Why patients with Parkinson’s disease have problems while moving

People with Parkinson’s disease have a form of impaired decision-making which leads to the movement problems – such as difficulty in walking – that characterise the disease, scientists have found. The finding suggests that the neurological factors underlying Parkinson’s may be more complex than commonly believed. The study also could pave the way for strategies to detect Parkinson’s earlier in its course.

Researchers from the University of California, Los Angeles found that compared to healthy individuals, people with early-stage Parkinson’s have difficulty with perceptual decision-making only when the sensory information before them is weak enough that they must draw on prior experiences. When the sensory information is strong, patients are able to make decisions as well as people who are healthy.

The finding may help explain a well-known phenomenon associated with Parkinson’s, called paradoxical movement, in which people with the disease – often even while medicated with dopamine therapy – have difficulty initiating walking.

Typically, these people have a shuffling gait, along with stooped posture. However, when the same people are assisted by strong sensory information, such as horizontal lines drawn on the floor for them to step over, their walking and gait are significantly improved. “This tells us that the problem for people with Parkinson’s disease is not walking per se, but rather in generating the walking pattern without the assistance of sensory information,” said Michele Basso, a professor at UCLA. The patients with Parkinson’s disease in our study were impaired only when they had to rely on memory information to guide their actions,” said Basso.

“We believe this fundamental problem of decision-making in the absence of sufficient sensory information may be what is underlying some of the movement disorder symptoms,” she said. In making perceptual decisions, people integrate memory information with the sensory information before them.

For example, when people are contemplating crossing a street when a car is headed their way from a distance, they use past experience to help determine whether they have sufficient time to proceed safely. The researchers conducted decision-making experiments with a dozen early-stage Parkinson’s disease patients and a comparison group of healthy individuals.

The task involved making decisions about visual information that was more or less ambiguous, requiring the participants to draw on memories of similar previous experiences. In those cases, the patients with Parkinson’s disease had trouble integrating the information from memory and making a decision, even when verbally instructed by the research team. The study was published in the journal Current Biology.