Research Grant - 2019

Project Summary:

We all hope to live independently, for as long as possible. This functional independence requires a form of motor learning called sensorimotor adaptation, which is the capacity to adapt movement to change. For example, problems adapting to changes in the body (e.g., arthritis) or in the environment (e.g., walking onto a slippery floor, manoeuvring obstacles, etc) increases risk of falls. Falls are common and costly: in Australia, a third of community-dwelling older adults (>65 years old) fall at least once a year, with many falls resulting in hospitalization (>100,000 hospitalizations in 2014–15). Unfortunately, sensorimotor adaptation is impaired in older adulthood), even pre-retirement. Why does ageing impair sensorimotor adaptation?

One likely culprit is the profound degeneration of our dopaminergic system. In older adulthood, we lose up to 50% of our dopamine neurons in the substantia nigra/ventral tegmental area. Every decade after age 20, we lose 5-10% of our dopamine receptors and transporters. This project directly tests the idea that deficient dopamine neurotransmission with ageing impairs multiple components of sensorimotor adaptation. Our approach is two-pronged. First, we pharmacologically manipulate dopamine in older adults. Second, we leverage state-of-the-art methods of experimentally dissociating the multiple components of adaptation. Our approach will elucidate the role of dopamine in sensorimotor adaptation, a crucial step towards forming a comprehensive framework of the neural mechanisms that underpin age-related declines in sensorimotor adaptation. More importantly, our work will test the feasibility of remediating age-related decline of sensorimotor adaptation through pharmacological means. Increasing evidence from animal and human clinical studies suggest that dopamine pharmacotherapy can improve outcomes in movement rehabilitation, however, how dopamine pharmacotherapy improves rehabilitation is unknown. This work will fill this knowledge gap by testing how dopamine pharmacotherapy affects the multiple components of sensorimotor adaptation, which forms the basis of many forms of movement rehabilitation.

Outcomes:

Due to the lockdown and the coronavirus pandemic, we were unable to commence testing on vulnerable older adult populations, as the University of Queensland increased its COVID-19 risk reduction procedures to protect older Australians. However, we are currently recruiting older adults from our collaborator Prof Paul Dux’s lab, who has dopamine genotype information for their participants (COMT/BDNF) from their recently published work (Horne et al., 2020, Nature Human Behaviour). The capacity to share the genotype data promises to increase the explanatory power of our study dopamine manipulations, as previous work has shown that effects of dopamine manipulations depend on dopamine genotype (Furman et al., 2020)

In absence of data collection in older adults, we completed data collection in young adults, where we found that pharmacological manipulation of dopamine modulated movement vigor in implementing effortful strategies in motor learning. Specifically, dopamine manipulation slowed reaction times and peak velocities when participants engaged in cognitively effortful movement strategies. This idea is consistent with the extant literature demonstrating that dopamine plays an essential role in modulating the decision to engage effort (Walton & Bouret, 2019).

Here, we show that pharmacological manipulation of dopamine altered movement vigor in the use of effortful strategies. This work has implications for motor learning in older adults (e.g., within leisure or rehabilitation settings), where age-related decrements in dopamine function might reduce the vigor with which older adults choose to engage physically or mentally effortful processes in motor learning. It remains to be seen if the results shown in young adults will generalise to that in older adults.

Outcomes submitted October 2020.