Cognitive impairment and Charles Bonnet syndrome: a prospective study

Explanatory power by vagueness. Challenges to the strong prior hypothesis on hallucinations exemplified by the Charles-Bonnet-Syndrome

Predictive processing models are often ascribed a certain generality in conceptually unifying the relationships between perception, action, and cognition or the potential to posit a 'grand unified theory' of the mind. The limitations of this unification can be seen when these models are applied to specific cognitive phenomena or phenomenal consciousness. Our article discusses these shortcomings for predictive processing models of hallucinations by the example of the Charles-Bonnet-Syndrome. This case study shows that the current predictive processing account omits essential characteristics of stimulus-independent perception in general, which has critical phenomenological implications. We argue that the most popular predictive processing model of hallucinatory conditions - the strong prior hypothesis - fails to fully account for the characteristics of nonveridical perceptual experiences associated with Charles-Bonnet-Syndrome. To fill this explanatory gap, we propose that the strong prior hypothesis needs to include reality monitoring to apply to more than just veridical percepts.

Investigation of structural brain changes in Charles Bonnet Syndrome

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Reduced grey matter in the occipital cortex in eye disease groups.

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Widespread altered diffusivity in eye disease groups.

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No cortical or white matter changes associated with presence of visual hallucinations.

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Negative association between hippocampal volume and Hallucination severity.

Background and objectives

In Charles Bonnet Syndrome (CBS), visual hallucinations (VH) are experienced by people with sight loss due to eye disease or lesional damage to early visual pathways. The aim of this cross-sectional study was to investigate structural brain changes using magnetic resonance imaging (MRI) in CBS.

Methods

Sixteen CBS patients, 17 with eye disease but no VH, and 19 normally sighted people took part. Participants were imaged on a 3T scanner, with 1 mm resolution T1 weighted structural imaging, and diffusion tensor imaging with 64 diffusion directions.

Results

The three groups were well matched for age, sex and cognitive scores (MMSE). The two eye disease groups were matched on visual acuity. Compared to the sighted controls, we found reduced grey matter in the occipital cortex in both eye disease groups. We also found reductions of fractional anisotropy and increased diffusivity in widespread areas, including occipital tracts, the corpus callosum, and the anterior thalamic radiation. We did not find any significant differences between the eye disease participants with VH versus without VH, but did observe a negative association between hippocampal volume and VH severity in the CBS group.

Discussion

Our findings suggest that although there are cortical and subcortical effects associated with sight loss, structural changes do not explain the occurrence of VHs. CBS may relate instead to connectivity or excitability changes in brain networks linked to vision.

Vision loss and hallucinations: perspectives from neurology and ophthalmology

PURPOSE OF REVIEW

The aim of this article is to summarize the evidence for visual impairment as a risk factor for visual hallucinations in neurologic disease and recent advances in our understanding of the central visual pathways that mediate this association.

RECENT FINDINGS

Recent studies have described the prevalence Charles Bonnet syndrome and questioned its lack of association with cognitive impairment, used advanced neuroimaging to show that disinhibition of the occipital lobe is involved in the pathogenesis of visual hallucinations in Parkinson's disease, and demonstrated that visual impairment because of eye disease is a consistent risk factor for visual hallucinations across a number of different neurodegenerative disease populations.

SUMMARY

Through connections between the primary visual cortex and other brain structures, visual function is closely tied to visual hallucinations. Given that the vast majority of vision loss is caused by ophthalmic disease, much of which is preventable or treatable, the detection and treatment of vision loss in at-risk populations may reduce the burden and consequences of visual hallucinations in older adults.

Frightening Complex Visual Hallucinations in an Elderly Patient with Ophthalmological Pathology and Vascular Dementia

A lady in her 90s was referred to the Later Life Team (LLT) in a rural area of the United Kingdom with complex visual hallucinations (VH). She had significant ophthalmological pathology, including cataracts, a branch retinal vein occlusion, and vitreous haemorrhage. The hallucinations included seeing monkeys ripping the heads off of her cats and lions prowling the garden. The patient was distressed by the hallucinations and believed them to be real events. Her management involved low dose olanzapine and requesting that her ophthalmological surgery be expedited. The surgery resulted in a significant reduction in VH. A diagnosis of vascular dementia went on to be made following cognitive testing and imaging. The cognitive impairment may have contributed to the patient's inability to identify her experiences as hallucinations and thus render her without insight. A review of the computed tomography (CT) scans performed prior to the patient's presentation to our service confirmed significant vascular pathology including small vessel disease and lacunar infarcts. Cognitive testing confirmed a cognitive impairment which had gone unnoticed by her family. This case leads to an interesting discussion regarding diagnosis in complex VH in cases of significant ophthalmological pathology but a lack of insight. Various authors have proposed theories to explain VH; cortical release and the Perception and Attention Deficit (PAD) model are explored as possible explanations for the experiences of this patient.

Resting-state functional connectivity and cortical thickness characterization of a patient with Charles Bonnet syndrome

Charles Bonnet syndrome (CBS) is a rare condition characterized by visual impairment associated with complex visual hallucinations in elderly people. Although studies suggested that visual hallucinations may be caused by brain damage in the visual system in CBS patients, alterations in specific brain regions in the occipital cortex have not been studied. Functional connectivity during resting-state functional magnetic resonance imaging (rs-fMRI; without hallucinations) in CBS patients, has never been explored. We aimed to investigate brain structural and functional changes in a patient with CBS, as compared with late blind (LB) and normally sighted subjects. We employed voxel-based morphometry and cortical thickness analyses to investigate alterations in grey matter characteristics, and rs-fMRI to study changes in functional brain connectivity. Decreased grey matter volume was observed in the middle occipital gyrus and in the cuneus in the CBS patient, and in the middle occipital gyrus and in the lingual gyrus within LB subjects, compared to their respective control groups. Reductions in cortical thickness in associative and multimodal cortices were observed in the CBS patient when comparing with LB subjects. The precuneus exhibited increased functional connectivity with the secondary visual cortex in the CBS patient compared to the controls. In contrast, LB patients showed decreased functional connectivity compared to sighted controls between the DMN and the temporo-occipital fusiform gyrus, a region known to support hallucinations. Our findings suggest a reorganization of the functional connectivity between regions involved in self-awareness and in visual and salience processing in CBS that may contribute to the appearance of visual hallucinations.

FDG-PET Scanning Shows Distributed Changes in Cortical Activity Associated with Visual Hallucinations in Eye Disease

BACKGROUND AND OBJECTIVE

Charles Bonnet Syndrome (CBS) has been defined as complex visual hallucinations (CVH) due to visual loss. The underlying mechanism of CBS is not clear and the underlying pathophysiology of the visual hallucinations in CBS patients and pure visually impaired patients is still not clear.

METHODS

In our study, we have scanned three patients with eye disease and CBS (VH+) and three patients with eye disease without CBS (VH-) using FDG-PET.

RESULTS

Our results showed underactivity in the pons and overactivity in primary right left visual cortex and inferior parietal cortex in VH- patients and underactivity in left Broca, left inf frontal primary visual cortex and anterior and posterior cingulate cortex in VH+ patients relative to the normative 18FFDG PET data that was taken from the database consisting of 50 age-matched healthy adults without neuropsychiatric disorders.

CONCLUSION

From this distributed pattern of activity changes, we conclude that the generation of visual hallucination in CBS is associated with bottom-up and top-down mechanism rather than the generally accepted visual deafferentation-related hyperexcitability theory.

Charles Bonnet syndrome: development and validation of a screening and multidimensional descriptive questionnaire

OBJECTIVE

The purpose of this study was to develop a French Canadian questionnaire for the detection of Charles Bonnet syndrome that allows for (i) valid screening and (ii) the examination of different dimensions of the client's visual hallucinations in order to better assess the resulting needs.

METHOD

Questionnaire development was guided by interviews with visually impaired individuals experiencing visual hallucinations, as well as supported by scientific literature and expert experience. A clinical study involving 76 individuals with low vision was conducted to determine the sensitivity and specificity of the instrument according to criterion validation.

RESULTS

Of the 54 closed-ended questions, a subset of 11 revealed a sensitivity of 1.00 and a specificity of 0.77. Two additional questions showed high discriminating potential. Improvements to the wording and structure of some questions aiming at needs assessment were identified and applied. The improved version consists of 55 questions grouped in 8 dimensions: (1) Screening; (2) Characteristics of hallucinations; (3) Psychological impact; (4) Psychopathological origin; (5) Coping strategies; (6) Context of appearance of hallucinations; (7) Time-related matters; (8) Psychosocial support. The screening is operationalized through an algorithm applied to the set of 13 questions.

CONCLUSION

The questionnaire will be a valuable aid in screening for Charles Bonnet syndrome among the low vision clientele. However, the screening will need to be supplemented by a focused low vision interdisciplinary assessment including a visual examination and a clinical interview with a psychologist.

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.