Imagine that: elevated sensory strength of mental imagery in individuals with Parkinson's disease and visual hallucinations

Abstract

Visual hallucinations occur when our conscious experience does not accurately reflect external reality. However, these dissociations also regularly occur when we imagine the world around us in the absence of visual stimulation. We used two novel behavioural paradigms to objectively measure visual hallucinations and voluntary mental imagery in 19 individuals with Parkinson's disease (ten with visual hallucinations; nine without) and ten healthy, age-matched controls. We then used this behavioural overlap to interrogate the connectivity both within and between the major attentional control networks using restingstate functional magnetic resonance imaging. Patients with visual hallucinations had elevated mental imagery strength compared with patients without hallucinations and controls. Specifically, the sensory strength of imagery predicted the frequency of visual hallucinations. Together, hallucinations and mental imagery predicted multiple abnormalities in functional connectivity both within and between the attentional control networks, as measured with resting-state functional magnetic resonance imaging. However, the two phenomena were also dissociable at the neural level, with both mental imagery and visual misperceptions associated with specific abnormalities in attentional network connectivity. Our results provide the first evidence of both the shared and unique neural correlates of these two similar, yet distinct phenomena.

Remembering verbally-presented items as pictures: Brain activity underlying visual mental images in schizophrenia patients with visual hallucinations

“…It was suggested that these patients used visual imagery of the target words as a mnemonic strategy in preference to the verbal strategies implemented by the other patients. A link between visual hallucinations and strength of visual mental imagery was recently reported in patients with Parkinson's disease (Shine et al, 2015). In similar manner, verbal hallucinations, which were not associated with visual imagery in our study, might M A N U S C R I P T…”

The psychosis spectrum in Parkinson disease

“…In the attentional control model 90 , the core pathology of PD psychosis is dysfunctional integration between three networks (dorsal attention network, ventral attention network and default mode network), with a failure to engage the dorsal attention network in the context of ambiguous visual input and the intrusion of default mode contents into perceptual consciousness 90–92 . This account is supported by evidence from PD patients with visual hallucinations or illusions of elevated strength of mental imagery 93 , attentional set-shifting deficits 94 , altered resting state and task activation networks 95 , and increased functional connectivity in the default mode network 96 . A dopamine-based model of PD psychosis 97 argues for abnormalities of biasing and gating access to a global workspace that is thought, according to some accounts, to underlie conscious experience.…”

Resting state in Parkinson's disease dementia and dementia with Lewy bodies: commonalities and differences

“…Furthermore, there is currently a growing trend of research evidence suggesting impaired connectivity between the DMN and FPN and also within the FPN between its ventral and dorsal aspects [DAN and ventral attention network (VAN)]. Certainly, dysfunctional connectivity between DMN, DAN and VAN has been implicated in the aetiology of complex VHs in PD (Shine et al ., ; Shine et al ., ). In this regard, we also observed reduced FC between the FPN seeds located in the IPS and frontal and precuneal cortices in our participants with PDD, which agree with observations of impaired communication between attention networks and DMN in Lewy body diseases (Shine et al ., ).…”