New study provides insight into Parkinson's patients decisions

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A new Goldsmiths study shows that the association between decision-making and motor performance is preserved in people with Parkinson's disease on medication.

Stock image of someone playing the keys of a piano

Participants had to play a piano melody that they identified as being more likely to be rewarded. Yet this changed over time, so they had to adapt their learning.

The findings show that people with Parkinson’s disease in their medicated state and healthy ageing subjects can engage in complex decision-making and estimate volatile environmental changes like healthy young adults. They can then use these estimates to invigorate their motor actions, executing faster movements when they predict they are likely to be rewarded.

The research by Dr Maria Herrojo Ruiz and PhD student Margherita Tecilla from Goldsmiths Department of Psychology was published in the Journal of Neuroscience on February 22, 2023, and helps us to understand how updating beliefs about our actions leading to rewards invigorate motor behaviour.

Dr Maria Herrojo Ruiz said: “Previous studies have looked at whether people with Parkinson's and older adults can identify and adjust to changes in a task, a cognitive process called reversal learning. This involves adapting to new information and changing our actions accordingly. However, the results of these studies have been mixed. It was also unclear if individuals in these groups can use their predictions to perform actions more quickly, like younger adults can.

“Our study sheds light on these questions, showing that people with Parkinson's who are taking medication and older adults are able to infer and adapt to changing circumstances as well as healthy younger adults. Additionally, our study has found that these individuals can also dynamically adjust their movements to match their expectations, similar to what younger adults can do. This is an encouraging finding, as it suggests that medication can help to maintain some sophisticated aspects of cognitive and motor function in people with Parkinson's.”

The study investigated how people learn the reward associated with different movement sequences, using a piano melody. They also looked at how they adjust to changes in these learned associations and how their predictions speed up their motor performance. This is an effect termed motor vigour in the scientific community. In the main experiment, the research looked at a total of 94 participants across three groups, healthy younger adults (HYA), healthy older adults (HOA) and medicated Parkinson's disease (PD) patients. 

The results found that all three groups, HYA, HOA and PD, exhibited similar sensitivity of motor behaviour to reward expectations. That is, individuals in all groups executed faster movements when they predicted they were more likely to be rewarded for the movement sequence they had chosen to execute. And this speeding of performance was similar across groups, although Parkinson’s and healthy ageing were slower in general.

The study shows that when people believe that their actions will lead to a reward, they perform the movement faster. This pattern is not only observed in young participants, but also in healthy ageing and in medicated Parkinson’s Disease patients.

The significant statement reads: “Navigating a world rich in uncertainty relies on updating beliefs about the probability that our actions lead to reward. Here we investigated how inferring the action-reward contingencies in a volatile environment modulated motor vigour trial-by-trial in healthy younger and older adults, and in Parkinson’s Disease patients on medication.

“We found an association between trial-by-trial predictions about the tendency of the action-reward contingency and performance tempo, with stronger expectations speeding the movement.

“We additionally provided evidence for a similar sensitivity of performance tempo to the strength of these predictions in all groups. Thus, dynamic beliefs about the changing relationship between actions and their outcome enhanced motor vigour. This positive bias was not compromised by age or Parkinson’s disease.”

The work may also help to dispel some of the misconceptions about Parkinson's disease, such as the belief that people with the disease are unable to adapt their actions to changing circumstances.

The paper, titled ‘Modulation of Motor Vigor by Expectation of Reward Probability Trial-by-Trial Is Preserved in Healthy Ageing and Parkinson’s Disease Patients’ was published in the Journal of Neuroscience.