Motivation in Parkinson’s disease: apathetic before you know it

Motivation is the drive that pushes people to take action and pursue goals. In Parkinson's disease (PD), a lack of motivation, known as apathy, is a common and disabling symptom. Apathy is not only seen in PD but also in conditions like Alzheimer's, stroke, and depression. In Parkinson’s, apathy tends to worsen as the disease progresses, with about 20% of patients experiencing it early on, and up to 40% in later stages. Research has shown that the loss of dopamine, a brain chemical important for movement and motivation, begins long before the visible symptoms of Parkinson’s appear. A recent study explored whether subtle changes in motivation can be detected even in the early stages of PD. The study involved patients newly diagnosed with Parkinson’s, mostly before starting any treatment. These patients were asked to perform a task where they squeezed a handle to earn money, with greater effort leading to higher rewards. The findings revealed that even early-stage PD patients showed signs of reduced motivation similar to apathy, especially when the reward was low. The degree of motivation was linked to the integrity of dopamine-producing cells in the brain, particularly in a region called the putamen. This suggests that dopamine loss might contribute to both motor symptoms like slow movement (bradykinesia) and motivational deficits like apathy, even before these issues become obvious to the patients themselves. Interestingly, the study found that the motivation to gain a reward was similar to the motivation to avoid a loss, which challenges some previous ideas about how dopamine influences motivation. This indicates that other roles of dopamine, beyond just reward prediction, might be important in understanding apathy in Parkinson’s. These insights are important for developing treatments for apathy in PD. While some patients respond to dopamine-boosting drugs, these medications can also increase impulsivity, making treatment challenging. The study highlights the need for further research into how different brain systems and chemicals contribute to motivation in Parkinson's, which could lead to better strategies for managing apathy.