Millions of people worldwide are affected by Parkinson’s disease, which can cause movement disorders like tremor. But a different disorder known as essential tremor may impact even more people. Scientists have now discovered neurochemical signals that can differentiate between these two common movement disorders. The findings have been reported in Nature Communications.
The investigators wanted to learn more about how brain chemistry was changing during decision making. In this work, the scientists used a technique called deep brain stimulation (DBS) and applied computational tools to the results. They were able to analyze recordings that were taken with carbon fiber electrodes that were placed in the brains of Parkinson's disease and essential tremor patients. Measurements were taken as the patients played a game in which offers were accepted or rejected.
These measurements were taken in a region of the brain known as the caudate of the striatum, which is known to be related to decision making and reward processing. The game was based on offers that could be perceived as fair or unfair. The computational tools tracked how particpants' expectations were set or changed during the game, and chemical patterns were revealed that were related to each disorder.
This work revealed unique signaling patterns in the neurotransmitters dopamine and serotonin. In the essential tremor patients, dopamine levels went up and serotonin went down as a participants' expectations were contradicted. This pattern has been observed in previous studies of brain chemicals and decision making.
But this signaling pattern was not seen in Parkinson’s patients.
In Parkinson’s patients, neurons that generate dopamine begin to die off. Dopamine signaling was expected to be quite different in the different patient groups. But this study has indicated that serotonin levels were a better signal that could distinguish between essential tremor and Parkinson’s disease.
Since serotonin is not typically considered in the context of Parkinson’s, this work may open up new ways of thinking about and studying the disease.
"What surprised us was how much serotonin stood out," said co-corresponding study author William "Matt" Howe, an assistant professor at the Virginia Tech College of Science. "It wasn't just that dopamine was disrupted. It was that the normal back-and-forth between dopamine and serotonin was gone. There's neither the serotonin dip nor the dopamine rise. It's not just one system being disrupted—it's the lack of that dynamic interaction that turned out to be the clearest difference between Parkinson's and essential tremor."
"It's exciting to see that effort applied in a way that might help diagnose or stratify real clinical populations," noted co-corresponding study author Read Montague, a professor at the Virginia Tech College of Science, among many other appointments.
This study could change how Parkinson’s is studied, and may provide a foundation for many new insights.
Sources: Virginia Tech, Nature Communications
