Motor Symptoms in Parkinson’s Traced in Study to Problems with Complex Decisions

Poor decision-making processes — common enough among patients with Parkinson’s disease — may contribute to the movement difficulties that characterize the disease, a view that redefines Parkinson’s as more than a movement disorder. The findings may also lead to new discoveries of early disease markers, improving chances of halting brain degeneration at an early stage.

Perceptual decisions are often a mix between available sensory information and previous experiences. Determining if there is enough time to cross the street when you see a car approaching might be easy if the car is close. But if a person spots the car at a distance, stored memories of earlier crossings integrate with the new sensory information, to  interpret the car’s speed and estimate the safety of a crossing.

Exploring how people with early stage Parkinson’s disease approach decisions, a research team at the University of California, Los Angeles discovered that perceptual decision-making is only problematic for patients when the sensory information is weak and previous experiences need to be part of forming a decision.

Both patients and healthy controls in the study had to make decisions based on visual information that varied in its degrees of ambiguity. Findings demonstrated that when patients had to rely on their memory, they had a hard time integrating memory and visual information, and a tough time making decisions, even when researchers verbally instructed them.

But when these same patients were exposed to situations where the sensory information was strong, they arrived at decisions as easily as healthy people. The study, Patients with Parkinson’s Disease Show Impaired Use of Priors in Conditions of Sensory Uncertainty,” was published in the journal Current Biology.

Drawing parallels between decision-making and movement, scientists realized their findings might explain why patients with Parkinson’s find it so difficult to initiate movement, even when treated with dopamine-increasing drugs. When assisted by strong sensory information, such as horizontal lines on the floor that a patient can follow, problems in initiating movement are less severe, with less shuffling and better gait.

“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,” Michele Basso, the study’s senior author and a professor at UCLA’s Semel Institute for Neuroscience and Human Behavior, said in a news release.

“The patients with Parkinson’s disease in our study were impaired only when they had to rely on memory information to guide their actions. 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,” said Basso.

These findings contribute to a view — growing in popularity — that Parkinson’s disease is not merely a movement disorder.

“Parkinson’s disease has long been seen as purely a motor problem, limited mostly to a section of the brain called the basal ganglia and a neurotransmitter called dopamine that is not produced at sufficient levels,” Basso said.

“The field is realizing that Parkinson’s disease is a multisystem disease that probably involves many brain areas and neurotransmitter systems,” she said. “Our finding suggests that the dysfunction we uncovered may actually be unrelated to dopamine. New efforts by us and others are geared at finding out which other brain areas and neurotransmitters are involved, and how.”

Basso and her team noted that impaired decision-making was not helped by dopamine medication. They also highlighted that all the patients studied were in early disease stages, indicating there might be other biological markers of early stage disease, not related to disrupted dopamine signaling.

The research team now hopes to identify such factors — a discovery that promises to be a huge step forward for early treatment, given that once people become symptomatic, the brain has already suffered substantial damage.

As a part of this process, the researchers will now repeat the decision-making experiments while scanning the brains of both patients and healthy controls to identify factors involved in impaired decision-making processes.