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

Abstract

Parkinson’s disease (PD) is a severe neurodegenerative disorder characterized by motor dysfunctions such as resting tremor, rigidity, and slowing of movement. Although PD is known for its motor deficits, visual hallucations (VH) could occur in upto 15%-40% of PD patients which lead to severe disability. To date, the pathophysiological mechanisms of the central nervous system 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 hypothesis, we measured the temporal resolution of visual perception in healthy subjects and PD patients with and without VH using the two-flash discrimination task with EEG recording over the occipital site. We assessed the speed of visual perception via the two-flash fusion threshold (i.e., the inter-stimulus interval [ISI], in which subjects could not discriminate the appearance of the two flashes) and the frequency of the alpha band oscillations (8–13 Hz), thought to reflect the transfer of the phasic information in the thalamocortical neurons of the visual system. We found significantly lower sampling frequencies across both of these behavioral and neurophysiological indexes in PD patients with VH compared to those without VH and the healthy control group. Interestingly, the patients without VH also exhibited significant slowing in periodic visual perception compared to the health control but to a lesser degree than those with VH had. Moreover, there is a significant inter-subject correlation between these behavioral and neural measurements. Together, these findings emphasize the essential role of the thalamocortical interaction in supporting periodic visual perception and expand our understanding about the neuropathological mechanism of PD. PD did not only have slowness in the motor domain but slowness in visual perception especially in PD with visual hallucination.