The role of dopamine in the brain – lessons learned from Parkinson’s disease

Authors: David Meder et al. (2019)

Link: https://www.sciencedirect.com/science/article/pii/S1053811918320925

Background Information:

Parkinson’s disease (PD) is a progressive neurological condition marked by tremors, slowness of movement (bradykinesia), stiffness, and balance problems. These symptoms occur when dopamine-producing neurons in the brain's substantia nigra die off—or stop working properly—leading to lower dopamine levels. Dopamine plays a key role in controlling movement, cognitive flexibility, and learning from rewards and punishment. Scientists use functional MRI (fMRI) to study how dopamine loss impacts brain function, aiming to understand the brain circuits involved and how treatments might help.

Purpose of the Study:

The authors wanted to summarize what fMRI studies have revealed about dopamine’s role in motor control and cognition in people with Parkinson’s. They aimed to tie specific brain activation and connectivity patterns—captured during movement and cognitive tests—to the underlying dopamine deficiency, patients’ medication status, genetic background, and real performance. This integration helps clarify how dopamine affects brain behavior and informs better therapeutic strategies.

Methods and Data Analysis:

This was a literature review: no new experiments were conducted. Instead, the authors carefully examined a wide range of studies combining fMRI with dopamine medication status and task performance in PD patients. These studies looked at brain activation during movement and cognitive tasks, as well as brain network connectivity. They also analyzed how dopamine medication (e.g., levodopa) alters fMRI signals, mapped changes in brain wave patterns, and explored non-linear relationships between dopamine levels and cognitive performance.

Key Findings and Conclusions:

fMRI studies reveal that dopamine is essential for generating movement vigor—its lack causes sluggish motion—and for controlling excessive involuntary movements (dyskinesia). Changes in activation and connectivity were seen across the putamen, premotor cortex, motor cortex, and the right inferior frontal gyrus. Cognitive flexibility showed a U-shaped relationship with dopamine: both too little and too much dopamine impair performance, meaning the right balance is critical. Dopamine also deeply influences how the brain processes rewards and punishments, which affects learning. These findings highlight that dopamine isn’t just a 'chemical—disease' but influences complex brain circuits.

Applications & Limitations:

Understanding dopamine’s role in specific brain connections helps explain why treatments like levodopa and deep brain stimulation (DBS) help—but also why they can cause side effects such as dyskinesia. The insights suggest that future therapies may need to monitor and dynamically adjust brain activity (e.g., via adaptive DBS) to achieve better outcomes. However, challenges remain: fMRI findings can be hard to interpret due to variables like disease stage, medication effects, and individual differences. Many studies have small sample sizes and complex interactions, so applying these insights clinically takes further research and refinement.