Functional network dynamics underlying cognitive impairments in Parkinson’s Disease

Every day we achieve goals. Whether it be waking up and getting to work on time, navigating traffic routes safely and efficiently, or simply following a recipe to make dinner, our brain is always working toward achieving a goal. To do this well, multiple brain regions must communicate with each other clearly in “networks.” Think of an orchestra that has different sections, like strings, brass, and percussion. Each of these sections are akin to different brain regions. While each section has their own role, they must play in a coordinated way with other sections for a song to be heard correctly. Now, imagine that the percussion section is off beat; the song will not be played or heard correctly because the “network” of orchestra sections is not playing together. This metaphor represents what can happen to functional brain networks in neurological diseases, like Parkinson’s disease (PD). Instead of a song being played incorrectly, though, the way in which one thinks becomes unorganized and cognition becomes impaired. People with PD have difficulty with goal-directed thoughts, which negatively impacts their daily lives, as well as their disease progression. Unfortunately, there are few effective treatments for cognitive impairments in PD because we do not have a robust understanding of how the networks that support goal-directed thoughts and behaviors are affected in PD.

My dissertation work asks the question of how functional brain networks are associated with cognitive impairments in PD and if those networks can be changed to improve cognition. I examined these questions using brain imaging and brain stimulation techniques to study how networks support cognition in PD. Using functional magnetic resonance imaging (fMRI), I identified large-scale functional brain networks that were linked to cognition. I found that communication between brain regions in the frontal cortex and basal ganglia was related to cognitive performance in people with PD, and that connections among frontal brain networks were especially important for cognition over time. I also examined whether these brain networks function differently between females and males with PD. I found that males tended to perform worse on tasks requiring goal-directed thinking and showed weaker brain rhythms that support these processes compared to females. Finally, I tested whether it was possible to change these networks using a form of noninvasive brain stimulation called transcranial alternating current stimulation (tACS). While this stimulation technique was designed to strengthen network dynamics that support cognitive control, it did not reliably improve cognitive performance.

Together, these results show that brain networks are important for cognition in PD, but if and how they can be modified with brain stimulation to improve cognition remains unclear. I hope that these experiments will improve what we know about the brain origins of goal-directed cognition in PD and lead to the development of new treatments for cognitive impairments in PD.