Study investigates effects of dopamine replacement therapy on cognition in patients with Parkinson's

Dopamine replacement therapy, which is used to manage motor symptoms associated with Parkinson's disease, can, at times, adversely affect cognition. Dr. Oury Monchi, Ph. D. in neuronal modeling and Head of the Neurophysiological and Neuroimaging Research theme at the Centre de recherche de l'Institut universitaire de gériatrie de Montréal (IUGM), which is affiliated with the Université de Montréal, and Dr. Penny A. MacDonald, Neurologist and postdoctoral fellow in Dr. Monchi's laboratory, have identified the reasons why within the framework of a clinical study recently published in Brain: A Journal of Neurology. This marks the second time in three months that Brain has published the results of IUGM researchers.

"The aim of our study was to understand the effects of dopamine replacement therapy on various aspects of cognition in patients with Parkinson's disease. When it comes to this particular disease, the part of the brain most affected by dopamine depletion is the striatum which is divided into several structures. In Parkinson's disease, the dorsal striatum is more severely affected than the ventral striatum, which remains relatively unaffected, at least during the first phases of the disease. We observed that while dopamine replacement therapy enhances the functions of the dorsal striatum, it is at the expense of the ventral striatum which suffers a dopamine overdose, impairing its function", states Dr. Monchi.

Until now, the effect of dopamine replacement therapy on cognition in individuals with Parkinson's disease was controversial. The purpose of this study however, was to further investigate. This led to a series of laboratory tests and neuroimaging studies that allowed researchers to clearly define the distinct cognitive functions performed by the dorsal and ventral striatum, thereby shedding some light on the issue.

"The best treatment option for managing the motor symptoms of Parkinson's disease remains dopamine replacement therapy.  In some patients however, it can have a negative effect on specific aspects of cognition. Our discovery will therefore enable us to explore different medication and non-medication based avenues that could help improve the overall health of those affected. Our findings may contribute to helping develop personalized medicine - an avenue that is currently commanding a great deal of attention", exclaims Dr. MacDonald.