This work stands apart: there is almost no one nearby, the closest neighbor is at a distance of 0.547, and there is not a single work right next to it. Thematically it adjoins research on the brain, recurrent neural networks, and synapses, but in essence it is an experimental study of motor control in humans. Around it there are already papers on how movement changes decisions, how aging takes away the body's 'steering wheel,' why a second touch feels different, why people differ in the morning and evening, how genes and environment shape adolescent behavior, how to map noise for molecular motion, why a pair of robot guides is better than one, and how rotation confuses the age of stars. Against this background, this study stands out for its direct comparison of age groups in a goal-reaching task with a monetary incentive.
The experiment involved 28 young people (18–25 years) and 28 older adults (40–81 years). They performed a task on a KINARM robotic handle: they had to move a cursor to a target on a screen. In some trials only one target appeared; in others, a distractor stimulus first appeared, which had to be ignored and the correct target awaited. Money (50 pence) was awarded for fast and accurate movements; in control trials there was no reward. The threshold for receiving the reward was adjusted to each participant's recent performance to equalize difficulty. Movements were recorded at 1000 Hz, and peak velocity, movement time, stopping accuracy, reaction time, and the proportion of correct target choices were analyzed.
Reward sped up movement execution in everyone: peak velocity increased and movement time decreased. In young people the velocity gain was 22.3 cm/s, in older adults 12.9 cm/s; the difference is statistically significant (p = 0.013). Movement time decreased by 94.6 ms in young people and by 44.4 ms in older adults (p = 0.005). Stopping accuracy did not worsen, and older adults generally stopped more accurately than young people. In trials with a distractor, reward reduced reaction time equally in both groups but lowered target selection accuracy: participants more often responded to the distractor. This shift toward speed at the expense of accuracy did not depend on age.
The work shows that aging does not blunt the response to reward as a whole but acts selectively. Unlike neighboring studies that examined either only young people or individual aspects of aging, here two components of motor control, action selection and its execution, are separated in a single experiment. It turned out that age weakens only the influence of reward on execution, but not on selection. This refines the picture of age-related changes in the reward system and the motor system.
In the future, it is worth testing how different incentive schemes (for speed, for accuracy, for both) affect selection and execution in people of different ages. One could also measure the subjective value of money for each group to understand whether that is the issue. It would be promising to use neuroimaging or pharmacological probes to test the role of dopamine in the weakened reward effect in older adults.
The results may influence the development of rehabilitation programs after stroke and other motor impairments, where motivation plays a key role. They are also important for gerontology and neuroeconomics, because they show that monetary incentives act differently on different components of behavior depending on age.
The next step is to conduct a similar experiment with patients who have had a stroke and compare their response to reward with that of healthy older adults. It is also worth checking whether the weakened reward effect in older adults persists with larger reward amounts.
In gerontology, the question remains open as to why some cognitive and motor functions decline more strongly with age than others. This work shows that sensitivity to reward in the motor domain is heterogeneous: movement execution is less responsive to incentive in older adults than action selection. This is consistent with the hypothesis of uneven aging of dopaminergic pathways, but requires direct neurobiological confirmation.
Older participants on average stopped more accurately than young ones, even when they moved more slowly. This confirms a everyday observation: with age, people more often prefer reliability over speed.
Not published on arXiv. Here are its page, the PDF and the formalization: you can check it yourself, not only read our account.