Cerebral atrophy in Parkinson's disease patients with visual hallucinations

Parkinson disease psychosis: from phenomenology to neurobiological mechanisms

Parkinson disease (PD) psychosis (PDP) is a spectrum of illusions, hallucinations and delusions that are associated with PD throughout its disease course. Psychotic phenomena can manifest from the earliest stages of PD and might follow a continuum from minor hallucinations to structured hallucinations and delusions. Initially, PDP was considered to be a complication associated with dopaminergic drug use. However, subsequent research has provided evidence that PDP arises from the progression of brain alterations caused by PD itself, coupled with the use of dopaminergic drugs. The combined dysfunction of attentional control systems, sensory processing, limbic structures, the default mode network and thalamocortical connections provides a conceptual framework to explain how new incoming stimuli are incorrectly categorized, and how aberrant hierarchical predictive processing can produce false percepts that intrude into the stream of consciousness. The past decade has seen the publication of new data on the phenomenology and neurobiological basis of PDP from the initial stages of the disease, as well as the neurotransmitter systems involved in PDP initiation and progression. In this Review, we discuss the latest clinical, neuroimaging and neurochemical evidence that could aid early identification of psychotic phenomena in PD and inform the discovery of new therapeutic targets and strategies.

Effective connectivity abnormalities in Lewy body disease with visual hallucinations

OBJECTIVE

To assess the changes in effective connectivity of important regions of the visual network (VIS) and dorsal attention network (DAN) underlying visual hallucinations (VHs) in Dementia with Lewy Bodies (DLB), Parkinson's Disease (PD) and Parkinson's Disease Dementia (PDD), as measured by a transcranial magnetic stimulation-electroencephalographic technique (TMS-EEG).

METHODS

We stimulated the right visual cortex (V1/V2), the right intraparietal sulcus and the right frontal eye fields, two key regions of the DAN, and measured TMS-evoked cortical activation within the VIS and the DAN. We compared 11 patients with VHs and 15 patients without VHs.

RESULTS

Patients with VHs showed lower TMS-evoked cortical activation within the DAN following intraparietal sulcus and frontal eye fields stimulation than patients without VHs. No difference was found between patients with and without cognitive impairment. Also, when considering only patients with cognitive impairment, VHs were associated with lower TMS-evoked cortical activation following intraparietal sulcus stimulation.

CONCLUSIONS

DLB, PD, and PDD patients with VHs had less effective connectivity of the right intraparietal sulcus within the DAN than patients without VHs.

SIGNIFICANCE

We provided the first evidence that VHs are associated with specific intraparietal sulcus dysfunction within the DAN in patients with PDD, PD, and DLB.

Visual Dysfunction in Parkinson's Disease

Non-motor symptoms in Parkinson's disease (PD) include ocular, visuoperceptive, and visuospatial impairments, which can occur as a result of the underlying neurodegenerative process. Ocular impairments can affect various aspects of vision and eye movement. Thus, patients can show dry eyes, blepharospasm, reduced blink rate, saccadic eye movement abnormalities, smooth pursuit deficits, and impaired voluntary and reflexive eye movements. Furthermore, visuoperceptive impairments affect the ability to perceive and recognize visual stimuli accurately, including impaired contrast sensitivity and reduced visual acuity, color discrimination, and object recognition. Visuospatial impairments are also remarkable, including difficulties perceiving and interpreting spatial relationships between objects and difficulties judging distances or navigating through the environment. Moreover, PD patients can present visuospatial attention problems, with difficulties attending to visual stimuli in a spatially organized manner. Moreover, PD patients also show perceptual disturbances affecting their ability to interpret and determine meaning from visual stimuli. And, for instance, visual hallucinations are common in PD patients. Nevertheless, the neurobiological bases of visual-related disorders in PD are complex and not fully understood. This review intends to provide a comprehensive description of visual disturbances in PD, from sensory to perceptual alterations, addressing their neuroanatomical, functional, and neurochemical correlates. Structural changes, particularly in posterior cortical regions, are described, as well as functional alterations, both in cortical and subcortical regions, which are shown in relation to specific neuropsychological results. Similarly, although the involvement of different neurotransmitter systems is controversial, data about neurochemical alterations related to visual impairments are presented, especially dopaminergic, cholinergic, and serotoninergic systems.

Intrinsic brain activity alterations in patients with Parkinson's disease

OBJECTIVE

The objective of this study is to explore the brain activity alterations in Parkinson's disease (PD) from the perspectives of neuronal activity, synchronization of neuronal activity, and coordination of whole-brain activity.

METHODS

In this study, we recruited 38 PD patients and 35 matched healthy controls (HCs). We explored intrinsic brain activity alterations in PD by comparing resting-state functional magnetic resonance imaging (rs-fMRI) metrics of the amplitude of low-frequency of fluctuation (ALFF), the fractional amplitude of low-frequency fluctuation (fALFF), percent amplitude of fluctuation (PerAF), regional homogeneity (ReHo), and degree centrality (DC). Two-sample t-tests were used to determine the differences between the two groups. Spearman correlation analysis was used to explore the relationships between abnormal ALFF, fALFF, PerAF, ReHo, and DC values and clinical indicators such as the Movement Disorder Society's Unified Parkinson's Disease Rating Scale (MDS-UPDRS), Hoehn and Yahr (H&Y) stage, and duration of disease.

RESULTS

Compared with the HCs, PD had increased ALFF,fALFF, and PerAF in the temporal lobe and cerebellum, and decreased ALFF,fALFF, and PerAF in the occipital-parietal lobe in the neuronal activity. In the synchronization of neuronal activity, PD patients had increased ReHo in the right inferior parietal lobule and decreased ReHo in the caudate. In the coordination of whole-brain activity, PD patients had increased DC in the cerebellum and decreased DC in the occipital lobe. Correlation analysis showed that there is a correlation between abnormal brain regions and clinical indicators in PD. Notably, the changes in occipital lobe brain activity were found in ALFF, fALFF, PerAF, and DC, and were most correlated with the clinical indicators of PD patients.

CONCLUSIONS

This study found that intrinsic brain function in several occipital-temporal-parietal and cerebellum regions was altered in PD patients, potentially related to the clinical indicators of PD. These results may enhance our understanding of the underlying neural mechanisms of PD and may contribute to further exploring the selection of therapeutic targets in PD patients.

A multicentre study on grey matter morphometric biomarkers for classifying early schizophrenia and parkinson's disease psychosis

Psychotic symptoms occur in a majority of schizophrenia patients and in ~50% of all Parkinson's disease (PD) patients. Altered grey matter (GM) structure within several brain areas and networks may contribute to their pathogenesis. Little is known, however, about transdiagnostic similarities when psychotic symptoms occur in different disorders, such as in schizophrenia and PD. The present study investigated a large, multicenter sample containing 722 participants: 146 patients with first episode psychosis, FEP; 106 individuals in at-risk mental state for developing psychosis, ARMS; 145 healthy controls matching FEP and ARMS, Con-Psy; 92 PD patients with psychotic symptoms, PDP; 145 PD patients without psychotic symptoms, PDN; 88 healthy controls matching PDN and PDP, Con-PD. We applied source-based morphometry in association with receiver operating curves (ROC) analyses to identify common GM structural covariance networks (SCN) and investigated their accuracy in identifying the different patient groups. We assessed group-specific homogeneity and variability across the different networks and potential associations with clinical symptoms. SCN-extracted GM values differed significantly between FEP and Con-Psy, PDP and Con-PD, PDN and Con-PD, as well as PDN and PDP, indicating significant overall grey matter reductions in PD and early schizophrenia. ROC analyses showed that SCN-based classification algorithms allow good classification (AUC ~0.80) of FEP and Con-Psy, and fair performance (AUC ~0.72) when differentiating PDP from Con-PD. Importantly, the best performance was found in partly the same networks, including the thalamus. Alterations within selected SCNs may be related to the presence of psychotic symptoms in both early schizophrenia and PD psychosis, indicating some commonality of underlying mechanisms. Furthermore, results provide evidence that GM volume within specific SCNs may serve as a biomarker for identifying FEP and PDP.

Grey matter volume loss in Parkinson's disease psychosis and its relationship with serotonergic gene expression: A meta-analysis

BACKGROUND

Neuroanatomical alterations underlying psychosis in Parkinson's Disease (PDP) remain unclear. We carried out a meta-analysis of MRI studies investigating the neural correlates of PDP and examined its relation with dopaminergic and serotonergic receptor gene expression.

METHODS

PubMed, Web of Science and Embase were searched for MRI studies (k studies = 10) of PDP compared to PD patients without psychosis (PDnP). Seed-based d Mapping with Permutation of Subject Images and multiple linear regression analyses was used to examine the relationship between pooled estimates of grey matter volume (GMV) loss in PDP and D1/D2 and 5-HT1a/5-HT2a receptor gene expression estimates from Allen Human Brain Atlas.

RESULTS

We observed lower grey matter volume in parietal-temporo-occipital regions (PDP n = 211, PDnP, n = 298). GMV loss in PDP was associated with local expression of 5-HT1a (b = 0.109, p = 0.012) and 5-HT2a receptors (b= -0.106, p = 0.002) but not dopaminergic receptors.

CONCLUSION

Widespread GMV loss in the parieto-temporo-occipital regions may underlie PDP. Association between grey matter volume and local expression of serotonergic receptor genes may suggest a role for serotonergic receptors in PDP.

Optic radiation atrophy in Lewy body disease with visual hallucination on phase difference enhanced magnetic resonance images

Visual hallucinations (VH) occur commonly in Lewy body disease (LBD), including Parkinson's disease (PD), PD with dementia, and dementia with Lewy bodies. We aimed to use phase difference enhanced imaging (PADRE) to assess structural abnormalities of optic radiation (OR) in patients with Lewy body disease (LBD) concomitant with VH. Firstly, two radiologists reviewed the OR appearances in healthy subjects (HS) on PADRE. Next, based on the OR abnormalities, two reviewers assessed the PADRE images from 18 HS and 38 and 110 patients with LBD, with and without VH, respectively, in a blinded manner. Finally, all patients with LBD without VH were eventually followed up for at least 5 years after magnetic resonance imaging to determine the appearance of VH. The radiologists identified three layers, namely external sagittal stratum, internal sagittal stratum, and tapetum, in OR on the PADRE in HS. Moreover, they were able to consensually define the OR as abnormal when the layers were obscured and the disappearance of the cranial side. The sensitivity/specificity of abnormal OR for each case was 68%/81% (LBD with VH vs. LBD without VH). Furthermore, VH appeared in 12 of the 21 (57%) patients with LBD and abnormal OR during the follow-up period. However, no patients without abnormal OR reported VH. Patients with LBD and VH demonstrated the abnormal OR. This, in turn, might be a useful marker to distinguish the patients with VH from those without VH and HS. Moreover, abnormal OR on PADRE may precede the appearance of VH in LBD.

The role of attentional control over interference in minor hallucinations in Parkinson's disease

BACKGROUND

Minor hallucinations in Parkinson's disease are associated with connectivity changes in attentional networks and increased risk of structured hallucinations. However, the clinical translation of these abnormalities in attention processes is not well-defined, and commonly used neuropsychological tests are not able to detect significant deficits in Parkinson's disease patients with isolated minor hallucinations.

OBJECTIVES

To analyze the behavioral and electrophysiological correlates of minor hallucinations in Parkinson's disease during an attentional task assessing response inhibition and interference control.

METHODS

Fifty-five non-demented Parkinson's disease patients with (PD-mH; n = 27) and without minor hallucinations (PD-NH; n = 28) were included in the analysis. An Ericksen flanker task was performed to compare the effect of presenting congruent and incongruent stimuli on accuracy, reaction times and stimulus-locked event-related potentials morphology.

RESULTS

Although both groups showed equivalent performance in a standard neuropsychological assessment, in the flanker task accuracy rates were lower in the PD-mH group in incongruent trials (p = 0.005). In the event-related potentials, PD-mH patients showed increased amplitude of the N2 at Fz [t(53); p < 0.05] and decreased amplitude of the P300 at Pz [t(53); p < 0.05] for the incongruent trials.

CONCLUSIONS

Parkinson's disease patients with isolated minor hallucinations were more susceptible to interference mediated by irrelevant stimuli and had less cognitive control for suppressing these interferences. The failure of these systems could precipitate the intrusion and overrepresentation of peripheral irrelevant stimuli perceived as minor hallucinations. The Ericksen flanker task could be used as a sensitive clinical marker of the attentional defects leading to hallucinations in Parkinson's disease.

Neuroimaging approaches to cognition in Parkinson's disease

While direct visualization of Lewy body accumulation within the brain is not yet possible in living Parkinson's disease patients, brain imaging studies offer insights into how the buildup of Lewy body pathology impacts different regions of the brain. Unlike biological biomarkers and purely behavioral research, these brain imaging studies therefore offer a unique opportunity to relate brain localization to cognitive function and dysfunction in living patients. Magnetic resonance imaging studies can reveal physical changes in brain structure as they relate to different cognitive domains and task specific impairments. Functional imaging studies use a combination of task and resting state magnetic resonance imaging, as well as positron emission tomography and single photon emission computed tomography, and can be used to determine changes in blood flow, neuronal activation and neurochemical changes in the brain associated with PD cognition and cognitive impairments. Other unique advantages to brain imaging studies are the ability to monitor changes in brain structure and function longitudinally as patients progress and the ability to study changes in brain function when patients are exposed to different pharmacological manipulations. This is particularly true when assessing the effects of dopaminergic replacement therapy on cognitive function in Parkinson's disease patients. Together, this chapter will describe imaging studies that have helped identify structural and functional brain changes associated with cognition, cognitive impairment, and dementia in Parkinson's disease.

Cognitive Deficit and Aberrant Intrinsic Brain Functional Network in Early-Stage Drug-Naive Parkinson’s Disease

Background

Although cognitive deficit is a common non-motor symptom of Parkinson’s disease (PD), the mechanism and valid biomarkers of it have not been identified. To our best knowledge, this was the first study to investigate the intrinsic dysconnectivity pattern of whole-brain functional networks in early-stage drug-naive (ESDN) PD patients and its association with cognitive deficit of PD using voxel-wise Degree Centrality (DC) approach.

Methods

A total of 53 ESDN PD patients and 53 healthy controls (HC) were recruited. Resting-state fMRI (rs-fMRI) data were acquired, and voxel-wise DC approach was applied. Electrophysiological testing at P300 amplitude was recorded. The Montreal Cognitive Assessment (MoCA) was conducted to evaluate cognitive performance.

Results

ESDN PD patients had lower MoCA scores and P300 amplitudes, but higher P300 latency, than HC (all p < 0.0001). PD patients displayed higher DC in the right inferior frontal gyrus (IFG), left medial frontal gyrus (MFG) and left precentral gyrus (PreCG); but lower DC in the left inferior parietal lobule (IPL), left inferior temporal gyrus (ITG), right occipital lobe, and right postcentral gyrus (PoCG) (p_{Bonferroni correction} < 0.0001). Interestingly, the DC values of left MFG, right PoCG and right occipital lobe were negatively associated with P300 latency but positively associated with P300 amplitudes and MoCA scores (all p_{Bonferroni correction} < 0.0001).

Conclusions

Our results indicate the cognitive deficit and abnormal intrinsic brain functional network in ESDN PD patients. The damage of Default Mode Network (DMN) may be contributes to the pathogenesis of cognitive dysfunction in ESDN PD.

Parkinson's Disease With Visual Hallucinations Is Associated With Epileptiform Activity on EEG

Background: Visual hallucinations (VHs) in Parkinson's disease (PD) are the cardinal symptoms which declare the onset of PD psychosis (PDP). The anthropomorphic and zoomorphic VHs of PD resemble those of Charles Bonnet syndrome and temporal lobe epilepsy. In both of these disorders electroencephalography (EEG) abnormalities have been described. We therefore sought to examine whether VHs in PD were associated with similar EEG abnormalities.

Methods: This retrospective observational study searched the medical records of 300 PD patients and filtered for those containing clinical 20-min scalp EEGs. Remaining records were separated into two groups: patients with reported VHs and those without. The prevalence of epileptiform discharges in the EEGs of both groups was identified.

Results: Epileptiform discharges were present in 5 of 13 (38.5%) PD patients with VHs; all localized to the temporal lobe. No epileptiform discharges were observed in the EEGs of the 31 PD patients without VHs.

Conclusion: The significantly high incidence of temporal lobe epileptiform discharges in PD patients with VHs as compared to those without VHs lends to the possibility of an association visual cortex epileptogenic focus. Accordingly, for treatment-refractory patients, antiepileptic drugs might be considered, as in the case of Charles Bonnet syndrome, temporal lobe epilepsy and migraine with visual aura. Future prospective studies involving larger samples and multi-center cohorts are required to validate these observational findings.

Mapping brain structural differences and neuroreceptor correlates in Parkinson's disease visual hallucinations

Parkinson's psychosis (PDP) describes a spectrum of symptoms that may arise in Parkinson's disease (PD) including visual hallucinations (VH). Imaging studies investigating the neural correlates of PDP have been inconsistent in their findings, due to differences in study design and limitations of scale. Here we use empirical Bayes harmonisation to pool together structural imaging data from multiple research groups into a large-scale mega-analysis, allowing us to identify cortical regions and networks involved in VH and their relation to receptor binding. Differences of morphometrics analysed show a wider cortical involvement underlying VH than previously recognised, including primary visual cortex and surrounding regions, and the hippocampus, independent of its role in cognitive decline. Structural covariance analyses point to the involvement of the attentional control networks in PD-VH, while associations with receptor density maps suggest neurotransmitter loss may be linked to the cortical changes.

[Causes of visual hallucinations in Parkinson's disease]

BACKGROUND

Visual hallucinations (VH) have mainly been considered as late symptoms of Parkinson's disease (PD); however, minor forms of VH also occur in early stages of the disease. Initially dopaminergic overstimulation was discussed as the cause and later on VH have been considered as an early red flag of dementia in PD.

OBJECTIVE

The present study analyzed whether the pathophysiological concept of VH has been enlarged in recent years.

MATERIAL AND METHODS

Clinical, pharmacological, neuropathological as well as functional magnetic resonance imaging studies dealing with VH were reviewed. A systematic classification in monomodal and multimodal models of VH is proposed. The applicability to various forms of VH and various triggering situations is critically examined.

RESULTS

Reduction of the visual information input, erroneous visual processing, attention deficits, and dysfunctional connectivity between various cerebral networks have been shown. There is partial overlapping with the Lhermitte syndrome and the Charles Bonnet syndrome. No model is able to fully explain all VH variants. Not all VH have the same pathogenesis and the same poor prognosis.

CONCLUSION

The chain of causes underlying VH is complex and can vary from patient to patient. So far the therapeutic applications are largely unexplored; however, there is preliminary evidence that beside adjustment of the medication, improvement of visual acuity, active involvement of the partner, and possibly, individually adaptable coping strategies could be successfully implemented.

Structural and Functional Correlates of Hallucinations and Illusions in Parkinson's Disease

BACKGROUND

Visual illusions (VI) in Parkinson's disease (PD) are generally considered as an early feature of the psychosis spectrum leading to fully formed visual hallucinations (VH), although this sequential relationship has not been clearly demonstrated.

OBJECTIVE

We aimed to determine whether there are any overlapping, potentially graded patterns of structural and functional connectivity abnormalities in PD with VI and with VH. Such a finding would argue for a continuum between these entities, whereas distinct imaging features would suggest different neural underpinnings for the phenomena.

METHODS

In this case control study, we compared structural and resting state functional MRI brain patterns of PD patients with VH (PD-H, n = 20), with VI (PD-I, n = 19), and without VH or VI (PD-C, n = 23).

RESULTS

1) PD-H had hypo-connectivity between the ILO and anterior cingulate precuneus and parahippocampal gyrus compared to PD-C and PD-I; 2) In contrast, PD-I had hyper-connectivity between the inferior frontal gyrus and the postcentral gyrus compared to PD-C and PD-H. Moreover, PD-I had higher levels of functional connectivity between the amygdala, hippocampus, insula, and fronto-temporal regions compared to PD-H, together with divergent patterns toward the cingulate. 3) Both PD-I and PD-H had functional hypo-connectivity between the lingual gyrus and the parahippocampal region vs. PD-C, and no significant grey matter volume differences was observed between PD-I and PD-H.

CONCLUSION

Distinct patterns of functional connectivity characterized VI and VH in PD, suggesting that these two perceptual experiences, while probably linked and driven by at least some similar mechanisms, could reflect differing neural dysfunction.

Face Perception and Pareidolia Production in Patients With Parkinson's Disease

In Parkinson's disease (PD) patients, visual misperceptions are a major problem within the non-motor symptoms. Pareidolia, i.e., the tendency to perceive a specific, meaningful image in an ambiguous visual pattern, is a phenomenon that occurs also in healthy subjects. Literature suggests that the perception of face pareidolia may be increased in patients with neurodegenerative diseases. We aimed to examine, within the same experiment, face perception and the production of face pareidolia in PD patients and healthy controls (HC). Thirty participants (15 PD patients and 15 HC) were presented with 47 naturalistic photographs in which faces were embedded or not. The likelihood to perceive the embedded faces was modified by manipulating their transparency. Participants were asked to decide for each photograph whether a face was embedded or not. We found that PD patients were significantly less likely to recognize embedded faces than controls. However, PD patients also perceived faces significantly more often in locations where none were actually present than controls. Linear regression analyses showed that gender, age, hallucinations, and Multiple-Choice Vocabulary Intelligence Test (MWT) score were significant predictors of face pareidolia production in PD patients. Montreal Cognitive Assessment (MoCA) was a significant predictor for pareidolia production in PD patients in trials in which a face was embedded in another region [F _{(1, 13)} = 24.4, p = <0.001]. We conclude that our new embedded faces paradigm is a useful tool to distinguish face perception performance between HC and PD patients. Furthermore, we speculate that our results observed in PD patients rely on disturbed interactions between the Dorsal (DAN) and Ventral Attention Networks (VAN). In photographs in which a face is present, the VAN may detect this as a behaviourally relevant stimulus. However, due to the deficient communication with the DAN in PD patients, the DAN would not direct attention to the correct location, identifying a face at a location where actually none is present.

Evidence and implications of abnormal predictive coding in dementia

The diversity of cognitive deficits and neuropathological processes associated with dementias has encouraged divergence in pathophysiological explanations of disease. Here, we review an alternative framework that emphasizes convergent critical features of cognitive pathophysiology. Rather than the loss of ‘memory centres’ or ‘language centres’, or singular neurotransmitter systems, cognitive deficits are interpreted in terms of aberrant predictive coding in hierarchical neural networks. This builds on advances in normative accounts of brain function, specifically the Bayesian integration of beliefs and sensory evidence in which hierarchical predictions and prediction errors underlie memory, perception, speech and behaviour. We describe how analogous impairments in predictive coding in parallel neurocognitive systems can generate diverse clinical phenomena, including the characteristics of dementias. The review presents evidence from behavioural and neurophysiological studies of perception, language, memory and decision-making. The reformulation of cognitive deficits in terms of predictive coding has several advantages. It brings diverse clinical phenomena into a common framework; it aligns cognitive and movement disorders; and it makes specific predictions on cognitive physiology that support translational and experimental medicine studies. The insights into complex human cognitive disorders from the predictive coding framework may therefore also inform future therapeutic strategies.

Neuroanatomical and cognitive correlates of visual hallucinations in Parkinson's disease and dementia with Lewy bodies: Voxel-based morphometry and neuropsychological meta-analysis

Visual hallucinations (VH) are common in Parkinson's disease and dementia with Lewy bodies, two forms of Lewy body disease (LBD), but the neural substrates and mechanisms involved are still unclear. We conducted meta-analyses of voxel-based morphometry (VBM) and neuropsychological studies investigating the neuroanatomical and cognitive correlates of VH in LBD. For VBM (12 studies), we used Seed-based d Mapping with Permutation of Subject Images (SDM-PSI), including statistical parametric maps for 50% of the studies. For neuropsychology (35 studies), we used MetaNSUE to consider non-statistically significant unreported effects. VH were associated with smaller grey matter volume in occipital, frontal, occipitotemporal, and parietal areas (peak Hedges' g -0.34 to -0.49). In patients with Parkinson's disease without dementia, VH were associated with lower verbal immediate memory performance (Hedges' g -0.52). Both results survived correction for multiple comparisons. Abnormalities in these brain regions might reflect dysfunctions in brain networks sustaining visuoperceptive, attention, and executive abilities, with the latter also being at the basis of poor immediate memory performance.

Structural and functional magnetic resonance imaging in isolated REM sleep behavior disorder: A systematic review of studies using neuroimaging software

Isolated rapid eye movement sleep behavior disorder (iRBD) is a harbinger for developing clinical synucleinopathies. Magnetic resonance imaging (MRI) has been suggested as a tool for understanding the brain bases of iRBD and its evolution. This review systematically analyzed original full text articles on structural and functional MRI in patients with video-polysomnography-confirmed iRBD according to systematic procedures suggested by Reviews and Meta-analyses (PRISMA). The literature search was conducted via the PubMed database for articles related to structural and functional MRI in iRBD from 2000 to 2020. Investigations to date have been diverse in terms of methodology, but most agree that patients with iRBD have structural changes in deep gray matter nuclei, cortical gray matter atrophy, and disrupted functional connectivity within the basal ganglia, the cortico-striatal and cortico-cortical networks. Furthermore, there is evidence that MRI detects structural and functional brain changes associated with the motor and non-motor symptoms of iRBD. The current review highlights the need for larger multicenter and longitudinal studies, using complex approaches based on data-driven and unsupervised machine learning that will help to identify structural and functional patterns of brain degeneration. In turn, this may even allow for the prediction of subsequent phenoconversion from iRBD to the clinically defined synucleinopathies.

Brain Network Analysis by Stable and Unstable EEG Components

OBJECTIVE

Previous studies have already shown that electroencephalography (EEG) brain network (BN) can reflect the health status of individuals. However, novel methods are still needed for BN analysis. Therefore, in this study, BNs were constructed based on stable and unstable EEG components, and these may be implemented for disease diagnosis.

METHODS

Parkinson's disease (PD) was used as an example to illustrate this method. First, EEG signals were decomposed into dynamic modes (DMs). Each DM contains one eigenvalue that can determine not only the stability of that mode, but also its corresponding oscillatory frequency. Second, the stable and unstable components of EEG signals in each frequency band (delta, theta, alpha and beta) were calculated, which are based on the stable and unstable DMs within each respective frequency band. Third, newly developed BNs were constructed, including stable brain network (SBN), unstable brain network (UBN) and inter-connected brain network (IBN). Finally, their topological attributes were extracted in order to differentiate between PD patients and healthy controls (HC). Furthermore, topological attributes were also derived from traditional brain network (TBN) for comparison.

RESULTS

Most topological attributes of SBN, UBN and IBN can significantly differentiate between PD patients and HC ( p value 0.05). Furthermore, the area under the curve (AUC), precision and recall values of SBN analysis are all significantly higher than TBN.

CONCLUSION

We proposed a new perspective on EEG BN analysis.

SIGNIFICANCE

These newly developed BNs not only have biological significance, but also could be widely applied in most medical and engineering fields.

Cerebellar correlates of visual hallucinations in Parkinson's disease and Charles Bonnet Syndrome

Hallucinations, percepts in the absence of external stimuli, are a shared feature of eye-disease (Charles Bonnet Syndrome, CBS) and Parkinson's disease (PD) thought to arise through pathophysiologically distinct mechanisms: deafferentation and attentional network dysfunction respectively. Recent studies have found an association between visual hallucinations and structural changes in the cerebellum without obvious link to either mechanism. Here, we employed Voxel Based Morphometry (VBM), optimised for the cerebellum using the Spatially Unbiased Infratentorial Template (SUIT), to characterise similarities and differences in cerebellar structure associated with visual hallucinations in PD and CBS. Grey and white matter volume (GMV & WMV) from patients with eye-disease (n = 12 hallucinators; n = 9 non-hallucinators) and PD (n = 7 hallucinators; n = 9 non-hallucinators) was examined in a 2-way ANOVA controlling for age, sex, and intracranial volume. Comparing hallucinators to controls across both groups, lower GMV was found bilaterally within cerebellar lobule VIII extending to IX/VII. GMV reductions were also found in Crus 1, greater in PD than eye-disease. Predominantly within PD, hallucination-related lower WMV was found in the medulla. No regions of increased GMV or WMV were found. A correlation was observed between brainstem WMV and lobule VIIIb GMV suggesting a functional association. Lobule VIII comprises a functional node within the Dorsal Attention Network (DAN), linking these findings to current attentional theories of hallucinations, while Crus 1 is linked to cortical visual processing. These findings provide preliminary evidence of a cerebellar contribution to hallucinations that transcends clinical conditions.

Increasing Contrast Improves Object Perception in Parkinson's Disease with Visual Hallucinations

Background

Deficits in basic vision are associated with visual hallucinations in Parkinson's disease. Of particular interest is contrast sensitivity loss in this disorder and its effect on object identification.

Objectives

Evaluate whether increased contrast improves object perception in persons with Parkinson's disease and visual hallucinations, without dementia.

Methods

We assessed 26 individuals with mild to moderate idiopathic Parkinson's disease, half of whom reported one or more episodes of hallucinations/unusual perceptual experiences in the past month, with a letter-identification task that determined the contrast level required to achieve 80% accuracy. Contrast sensitivity was further assessed with a chart that presented stimuli at multiple spatial frequencies. The groups were closely matched for demographic and clinical characteristics except for experience of hallucinations.

Results

Relative to participants without visual hallucinations, those with hallucinations had poorer spatial frequency contrast sensitivity and required significantly greater contrast to correctly identify the letters on the identification task. Specifically, participants with hallucinations required a mean contrast of 52.8%, whereas participants without hallucinations required 35.0%. When given sufficient contrast, the groups with and without hallucinations were equally accurate in letter identification.

Conclusions

Compared to those without hallucinations, individuals with Parkinson's disease and hallucinations without dementia showed poorer contrast sensitivity. Once contrast was individually enhanced, the groups were equally accurate at object identification. These findings suggest the potential of visual perception tests to predict, and perception-based interventions to reduce, hallucinations in Parkinson's disease.

Minor hallucinations reflect early gray matter loss and predict subjective cognitive decline in Parkinson's disease

BACKGROUND AND PURPOSE

Well-structured hallucinations in Parkinson's disease (PD) are associated with poor prognosis and dementia. However, the predictive value of minor psychotic phenomena in cognitive deterioration is not well known. Cross-sectional studies have shown that PD patients with minor hallucinations have more severe cortical atrophy than non-hallucinators, but baseline and longitudinal studies addressing the evolution of these brain differences are lacking. The impact of developing minor hallucinations on cognitive impairment and cortical atrophy progression in early PD was explored.

METHODS

One hundred and thirty-one de novo PD patients from the Parkinson's Progression Marker Initiative for whom brain magnetic resonance imaging scans were available were included. Cognitive outcome at 5 years was compared between patients with and without minor hallucinations during follow-up. Additionally, using gray matter volume (GMV) voxel-based morphometry, cross-sectional (at baseline) and longitudinal (1- and 2-year GMV loss) structural brain differences between groups were studied.

RESULTS

During follow-up, 35.1% of patients developed minor hallucinations. At 5 years, these patients showed an increased prevalence of subjective cognitive decline compared to non-hallucinators (44.1% vs. 13.9%; p < 0.001), but not formal cognitive impairment. Additionally, compared to non-hallucinators, they exhibited reduced GMV at baseline in visuoperceptive areas and increased GMV loss in left temporal areas (p < 0.05 corrected).

CONCLUSIONS

Minor hallucinations seem to be an early clinical marker of increased neurodegeneration and are associated with mid-term subjective cognitive decline. Longer follow-up analyses would be needed to further define if these findings could reflect a higher risk of future cognitive deterioration.

Visual Hallucinations and Impaired Conscious Visual Perception in Parkinson Disease

Visual hallucinations (VHs) are common in patients with Parkinson disease (PD), especially those with dementia, whereas auditory hallucinations are quite rare. Recent studies have revealed the involvement of several regions along the visual information-processing system that contribute to the pathophysiological mechanism of VHs: the eyes and retina, retinofugal projection, lateral geniculate nucleus, striate cortex, ventral pathways in the temporal cortices, and frontal and parietal cortices. In addition, the concurrent involvement of other systems in the brainstem and basal forebrain further modify VHs in PD. In this review, we discuss the pathophysiological association between the regional involvement of these areas and VHs.

Cortical gray matter progression in idiopathic REM sleep behavior disorder and its relation to cognitive decline

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Cortical degeneration over time in IRBD patients is larger than in normal aging.

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IRBD patients have progressive parieto-occipital and orbitofrontal thinning.

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Visuospatial decline in IRBD is associated with degeneration in parietal regions.

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Increasing motor signs in IRBD are related to frontal and parietal degeneration.

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Cortical thinning in posterior regions is associated with late-onset IRBD.

Background

Idiopathic Rapid eye movement sleep behavior disorder (IRBD) is recognized as the prodromal stage of the alpha-Synucleinopathies. Although some studies have addressed the characterization of brain structure in IRBD, little is known about its progression.

Objective

The present work aims at further characterizing gray matter progression throughout IRBD relative to normal aging and investigating how these changes are associated with cognitive decline.

Methods

Fourteen patients with polysomnography-confirmed IRBD and 18 age-matched healthy controls (HC) underwent neuropsychological, olfactory, motor, and T1-weighted MRI evaluation at baseline and follow-up. We compared the evolution of cortical thickness (CTh), subcortical volumes, smell, motor and cognitive performance in IRBD and HC after a mean of 1.6 years. FreeSurfer was used for CTh and volumetry preprocessing and analyses. The symmetrized percent of change (SPC) of the CTh was correlated with the SPC of motor and neuropsychological performance.

Results

IRBD and HC differed significantly in the cortical thinning progression in regions encompassing bilateral superior parietal and precuneus, the right cuneus, the left occipital pole and lateral orbitofrontal gyri (FWE corrected, p < 0.05). The Visual form discrimination test showed worse progression in the IRBD relative to HC, that was associated with gray matter loss in the right superior parietal and the left precuneus. Increasing motor signs in IRBD were related to cortical thinning mainly involving frontal regions, and late-onset IRBD was associated with cortical thinning involving posterior areas (FWE corrected, p < 0.05). Despite finding olfactory identification deficits in IRBD, results did not show decline over the disease course.

Conclusion

Progression in IRBD patients is characterized by parieto-occipital and orbitofrontal thinning and visuospatial loss. The cognitive decline in IRBD is associated with degeneration in parietal regions.

Structural brain changes in Ser129-phosphorylated alpha-synuclein rats based on voxel-based morphometry

Parkinson's disease has become one of the most common neurodegenerative diseases. Pathological changes typically manifest following dopaminergic neuron loss in the substantia nigra and abnormal alpha-synuclein (α-syn) aggregation in the neurons. α-Syn is the major component of Lewy bodies. However, research pertaining to the spread of abnormal α-syn aggregations, which results in specific damage to the brain structure and function, is lacking. In the present study, full-length human α-syn fibrils were injected into the medial forebrain bundle of rats, with an experimental endpoint of 6 months. Histological analysis was conducted to observe the pathological progress of abnormal endogenous α-syn aggregation and nerve fiber quality. Changes in gray and white matter integrity were quantitatively analyzed using voxel-based morphometry (VBM). Behavioral changes were observed over the 6-month period. Histological analysis showed reduced dopamine transporter levels in the striatum of the experimental rats; widespread abnormal endogenous α-syn accumulation; and damaged, sparse, and disordered nerve fibers in the experimental group. VBM showed that at 6 months after surgery, bilateral anterior limbic, bilateral inferior limbic, right hippocampal, and right cortical volumes had reduced, whereas thalamic volume had increased in the experimental group compared with that in the control group. Damage to the limbic and thalamic fiber structure may occur in the earlier stages of Parkinson's disease.

A Study of the Relationship Between Uric Acid and Substantia Nigra Brain Connectivity in Patients With REM Sleep Behavior Disorder and Parkinson's Disease

Low levels of the natural antioxidant uric acid (UA) and the presence of REM sleep behavior disorder (RBD) are both associated with an increased likelihood of developing Parkinson's disease (PD). RBD and PD are also accompanied by basal ganglia dysfunction including decreased nigrostriatal and nigrocortical resting state functional connectivity. Despite these independent findings, the relationship between UA and substantia nigra (SN) functional connectivity remains unknown. In the present study, voxelwise analysis of covariance was used in a cross-sectional design to explore the relationship between UA and whole-brain SN functional connectivity using the eyes-open resting state fMRI method in controls without RBD, patients with idiopathic RBD, and PD patients with and without RBD. The results showed that controls exhibited a positive relationship between UA and SN functional connectivity with left lingual gyrus. The positive relationship was reduced in patients with RBD and PD with RBD, and the relationship was found to be negative in PD patients. These results are the first to show differential relationships between UA and SN functional connectivity among controls, prodromal, and diagnosed PD patients in a ventral occipital region previously documented to be metabolically and structurally altered in RBD and PD. More investigation, including replication in longitudinal designs with larger samples, is needed to understand the pathophysiological significance of these changes.

Reduced Gray Matter Volume and Risk of Falls in Parkinson's Disease with Dementia Patients: A Voxel-Based Morphometry Study

Purpose: Risk of falls is a common sequela affecting patients with Parkinson’s disease (PD). Although motor impairment and dementia are correlated with falls, associations of brain structure and cognition deficits with falls remain unclear. Material and Methods: Thirty-five PD patients with dementia (PDD), and 37 age- and sex-matched healthy subjects were recruited for this study. All participants received structural magnetic resonance imaging (MRI) scans, and disease severity and cognitive evaluations. Additionally, patient fall history was recorded. Regional structural differences between PDD with and without fall groups were performed using voxel-based morphometry processing. Stepwise logistic regression analysis was used to predict the fall risk in PDD patients. Results: The results revealed that 48% of PDD patients experienced falls. Significantly lower gray matter volume (GMV) in the left calcarine and right inferior frontal gyrus in PDD patients with fall compared to PDD patients without fall were noted. The PDD patients with fall exhibited worse UPDRS-II scores compared to PDD patients without fall and were negatively correlated with lower GMV in the left calcarine (p/r = 0.004/−0.492). Furthermore, lower GMV in the left calcarine and right inferior frontal gyrus correlated with poor attention and executive functional test scores. Multiple logistic regression analysis showed that the left calcarine was the only variable (p = 0.004, 95% CI = 0.00–0.00) negatively associated with the fall event. Conclusions: PDD patients exhibiting impaired motor function, lower GMV in the left calcarine and right inferior frontal gyrus, and notable cognitive deficits may have increased risk of falls.

Visual hallucinations and illusions in Parkinson's disease: the role of ocular pathology

INTRODUCTION

Whether different mechanisms, particularly ocular pathology, could lead to the emergence of visual hallucinations (VH) (defined as false perceptions with no external stimulus) versus visual illusions (VI) (defined as a misperception of a real stimulus) in Parkinson's disease (PD) remains debated. We assessed retinal, clinical and structural brain characteristics depending on the presence of VH or VI in PD.

METHODS

In this case-control study, we compared retinal thickness using optical coherence tomography (OCT), between PD patients with: VI (PD-I; n = 26), VH (PD-H; n = 28), and without VI or VH (PD-C; n = 28), and assessed demographic data, disease severity, treatment, anatomical and functional visual complaints, cognitive and visuo-perceptive functions and MRI brain volumetry for each group of PD patients.

RESULTS

Parafoveal retina was thinner in PD-H compared to PD-C (p = 0.005) and PD-I (p = 0.009) but did not differ between PD-I and PD-C (p = 0.85). Multivariate analysis showed that 1/retinal parafoveal thinning and total brain gray matter atrophy were independently associated with the presence of VH compared to PD-I; 2/retinal parafoveal thickness, PD duration, sleep quality impairment and total brain gray matter volume were independent factors associated with the presence of VH compared to PD-C; 3/anterior ocular abnormalities were the only factor independently associated with the presence of illusions compared to PD-C.

CONCLUSION

These findings reinforce the hypothesis that there may be different mechanisms contributing to VH and VI in PD, suggesting that these two entities may also have a different prognosis rather than simply lying along a continuous spectrum.

REGISTRATION NUMBER

Clinicaltrials.gov number NCT01114321.

MRI of Motor and Nonmotor Therapy-Induced Complications in Parkinson's Disease

Levodopa therapy remains the most effective drug for the treatment of Parkinson's disease, and it is associated with the greatest improvement in motor function as assessed by the Unified Parkinson's Disease Rating Scale. Dopamine agonists have also proven their efficacy as monotherapy in early Parkinson's disease but also as adjunct therapy. However, the chronic use of dopaminergic therapy is associated with disabling motor and nonmotor side effects and complications, among which levodopa-induced dyskinesias and impulse control behaviors are the most common. The underlying mechanisms of these disorders are not fully understood. In the last decade, classic neuroimaging methods and more sophisticated techniques, such as analysis of gray-matter structural imaging and functional magnetic resonance imaging, have given access to anatomical and functional abnormalities, respectively, in the brain. This review presents an overview of structural and functional brain changes associated with motor and nonmotor therapy-induced complications in Parkinson's disease. Magnetic resonance imaging may offer structural and/or functional neuroimaging biomarkers that could be used as predictive signs of development, maintenance, and progression of these complications. Neurophysiological tools, such as theta burst stimulation and transcranial magnetic stimulation, might help us to integrate neuroimaging findings and clinical features and could be used as therapeutic options, translating neuroimaging data into clinical practice. © 2020 International Parkinson and Movement Disorder Society.

Sleep disturbances and gastrointestinal dysfunction are associated with thalamic atrophy in Parkinson's disease

Background

Non-motor symptoms are common aspects of Parkinson’s disease (PD) occurring even at the prodromal stage of the disease and greatly affecting the quality of life. Here, we investigated whether non-motor symptoms burden was associated with cortical thickness and subcortical nuclei volume in PD patients.

Methods

We studied 41 non-demented PD patients. Non-motor symptoms burden was assessed using the Non-Motor Symptoms Scale grading (NMSS). Cortical thickness and subcortical nuclei volume analyses were carried out using Free-Surfer. PD patients were divided into two groups according to the NMSS grading: mild to moderate (NMSS: 0–40) and severe (NMSS: ≥ 41) non-motor symptoms.

Results

Thalamic atrophy was associated with higher NMSQ and NMSS total scores. The non-motor symptoms that drove this correlation were sleep/fatigue and gastrointestinal tract dysfunction. We also found that PD patients with severe non-motor symptoms had significant thalamic atrophy compared to the group with mild to moderate non-motor symptoms.

Conclusions

Our findings show that greater non-motor symptom burden is associated with thalamic atrophy in PD. Thalamus plays an important role in processing sensory information including visceral afferent from the gastrointestinal tract and in regulating states of sleep and wakefulness.

Neuroimaging in Parkinson's disease dementia: connecting the dots

Dementia is a common and devastating symptom of Parkinson's disease but the anatomical substrate remains unclear. Some evidence points towards hippocampal involvement but neuroimaging abnormalities have been reported throughout the brain and are largely inconsistent across studies. Here, we test whether these disparate neuroimaging findings for Parkinson's disease dementia localize to a common brain network. We used a literature search to identify studies reporting neuroimaging correlates of Parkinson's dementia (11 studies, 385 patients). We restricted our search to studies of brain atrophy and hypometabolism that compared Parkinson's patients with dementia to those without cognitive involvement. We used a standard coordinate-based activation likelihood estimation meta-analysis to assess for consistency in the neuroimaging findings. We then used a new approach, coordinate-based network mapping, to test whether neuroimaging findings localized to a common brain network. This approach uses resting-state functional connectivity from a large cohort of normative subjects (n = 1000) to identify the network of regions connected to a reported neuroimaging coordinate. Activation likelihood estimation meta-analysis failed to identify any brain regions consistently associated with Parkinson's dementia, showing major heterogeneity across studies. In contrast, coordinate-based network mapping found that these heterogeneous neuroimaging findings localized to a specific brain network centred on the hippocampus. Next, we tested whether this network showed symptom specificity and stage specificity by performing two further analyses. We tested symptom specificity by examining studies of Parkinson's hallucinations (9 studies, 402 patients) that are frequently co-morbid with Parkinson's dementia. We tested for stage specificity by using studies of mild cognitive impairment in Parkinson's disease (15 studies, 844 patients). Coordinate-based network mapping revealed that correlates of visual hallucinations fell within a network centred on bilateral lateral geniculate nucleus and correlates of mild cognitive impairment in Parkinson's disease fell within a network centred on posterior default mode network. In both cases, the identified networks were distinct from the hippocampal network of Parkinson's dementia. Our results link heterogeneous neuroimaging findings in Parkinson's dementia to a common network centred on the hippocampus. This finding was symptom and stage-specific, with implications for understanding Parkinson's dementia and heterogeneity of neuroimaging findings in general.

Different patterns of gray matter density in early- and middle-late-onset Parkinson's disease: a voxel-based morphometry study

Early-onset Parkinson's disease (EOPD) has a clinical course and characteristics distinct from middle-late-onset Parkinson's disease (M-LOPD). Although many studies have investigated these differences, the neural mechanisms of these characteristics remain unclear. This study aimed to investigate the morphological differences, and their related clinical significance, between EOPD and M-LOPD patients. We recruited two groups of patients, 28 EOPD patients and 37 M-LOPD patients, and two age- and sex-matched control groups (23 controls in each group). The voxel-based morphometry (VBM) technique was used to examine changes in gray matter (GM) density between patients and their corresponding controls. Compared with controls, EOPD patients had lower GM density in the left putamen, inferior frontal gyrus and insula, and higher GM density in the right occipital lobe and bilateral cerebellum posterior lobes. M-LOPD patients had lower GM density in the left cerebellum posterior lobe, occipital lobe and right supplementary motor area (SMA), and higher GM density in the left middle temporal gyrus. Correlation analyses showed that GM density values in the right cerebellum posterior lobe positively correlated with the Unified Parkinson's Disease Rating Scale (UPDRS) motor scores and the Hoehn-Yahr stages in EOPD patients. Our results reveal different patterns of structural changes in EOPD and M-LOPD patients. A probable compensatory effect of the cerebellum was observed and may partly explain the slower decline of motor function in EOPD patients.

Meta-analytic Evidence for the Plurality of Mechanisms in Transdiagnostic Structural MRI Studies of Hallucination Status

BACKGROUND

Hallucinations are transmodal and transdiagnostic phenomena, occurring across sensory modalities and presenting in psychiatric, neurodegenerative, neurological, and non-clinical populations. Despite their cross-category occurrence, little empirical work has directly compared between-group neural correlates of hallucinations.

METHODS

We performed whole-brain voxelwise meta-analyses of hallucination status across diagnoses using anisotropic effect-size seed-based d mapping (AES-SDM), and conducted a comprehensive systematic review in PubMed and Web of Science until May 2018 on other structural correlates of hallucinations, including cortical thickness and gyrification.

FINDINGS

3214 abstracts were identified. Patients with psychiatric disorders and hallucinations (eight studies) exhibited reduced gray matter (GM) in the left insula, right inferior frontal gyrus, left anterior cingulate/paracingulate gyrus, left middle temporal gyrus, and increased in the bilateral fusiform gyrus, while patients with neurodegenerative disorders with hallucinations (eight studies) showed GM decreases in the left lingual gyrus, right supramarginal gyrus/parietal operculum, left parahippocampal gyrus, left fusiform gyrus, right thalamus, and right lateral occipital gyrus. Group differences between psychiatric and neurodegenerative hallucination meta-analyses were formally confirmed using Monte Carlo randomizations to determine statistical significance, and a jackknife sensitivity analysis established the reproducibility of results across nearly all study combinations. For other structural measures (28 studies), the most consistent findings associated with hallucination status were reduced cortical thickness in temporal gyri in schizophrenia and altered hippocampal volume in Parkinson's disease and dementia. Additionally, increased severity of hallucinations in schizophrenia correlated with GM reductions within the left superior temporal gyrus, right middle temporal gyrus, bilateral supramarginal and angular gyri.

INTERPRETATION

Distinct patterns of neuroanatomical alteration characterize hallucination status in patients with psychiatric and neurodegenerative diseases, suggesting a plurality of anatomical signatures. This approach has implications for treatment, theoretical frameworks, and generates refutable predictions for hallucinations in other diseases and their occurrence within the general population.

FUNDING

None.

Disruption of the default mode network and its intrinsic functional connectivity underlies minor hallucinations in Parkinson's disease

BACKGROUND

Minor hallucinations and well-structured hallucinations are considered in the severity continuum of the psychotic spectrum associated with Parkinson's disease. Although their chronological relationship is largely unknown, the spatial patterns of brain atrophy in these 2 forms of hallucinations partially overlap, suggesting they share similar pathophysiological processes. Functional connectivity studies show that disruption of functional networks involved in perception and attention could be relevant in the emergence of well-structured hallucinations. However, functional neuroimaging studies in patients with isolated minor hallucinations are lacking. The objectives of this study were to explore the structural and functional changes underlying minor hallucinations.

METHODS

We compared patients with (n = 18) and without (n = 14) minor hallucinations using a multimodal structural (gray-matter volume voxel-based morphometry) and functional (seed-to-whole-brain resting-state functional MRI) neuroimaging study.

RESULTS

Coincident with previously described structural changes in well-structured hallucinations in Parkinson's disease, patients with minor hallucinations exhibited gray-matter atrophy with significant voxel-wise differences in visuoperceptual processing areas and core regions of the default mode network. Functional connectivity changes consisted of altered connectivity within the default mode network, reduced negative correlation with task-positive network, and aberrant connectivity between posterior regions of the default mode network and visual-processing areas. These changes are in accordance with the attentional networks hypothesis proposed for well-structured hallucinations.

CONCLUSIONS

Although longitudinal studies are needed to assess the potential role of minor hallucinations as an early clinical biomarker of progression to well-structured hallucinations, the present findings show that the 2 phenomena share similar structural and functional brain correlates. © 2018 International Parkinson and Movement Disorder Society.

Interaction Between Neuropsychiatric Symptoms and Cognitive Performance in Parkinson's Disease: What Do Clinical and Neuroimaging Studies Tell Us?

PURPOSE OF REVIEW

Parkinson's disease was studied for a long time from the prism of a motor impairment. Recent advances have outlined the importance of cognitive and neuropsychiatric symptoms (NPS) in the PD equation. This review concentrates on the present possibilities of using neuroimaging techniques in order to quantify the cognitive performance and NPS in PD patients.

RECENT FINDINGS

Mild cognitive impairment as well as many NPS have been acknowledged as important criteria for assessing the quality of life in patients with Parkinson's disease and have been shown as potential factors in predicting further evolution of PD from a clinical perspective. Some NPS strongly influence cognition (depression, REM sleep behavior disorder), while others are less specifically associated with it (impulse control disorders). Neuroimaging techniques reported specific structural, functional, and metabolic brain changes that might be specific for each NPS type. Recent neuroimaging advances report a strong interrelation between NPS and cognitive performance in PD. A special place for consideration is given to REM sleep behavior disorder, depression, and hallucinations. Nevertheless, some studies report distinct results, outlining that the neuroimaging acquisition and analysis techniques still have limitations and also likely represent the complexity of the manifestation of NPS in PD.

Considering total intracranial volume and other nuisance variables in brain voxel based morphometry in idiopathic PD

Voxel-based morphometry (VBM) studies of Parkinson's disease (PD), have yielded mixed results, possibly due to several studies not accounting for common nuisance variables (age, sex, and total intracranial volume [TICV]). TICV is particularly important because there is evidence for larger TICV in PD. We explored the influence of these covariates on VBM by 1) comparing PD patients and controls before adding covariates, after adding age and sex, and after adding age, sex and TICV, and 2) by comparing controls split into large and small TICV before and after controlling for TICV, with age and sex accounted for in both analyses. Experiment 1 consisted of 40 PD participants and 40 controls. Experiment 2 consisted of 88 controls median split by TICV. All participants completed an MRI on a 3 T scanner. TICV was calculated as gray + white + CSF from Freesurfer. VBM was performed on T1 images using an optimized VBM protocol. Volume differences were assessed using a voxel-wise GLM analysis. Clusters were considered significant at >10 voxels and p < .05 corrected for familywise error. Before controlling for covariates, PD showed reduced GM in temporal, occipital, and cerebellar regions. Controlling for age and sex did not affect the pattern of significance. Controlling for TICV reduced the size of the significant region although it still contained portions of bilateral temporal lobes, occipital lobes and cerebellum. The large TICV group showed reduced volume in temporal, parietal, and cerebellar areas. None of these differences survived controlling for TICV. This demonstrates that TICV influences VBM results independently from other factors. Controlling for TICV in VBM studies is recommended.

Altered intrinsic brain functional connectivity in drug-naïve Parkinson's disease patients with LRRK2 mutations

BACKGROUND

Leucine-rich repeat kinase 2 (LRRK2) has been recently identified as a causative gene of Parkinson's disease (PD), and the LRRK2 R1628P and G2385R mutations are common in ethnic Han-Chinese PD patients. However, the pathogenic mechanism of LRRK2 mutations in PD remains largely unknown.

METHODS

Resting-state functional MRI (fMRI) was used to assess the functional connectivity (FC) of the striatal subregions of 11 ethnic Han-Chinese drug-naïve PD patients with the LRRK2 R1628P or G2385R mutations, 11 ethnic Han-Chinese drug-naïve PD patients without such mutations, and 22 healthy control (HC) subjects.

RESULTS

Compared with the HC subjects, both subgroups of the PD patients showed alterations in the FC within the sensorimotor-striatal and posterior putamen-striatal circuits. In addition, relative to the subgroup of PD patients without the LRRK2 mutations, the subgroup of PD patients with the LRRK2 mutation exhibited decreased FC between the putamen and the bilateral superior frontal gyri, precuneus and calcarine gyri. The FC between the putamen and the bilateral superior frontal gyri decreased with age in the LRRK2 mutation carriers but not in the non-carriers.

CONCLUSION

Differences in the FC between ethnic Han-Chinese drug-naïve PD patients with and without the LRRK2 mutation may provide new insights into the understanding of the neural functional changes in ethnic Han-Chinese PD patients with LRRK2 mutations. However, our results are preliminary, and further investigations are needed.

Structural and Functional Brain Patterns of Non-Motor Syndromes in Parkinson's Disease

Parkinson’s disease (PD) is a common, progressive and multisystem neurodegenerative disorder characterized by motor and non-motor symptoms. Advanced magnetic resonance imaging, positron emission tomography, and functional magnetic resonance imaging can render the view toward understanding the neural basis of these non-motor syndromes, as they help to understand the underlying pathophysiological abnormalities. This review provides an up-to-date description of structural and functional brain alterations in patients with PD with cognitive deficits, visual hallucinations, fatigue, impulsive behavior disorders, sleep disorders, and pain.

Cortical Thinning and Cognitive Impairment in Parkinson's Disease without Dementia

Parkinson's disease (PD) is a progressive neurodegenerative disorder characterized clinically by motor dysfunction (bradykinesia, rigidity, tremor, and postural instability), and pathologically by the loss of dopaminergic neurons in the substantia nigra of the basal ganglia. Growing literature supports that cognitive deficits may also be present in PD, even in non-demented patients. Gray matter (GM) atrophy has been reported in PD and may be related to cognitive decline. This study investigated cortical thickness in non-demented PD subjects and elucidated its relationship to cognitive impairment using high-resolution T1-weighted brain MRI and comprehensive cognitive function scores from 71 non-demented PD and 48 control subjects matched for age, gender, and education. Cortical thickness was compared between groups using a flexible hierarchical multivariate Bayesian model, which accounts for correlations between brain regions. Correlation analyses were performed among brain areas and cognitive domains as well, which showed significant group differences in the PD population. Compared to Controls, PD subjects demonstrated significant age-adjusted cortical thinning predominantly in inferior and superior parietal areas and extended to superior frontal, superior temporal, and precuneus areas (posterior probability >0.9). Cortical thinning was also found in the left precentral and lateral occipital, and right postcentral, middle frontal, and fusiform regions (posterior probability >0.9). PD patients showed significantly reduced cognitive performance in executive function, including set shifting (p = 0.005) and spontaneous flexibility (p = 0.02), which were associated with the above cortical thinning regions (p < 0.05).

Alteration in the Local and Global Functional Connectivity of Resting State Networks in Parkinson's Disease

OBJECTIVE

Parkinson's disease (PD) is a neurodegenerative disorder that mainly leads to the impairment of patients' motor function, as well as of cognition, as it progresses. This study tried to investigate the impact of PD on the resting state functional connectivity of the default mode network (DMN), as well as of the entire brain.

METHODS

Sixty patients with PD were included and compared to 60 matched normal control (NC) subjects. For the local connectivity analysis, the resting state fMRI data were analyzed by seed-based correlation analyses, and then a novel persistent homology analysis was implemented to examine the connectivity from a global perspective.

RESULTS

The functional connectivity of the DMN was decreased in the PD group compared to the NC, with a stronger difference in the medial prefrontal cortex. Moreover, the results of the persistent homology analysis indicated that the PD group had a more locally connected and less globally connected network compared to the NC.

CONCLUSION

Our findings suggest that the DMN is altered in PD, and persistent homology analysis, as a useful measure of the topological characteristics of the networks from a broader perspective, was able to identify changes in the large-scale functional organization of the patients' brain.

Psychosis in Parkinson Disease: A Review of Etiology, Phenomenology, and Management

Parkinson disease psychosis (PDP) is a common phenomenon in Parkinson disease (PD) patients treated with dopaminergic drugs, and is associated with high morbidity and mortality. It also correlates with depression and dementia, and can contribute to considerable caregiver stress and burnout. While symptoms can be relieved by decreasing doses or number of anti-PD medications, this may lead to an unacceptable worsening of motor function. When general medical or psychiatric conditions have been ruled out, and decreasing dopaminergic agents is not effective in treating psychosis, therapies include atypical antipsychotics, primarily clozapine and quetiapine. Of these, clozapine is effective but is associated with a poor side-effect profile and the necessity for frequent blood draws. Clinicians prefer quetiapine for its theoretically better safety profile, although there is no evidence for efficacy in treating psychosis. All atypical antipsychotics are associated with increased mortality in this patient population. Cholinesterase inhibitors can ameliorate psychosis symptoms. The serotonin 5-HT_2A receptor inverse agonist pimavanserin was recently approved by the US FDA for the treatment of PDP and may prove to be a more targeted therapy without the downsides of atypical antipsychotics.

Magnetic resonance imaging for the diagnosis of Parkinson's disease

The differential diagnosis of parkinsonian syndromes is considered one of the most challenging in neurology and error rates in the clinical diagnosis can be high even at specialized centres. Despite several limitations, magnetic resonance imaging (MRI) has undoubtedly enhanced the diagnostic accuracy in the differential diagnosis of neurodegenerative parkinsonism over the last three decades. This review aims to summarize research findings regarding the value of the different MRI techniques, including advanced sequences at high- and ultra-high-field MRI and modern image analysis algorithms, in the diagnostic work-up of Parkinson's disease. This includes not only the exclusion of alternative diagnoses for Parkinson's disease such as symptomatic parkinsonism and atypical parkinsonism, but also the diagnosis of early, new onset, and even prodromal Parkinson's disease.

Structural and Functional Neuroimaging of Visual Hallucinations in Lewy Body Disease: A Systematic Literature Review

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 critically reviewed and evaluated for quality assessment. The main structural neuroimaging results on VH in LBD revealed grey matter loss in frontal areas in patients with dementia, and parietal and occipito-temporal regions in PD without dementia. Parietal and temporal hypometabolism was also reported in hallucinating PD patients. Disrupted functional connectivity was detected especially in the default mode network and fronto-parietal regions. However, evidence on structural and functional connectivity is still limited and requires further investigation. The current literature is in line with integrative models of VH suggesting a role of attention and perception deficits in the development of VH. However, despite the close relationship between VH and cognitive impairment, its associations with brain structure and function have been explored only by a limited number of studies.

Psychosis in Parkinson's Disease: Epidemiology, Pathophysiology, and Management

Psychotic symptoms are common in Parkinson's disease (PD) and are associated with poorer quality of life and increased caregiver burden. PD psychosis is correlated with several factors, such as more advanced disease, cognitive impairment, depression, and sleep disorders. The underlying causes of psychosis in PD thus involve a complex interplay between exogenous (e.g., drugs, intercurrent illnesses) and endogenous (e.g., PD disease pathology) factors. Current theories of the pathophysiology of PD psychosis have come from several neuropathological and neuroimaging studies that implicate pathways involving visual processing and executive function, including temporo-limbic structures and neocortical gray matter with altered neurotransmitter functioning (e.g., dopamine, serotonin, and acetylcholine). Treatment of PD psychosis requires a step-wise process, including initial careful investigation of treatable triggering conditions and a comprehensive evaluation with adjustment of PD medications and/or initiation of specific antipsychotic therapies. Clozapine remains the only recommended drug for the treatment of PD psychosis; however, because of regular blood monitoring, quetiapine is usually first-line therapy, although less efficacious. Emerging studies have focused on agents involving other neurotransmitters, including the serotonin 5-HT2A receptor inverse agonist pimavanserin, cholinesterase inhibitors, and antidepressants and anxiolytics.

In vitro α-synuclein neurotoxicity and spreading among neurons and astrocytes using Lewy body extracts from Parkinson disease brains

Synucleinopathies are a group of diseases characterized by the presence of intracellular protein aggregates containing α-synuclein (α-syn). While α-syn aggregates have been shown to induce multimodal cellular dysfunctions, uptake and transport mechanisms remain unclear. Using high-content imaging on cortical neurons and astrocytes, we here define the kinetics of neuronal and astrocytic abnormalities induced by human-derived α-syn aggregates grounding the use of such system to identify and test putative therapeutic compounds. We then aimed at characterizing uptake and transport mechanisms using primary cultures of cortical neurons and astrocytes either in single well or in microfluidic chambers allowing connection between cells and cell-types. We report that astrocytes take up α-syn-aggregates far more efficiently than neurons through an endocytic event. We also highlight that active α-syn transport occurs between cells and any cell-types. Of special interest regarding the disease, we also show that uptake and spreading of α-syn from astrocytes to neurons can lead to neuronal death. Altogether, we here show that patients-derived α-synuclein aggregates, which are taken up by neurons and astrocytes, induce a differential endogenous response in the two cell types including a peculiar astrocytic toxic gain-of-function that leads to neuronal death.

The psychosis spectrum in Parkinson disease

In 2007, the clinical and research profile of illusions, hallucinations, delusions and related symptoms in Parkinson disease (PD) was raised with the publication of a consensus definition of PD psychosis. Symptoms that were previously deemed benign and clinically insignificant were incorporated into a continuum of severity, leading to the rapid expansion of literature focusing on clinical aspects, mechanisms and treatment. Here, we review this literature and the evolving view of PD psychosis. Key topics include the prospective risk of dementia in individuals with PD psychosis, and the causal and modifying effects of PD medication. We discuss recent developments, including recognition of an increase in the prevalence of psychosis with disease duration, addition of new visual symptoms to the psychosis continuum, and identification of frontal executive, visual perceptual and memory dysfunction at different disease stages. In addition, we highlight novel risk factors - for example, autonomic dysfunction - that have emerged from prospective studies, structural MRI evidence of frontal, parietal, occipital and hippocampal involvement, and approval of pimavanserin for the treatment of PD psychosis. The accumulating evidence raises novel questions and directions for future research to explore the clinical management and biomarker potential of PD psychosis.