Altered cortical visual processing in PD with hallucinations: an fMRI study.
ABSTRACT To compare fMRI activation during two visual stimulation paradigms in Parkinson disease (PD) subjects with chronic visual hallucinations vs PD patients who had never hallucinated.
Twelve pairs of PD subjects, matched for age, PD duration, and dopaminergic drug exposure duration, participated in this study. The authors examined group differences in activation during stroboscopic (flashing) vs no visual stimulation and kinematic (apparent motion) vs stationary visual stimulation.
During stroboscopic stimulation, non-hallucinating PD subjects showed significantly greater activation in the parietal lobe and cingulate gyrus compared to hallucinating PD subjects. In contrast, the hallucinating subjects showed significantly greater activation in the inferior frontal gyrus and the caudate nucleus. During kinematic stimulation, non-hallucinating PD subjects showed significantly greater activation in area V5/MT, parietal lobe, and cingulate gyrus compared to hallucinating PD subjects. Hallucinating PD subjects showed significantly greater activation in the superior frontal gyrus.
PD patients with chronic visual hallucinations respond to visual stimuli with greater frontal and subcortical activation and less visual cortical activation than non-hallucinating PD subjects. Shifting visual circuitry from posterior to anterior regions associated primarily with attention processes suggests altered network organization may play a role in the pathophysiology of visual hallucinations in PD.
- SourceAvailable from: Marco Muti[Show abstract] [Hide abstract]
ABSTRACT: BACKGROUND: Visual perception deficits are a recurrent manifestation in Parkinson's disease (PD). Recently, structural abnormalities of fronto-parietal areas and subcortical regions, implicated in visual stimuli analysis, have been observed in PD patients with cognitive decline and visual hallucinations. The aim of the present study was to investigate the salient aspects of visual perception in cognitively unimpaired PD patients. METHODS: Eleven right-handed non-demented right-sided onset PD patients without visuospatial impairment or hallucinations and eleven healthy controls were studied with fMRI while performing a specific visuoperceptual/visuospatial paradigm that allowed to highlight the specific process underlying visuospatial judgment. RESULTS: Significant changes in both cortical areas and subcortical regions involved in visual stimuli processing were observed. In particular, PD patients showed a reduced activation for the right insula, left putamen, bilateral caudate and right hippocampus, as well as an over-activation of the right dorso-lateral prefrontal and of the posterior parietal cortices, particularly in the right hemisphere. CONCLUSIONS: We found that both loss of efficiency and compensatory mechanisms occur in PD patients, providing further insight into the pathophysiological role of the functional alterations of basal ganglia and limbic structures in the impairment of visuoperceptual and visuospatial functions observed in PD.Frontiers in Neurology 07/2014;
- [Show abstract] [Hide abstract]
ABSTRACT: BACKGROUND: Visual hallucinations are an important non-motor complication of Parkinson's disease (PD) and carry a negative prognosis. Their biological basis is uncertain, but may relate to the activity of resting state networks in brain. We therefore aimed to investigate functional activity of brain in patients with visual hallucinations (PDVH) in resting state compared to patients without hallucinations (PDnonVH) and a healthy control group (HC). METHODS: Resting state functional MRI was acquired and the primary analysis compared the amplitude of low-frequency fluctuations (ALFF) across groups. This informed a secondary analysis, in the PD groups only, comparing functional connectivity between a 'seed' region in the occipital lobe and the rest of the brain. RESULTS: Individuals with PDVH showed lower ALFF in bilateral lingual gyrus and cuneus and greater ALFF in temporo-parietal regions, medial temporal gyrus and cerebellum than PDnonVH and HC. PDnonVH also had lower ALFF in occipitoparietal region and greater ALFF in medial temporal gyrus, temporo-parietal and cerebellum regions than HC. Functional connectivity analysis revealed that, although both PD groups had lower occipital functional connectivity relative to the HC group, occipital - corticostriatal connectivity was significantly higher in those with PDVH compared with PDnonVH. CONCLUSION: Our study reveals widespread hemodynamic alterations in PD. However, within a functionally abnormal occipital lobe, those with PDVH have even lower ALFF than non-hallucinators, but have higher occipital functional connectivity with cortical-striatal regions. These findings suggest disruption of pathways underpinning both primary visual perceptual and intrinsic visual integration may contribute to visual hallucinations in PD.Parkinsonism & Related Disorders 12/2014; · 4.13 Impact Factor
- [Show abstract] [Hide abstract]
ABSTRACT: Background: Visual hallucinations (VH) are one of the most striking nonmotor symptoms in Parkinson's disease (PD), and predict dementia and mortality. Aberrant default mode network (DMN) is associated with other psychoses. Here, we tested the hypothesis that DMN dysfunction contributes to VH in PD. Methods: Resting state functional data was acquired from individuals with PD with VH (PDVH) and without VH (PDnonVH), matched for levodopa drug equivalent dose, and a healthy control group (HC). Independent component analysis was used to investigate group differences in functional connectivity within the DMN. In addition, we investigated whether the functional changes associated with hallucinations were accompanied by differences in cortical thickness. Results: There were no group differences in cortical thickness but functional coactivation within components of the DMN was significantly lower in both PDVH and PDnonVH groups compared to HC. Functional coactivation within the DMN was found to be greater in PDVH group relative to PDnonVH group. Conclusion: Our study demonstrates, for the first time that, within a functionally abnormal DMN in PD, relatively higher "connectivity" is associated with VH. We postulate that aberrant connectivity in a large scale network affects sensory information processing and perception, and contributes to "positive" symptom generation in PD. Hum Brain Mapp, 2014. © 2014 Wiley Periodicals, Inc.Human Brain Mapping 07/2014; · 6.92 Impact Factor