The effects of sequence structure, age-related impairments, and Parkinson's disease on motor sequence learning

Abstract

Parkinson’s disease (PD) is a neurodegenerative movement disorder that affects over one million individuals in the US with approximately 60,000 new diagnoses every year. While characterized as a movement disorder, the effect of PD and aging on learning new motor skills has yielded equivocal results. Thus, the broad objective of this dissertation is to investigate the influence of PD on motor sequence learning. We begin by examining different sequence structures and how they are affected by age before investigating the effects of PD. To address the inadequacies of previous studies using fixed order sequences, we used probabilistic sequences, in which stimuli are linked by statistical associations. The first study directly compared the learning of probabilistic sequences to fixed sequences and randomly ordered stimuli in typical young adults (18-23 years) using a modified serial reaction time (SRT) paradigm. The results suggest that both fixed and probabilistic sequence groups exhibited learning, but the underlying learning processes were different in employing online and offline learning strategies. In the second and third studies, electroencephalography (EEG) was recorded from typical young adults (18-23 years), typically aging adults (55-75 years), and patients with PD (55-75 years) while they performed the same modified SRT task. We characterized the developmental landscape of 55-75 year old adults and found that cluster analysis separated typically aging adults into groups that provided a clearer understanding of their impairments. By unraveling movement and cognitive deficits and matching participants based on functional characteristics, we found that some typically aging adults and those with PD learned the fixed sequence, but not the probabilistic sequence, indicating age-related impairments in probabilistic motor sequence learning. We found cortical activations indicative of learning, even in the absence of behavioral indications suggesting that some adults may require more practice to learn the sequence, and possible compensatory mechanisms in patients with PD. Novel applications of these techniques prove effective for a deeper understanding of the dynamic motor learning process and provide evidence that impairments observed in patients with PD may be related more to the aging process than to Parkinson’s disease.