University of Arizona researchers have revealed new insights into one of the most common complications faced by Parkinson's disease patients: uncontrollable movements that develop after years of treatment.
Parkinson's disease – a neurological disorder of the brain that affects a person's movement – develops when the level of dopamine, a chemical in the brain that's responsible for bodily movements, begins to dwindle. To counter the loss of dopamine, a drug called levodopa is administered and later gets converted into dopamine in the brain. However, long-term treatment with levodopa induces involuntary and uncontrollable movements known as levodopa-induced dyskinesia.
A study published in the journal Brain has uncovered new findings about the nature of levodopa-induced dyskinesia and how ketamine, an anesthetic, can help address the challenging condition.
Over the years, the brain of a Parkinson's patient adapts to the levodopa treatment, which is why levodopa causes dyskinesia in the long term, said Abhilasha Vishwanath, the study's lead author and a postdoctoral research associate in the U of A Department of Psychology.
In the new study, the research team found that the motor cortex – the brain region responsible for controlling movement – becomes essentially "disconnected" during dyskinetic episodes. This finding challenges the prevailing view that the motor cortex actively generates these uncontrollable movements.
Because of the disconnect between motor cortical activity and these uncontrollable movements, there's probably not a direct link, but rather an indirect way in which these movements are being generated, Vishwanath said.
The researchers recorded activity from thousands of neurons in the motor cortex.
"There are about 80 billion neurons in the brain, and they hardly shut up at any point. So, there are a lot of interactions between these cells that are ongoing all the time," Vishwanath said.
The research group found that these neurons' firing patterns showed little correlation with the dyskinetic movements, suggesting a fundamental disconnection rather than direct causation.
"It's like an orchestra where the conductor goes on vacation," said Stephen Cowen, senior author of the study and an associate professor in the Department of Psychology.