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

Abstract

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.

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

“…Although longitudinal studies have found a temporal association between the two, it is unclear whether they share the same mechanism, and whether those proposed models can be used to explain MH. Some morphometric studies have found similar structural and functional characteristics between MH and well-structured VH (Pagonabarraga et al, 2014;Bejr-Kasem et al, 2019), while overlapping but graded patterns of structural and functional abnormalities have also been found (Marques et al, 2022).…”

Clinical features of minor hallucinations in different phenotypes of Parkinson’s disease: A cross-sectional study

“…In our study, the RBDSQ scores was higher in patients with the PIGD phenotype than in those with the TD phenotype, which may indicating possible RBD and lead to the higher incidence of VIs in the PIGD phenotype in this population. The proposed hypothesis observed that VIs and VHs were continuous situations with the same underlying processes (8,45). Clinically, VH is described as perceptions that occur in the absence of existing stimuli, while VI is characterized as misleading perceptions of real stimuli.…”

“…Clinically, VH is described as perceptions that occur in the absence of existing stimuli, while VI is characterized as misleading perceptions of real stimuli. Although they differ in definition, their neurologically related factors overlap considerably (45). According to a structural neuroimaging study, both symptoms have been linked to abnormalities of the temporoparietal cortices, which assist visual spatial processing (46).…”

Phantom Boarder Relates to Experimentally‐Induced Presence Hallucinations in Parkinson's Disease

“…Future studies should therefore acquire imaging data, investigating whether patients with PB recruit networks linked to PH 32 and/or whether brain regions involved in PD patients with PB rather overlap with networks of visual hallucinations. 54 , 55 , 56 Extended neuropsychological examination would be relevant in understanding the relationship between cognitive dysfunctions (or decline) and PB, and the cognitive mechanisms involved. 52 , 57 Additionally, a clearly defined scale for assessing PB and PH would allow to refine their phenomenological differences and similarities.…”

“…More experimental data in larger groups of patients, including a group with PB without PH (pure PD‐PB), are needed to further investigate the brain mechanisms of presences and phantom boarders in PD, and to determine the clinical, behavioral and neural similarities and differences between both symptoms. Future studies should therefore acquire imaging data, investigating whether patients with PB recruit networks linked to PH 32 and/or whether brain regions involved in PD patients with PB rather overlap with networks of visual hallucinations 54–56 . Extended neuropsychological examination would be relevant in understanding the relationship between cognitive dysfunctions (or decline) and PB, and the cognitive mechanisms involved 52,57 .…”