The hallmark of Parkinson’s disease (PD) is its motor features, but selective cognitive impairments are evident in over 40% of patients (1). Cognitive dysfunction is now recognized as a major clinical feature of PD that contributes more to disability, caregiver strain, and diminished quality of life over the disease course than motor deficits (2-4). Cognitive deficits associated with PD arise in part from neural changes in the frontostriatal circuits, leading to executive dysfunction (5). Thus, difficulties in executive skills such as working memory, inhibition, and cognitive flexibility (or set-shifting) are some of the most prominent and early cognitive changes associated with PD (6-7). With advances in medical interventions for motor symptoms, individuals with PD are living longer and facing greater disability related to cognitive impairments. Unfortunately, pharmacological treatments for PD cognitive changes are currently limited and have not demonstrated efficacy in reducing executive functioning impairments (8). The importance of investigating non-pharmacological treatment options for cognitive dysfunction is clear.

Cognitive rehabilitation is one such behavioral technique with promising evidence to improve and maintain cognitive skills in those with PD-related cognitive impairment. This type of intervention was originally designed for traumatic brain injury but has been adapted for other neurological conditions. However, research is in its infancy and there are no standardized guidelines for treatment in PD. Cognitive rehabilitation programs generally seek to reduce functional impairment and increase engagement in activities of daily living through skills training. Calleo and colleagues (9) conducted a critical integrative review of the PD cognitive rehabilitation literature at the time and found limited evidence for effectiveness across four studies (two of which were randomized controlled trials [RCTs]) 11-12. However, the authors noted numerous potential areas of improvement for future studies, such as the need for ecologically valid outcome measures and generalizability of findings to a larger sample of PD patients. A more recent review (13) found promising benefits for cognitive functioning in mild to moderate PD across seven RCTs, a reflection of both the growing attention to cognitive rehabilitation in this population and the increasing feasibility in this population. Five RCT studies have found statistically significant improvements with moderate effect sizes of cognitive rehabilitation on executive functioning in PD (11, 14-17). While these emerging studies highlight the increasing centrality of non-pharmacological approaches in the care of PD, these findings are preliminary in nature. Participants in these studies tended to be cognitively intact, which limits our understanding of the role of cognitive rehabilitation among those who may benefit the most (i.e., PD patients with mild cognitive impairment). These studies examined a variety of cognitive domains, which limit the generalizability of treatment effects. Executive dysfunction is the most prominent cognitive change in PD, and is more strongly associated with deleterious motor and neuropsychiatric effects in PD (18); therefore, it warrants targeted attention in the development of interventions.

In addition to findings that cognitive rehabilitation may ameliorate cognitive impairment associated with PD, growing attention has been paid to the generalizability of intervention effects to neuropsychiatric symptoms. However, even less research has been conducted in these domains, and the limited findings are inconclusive. Cognitive rehabilitation appears to have a moderate effect on improving depression (11, 14-16, 19), albeit with mixed findings. Even fewer studies have explicitly assessed quality of life, also with mixed findings (11, 16). Apathy, or the reduction in goal-oriented behavior, often overlaps with depression and cognitive impairment but can be evaluated separately (20). As such, apathy is prevalent in PD and associated with poorer quality of life and increased caregiver burden (21-22). Apathy has only been assessed in one RCT(15), with no change noted by authors. Therefore, little is known about potential improvements in apathy following cognitive rehabilitation. A related construct of self-efficacy, or the expectations one has around one’s ability to successfully execute goal-directed behavior(23), has also received limited attention in the PD literature. Self-efficacy is associated with social withdrawal, depression, and diminished functional capacity in patients with Alzheimer’s disease(24). It may operate similarly to the cycle in PD, in which physical deconditioning and cognitive deficits create a loop of helplessness and poor self-efficacy as patients increasingly cease to engage in hobbies, reduce physical activity, rely on others, and feel uncertain about their future. A decrease in self-efficacy may further accelerate physical and cognitive decline. Finally, executive dysfunction and related neuropsychiatric effects of depression, apathy, and poor self-efficacy have deleterious effects on caregiver burden and quality of life(25-27). However, interventions to reduce caregiver burden and improve patient quality of life are scarce. No study to date has assessed all of these interrelated constructs, so it is unknown which of these neuropsychiatric and psychosocial factors are the most amenable to change following participation in a cognitive rehabilitation intervention.

Cognitive rehabilitation has mounting evidence as an intervention relevant for improving quality of life for people living with PD (28-29). Using Calleo and colleagues’ (9) recommendations as a foundation, we developed a novel PD group cognitive rehabilitation program to target the executive functioning impairments in PD, called the Parkinson’s disease Cognitive Rehabilitation of Executive functioning (PD-CoRE) program. We addressed limitations of previous studies by implementing ecologically valid outcome measures in our neuropsychological battery and targeting the intervention to the cognitive deficits most commonly demonstrated in PD patients (i.e., executive functions).

The aim of the current study was to evaluate the efficacy of the PD-CoRE program in building compensatory strategies to improve applied executive functioning in individuals with PD and mild cognitive impairment. Standardized neuropsychological tests and ecologically valid outcome measures were used to assess executive functions in addition to mood, apathy, self-efficacy, life satisfaction, quality of life, and caregiver burden. The goal of PD-CoRE is to teach compensatory skills that address daily struggles secondary to executive dysfunction and to break the cycle of cognitive impairment, depression, apathy, poor self-efficacy, reduced quality of life, and increased caregiver burden. With the skills learned in the PDCoRE program, the following was hypothesized: 1) Participants would perform better on objective measures of executive functioning following the group; 2) Participants would report an improvement in problem-solving and adaptive abilities in their everyday lives, improved mood, increased quality of life, and greater sense of self-efficacy; and 3) Informants would report improved adaptive and self-regulatory abilities.