Cognition and Movement in Parkinson’s Disease
Parkinson’s disease is an incurable neurological disorder that impacts nearly 10 million people worldwide. Dr. Michele Basso, the director of the Fuster Laboratory of Cognitive Neuroscience in the Semel Institute for Neuroscience and Human Behavior at UCLA, is blazing the trail to unveil the mysteries surrounding this disease. Currently, Basso is exploring the malfunctions in the cognitive and movement pathways of patients with Parkinson’s Disease. Specifically, she is conducting research on the influence of the basal ganglia and the superior colliculus on rapid saccadic eye movements. These quick eye movements are elicited by an internal thought process, and thus are regulated by a degree of decision making. Unsurprisingly, people with Parkinson’s disease showcases abnormalities in their saccadic eye movements. Through her research, Basso aimed to verify the connection between saccadic eye movements and these two regions of the brain. By understanding the voluntary, cognitive process behind saccadic eye movements, Basso hoped to shed light on how Parkinson’s Disease impairs decision-making abilities.
Basso employed numerous test subjects and multiple experimental tests to confirm the role of the basal ganglia and superior colliculus on decision-making processes. Human subjects, those with and without Parkinson’s disease, were tested through behavioral and computation procedures. Monkeys were too experimented through these modes and were additionally administered electrophysiological tests. Finally, mice were used to explore how the desired neural circuit function through in vitro manipulations.
The superior colliculus is a structure of the midbrain the relies cortical information and additionally receives information from the basal ganglia, a deep within the cerebrum associated with voluntary motor movements. A preliminary study with monkeys showed that GABA released from the basal ganglia to the superior colliculus resulted in saccadic eye movements. Basso observed that the basal ganglia elicits saccadic eye movements that are modulated by memory. Without an electrical stimulus, monkeys could easily remember the location of an object that had previously been placed in their visual field; their memory of its position was confirmed by their saccadic eye movement to its location. However, when provided with an electric stimulus, the monkeys either showed no eye movement or movement towards the opposite direction, thereby suggesting that their memory had been impaired. The application of the electrical stimulus to the basal ganglia inhibited its function to solidify the monkey’s spatial memory.
Basso also aimed to illuminate the specific cause of decision-making impairments seen in patients with Parkinson’s disease. To test this symptom, Dr. Basso presented human test subjects with numerous computer images of dots traveling to the right or to the left. When asked to predict the orientation of the spots in an impending image, subjects without Parkinson’s disease readily coordinated their prediction with the orientation that appeared more often. However, patients with Parkinson’s disease failed to incorporate the information previously provided to them, and thus could not predict the orientation of the spots. These results suggest that the memory-construction process of the superior colliculus and the basal ganglia is impaired in people diagnosed with Parkinson’s disease. This inability to accumulate enough information to make a decision is independent of dopamine levels. Although their motor functions were improved with dopamine medication, patients still expressed malfunctions in the basal ganglia circuits and their decision-making abilities remained impaired.
Overall, Basso’s research suggests that impairments in the functions of the basal ganglia and the superior colliculus influences the decision-making impairments observed in people with Parkinson’s disease. Her research has direct clinical impact as it acts to illuminate the neurological impairments surrounding this incurable disease and propose possible treatments to ease the challenging symptoms.