US scientists have discovered that a specific group of brain cells in rats could hold the key to understanding risky decision-making in humans, as well as symptoms associated with Parkinson’s disease.
A team of researchers, led by psychiatry expert Dr Karl Deisseroth from Stanford University, used a reward-based experiment to test risky behaviour in rats and found that dopamine receptor type-2 (D2R)-expressing cells may play a crucial role in regulating decision-making. The study was published today in Nature.
In the experiment, rats were given a choice of food rewards via ‘safe’ and ‘risky’ levers that delivered different portions of food. The researchers found that by stimulating these D2 receptors, they were able to manipulate the decision-making process in the rat to make it choose the safe food option over the riskier one.
“Humans and rats have similar brain structures involved,” Deisseroth told The Guardian. “And we have found that a drug known to increase risk preference in people had the same effect on rats. So every indication is that these findings are relevant to humans.”
This breakthrough in rat neuroscience could actually help to understand impaired decision-making observed in patients with Parkinson’s disease who are prescribed a medication called Pramipexole; it has been linked to risky behaviour such as problem gambling.
“This is really exciting because it helps us to start understanding the mechanisms better,” says Dr Lyndsey Collins-Praino, a neuroscientist and Parkinson’s disease expert from the University of Adelaide.
According to Parkinson’s Australia, approximately 70,000 Australians are currently living with the neurodegenerative disease, however this number could be higher due to the difficulty of diagnosing Parkinson’s.
“One of the other things people need to know about Parkinson’s is that while we typically think of it as a motor disorder, there’s a large number of non-motor symptoms that can occur as well,” says Collins-Praino.
“One of those classes of non-motor symptoms actually affects cognitive function and decision-making, so something that we see in Parkinson’s patients is that they do tend to show more risky decision-making compared to similar elderly controls that don’t have Parkinson’s disease.”
These cognitive symptoms involve difficulty in decision-making, difficulty in maintaining attention and impaired multi-tasking ability; all of these have been linked to decline in dopamine production in the basal ganglia of the brain.
Dopamine holds the key
“Dopamine plays a really important role in Parkinson’s disease, so it’s actually loss of dopamine that leads to the emergence of motor symptoms, and in recent years we’re also learning that it can lead to cognitive symptoms,” says Collins-Praino.
According to her, Deisseroth’s findings in rats highlight the need to develop medication that not only works to increase dopamine levels in the brain, like the commonly prescribed Levodopa, but to also stimulate the D2 receptors in the decision-making regions of the brain, such as the frontal lobe.
“The treatments we currently have actually aren’t really that effective when it comes to being able to treat things like the risky decision-making, and in fact can even make it worse,” says Collins-Praino.
“One of the things that would be great to come out of this is a better understanding of what’s happening at an anatomical level when it comes to cognitive symptoms in Parkinson’s.”