to form an aversion to the sugar reward when the odor CS predicting sugar was paired with nausea. With an extended initial training, however, only PLCβ1-/- mice could form a RMTA. This persistent RMTA displayed by PLCβ1-/- mice shows their inability to distinguish real sugar from the CS-evoked representation of sugar at a stage in associative learning where wild-type mice normally could differentiate the two. These results demonstrate an impaired reality testing first observed in a genetic mouse model of schizophrenia, and suggest that RMTA paradigm may, with general applicability, allow diverse biological approaches to impaired reality testing.

Memory suppression in Alzheimer's disease

An important challenge for memory is the competition between appropriate and inappropriate information during retrieval. This competition is normally reduced thanks to controlled inhibitory processes that suppress irrelevant memories. In Alzheimer's disease (AD), compromise of suppression ability may result in strong competition between relevant and irrelevant memories during retrieval. The present review highlights this issue by examining studies using the directed forgetting method in AD. This method in which participants are typically instructed to forget no longer relevant information is argued to reflect suppression in memory. Studies using the directed forgetting method suggest that AD participants experience difficulties when they are asked to suppress no longer relevant information in working, autobiographical, source and destination memory. Difficulties in suppressing irrelevant information, as may be observed in AD, may hamper memory retrieval by activating irrelevant memories at the expense of relevant ones.

A Neuropsychological Approach to Auditory Verbal Hallucinations and Thought Insertion - Grounded in Normal Voice Perception

A neuropsychological perspective on auditory verbal hallucinations (AVH) links key phenomenological features of the experience, such as voice location and identity, to functionally separable pathways in normal human audition. Although this auditory processing stream (APS) framework has proven valuable for integrating research on phenomenology with cognitive and neural accounts of hallucinatory experiences, it has not yet been applied to other symptoms presumed to be closely related to AVH – such as thought insertion (TI). In this paper, I propose that an APS framework offers a useful way of thinking about the experience of TI as well as AVH, providing a common conceptual framework for both. I argue that previous self-monitoring theories struggle to account for both the differences and similarities in the characteristic features of AVH and TI, which can be readily accommodated within an APS framework. Furthermore, the APS framework can be integrated with predictive processing accounts of psychotic symptoms; makes predictions about potential sites of prediction error signals; and may offer a template for understanding a range of other symptoms beyond AVH and TI.