Differential impact of ageing on reward driven changes in motor control

Human movement is rarely just a mechanical act; it is deeply tied to motivation. When we reach for a cup of coffee or step onto a moving walkway, our brains weigh the value of the goal against the effort required to get there. This process, known as reward processing, helps us decide how fast to move and which path to take. As people grow older, the way their brains handle these rewards changes. Scientists have long wondered if these shifts in how older adults perceive value might also change how they move. If the brain's reward system becomes less sensitive with age, it could mean that older adults do not speed up or move with the same energy when a prize is on the line, potentially affecting their ability to perform daily tasks efficiently.

To explore this, researchers brought together two groups of volunteers: twenty-eight younger adults and twenty-eight older adults. They asked everyone to perform a simple task that involved reaching for a target on a screen. The experiment was designed to look at two different parts of movement. First, they examined how people moved once they had already decided where to go, which is called action execution. Second, they looked at how people chose where to go when a distracting option appeared on the screen, which is called action selection. In some trials, the researchers offered a monetary reward for completing the task quickly and accurately, while in others, no reward was offered. This setup allowed the team to see if the promise of money changed how the participants moved and whether these changes were different for the older group compared to the younger one.

The results revealed a clear pattern in how the promise of a reward influenced movement. When money was on the line, both younger and older adults moved their hands faster and completed the reaching task in less time. Crucially, this increase in speed did not come at the cost of accuracy; neither group made more mistakes when they were trying to win the reward. However, a closer look showed that the younger adults responded more strongly to the incentive. Their movements became significantly more vigorous, meaning they gained more speed and momentum, compared to the older adults. While the older adults did move faster when rewarded, the boost in their movement energy was not as large as it was for the younger group.

The story was different when the researchers looked at how people chose their targets. When a distracting option appeared, the promise of a reward made everyone react more quickly, but it also made them slightly less accurate in picking the right target. This trade-off between speed and precision happened in both age groups, and the size of this effect was the same for younger and older adults. This finding suggests that while the aging brain may become less responsive to rewards when it comes to the physical power of a movement, the way it balances speed and accuracy during a decision remains intact. The study indicates that aging does not blunt the brain's response to rewards in a uniform way. Instead, it specifically dampens the extra energy we put into our movements when motivated, while leaving our decision-making speed and accuracy under pressure unchanged. These insights help clarify how motivation and aging interact, suggesting that future efforts to encourage movement in older adults might need to focus on different strategies than those used for younger people.