Effects of Exercise and Cognitive Training on Executive Function in Parkinson's Disease

Parkinson's Disease (PD) is recognized as both a motor and nonmotor disorder. Gait and mobility impairments are often associated with a decline of cognitive function, particularly executive function (EF), among other non-motor signs. EF is a broad category of cognitive functions that is generally defined as those processes necessary for purposeful, goal-directed behavior and supervision of ongoing cognitive processes. Deficits in EF are frequently seen early in PD4 and progress with time, often resulting in disruption of daily activities. People with PD are often impaired in real life situations in which more than one activity needs to be performed at a time. Dual tasking (DT) is defined as the performance of two different tasks simultaneously, commonly a gait plus a cognitive task. This study investigates the interaction of motor (gait) and non-motor (cognitive) impairments in PD. Studies of DT suggest that reciprocal interactions exist between gait and mental functions that are fundamental to the performance of daily activities. Therefore, the model of DT encompasses 2 major areas of PD-related impairment in a single outcome measure that is highly correlated with daily function.

Performance on DT generally results in degradation of gait and/or cognitive performance. The investigators' pilot study in 125 people with PD has shown significant DT interference producing a 22% decline in gait velocity. This demonstrates deterioration of gait performance when subjects allocate attention to the cognitive task. Importantly, deficits on DT correlates with in problems in daily function, especially instrumental activities of daily living (IADLs), and is associated with increased risk of falling and driving impairment. Similarly, the investigators' pilot data in patients with moderate stage PD shows that deficits in DT performance are associated with poor IADL performance. Although cognitive deficits contribute to disability in PD, there are no treatments that effectively address this problem, and no studies have systematically investigated the potential benefits of rehabilitation strategies to improve cognitive function and related disability in this population.

Emerging evidence suggests the potential of physical exercise and cognitive training to improve cognitive function in healthy elderly and individuals with chronic neurologic conditions. A Cochrane meta-analysis on the cognitive effects of aerobic exercise in older adults has shown that improvement of peak VO2 levels by a mean of 14% (range 5-20%) was associated with improvement in cognitive function, particularly EF domains including speed of motor processing and attention. These are the same EF domains in which deficits commonly occur in PD. Pilot data from the investigators' Baltimore VA study show that the investigators can reproduce similar gains in cardiopulmonary fitness in PD, as reported in the Cochrane review, with a 3-month aerobic exercise program. The investigators' group has also reported improvement of selected EF domains (attention and speed of processing) following 2 months of aerobic exercise in stroke patients12. Cognitive training is another potential rehabilitation modality to improve cognitive function. Recent studies in numerous neurological conditions and healthy older adults show that cognitive training improves cognition, with EF most likely to respond among all cognitive domains.

In this project, the investigators are comparing the effectiveness of a treadmill aerobic exercise program (TAEX) versus a cognitive training program (TCOG) versus the combination of TAEX + TCOG for improving EF, DT performance and IADLs in the investigators' sample of Veterans and others with PD.

The investigators' fundamental hypothesis is that 3 months of combined TAEX+TCOG will be most effective in improving EF, DT performance, and IADLs, compared to either regimen alone.