Structural and Functional Neuroimaging of Visual Hallucinations in Lewy Body Disease: A Systematic Literature Review.
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SUBMITTER: Pezzoli S
PROVIDER: S-EPMC5532597 | biostudies-literature | 2017 Jul
REPOSITORIES: biostudies-literature
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Structural and Functional Neuroimaging of Visual Hallucinations in Lewy Body Disease: A Systematic Literature Review.
Pezzoli Stefania S Cagnin Annachiara A Bandmann Oliver O Venneri Annalena A
Brain sciences 20170715 7
Patients with Lewy body disease (LBD) frequently experience visual hallucinations (VH), well-formed images perceived without the presence of real stimuli. The structural and functional brain mechanisms underlying VH in LBD are still unclear. The present review summarises the current literature on the neural correlates of VH in LBD, namely Parkinson's disease (PD), and dementia with Lewy bodies (DLB). Following a systematic literature search, 56 neuroimaging studies of VH in PD and DLB were criti ...[more]
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Project description:Visual hallucinations are a common feature of Lewy body dementia. Previous studies have shown that visual hallucinations are highly specific in differentiating Lewy body dementia from Alzheimer's disease dementia and Alzheimer-Lewy body mixed pathology cases. Computational models propose that impairment of visual and attentional networks is aetiologically key to the manifestation of visual hallucinations symptomatology. However, there is still a lack of experimental evidence on functional and structural brain network abnormalities associated with visual hallucinations in Lewy body dementia. We used EEG source localization and network based statistics to assess differential topographical patterns in Lewy body dementia between 25 participants with visual hallucinations and 17 participants without hallucinations. Diffusion tensor imaging was used to assess structural connectivity between thalamus, basal forebrain and cortical regions belonging to the functionally affected network component in the hallucinating group, as assessed with network based statistics. The number of white matter streamlines within the cortex and between subcortical and cortical regions was compared between hallucinating and not hallucinating groups and correlated with average EEG source connectivity of the affected subnetwork. Moreover, modular organization of the EEG source network was obtained, compared between groups and tested for correlation with structural connectivity. Network analysis showed that compared to non-hallucinating patients, those with hallucinations feature consistent weakened connectivity within the visual ventral network, and between this network and default mode and ventral attentional networks, but not between or within attentional networks. The occipital lobe was the most functionally disconnected region. Structural analysis yielded significantly affected white matter streamlines connecting the cortical regions to the nucleus basalis of Meynert and the thalamus in hallucinating compared to not hallucinating patients. The number of streamlines in the tract between the basal forebrain and the cortex correlated with cortical functional connectivity in non-hallucinating patients, while a correlation emerged for the white matter streamlines connecting the functionally affected cortical regions in the hallucinating group. This study proposes, for the first time, differential functional networks between hallucinating and not hallucinating Lewy body dementia patients, and provides empirical evidence for existing models of visual hallucinations. Specifically, the outcome of the present study shows that the hallucinating condition is associated with functional network segregation in Lewy body dementia and supports the involvement of the cholinergic system as proposed in the current literature.
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Project description:Hallucinations are a common and distressing feature of many psychiatric and neurodegenerative conditions. In Lewy body disease, visual hallucinations are a defining feature, associated with worse outcomes; yet their mechanisms remain unclear and treatment options are limited. Here, we show that hallucinations in Lewy body disease are associated with altered integration of top-down predictions with incoming sensory evidence, specifically with an increased relative weighting of prior knowledge. We tested 37 individuals with Lewy body disease, 17 habitual hallucinators and 20 without hallucinations, and 20 age-matched healthy individuals. We employed an image-based learning paradigm to test whether people with Lewy body disease and visual hallucinations show higher dependence on prior knowledge. We used two-tone images that are difficult to disambiguate without any prior information but generate a strong percept when information is provided. We measured discrimination sensitivity before and after this information was provided. We observed that in people with Lewy body disease who experience hallucinations, there was greater improvement in discrimination sensitivity after information was provided, compared to non-hallucinators and controls. This suggests that people with Lewy body disease and hallucinations place higher relative weighting on prior knowledge than those who do not hallucinate. Importantly, increased severity of visual hallucinations was associated with an increased effect of prior knowledge. Together these findings suggest that visual hallucinations in Lewy body disease are linked to a shift towards top-down influences on perception and away from sensory evidence, perhaps due to an increase in sensory noise. This provides important mechanistic insights to how hallucinations develop in Lewy body disease, with potential for revealing new therapeutic targets.
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Project description:Visual hallucinations are a common, distressing, and disabling symptom of Lewy body and other diseases. Current models suggest that interactions in internal cognitive processes generate hallucinations. However, these neglect external factors. Pareidolic illusions are an experimental analogue of hallucinations. They are easily induced in Lewy body disease, have similar content to spontaneous hallucinations, and respond to cholinesterase inhibitors in the same way. We used a primed pareidolia task with hallucinating participants with Lewy body disorders (n = 16), non-hallucinating participants with Lewy body disorders (n = 19), and healthy controls (n = 20). Participants were presented with visual "noise" that sometimes contained degraded visual objects and were required to indicate what they saw. Some perceptions were cued in advance by a visual prime. Results showed that hallucinating participants were impaired in discerning visual signals from noise, with a relaxed criterion threshold for perception compared to both other groups. After the presentation of a visual prime, the criterion was comparable to the other groups. The results suggest that participants with hallucinations compensate for perceptual deficits by relaxing perceptual criteria, at a cost of seeing things that are not there, and that visual cues regularize perception. This latter finding may provide a mechanism for understanding the interaction between environments and hallucinations.
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Project description:BackgroundThe presence of recurrent, complex visual hallucinations (VH) is among the core clinical features of dementia with Lewy bodies (DLB). It has been proposed that VH arise from a disrupted organization of functional brain networks. However, studies are still limited, especially investigating the resting-state functional brain features underpinning VH in patients with dementia.ObjectiveThe aim of the present pilot study was to investigate whether there were any alterations in functional connectivity associated with VH in DLB.MethodsSeed-based analyses and independent component analysis (ICA) of resting-state fMRI scans were carried out to explore differences in functional connectivity between DLB patients with and without VH.ResultsSeed-based analyses reported decreased connectivity of the lateral geniculate nucleus, the superior parietal lobule and the putamen with the medial frontal gyrus in DLB patients with VH. Visual areas showed a pattern of both decreased and increased functional connectivity. ICA revealed between-group differences in the default mode network (DMN).ConclusionFunctional connectivity analyses suggest dysfunctional top-down and bottom-up processes and DMN-related alterations in DLB patients with VH. This impairment might foster the generation of false visual images that are misinterpreted, ultimately resulting in VH.
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Project description:INTRODUCTION:The generation of creative visual imagery contributes to technological and scientific innovation and production of visual art. The underlying cognitive and neural processes are, however, poorly understood. METHODS:This review synthesizes functional neuroimaging studies of visual creativity. Seven functional magnetic resonance imaging (fMRI) and 19 electroencephalography (EEG) studies were included, comprising 27 experiments and around 800 participants. RESULTS:Activation likelihood estimation meta-analysis of the fMRI studies comparing visual creativity to non-rest control tasks yielded significant clusters in thalamus, left fusiform gyrus, and right middle and inferior frontal gyri. The EEG studies revealed a tendency for decreased alpha power during visual creativity compared to baseline, but comparisons of visual creativity to non-rest control tasks revealed inconsistent findings. CONCLUSIONS:The findings are consistent with suggested contributions to visual creativity of prefrontally mediated inhibition, evaluation, and working memory, as well as visual imagery processes. Findings are discussed in relation to prominent theories of the neural basis of creativity.
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Project description:BackgroundComplex visual hallucinations are common in Lewy body dementia (LBD) and can cause significant patient and caregiver distress. Current treatments are primarily pharmacological in nature and have limited efficacy and associated side effects. The objective of this study was to assess the effects of consecutive sessions of transcranial direct current stimulation (tDCS) on visual hallucination frequency and severity in LBD, at short-term and long-term follow-up stages.MethodsThe study was a randomised, double-blind, placebo-controlled trial involving 40 participants with LBD (Mage = 75.52 years, SDage = 8.69 years) which was conducted at a single site between November 2013 and December 2017. Participants received two consecutive 20-min sessions of active (0.048 mA/cm2) or placebo tDCS, separated by a 30-min break, over 5 consecutive days. The anodal electrode was applied to the right parietal cortex (P4) and the cathodal electrode was applied to the occipital cortex (Oz). The primary outcome measure was the Neuropsychiatric Inventory (NPI) hallucinations subscale, as completed by a caregiver/informant at baseline and day 5 (short-term) follow-up, and month 1 and month 3 (long-term) follow-up. Secondary outcome measures included visual cortical excitability, as measured using transcranial magnetic stimulation, computerised attentional and visuoperceptual tasks, and measures of global cognition and cognitive fluctuations.ResultsComplete study data were obtained from 36 participants. There was an overall improvement in visual hallucinations (NPI) for both groups at day 5 relative to baseline, with a medium-to-large effect size; however, compared to placebo, active tDCS did not result in any improvements in visual hallucinations (NPI) at day 5 relative to baseline, or at month 1 or month 3 follow-up time points. Additionally, comparisons of secondary outcome measures showed that active tDCS did not result in any improvements on any measure (visual cortical excitability, attentional and visuoperceptual tasks or cognitive measures) at any time point.ConclusionsRepeated consecutive sessions of parietal anodal tDCS, and occipital cathodal tDCS, do not improve visual hallucinations or visuoperceptual function, or alter visual cortical excitability in LBD.Trial registrationISRCTN, ISRCTN40214749 . Registered on 25 October 2013.
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Project description:BackgroundIndividuals with Lewy body Dementia (LBD), which encompasses both Parkinson disease dementia (PDD) and Dementia with Lewy Bodies (DLB) experience functional decline through Parkinsonism and sedentariness exacerbated by motor, psychiatric and cognitive symptoms. Exercise may improve functional outcomes in Parkinson's disease (PD), and Alzheimer's disease (AD). However, the multi-domain nature of the LBD cluster of symptoms (physical, cognitive, psychiatric, autonomic) results in vulnerable individuals often being excluded from exercise studies evaluating physical function in PD or cognitive function in dementia to avoid confounding results. This review evaluated existing literature reporting the effects of exercise interventions or physical activity (PA) exposure on cluster symptoms in LBD.MethodsA high-sensitivity search was executed across 19 databases. Full-length articles of any language and quality, published or unpublished, that analysed effects of isolated exercise/physical activity on indicative Dementia with Lewy Bodies or PD-dementia cohorts were evaluated for outcomes inclusive of physical, cognitive, psychiatric, physiological and quality of life measures. The protocol for this review (Reg. #: CRD42015019002) is accessible at http://www.crd.york.ac.uk/PROSPERO/.Results111,485 articles were initially retrieved; 288 full articles were reviewed and 89.6% subsequently deemed ineligible due to exclusion of participants with co-existence of dementia and Parkinsonism. Five studies (1 uncontrolled trial, 1 randomized controlled trial and 3 case reports) evaluating 16 participants were included. Interventions were diverse and outcome homogeneity was low. Habitual gait speed outcomes were measured in 13 participants and increased (0.18m/s, 95% CI -0.02, 0.38m/s), exceeding moderate important change (0.14m/s) for PD cohorts. Other outcomes appeared to improve modestly in most participants.DiscussionScarce research investigating exercise in LBD exists. This review confirms exercise studies in PD and dementia consistently exclude LBD participants. Results in this cohort must be treated with caution until robustly designed, larger studies are commissioned to explore exercise efficacy, feasibility and clinical relevance.
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Project description:This review systematically explored structural, functional, and metabolic features of the cisgender brain compared with the transgender brain before hormonal treatment and the heterosexual brain compared to the homosexual brain from the analysis of the neuroimaging literature up to 2018, and identified and discussed subsequent studies published up to March 2021. Our main aim was to help identifying neuroradiological brain features that have been related to human sexuality to contribute to the understanding of the biological elements involved in gender identity and sexual orientation. We analyzed 39 studies on gender identity and 24 on sexual orientation. Our results suggest that some neuroanatomical, neurophysiological, and neurometabolic features in transgender individuals resemble those of their experienced gender despite the majority resembling those from their natal sex. In homosexual individuals the majority resemble those of their same-sex heterosexual population rather than their opposite-sex heterosexual population. However, it is always difficult to interpret findings with noninvasive neuroimaging. Given the gross nature of these measures, it is possible that more differences too subtle to measure with available tools yet contributing to gender identity and sexual orientation could be found. Conflicting results contributed to the difficulty of identifying specific brain features which consistently differ between cisgender and transgender or between heterosexual and homosexual groups. The small number of studies, the small-to-moderate sample size of each study, and the heterogeneity of the investigations made it impossible to meta-analyze all the data extracted. Further studies are necessary to increase the understanding of the neurological substrates of human sexuality.
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