Slower visual perception and alpha oscillation as a potential neural markers of visual hallucination in Parkinson’s Disease

Although Parkinson’s disease (PD) is known for its motor deficits, visual hallucinations (VH) could occur in upto 15%-40% of PD patients 1,2 (Barnes & David, 2001; Bhidayasiri et al., 2011). The pathophysiological mechanisms that underlie VH in PD are still unknown. We hypothesize that VH in PD is related to the slowing of the visual system in consciously sampling incoming sensory inputs. To test this, we measured the temporal resolution of visual perception in healthy subjects and PD patients with and without VH (PDwVH and PDwoVH) using the two-flash discrimination task with EEG recording from the occipital site. We assessed the speed of visual perception via the two-flash fusion threshold (i.e., the inter-stimulus interval [ISI]) and the alpha band oscillations frequency (8–13 Hz), thought to reflect the transfer of the phasic information in the thalamocortical neurons in the visual system 3,4,5 (Nelli et al., 2017; Busch et al., 2009; Dugué et al., 2011). We found significantly lower sampling frequencies across both behavioral and neurophysiological indexes in PD patients with PDwVH compared to PDwoVH and the healthy control group. There was also a significant inter-subject correlation between these behavioral and neural measurements. These findings suggest that slowing in periodic visual perception and in alpha-band oscillations underlies VH in PD, emphasizing the role of the thalamocortical interaction in supporting periodic visual perception and expanding our understanding about the neuropathological mechanism of PD outside the motor domain.