SAN DIEGO -- A pilot study by a multi-disciplinary team of investigators at Georgetown University suggests that a simple dot test could help doctors gauge the extent of dopamine loss in individuals with Parkinson's disease (PD). Their study is being presented at Neuroscience 2013, the annual meeting of the Society for Neuroscience.
"It is very difficult now to assess the extent of dopamine loss -- a hallmark of Parkinson's disease -- in people with the disease," says lead author Katherine R. Gamble, a psychology PhD student 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," she adds.
Gamble works in the Cognitive Aging Laboratory, led by the study's senior investigator, Darlene Howard, PhD, Davis Family Distinguished Professor in the department of psychology and member of the Georgetown Center for Brain Plasticity and Recovery.
The TLT tests implicit learning, a type of learning that occurs without awareness or intent, which relies on the caudate nucleus, an area of the brain affected by loss of dopamine.
The test is a sequential learning task that does not require complex motor skills, which tend to decline in people with PD. In the TLT, participants see four open circles, see two red dots appear, and are asked to respond when they see a green dot appear. Unbeknownst to them, the location of the first red dot predicts the location of the green target. Participants learn implicitly where the green target will appear, and they become faster and more accurate in their responses.
Previous studies have shown that the caudate region in the brain underlies implicit learning. In the study, PD participants implicitly learned the dot pattern with training, but a loss of dopamine appears to negatively impact that learning compared to healthy older adults.
"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," says Gamble.
In this study of 27 people with PD, the research team is now testing how implicit learning may differ by different PD stages and 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," explains Steven E. Lo, MD, associate professor of neurology at Georgetown University Medical Center, and a co-author of the study.
They hope the TLT may one day be a tool to help determine levels of dopamine loss in PD.
In addition to Gamble, Howard and Lo other authors of the study include Thomas J. Cummings Jr., MD, assistant professor of psychiatry at Georgetown University Medical Center (GUMC) and James H. Howard Jr., PhD, an adjunct professor of neurology at GUMC.
The study was supported by National Institutes of Health grant RO1AG036863. The authors report having no personal financial interests related to the study.
About the Center for Brain Plasticity and Recovery
The Center for Brain Plasticity and Recovery, a Georgetown University and MedStar National Rehabilitation Network collaboration, focuses on the study of biological processes underlying the brain's ability to learn, develop, and recover from injury. Through interdisciplinary laboratory and clinical research, the Center for Brain Plasticity and Recovery aims to find ways to restore cognitive, sensory, and motor function caused by neurological damage and disease.
About Georgetown University Medical Center
Georgetown University Medical Center is an internationally recognized academic medical center with a three-part mission of research, teaching and patient care (through MedStar Health). GUMC's mission is carried out with a strong emphasis on public service and a dedication to the Catholic, Jesuit principle of cura personalis - or "care of the whole person." The Medical Center includes the School of Medicine and the School of Nursing & Health Studies, both nationally ranked; Georgetown Lombardi Comprehensive Cancer Center, designated as a comprehensive cancer center by the National Cancer Institute; and the Biomedical Graduate Research Organization (BGRO), which accounts for the majority of externally funded research at GUMC including a Clinical and Translational Science Award from the National Institutes of Health.