Exploring the Role of Cognitive Reserve in Parkinson’s Disease Patient’s Responsiveness to Levodopa Treatment

Abstract

Parkinson’s disease (PD) is a progressive neurodegenerative disease characterised by dopamine loss. Dopamine medication as levodopa has been established to reduce PD motor symptoms and seemingly has erratic consequences for cognition. Cognitive reserve (CR), the mind’s resistance to brain damage, has been proposed to justify PD patients experiencing different impairments despite no significant neuropathological differences. Given the interaction between CR and levodopa state change is unexplored for PD, we sought to determine if CR predicts levodopa responsiveness and the role of other possible predictors. We tested six PD patient’s motor and fluid intelligence performance ON and OFF levodopa, to determine any variations in levodopa responsiveness. CR was measured with the comprehensive Cognitive Reserve Index questionnaire and a premorbid intelligence test. Motor and fluid intelligence performance was assessed with five precise measures of different abilities in ON and OFF levodopa states. Time limited data collection, meaning 80 PD patients were simulated from the six PD patients to meet regression conditions. We found CR did not significantly predict how PD patients responded to levodopa when controlling for age and levodopa equivalent dose (LED). However, LED was a significant predictor of change in motor and fluid intelligence performance, therefore acting as the most important contributing variable towards levodopa responsiveness. Age displayed a significant relationship with change in fluid intelligence performance. These findings suggest CR’s protective ability for PD was negligible when considering change in levodopa states and LED was the predominant levodopa responsiveness predictor. Implications for PD treating clinicians and patients are explored.