Visual misperceptions and hallucinations in Parkinson's disease: dysfunction of attentional control networks?

Visual misperceptions and hallucinations are a major cause of distress in patients with Parkinson's disease (PD), particularly in the advanced stages of the condition. Recent work has provided a framework for understanding the pathogenesis of these symptoms, implicating impairments from the retina to the integration of external information with preformed internal images. In this article, we propose a novel hypothesis that attempts to explain the presence of visual misperceptions and hallucinations in PD through the aberrant coordination of complimentary yet competing neural networks. We propose that hallucinations in PD reflect the relative inability to recruit activation in the dorsal attention network in the presence of an ambiguous percept, leading to overreliance on default mode network processing and salience arising from the ventral attention network. This inability is proposed to stem from improper function across cortical and subcortical structures secondary to the presence of Lewy body pathology. This hypothesis may be empirically tested by the use of targeted cognitive paradigms. In turn, this may assist our understanding of the pathophysiological mechanisms and cognitive processes contributing to visual misperceptions and hallucinations and ultimately may inform more effective treatment strategies for this troubling symptom.