“It is very difficult now to assess the extent of dopamine loss — a hallmark of Parkinson’s disease — in people with the disease,” said lead author Katherine R. Gamble, a psychology Ph.D. student at Georgetown University, who is working with two Georgetown psychologists, a psychiatrist and a neurologist.
“Use of this test, called the Triplets Learning Task (TLT), may provide some help for physicians who treat people with Parkinson’s disease, but we still have much work to do to better understand its utility.”
The TLT tests implicit learning, a type of learning that occurs without awareness or intent. Implicit learning relies on the caudate nucleus, an area of the brain affected by loss of dopamine, the researcher explains.
The test is a sequential learning task that does not require complex motor skills, which tend to decline in people with Parkinson’s disease (PD), she added.
During the test, participants see four open circles, then see two red dots appear. They are then asked to respond when they see a green dot appear.
Unknown to them is that the location of the first red dot predicts the location of the green dot. Participants learn implicitly where the green dot will appear, making them faster and more accurate in their responses, the researcher explains.
Previous studies have shown that the caudate region in the brain underlies implicit learning.
In the latest study, 27 participants with Parkinson’s implicitly learned the dot pattern with training, but a loss of dopamine appeared to negatively impact that learning compared to healthy older adults, the researcher noted.
“Their performance began to decline toward the end of training, suggesting that people with Parkinson’s disease lack the neural resources in the caudate, such as dopamine, to complete the learning task,” she said.
The research team is now testing how implicit learning may differ in different stages of the disease and with different drug doses.
“This work is important in that it may be a non-invasive way to evaluate the level of dopamine deficiency in PD patients, and which may lead to future ways to improve clinical treatment of PD patients,” said Steven E. Lo, M.D., associate professor of neurology at Georgetown University Medical Center, and a co-author of the study.
The study is being presented at Neuroscience 2013, the annual meeting of the Society for Neuroscience.