Visual Priming and Visual Hallucinations in Parkinson’s Disease. Evidence for Normal Top-Down Processes

Abstract

Background: Visual hallucinations (VH) are common in Parkinson's disease (PD) and are associated with increased morbidity and mortality. Current explanations for VH in PD suggest combined impairments in top-down attentional and bottom-up perceptual processes, which allow the passive ''release'' of stored images. Alternative models in other disorders have suggested that top-down factors may actively encourage hallucinations. In order to explore the interaction between top-down and bottom-up visual processing in PDVH, we developed novel experimental priming tasks in which top-down verbal cues were used to prime the bottom-up recognition of partial or ambiguous pictures. Method: Two groups of PD participants with (PD þ VH, n ¼ 16), and without VH (PD -VH, n ¼ 20) were compared to a group of healthy older adults (NC, n ¼ 20) on 3 novel measures of visual priming. Results: All tasks showed significant priming effects. The PD þ VH group was more impaired at accurately identifying silhouette and fragmented images compared to the PD -VH group. There were no differences in priming between the 2 PD groups. Conclusions: The study showed that VH in PD are not associated with relatively greater top-down activation, and that the interaction between top-down and bottom-up processes is intact.

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

“…The current study aimed to extend the findings of Straughan et al (2016) and Yokoi et al (2014) by assessing differences between patients with and without hallucinations and by adding associative priming to experimentally examine the effects of environmental factors.…”

“…Consistent with these models, combined impairments in top-down and bottom-up processes are risk factors for visual hallucinations in LBD (Barnes & Boubert, 2008; Bronnick, Emr, Tekin, Haughen, & Aarsland, 2011; Gallagher, Parkkinen, O’Sullivan, Spratt, Shah et al, 2011; Imamura, Wada-Isoe, Kitayama, & Nakashima, 2008; Meppelink, De Jong, Teune, & Van Laar, 2009; Ozer, Meral, Hanoglu, Ozturk, Cetin et al, 2007; Ramírez-Ruiz, Junqué, Martí, Valldeoriola, & Tolosa, 2006, 2007; Straughan, Collerton, & Bruce, 2016). This focus on factors within participants, however, neglects potential interactions with the environment and does not provide an explanation of why hallucinatory episodes tend to occur at specific times and locations and to be tightly integrated with the visual environment (Collerton, Taylor, Tsuda, Fujii, Nara et al, 2016).…”

“…A recent study from our group (Straughan et al, 2016) examined the role of priming of visually ambiguous images (e.g., silhouettes, fragmented images) in hallucinating and non-hallucinating participants with Parkinson’s disease (this was a separate sample from the current study). Significant priming effects emerged across both groups, demonstrating the preserved priming in participants with LBD.…”

Presynaptic dopaminergic terminal imaging and non-motor symptoms assessment of Parkinson’s disease: evidence for dopaminergic basis?

“…128–132 A dopaminergic basis of VH and other perceptional disorders is being researched. A cortico-striato-thalamocortical dysfunction has been suggested, 89,133,134 however at present, work is required to determine and distinguish the differing forms of hallucinations.…”

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

“…The scrambled images were used to assess whether PD-VH patients are prone to report real objects while none is physically present. Since recent studies suggested that the usage of visual illusions might contribute to the sensitivity detecting Parkinson patients with hallucinations (Shine et al., 2012; Straughan et al., 2016), we also implemented a Continuous Flash Suppression condition (CFS) that suppresses salient stimuli from perceptual awareness due to binocular rivalry (Stein et al., 2011; Tsuchiya and Koch, 2005).…”