Parkinson disease (PD) noticeably impacts motor function but can also impact cognition. Cognitive problems can include difficulty with psychomotor function, cognitive slowing, set-shifting and multi-tasking, working memory, and forgetfulness. However, with neuroplasticity mechanisms (the ability for brain cells to form new connections and strengthen existing ones based on experience), habitual exercise may be able to blunt cognitive decline. Recently, researchers have begun exploring exercise effects on cognition in PD, and they are cautiously optimistic about the findings.
A recent review considered six pre-clinical studies in rodent models of PD (Murray, Sacheli, Eng, & Stoessl, 2014). The results revealed some positive effects of exercise on cognition in these rodents, specifically improving long term memory, motor learning, and short term social memory. Along with these behavioral changes were neurobiological changes including upregulation of the important neurotrophic factors, BDNF, and GDNF in the basal ganglia, and increased dopamine in the basal ganglia. These findings are in line with three proposed mechanisms of improved cognition via exercise specifically for individuals with PD: (1) enhanced availability of dopamine (DA) projections to the striatum; (2) increased neurotrophic factor availability; and/or (3) decreased neuro-inflammation in the basal ganglia.
Probably the strongest evidence to suggest the benefits of exercise for cognition in PD were produced by Uc et al., (2014), who demonstrated that 6 months (thrice weekly) of an aerobic walking program in 60 independently ambulatory individuals with PD led to improvements in gait speed and motor aspects of disease severity. Importantly, the researchers also observed improvement in resistance to interference, as measured by the flanker task- a test which examines the ability to suppress responses that are inappropriate in a given context (Uc et al., 2014).
Other researchers have demonstrated the motor and cognitive effects of dance exercise. McKee and Hackney (2013) demonstrated that, in addition to motor improvements, 30 hours of adapted tango over 12 weeks improved spatial cognition (as measured with the mental imagery, Brooks task) in individuals with mild-moderate PD (McKee & Hackney, 2013). Tango could be considered light-moderate exercise. Participants are stepping at 60-120 beats/minute (tempi of tango music) and expending at least 3 Metabolic Equivalent of Task (METs) per minute (Heyward, 2010). Further, the dose of exercise in this study—30 hours over 10-12 weeks— exceeds weekly exercise dosage recommendations for deconditioned older adults with chronic illness (Chodzko-Zajko et al., 2009), which may have contributed to cognitive and motor improvements. Thus, cognitive gains noted in the adapted tango group occurred because aerobic exercise has beneficial effects upon cognition (Kraft, 2012; Ratey & Loehr, 2011). Notably, the researchers in this study ruled out partnered/social learning and interaction as being responsible for gains. A within-group improvement of Tango participants in global cognitive function, as measured by the Montreal Cognitive Assessment (MoCA), represented only a small absolute change, but this change in the adapted tango group’s scores represented moving from a diagnosis of MCI (<26 points) to normal cognition (>26 points) (Nasreddine et al., 2005).
Several other studies have examined the benefits of exercise for those with PD on various aspects of cognition. Six months of generalized moderate-intensity, multimodal physical training (consisting of aerobic, resistance, coordination and balance elements) led to improvements in abstraction and mental flexibility as measured by the Wisconsin Card Sorting Task in 10 older individuals with PD in comparison to a non-exercising control group (Tanaka et al., 2009). Fifteen individuals with PD who participated in programs of anabolic and aerobic exercise two times weekly for 12 weeks showed improvements in verbal fluency (Cruise et al., 2011). Low intensity passive cycling on a tandem bike, in a ‘forced exercise’ situation one time per week over 4 weeks has led to improvements by 19 people with PD on the Trails Making Test A&B, a task-switching executive function measure (Ridgel, Kim, Fickes, Muller, & Alberts, 2011). Dos Santos Mendes et al. (2012) assigned 16 individuals with early PD to Wii Fit training, to evaluate the motor and cognitive demands of the games on people with PD, in comparison to 11 healthy older adults. Compared to healthy controls, those with PD demonstrated learning deficits on three of the ten games. Importantly, the PD cohort was able to transfer motor ability gained from the games to a similar, but untrained task (dos Santos Mendes et al., 2012). Muller and Muhlack (2010) investigated the effects of a single session of high-intensity endurance aerobic exercise (heart rate-targeted cycling) or rest following L-dopa administration on reaction time, and complex movement sequence ability in 22 individuals with PD in a crossover design. Participants improved on reaction time, tapping rate and peg insertion interval time after exercise, whereas they gave fewer correct answers after rest, and reaction time increased after rest (Muller & Muhlack, 2010).
These recent studies are encouraging and provide preliminary evidence that supports the effects of exercise on a variety of aspects of cognition for those with PD. The findings by Uc et al. are especially encouraging because they agree with research supporting the beneficial effects of aerobic exercise on cognition in older adults; however these findings must be replicated in larger clinical trials.
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