Neuropsychological and neuroanatomical underpinnings of the face pareidolia errors on the noise pareidolia test in patients with mild cognitive impairment and dementia due to Lewy bodies

OBJECTIVE

Prior research on the Noise Pareidolia Test (NPT) has demonstrated its clinical utility in detecting patients with mild cognitive impairment and dementia due to Lewy Body Disease (LBD). However, few studies to date have investigated the neuropsychological factors underlying pareidolia errors on the NPT across the clinical spectrum of LBD. Furthermore, to our knowledge, no research has examined the relationship between cortical thickness using MRI data and NPT subscores. As such, this study sought to explore the neuropsychological and neuroanatomical factors influencing performance on the NPT utilizing the National Alzheimer's Coordinating Center Lewy Body Dementia Module.

METHODS

Our sample included participants with normal cognition (NC; n = 56), LBD with mild cognitive impairment (LBD-MCI; n = 97), and LBD with dementia (LBD-Dementia; n = 94). Archival data from NACC were retrospectively analyzed for group differences in neuropsychological test scores and cognitive and psychiatric predictors of NPT scores. Clinicoradiological correlates between NPT subscores and a small subsample of the above LBD participants were also examined.

RESULTS

Analyses revealed significant differences in NPT scores among groups. Regression analysis demonstrated that dementia severity, attention, and visuospatial processing contributed approximately 24% of NPT performance in LBD groups. Clinicoradiological analysis suggests a potential contribution of the right fusiform gyrus, but not the inferior occipital gyrus, to NPT pareidolia error scores.

CONCLUSIONS

Our findings highlight the interplay of attention and visuoperceptual functions in complex pareidolia in LBD. Further investigation is needed to refine the utility of NPT scores in clinical settings, including identifying patients at risk for visual illusions and hallucinations.

Abnormal multisensory temporal discrimination in Parkinson's disease

Cognitive deficits are prevalent in Parkinson's disease (PD), ranging from mild deficits in perception and executive function to severe dementia. Multisensory integration (MSI), the ability to pool information from different sensory modalities to form a combined, coherent perception of the environment, is known to be impaired in PD. This study investigated the disruption of audiovisual MSI in PD patients by evaluating temporal discrimination ability between auditory and visual stimuli with different stimulus onset asynchronies (SOAs). The experiment was conducted with Fifteen PD patients and fifteen age-matched healthy controls where participants were requested to report whether the audiovisual stimuli pairs were temporal simultaneous. The temporal binding window (TBW), the time during which sensory modalities are perceived as synchronous, was adapted as the comparison index between PD patients and healthy individuals. Our results showed that PD patients had a significantly wider TBW than healthy controls, indicating abnormal audiovisual temporal discrimination. Furthermore, PD patients had more difficulty in discriminating temporal asynchrony in visual-first, but not in auditory-first stimuli, compared to healthy controls. In contrast, no significant difference was observed for auditory-first stimuli. PD patients also had shorter reaction times than healthy controls regardless of stimulus priority. Together, our findings point to abnormal audiovisual temporal discrimination, a major component of MSI irregularity, in PD patients. These results have important implications for future models of MSI experiments and models that aim to uncover the underlying mechanism of MSI in patients afflicted with PD.

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.

Altered connectivity in the cognitive control-related prefrontal cortex in Parkinson's disease with rapid eye movement sleep behavior disorder

Rapid eye movement sleep behavior disorder (RBD) frequently occurs in Parkinson's disease (PD), however, the exact pathophysiological mechanism is not clear. The prefrontal cortex (PFC), especially ventrolateral prefrontal cortex (VLPFC), dorsolateral prefrontal cortex (DLPFC), and inferior frontal gyrus (IFG) which may play roles by regulating cognitive control processes. The purpose of this study was to investigate whether there is abnormal functional connectivity (FC) maps and volume changes in PD with RBD(PD-RBD). We recruited 20 PD-RBD, 20 PD without RBD (PD-nRBD), and 20 normal controls (NC). We utilized resting-state functional Magnetic Resonance Imaging (rs-MRI) to explore FC changes based on regions of interest (VLPFC, DLPFC, and IFG), and used voxel-based morphology technology to analyze whole-brain volumes by 3D-T1 structural MRI. Except the REM sleep behavioral disorders questionnaire (RBDSQ), the PD-RBD showed lower visuospatial/executive and attention scores than the NC group. The RBDSQ scores were significantly positively correlated with zFC of right DLPFC to bilateral posterior cingulate cortex (PCC) (P = 0.0362, R = 0.4708, AlphaSim corrected) and also significantly positively correlated with zFC of left VLPFC to right inferior temporal (P = 0.0157, R = 0.5323, AlphaSim corrected) in PD-RBD group. Furthermore, abnormal correlations with zFC values were also found in some cognitive subdomains in PD-RBD group. The study may suggest that in PD-RBD patients, the presence of RBD may be related to the abnormal FC of VLPFC and DLPFC, meanwhile, the abnormal FC of DLPFC and IFG may be related to the mechanisms of cognitive impairment.

Alterations of PAC-based resting state networks in Parkinson's disease are partially alleviated by levodopa medication

Introduction

Parkinson's disease (PD) is a neurodegenerative disorder affecting the whole brain, leading to several motor and non-motor symptoms. In the past, it has been shown that PD alters resting state networks (RSN) in the brain. These networks are usually derived from fMRI BOLD signals. This study investigated RSN changes in PD patients based on maximum phase-amplitude coupling (PAC) throughout the cortex. We also tested the hypothesis that levodopa medication shifts network activity back toward a healthy state.

Methods

We recorded 23 PD patients and 24 healthy age-matched participants for 30 min at rest with magnetoencephalography (MEG). PD patients were measured once in the dopaminergic medication ON and once in the medication OFF state. A T1-MRI brain scan was acquired from each participant for source reconstruction. After correcting the data for artifacts and performing source reconstruction using a linearly constrained minimum variance beamformer, we extracted visual, sensorimotor (SMN), and frontal RSNs based on PAC.

Results

We found significant changes in all networks between healthy participants and PD patients in the medication OFF state. Levodopa had a significant effect on the SMN but not on the other networks. There was no significant change in the optimal PAC coupling frequencies between healthy participants and PD patients.

Discussion

Our results suggest that RSNs, based on PAC in different parts of the cortex, are altered in PD patients. Furthermore, levodopa significantly affects the SMN, reflecting the clinical alleviation of motor symptoms and leading to a network normalization compared to healthy controls.

Task Cortical Connectivity Reveals Different Network Reorganizations between Mild Stroke Patients with Cortical and Subcortical Lesions

Accumulating efforts have been made to investigate cognitive impairment in stroke patients, but little has been focused on mild stroke. Research on the impact of mild stroke and different lesion locations on cognitive impairment is still limited. To investigate the underlying mechanisms of cognitive dysfunction in mild stroke at different lesion locations, electroencephalograms (EEGs) were recorded in three groups (40 patients with cortical stroke (CS), 40 patients with subcortical stroke (SS), and 40 healthy controls (HC)) during a visual oddball task. Power envelope connectivity (PEC) was constructed based on EEG source signals, followed by graph theory analysis to quantitatively assess functional brain network properties. A classification framework was further applied to explore the feasibility of PEC in the identification of mild stroke. The results showed worse behavioral performance in the patient groups, and PECs with significant differences among three groups showed complex distribution patterns in frequency bands and the cortex. In the delta band, the global efficiency was significantly higher in HC than in CS (p = 0.011), while local efficiency was significantly increased in SS than in CS (p = 0.038). In the beta band, the small-worldness was significantly increased in HC compared to CS (p = 0.004). Moreover, the satisfactory classification results (76.25% in HC vs. CS, and 80.00% in HC vs. SS) validate the potential of PECs as a biomarker in the detection of mild stroke. Our findings offer some new quantitative insights into the complex mechanisms of cognitive impairment in mild stroke at different lesion locations, which may facilitate post-stroke cognitive rehabilitation.

Disrupted topological organization of resting-state functional brain networks in Parkinson's disease patients with glucocerebrosidase gene mutations

PURPOSE

The mutations of the glucocerebrosidase (GBA) gene are the greatest genetic risk factor for Parkinson's disease (PD). The mechanism underlying the association between GBA mutations and PD has not been fully elucidated.

METHODS

Using resting-state functional magnetic resonance imaging and graph theory analysis to investigate the disrupted topological organization in PD patients with GBA mutation (GBA-PD). Eleven GBA-PD patients, 11 noncarriers with PD, and 18 healthy controls (HCs) with a similar age and sex distribution were recruited. Individual whole-brain functional connectome was constructed, and the global and nodal topological disruptions were calculated among groups. Partial correlation analyses between the clinical features of patients with PD and topological alterations were performed.

RESULTS

The GBA-PD group showed prominently decreased characteristic path length (L_p) and increased global efficiency (E_g) compared to HCs at the global level; a significantly increased nodal betweenness centrality in the medial prefrontal cortex (mPFC) and precuneus within the default mode network, and precentral gyrus within the sensorimotor network, while a significantly decreased betweenness centrality in nodes within the cingulo-opercular network compared to the noncarrier group at the regional level. The altered nodal betweenness centrality of mPFC was positively correlated with fatigue severity scale scores in all patients with PD.

CONCLUSION

The preliminary pilot study found that GBA-PD patients had a higher functional integration at the global level. The nodal result of the mPFC is congruent with the potential fatigue pathology in PD and is suggestive of a profound effect of GBA mutations on the clinical fatigue in patients with PD.

Changes in both top-down and bottom-up effective connectivity drive visual hallucinations in Parkinson's disease

Visual hallucinations are common in Parkinson's disease and are associated with a poorer quality of life and a higher risk of dementia. An important and influential model that is widely accepted as an explanation for the mechanism of visual hallucinations in Parkinson's disease and other Lewy body diseases is that these arise due to aberrant hierarchical processing, with impaired bottom-up integration of sensory information and overweighting of top-down perceptual priors within the visual system. This hypothesis has been driven by behavioural data and supported indirectly by observations derived from regional activation and correlational measures using neuroimaging. However, until now, there was no evidence from neuroimaging for differences in causal influences between brain regions measured in patients with Parkinson's hallucinations. This is in part because previous resting-state studies focused on functional connectivity, which is inherently undirected in nature and cannot test hypotheses about the directionality of connectivity. Spectral dynamic causal modelling is a Bayesian framework that allows the inference of effective connectivity-defined as the directed (causal) influence that one region exerts on another region-from resting-state functional MRI data. In the current study, we utilize spectral dynamic causal modelling to estimate effective connectivity within the resting-state visual network in our cohort of 15 Parkinson's disease visual hallucinators and 75 Parkinson's disease non-visual hallucinators. We find that visual hallucinators display decreased bottom-up effective connectivity from the lateral geniculate nucleus to primary visual cortex and increased top-down effective connectivity from the left prefrontal cortex to primary visual cortex and the medial thalamus, as compared with non-visual hallucinators. Importantly, we find that the pattern of effective connectivity is predictive of the presence of visual hallucinations and associated with their severity within the hallucinating group. This is the first study to provide evidence, using resting-state effective connectivity, to support a model of aberrant hierarchical predictive processing as the mechanism for visual hallucinations in Parkinson's disease.

The Dashboard Vitals of Parkinson's: Not to Be Missed Yet an Unmet Need

The vitals of Parkinson's disease (PD) address the often-ignored symptoms, which are considered either peripheral to the central core of motor symptoms of PD or secondary symptoms, which, nevertheless, have a key role in the quality of life (QoL) and wellness of people with Parkinson's (PwP) [...].

Motor progression marker for newly diagnosed drug-naïve patients with Parkinson's disease: A resting-state functional MRI study

The effective early prediction of clinical outcomes of Parkinson's disease (PD) is of great significance in the implementation of appropriate interventions. We aimed to propose a method based on the use of baseline resting-state functional characteristics (i.e., fractional amplitude of low-frequency fluctuations, fALFF) to predict motor progression in PD patients. Resting-state functional magnetic resonance imaging was performed on 48 newly-diagnosed drug-naïve PD patients and 27 age- and sex- matched healthy controls (HCs). Two PD subgroups were defined with different annual increase of Unified PD Rating Scale Part III motor scores. Least absolute shrinkage and selection operator regression analysis was performed to explore the baseline region-functional indicators for PD discrimination as well as the predictors for future motor deficits. Two significant models composed of baseline fALFF values from cerebral subregions were proposed. The classification model that distinguished PD patients from HCs (area under the curve [AUC] = 0.897) showed the most significant imaging characteristics in the putamen and precentral gyrus. The other prediction model that evaluated the degree of future deterioration of motor symptoms in PD patients (AUC = 0.916) showed the most significant imaging characteristics in the superior occipital gyrus and caudate nucleus. Furthermore, the increased regional function in bilateral caudate nuclei was correlated with the lower annual increase in motor deficits in all PD patients. The caudate nucleus might be the core region responsible for future motor deficits in newly-diagnosed PD patients, which may aid the development of disease progression preventive strategies in clinical practice.

Aberrant gray matter volume and functional connectivity in Parkinson’s disease with minor hallucination

Background

Minor hallucination (MH) is the most common psychotic symptom in Parkinson’s disease (PD); it can develop into well-structured visual hallucination (VH), suggesting that MH may be a staccato form of well-structured VH. However, it remains unclear whether the pathogenesis is the same. Therefore, the aim of this study was to investigate the altered gray matter volume (GMV) and functional connectivity (FC) of MH in PD to further understand the complex mechanisms.

Materials and methods

We included 67 PD patients who attended the outpatient clinic of Nanjing Medical University Affiliated Brain Hospital and recruited 31 healthy controls (HC). Demographic data and clinical characteristics of all subjects were recorded, and cranial structural magnetic resonance imaging (MRI) and resting-state functional MRI data were acquired. Patients were classified into the PD with MH (PD-MH) group and PD without hallucinations or delusions (PD-NH) group. Voxel-based morphometry was used to analyze the differences in GMV in the structural pattern. Seed-based FC was used to analyze the functional pattern. Gaussian random field correction was used, with voxel level P < 0.001 and cluster level P < 0.05 representing statistically significant differences. Finally, the correlation between FC values and scores on the clinical characteristics assessment scale was analyzed.

Results

In the GMV analysis, compared to the PD-NH group, the PD-MH group had reduced GMV in the medial superior frontal gyrus (SFGmed). In the FC analysis, the FC between the SFGmed and the left middle occipital gyrus and right calcarine sulcus decreased in the PD-MH group compared with the PD-NH group, while the FC between SFGmed and the left middle temporal gyrus increased. Correlation analysis revealed that the FC values of the SFGmed and right calcarine sulcus were correlated with the assessment scores for anxiety and sleep symptoms. The FC values of the SFGmed and left middle occipital gyrus were correlated with assessment scores for rapid eye movement disorder.

Conclusion

The aberrant structure and function of the default mode network and visual processing areas seems to facilitate the generation of MH in PD, as the alteration was previously found in well-structured VH, suggesting that the two hallucinations have similar pathophysiological mechanisms.

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.

Modulation of cortical resting state functional connectivity during a visuospatial attention task in Parkinson's disease

Visual dysfunction is a recognized early symptom of Parkinson's disease (PD) that partly scales motor symptoms, yet its background is heterogeneous. With additional deficits in visuospatial attention, the two systems are hard to disentangle and it is not known whether impaired functional connectivity in the visual cortex is translative in nature or disrupted attentional modulation also contributes. In this study, we investigate functional connectivity modulation during a visuospatial attention task in patients with PD. In total, 15 PD and 16 age-matched healthy controls performed a visuospatial attention task while undergoing fMRI, in addition to a resting-state fMRI scan. Tensorial independent component analysis was used to investigate task-related network activity patterns. Independently, an atlas-based connectivity modulation analysis was performed using the task potency method. Spearman's rank correlation was calculated between task-related network expression, connectivity modulation, and clinical characteristics. Task-related networks including mostly visual, parietal, and prefrontal cortices were expressed to a significantly lesser degree in patients with PD (p < 0.027). Resting-state functional connectivity did not differ between the healthy and diseased cohorts. Connectivity between the precuneus and ventromedial prefrontal cortex was modulated to a higher degree in patients with PD (p < 0.004), while connections between the posterior parietal cortex and primary visual cortex, and also the superior frontal gyrus and opercular cortex were modulated to a lesser degree (p < 0.001 and p < 0.011). Task-related network expression and superior frontal gyrus–opercular cortex connectivity modulation were significantly associated with UPDRSIII motor scores and the Hoehn–Yahr stages (R = −0.72, p < 0.006 and R = −0.90, p < 0.001; R = −0.68, p < 0.01 and R = −0.71, p < 0.007). Task-related networks function differently in patients with PD in association with motor symptoms, whereas impaired modulation of visual and default-mode network connectivity was not correlated with motor function.

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.

[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.

Aberrant brain functional hubs and causal connectivity in presbycusis

To investigate resting-state connectivity and further understand directional aspects of implicit alterations in presbycusis patients, we used degree centrality (DC) and Granger causality analysis (GCA) to detect functional hubs of the whole-brain network and then analyze directional connectivity. Resting-state functional magnetic resonance imaging (fMRI) scans were performed on 40 presbycusis patients and 40 healthy controls matched for age, gender, and education. We used DC analysis and GCA to characterize abnormal brain networks in presbycusis patients. The associations of network centrality and directed functional connectivity (FC) with clinical measures of presbycusis were also examined according to the above results. We found that the network centrality of left frontal middle gyrus (MFG) was significantly lower than that of healthy control group. Unidirectionally, the left MFG revealed increased directional connectivity to the left superior frontal gyrus (SFG), while the left MFG exhibited decreased directional connectivity to the left middle temporal gyrus (MTG) and right lingual gyrus (LinG). And the decreased directional connectivity was found from the left precentral gyrus (PrCG) to the left MFG. In addition, the Trail-Making Test B (TMT-B) score was negatively correlated with the decreased DC of the left MFG (r = -0.359, p = 0.032). Resting-state fMRI provides a novel method for identifying aberrant brain network architecture. These results primarily indicate altered functional hubs and abnormal frontal lobe connectivity patterns that may further reflect executive dysfunction in patients with presbycusis.

How do the blind 'see'? The role of spontaneous brain activity in self-generated perception

Spontaneous activity of the human brain has been well documented, but little is known about the functional role of this ubiquitous neural phenomenon. It has previously been hypothesized that spontaneous brain activity underlies unprompted (internally generated) behaviour. We tested whether spontaneous brain activity might underlie internally-generated vision by studying the cortical visual system of five blind/visually-impaired individuals who experience vivid visual hallucinations (Charles Bonnet syndrome). Neural populations in the visual system of these individuals are deprived of external input, which may lead to their hyper-sensitization to spontaneous activity fluctuations. To test whether these spontaneous fluctuations can subserve visual hallucinations, the functional MRI brain activity of participants with Charles Bonnet syndrome obtained while they reported their hallucinations (spontaneous internally-generated vision) was compared to the: (i) brain activity evoked by veridical vision (externally-triggered vision) in sighted controls who were presented with a visual simulation of the hallucinatory streams; and (ii) brain activity of non-hallucinating blind controls during visual imagery (cued internally-generated vision). All conditions showed activity spanning large portions of the visual system. However, only the hallucination condition in the Charles Bonnet syndrome participants demonstrated unique temporal dynamics, characterized by a slow build-up of neural activity prior to the reported onset of hallucinations. This build-up was most pronounced in early visual cortex and then decayed along the visual hierarchy. These results suggest that, in the absence of external visual input, a build-up of spontaneous fluctuations in early visual cortex may activate the visual hierarchy, thereby triggering the experience of vision.

Disrupted morphological grey matter networks in early-stage Parkinson's disease

While previous structural-covariance studies have an advanced understanding of brain alterations in Parkinson's disease (PD), brain–behavior relationships have not been examined at the individual level. This study investigated the topological organization of grey matter (GM) networks, their relation to disease severity, and their potential imaging diagnostic value in PD. Fifty-four early-stage PD patients and 54 healthy controls (HC) underwent structural T1-weighted magnetic resonance imaging. GM networks were constructed by estimating interregional similarity in the distributions of regional GM volume using the Kullback–Leibler divergence measure. Results were analyzed using graph theory and network-based statistics (NBS), and the relationship to disease severity was assessed. Exploratory support vector machine analyses were conducted to discriminate PD patients from HC and different motor subtypes. Compared with HC, GM networks in PD showed a higher clustering coefficient (P = 0.014) and local efficiency (P = 0.014). Locally, nodal centralities in PD were lower in postcentral gyrus and temporal-occipital regions, and higher in right superior frontal gyrus and left putamen. NBS analysis revealed decreased morphological connections in the sensorimotor and default mode networks and increased connections in the salience and frontoparietal networks in PD. Connection matrices and graph-based metrics allowed single-subject classification of PD and HC with significant accuracy of 73.1 and 72.7%, respectively, while graph-based metrics allowed single-subject classification of tremor-dominant and akinetic–rigid motor subtypes with significant accuracy of 67.0%. The topological organization of GM networks was disrupted in early-stage PD in a way that suggests greater segregation of information processing. There is potential for application to early imaging diagnosis.

Retinal ganglion cell dysfunction is correlated with disturbed visual cognition in schizophrenia patients with visual hallucinations

Patients with schizophrenia have altered visual cognition and retinal functions. No studies have explored if retinal anomalies are related to visual cognition and the presence of visual hallucinations (VH). We explored functional responses of the retinal ganglion cells in schizophrenia patients with or without VH and conducted a neuropsychological evaluation to explore the links between cognition and retinal function. The VH+ group showed poorer visual cognition and we found correlations between the amplitudes of the P50 and the N95 waves and visual cognition. Our results provide arguments for a link between retinal dysfunction, impaired visual processing and VH in schizophrenia.

Visual hallucinations and inferior longitudinal fasciculus in Parkinson's disease

INTRODUCTION

We investigated whether disruption of the inferior longitudinal fasciculus and inferior fronto-occipital fasciculus are associated with visual hallucinations in Parkinson's disease (PD).

METHODS

Sixty consecutive right-handed patients with PD with and without visual hallucinations were enrolled in this cross-sectional study. Diffusion tensor imaging was acquired by 3.0 T magnetic resonance imaging. We measured fractional anisotropy and mean diffusivity of the bilateral inferior longitudinal fasciculus and inferior fronto-occipital fasciculus using diffusion tensor tractography analysis software.

RESULTS

Seventeen patients with PD had visual hallucinations; these patients tended to have lower fractional anisotropy and higher mean diffusivity values in all fasciculi than did patients without visual hallucinations. A univariate logistic analysis showed that the presence of visual hallucinations was significantly associated with lower fractional anisotropy and higher mean diffusivity of the left inferior longitudinal fasciculus, and lower Mini-Mental State Examination (MMSE) scores. A multivariable logistic analysis adjusted by MMSE scores and disease duration showed a significant association between the presence of visual hallucinations and fractional anisotropy and mean diffusivity values of the left inferior longitudinal fasciculus.

CONCLUSIONS

Our results suggest that disruption of left inferior longitudinal fasciculus integrity is associated with visual hallucinations in patients with PD, independent of cognitive impairment and disease duration.

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.

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.

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.

Event-Related Potentials Elicited by Face and Face Pareidolia in Parkinson's Disease

Background

Parkinson's disease is associated with impaired ability to recognize emotional facial expressions. In addition to a visual processing disorder, a visual recognition disorder may be involved in these patients. Pareidolia is a type of complex visual illusion that permits the interpretation of a vague stimulus as something known to the observer. Parkinson's patients experience pareidolic illusions. N170 and N250 waveforms are two event-related potentials (ERPs) involved in emotional facial expression recognition.

Objective

In this study, we investigated how Parkinson's patients process face and face-pareidolia stimuli at the neural level using N170, vertex positive potential (VPP), and N250 components of event-related potentials.

Methods

To examine the response of face and face-pareidolia processing in Parkinson's patients, we measured the N170, VPP, and N250 components of the event-related brain potentials in a group of 21 participants with Parkinson's disease and 26 control participants.

Results

We found that the latencies of N170 and VPP responses to both face and face-pareidolia stimuli were increased along with their amplitudes, and the amplitude of N250 responses decreased in Parkinson's patients compared to the control group. In both control and Parkinson's patients, face stimuli generated greater ERP amplitude and shorter latency in responses than did face-pareidolia stimuli.

Conclusion

The results of our study showed that ERPs associated with face and also face-pareidolia stimuli processing are changed in early-stage neurophysiological activity in the temporoparietal cortex of Parkinson's patients.

Increased substantia nigra echogenicity correlated with visual hallucinations in Parkinson's disease: a Chinese population-based study

As a noninvasive technique, transcranial sonography (TCS) of substantia nigra (SN) has gradually showed its effectiveness not only in diagnosis but also in understanding clinical features of Parkinson’s Disease (PD). This study aimed to further evaluate TCS for clinical diagnosis of PD, and to explore the association between sonographic manifestations and visual hallucinations (VH). A total of 226 subjects including 141 PD patients and 85 controls were recruited. All participants received TCS. A series of rating scales to evaluate motor and non-motor symptoms were performed in PD patients. Results showed that 172 subjects were successfully assessed by TCS. The area of SN was greater in PD patients than that in controls (P < 0.001). As receiver-operating characteristic (ROC) curve analysis showed, the best cutoff value for the larger SN echogenicity size was 23.5 mm² (sensitivity 70.3%, specificity 77.0%). Patients with VH had larger SN area (P = 0.019), as well as higher Non-Motor Symptoms Scale (NMSS) scores (P = 0.018). Moreover, binary logistic regression analysis indicated that SN hyperechogenicity (odds ratio = 4.227, P = 0.012) and NMSS scores (odds ratio = 0.027, P = 0.042) could be the independent predictors for VH. In conclusion, TCS can be used as an auxiliary diagnostic tool for Parkinson’s disease. Increased SN echogenicity is correlated with VH in Parkinson’s disease, possibly because the brain stem is involved in the mechanism in the onset of VH. Further studies are needed to confirm these findings.

Aberrant functional connectivity of resting state networks related to misperceptions and intra-individual variability in Parkinson's disease

Patients with Parkinson's disease (PD) frequently suffer from visual misperceptions and hallucinations, which are difficult to objectify and quantify. We aimed to develop an image recognition task to objectify misperceptions and to assess performance fluctuations in PD patients with and without self-reported hallucinations. Thirty-two non-demented patients with Parkinson's disease (16 with and 16 without self-reported visual hallucinations) and 25 age-matched healthy controls (HC) were tested. Participants performed a dynamic image recognition task with real and scrambled images. We assessed misperception scores and intra-individual variability in recognition times. To gain insight into possible neural mechanisms related to misperceptions and performance fluctuations we correlated resting state network connectivity to the behavioral outcomes in a subsample of Parkinson's disease patients (N = 16). We found that PD patients with self-reported hallucinations (PD-VH) exhibited higher perceptual error rates, due to decreased perceptual sensitivity and not due to changed decision criteria. In addition, PD-VH patients exhibited higher intra-individual variability in recognition times than HC or PD-nonVH patients. Both, misperceptions and intra-individual variability were negatively correlated with resting state functional connectivity involving frontal and parietal brain regions, albeit in partly different subregions. Consistent with previous research suggesting that hallucinations arise from dysfunction in attentional networks, misperception scores correlated with reduced functional connectivity between the dorsal attention and salience network. Intra-individual variability correlated with decreased connectivity between somatomotor and right fronto-parietal networks. We conclude that our task can detect visual misperceptions that are more prevalent in PD-VH patients. In addition, fluctuating visual performance appear to be a signature of PD-VH patients, which might assist further studies of the underlying pathophysiological mechanisms and cognitive processes.

Auditory and visual hallucination prevalence in Parkinson's disease and dementia with Lewy bodies: a systematic review and meta-analysis

BACKGROUND

Non-motor features of Parkinson's disease (PD) and dementia with Lewy bodies (DLB), such as auditory hallucinations (AH), contribute to disease burden but are not well understood.

METHODS

Systematic review and random-effects meta-analyses of studies reporting AH associated with PD or DLB. Prevalence of visual hallucinations (VH) in identified studies meeting eligibility criteria were included in meta-analyses, facilitating comparison with AH. Synthesis of qualitative descriptions of AH was performed. PubMed, Web of Science and Scopus databases were searched for primary journal articles, written in English, published from 1970 to 2017. Studies reporting AH prevalence in PD or DLB were screened using PRISMA methods.

RESULTS

Searches identified 4542 unique studies for consideration, of which, 26 met inclusion criteria. AH pooled prevalence in PD was estimated to be 8.9% [95% confidence interval (CI) 5.3-14.5], while in DLB was estimated to be 30.8% (±23.4 to 39.3). Verbal hallucinations, perceived as originating outside the head, were the most common form of AH. Non-verbal AH were also common while musical AH were rare. VH were more prevalent, with an estimated pooled prevalence in PD of 28.2% (±19.1 to 39.5), while in DLB they were estimated to be 61.8% (±49.1 to 73.0). Meta-regression determined that the use of validated methodologies to identify hallucinations produced higher prevalence estimates.

CONCLUSIONS

AH and VH present in a substantial proportion of PD and DLB cases, with VH reported more frequently in both conditions. Both AH and VH are more prevalent in DLB than PD. There is a need for standardised use of validated methods to detect and monitor hallucinations.

Aberrant resting-state oscillatory brain activity in Parkinson's disease patients with visual hallucinations: An MEG source-space study

To gain insight into possible underlying mechanism(s) of visual hallucinations (VH) in Parkinson's disease (PD), we explored changes in local oscillatory activity in different frequency bands with source-space magnetoencephalography (MEG). Eyes-closed resting-state MEG recordings were obtained from 20 PD patients with hallucinations (Hall+) and 20 PD patients without hallucinations (Hall-), matched for age, gender and disease severity. The Hall+ group was subdivided into 10 patients with VH only (unimodal Hall+) and 10 patients with multimodal hallucinations (multimodal Hall+). Subsequently, neuronal activity at source-level was reconstructed using an atlas-based beamforming approach resulting in source-space time series for 78 cortical and 12 subcortical regions of interest in the automated anatomical labeling (AAL) atlas. Peak frequency (PF) and relative power in six frequency bands (delta, theta, alpha1, alpha2, beta and gamma) were compared between Hall+ and Hall-, unimodal Hall+ and Hall-, multimodal Hall+ and Hall-, and unimodal Hall+ and multimodal Hall+ patients. PF and relative power per frequency band did not differ between Hall+ and Hall-, and multimodal Hall+ and Hall- patients. Compared to the Hall- group, unimodal Hall+ patients showed significantly higher relative power in the theta band (p = 0.005), and significantly lower relative power in the beta (p = 0.029) and gamma (p = 0.007) band, and lower PF (p = 0.011). Compared to the unimodal Hall+, multimodal Hall+ showed significantly higher PF (p = 0.007). In conclusion, a subset of PD patients with only VH showed slowing of MEG-based resting-state brain activity with an increase in theta activity, and a concomitant decrease in beta and gamma activity, which could indicate central cholinergic dysfunction as underlying mechanism of VH in PD. This signature was absent in PD patients with multimodal hallucinations.

The utility and application of electrophysiological methods in the study of visual hallucinations

Visual hallucinations (VH) are a common symptom in multiple clinical and non-clinical populations. Although structural and functional neuroimaging has informed the understanding of VH, temporal resolution is limited. Electrophysiological techniques provide a complementary perspective on dynamic and temporal aspects of neural functioning, offering greater insight into the mechanisms underlying their formation. In this review we examine and critically evaluate the emerging evidence base utilising electrophysiological approaches in the study of VH. Overall, increased visual system excitability, dysfunctional visual processing and network connectivity, and cholinergic dysfunction have been consistently observed in VH-prone pathologies. However, a major limitation is in the lack of robust experimental studies and the reliance on single case reports. We conclude that electrophysiology provides tentative evidence for the contribution of bottom-up, top-down, and network dysfunction in the aetiology of VH, supporting several existing VH models. Furthermore, we discuss how electrophysiology has been directly utilised in specific clinical interventions for VH. Further exploration utilising electrophysiology in combination with, for example, neuroimaging will help better understand VH aetiology while aiding in the development of novel therapeutic interventions for this difficult to treat symptom.

Can neuroimaging predict dementia in Parkinson's disease?

Dementia in Parkinson's disease affects 50% of patients within 10 years of diagnosis but there is wide variation in severity and timing. Thus, robust neuroimaging prediction of cognitive involvement in Parkinson's disease is important: (i) to identify at-risk individuals for clinical trials of potential new treatments; (ii) to provide reliable prognostic information for individuals and populations; and (iii) to shed light on the pathophysiological processes underpinning Parkinson's disease dementia. To date, neuroimaging has not made major contributions to predicting cognitive involvement in Parkinson's disease. This is perhaps unsurprising considering conventional methods rely on macroscopic measures of topographically distributed neurodegeneration, a relatively late event in Parkinson's dementia. However, new technologies are now emerging that could provide important insights through detection of other potentially relevant processes. For example, novel MRI approaches can quantify magnetic susceptibility as a surrogate for tissue iron content, and increasingly powerful mathematical approaches can characterize the topology of brain networks at the systems level. Here, we present an up-to-date overview of the growing role of neuroimaging in predicting dementia in Parkinson's disease. We discuss the most relevant findings to date, and consider the potential of emerging technologies to detect the earliest signs of cognitive involvement in Parkinson's disease.

Absent Audiovisual Integration Elicited by Peripheral Stimuli in Parkinson's Disease

The basal ganglia, which have been shown to be a significant multisensory hub, are disordered in Parkinson's disease (PD). This study was to investigate the audiovisual integration of peripheral stimuli in PD patients with/without sleep disturbances. Thirty-six age-matched normal controls (NC) and 30 PD patients were recruited for an auditory/visual discrimination experiment. The mean response times for each participant were analyzed using repeated measures ANOVA and race model. The results showed that the response to all stimuli was significantly delayed for PD compared to NC (all p < 0.01). The response to audiovisual stimuli was significantly faster than that to unimodal stimuli in both NC and PD (p < 0.001). Additionally, audiovisual integration was absent in PD; however, it did occur in NC. Further analysis showed that there was no significant audiovisual integration in PD with/without cognitive impairment or in PD with/without sleep disturbances. Furthermore, audiovisual facilitation was not associated with Hoehn and Yahr stage, disease duration, or the presence of sleep disturbances (all p > 0.05). The current results showed that audiovisual multisensory integration for peripheral stimuli is absent in PD regardless of sleep disturbances and further suggested the abnormal audiovisual integration might be a potential early manifestation of PD.

Impaired topological architecture of brain structural networks in idiopathic Parkinson's disease: a DTI study

Parkinson's disease (PD) is considered as a neurodegenerative disorder of the brain central nervous system. But, to date, few studies adopted the network model to reveal topological changes in brain structural networks in PD patients. Additionally, although the concept of rich club organization has been widely used to study brain networks in various brain disorders, there is no study to report the changed rich club organization of brain networks in PD patients. Thus, we collected diffusion tensor imaging (DTI) data from 35 PD patients and 26 healthy controls and adopted deterministic tractography to construct brain structural networks. During the network analysis, we calculated their topological properties, and built the rich club organization of brain structural networks for both subject groups. By comparing the between-group differences in topological properties and rich club organizations, we found that the connectivity strength of the feeder and local connections are lower in PD patients compared to those of the healthy controls. Furthermore, using a network-based statistic (NBS) approach, we identified uniformly significantly decreased connections in two modules, the limbic/paralimbic/subcortical module and the cognitive control/attention module, in patients compared to controls. In addition, for the topological properties of brain network topology in the PD patients, we found statistically increased shortest path length and decreased global efficiency. Statistical comparisons of nodal properties were also widespread in the frontal and parietal regions for the PD patients. These findings may provide useful information to better understand the abnormalities of brain structural networks in PD patients.

Damaged fiber tracts of the nucleus basalis of Meynert in Parkinson's disease patients with visual hallucinations

Damage to fiber tracts connecting the nucleus basalis of Meynert (NBM) to the cerebral cortex may underlie the development of visual hallucinations (VH) in Parkinson’s disease (PD), possibly due to a loss of cholinergic innervation. This was investigated by comparing structural connectivity of the NBM using diffusion tensor imaging in 15 PD patients with VH (PD + VH), 40 PD patients without VH (PD − VH), and 15 age- and gender-matched controls. Fractional anisotropy (FA) and mean diffusivity (MD) of pathways connecting the NBM to the whole cerebral cortex and of regional NBM fiber tracts were compared between groups. In PD + VH patients, compared to controls, higher MD values were observed in the pathways connecting the NBM to the cerebral cortex, while FA values were normal. Regional analysis demonstrated a higher MD of parietal (p = 0.011) and occipital tracts (p = 0.027) in PD + VH, compared to PD − VH patients. We suggest that loss of structural connectivity between the NBM and posterior brain regions may contribute to the etiology of VH in PD. Future studies are needed to determine whether these findings could represent a sensitive marker for the hypothesized cholinergic deficit in PD + VH patients.

Impaired brain network architecture in newly diagnosed Parkinson's disease based on graph theoretical analysis

BACKGROUND

Resting state functional magnetic resonance imaging (rs-fMRI) has been applied to investigate topographic structure in Parkinson's disease (PD). Alteration of topographic architecture has been inconsistent in PD AIM: To investigate the network profile of PD using graph theoretical analysis.

METHOD

Twenty six newly diagnosed PD and 19 age- and gender- matched healthy controls (HC) were included in our analysis. Small-world profile and topographic profiles (nodal degree, global efficiency, local efficiency, cluster coefficient, shortest path length, betweenness centrality) were measured and compared between groups, with age and gender as covariates. We also performed correlation analysis between topographic features with motor severity measured by UPDRS III.

RESULTS

Small-world property was present in PD. Nodal degree, global efficiency, local efficiency and characteristic path length consistently revealed disruptive sensorimotor network, and visual network to a less degree in PD. By contrast, default mode network (DMN) and cerebellum in PD showed higher nodal degree, global efficiency and local efficiency, and lower characteristic path length. Global and local efficiency in the midbrain was higher in PD excluding substantia nigra. PD group also exhibited lower cluster coefficient in the subcortical motor network (thalamus and caudate nucleus). No significant correlation was found between topographic properties and motor severity.

CONCLUSION

PD exhibited disruptive sensorimotor and visual networks in early disease stage. DMN, a certain areas in the cerebellum and midbrain may compensate for disruptive sensorimotor and visual network in PD. Disruptive network architecture may be an early alteration of PD pathophysiology but may not serve as a valid biomarker yet.

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.

Imaging the Nonmotor Symptoms in Parkinson's Disease

Parkinson's disease is acknowledged to be a multisystem syndrome, manifesting as a result of multineuropeptide dysfunction, including dopaminergic, cholinergic, serotonergic, and noradrenergic deficits. This multisystem disorder ultimately leads to the presentation of a range of nonmotor symptoms, now appreciated to be an integral part of the disease-specific spectrum of symptoms, often preceding the diagnosis of motor Parkinson's disease. In this chapter, we review the dopaminergic and nondopaminergic basis of these symptoms by exploring the neuroimaging evidence based on several techniques including positron emission tomography, single-photon emission computed tomography molecular imaging, magnetic resonance imaging, functional magnetic resonance imaging, and diffusion tensor imaging. We discuss the role of these neuroimaging techniques in elucidating the underlying pathophysiology of NMS in Parkinson's disease.

Compensatory shifts in visual perception are associated with hallucinations in Lewy body disorders

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.