When people with Parkinson’s disease (PD) have difficulty walking, their problem is not walking itself, it’s walking without having enough sensory information, according to a study.
People with early PD can walk as well as healthy people when they are given strong sensory information, such as horizontal lines on the floor to step over.
But when the sensory information is so weak they are forced to rely on their prior experiences, they have problems, which may explain their stooped posture and shuffling gate, the authors wrote in a news release.
“Some motor dysfunction in PD may be related to impaired cognitive processing – an impairment in combining sensory and memory information, rather than in movement, per se,” principal investigator Michele A. Basso, of the University of California, Los Angeles, said.
As reported in Current Biology, Basso and colleagues recruited 30 participants who had early-stage PD without any history of other neurological conditions, 27 age- and sex- matched healthy controls (asmHCs) and 102 young healthy controls for validation. They excluded people with dementia or depression.
Participants were not colourblind and had normal or corrected-to-normal vision. Those with PD were on medication that normalised their dopamine production without affecting their decision-making abilities. The authors tested participants with Glass pattern dots, formed by creating a dot pattern and superimposing a copy of the same pattern over the original and offsetting it. The offset creates a pattern of twin dots oriented in a specific direction.
Participants were shown a series of black-and-white and red-and-green Glass pattern dots on a monitor, with some images being more obvious than others.
In two-alternative forced choice task tests, they chose whether each pattern was oriented leftward or rightward by moving their eyes left or right or by pressing a left or right keyboard key.
An infrared camera tracked their eye movements.
Both groups performed the task well, with >90 per cent correct performance when the patterns were more obvious. But with more ambiguous patterns, the groups differed in their ability to draw from their experience with prior patterns. The asmHCs used prior information to help them decide (p<0.01) while the patients with PD did not (p>0.05).
“The common textbook notion is that PD is a movement disorder, but these data suggest that the disease impacts brain processing in a much more complicated way than simply movement initiation. This is important for clinicians to consider,” Basso said in an e-mail.
“A growing body of evidence suggests that patients with PD are impaired at learning, in particular learning about reward signals. Our results show that patients have no problem learning, but rather the problems are in combining sensory and memory signals and in performance, not learning,” she added.
Jochen Ditterich, co-investigator, of the University of California, Davis, said: “We did not necessarily anticipate these findings in detail. They provide insight into mechanisms that contribute to cognitive deficits in Parkinson’s disease. More work in this area is needed to potentially benefit patient care in the future.”