Visual hallucinations in Parkinson’s disease may arise from a global loss of network efficiency in the brain that disturbs visual attention and visual processing, according to research published online ahead of print September 27 in Radiology. A specific pattern of brain disconnection on fMRI may therefore help predict the development of visual hallucinations in patients with Parkinson’s disease.
An imperfect understanding of the pathophysiology behind visual hallucinations in Parkinson’s disease has hindered the development of effective treatments. Previous fMRI studies of these symptoms focused on task-based imaging, but visual hallucinations are associated with the development of cognitive decline, which could have influenced participants’ ability to perform specific tasks in the imager.
Dagmar H. Hepp, MD, of the Department of Neurology at VU University Medical Center in Amsterdam, and colleagues retrospectively examined resting-state fMRI data for 55 patients with Parkinson’s disease and 15 healthy controls who participated in a prospective cohort study. Of the participants with Parkinson’s disease, 15 had visual hallucinations. Dr. Hepp’s team calculated functional connectivity between 47 brain regions of interest. They compared whole-brain and region-specific means of connectivity using a general linear model with false discovery rate control for multiple comparisons.
In eight regions in the occipital lobe and paracentral area, functional connectivity was lower in all patients with Parkinson’s disease, compared with controls. Compared with controls, patients with Parkinson’s disease and visual hallucinations—but not patients with Parkinson’s disease without visual hallucinations—had nine brain regions with reduced functional connectivity. These regions were in the frontal cortex (ie, the superior frontal gyrus), temporal cortex (eg, the superior temporal gyrus), rolandic operculum, occipital cortex, and striatum. Connectivity of the superior temporal gyrus was correlated with orientation, attention, praxis, perception, and intraextra dimensional set shifting. Loss of functional connectivity of the rolandic operculum correlated with lower cognitive test scores in the subdomains of praxis and perception.
The superior frontal gyrus contributes to the allocation and maintenance of visuospatial attention and inhibitory control. This region also may allow an individual to reflect on sensory experience and judge its possible significance in relation to the self. Investigators believe that the superior temporal gyrus influences visual attention and controls the dorsal and ventral visual streams. Disconnection of frontal and temporal areas may impair the discrimination of external perceptions from internally generated information.
“Our findings argue against the notion that a single specific functional brain region or network is the neural substrate of visual hallucinations in Parkinson’s disease, but rather supply further evidence for a more global loss of network efficiency, which could drive disturbed attentional and visual processing and thereby lead to visual hallucinations in Parkinson’s disease,” the authors concluded.
—Erik Greb
Suggested Reading
Hepp DH, Foncke EMJ, Olde Dubbelink KTE, et al. Loss of functional connectivity in patients with Parkinson disease and visual hallucinations. Radiology. 2017 Sep 27 [Epub ahead of print].
