|Study participants undertaking a perceptual decision-making task to assess how healthy people and patients with Parkinson’s disease integrate memory with sensory information before making a decision must discriminate the orientation of red and green visual patterns appearing on a screen. Healthy participants were able to combine memory and sensory information to guide their decisions; patients with Parkinson’s disease failed to do so.
Images: Courtesy of Dr. Michele Basso
UCLA researchers have discovered that people with Parkinson’s disease have a form of impaired decision-making that may be a major contributor to the movement problems that characterize the disease. The finding suggests that the neurological factors underlying Parkinson’s, which affects nearly 1-million people in the U.S., may be more complex than commonly believed. The study also could pave the way for strategies to detect Parkinson’s earlier.
The UCLA-led team 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, individuals with Parkinson’s 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. But 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,” says Michele Basso, PhD, professor of psychiatry and biobehavioral sciences and neurobiology and director of the Fuster Laboratory of Cognitive Neuroscience in the Jane and Terry Semel Institute for Neuroscience and Human Behavior at UCLA. Dr. Basso notes that patients with Parkinson’s disease were impaired only when they had to rely on memory information to guide their actions.
The UCLA team conducted decision-making experiments with a dozen early-stage Parkinson’s patients and a comparison group of healthy individuals. The tasks involved making decisions about visual information that was more or less ambiguous, requiring the participants to rely 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 discovery builds on more than 15 years of work done by Dr. Basso and others and adds to a growing body of evidence that is beginning to redefine Parkinson’s as “a multisystem disease that probably involves many brain areas and neurotransmitter systems,” Dr. Basso says.
Because all of the patients in the study were in the early stage of the disease but still showed the decision-making dysfunction, Dr. Basso and her colleagues also hope to build on the discovery to identify a biological marker for early-stage Parkinson’s disease. The next steps for the UCLA team are to perform imaging experiments in healthy people and patients with Parkinson’s disease to determine the neurological factors involved in the decision-making dysfunction.
“Patients with Parkinson’s Disease Show Impaired Use of Priors in Conditions of Sensory Uncertainty,” Current Biology, June 16, 2016