Motivation to learn new things and engage with life declines with age due to falling activity in a brain circuit that weighs costs and benefits, a study on mice suggested.
US experts have been studying ‘striosomes’ — clusters of cells in the basal ganglia, a brain area linked to habit formation, movement control, emotion and addiction.
They team found that striosomes are key to the decision making process when dealing with ‘approach-avoidance conflict’ — when a choice has both pros and cons.
For example, one such thorny problem might be whether or not to take a new job that pays better, but would also call for a move away from family and friends.
Working with mice, the researchers found that striosomal activity is correlated to the evaluation of costs and benefits — but that this activity diminishes with age.
In a similar fashion, older mice were seen to be less motivated to engage with the experiment that forced them to deal with approach-avoidance conflict.
However, the team found that they could increase or decrease the motivation of mice in the decision-making activity by boosting or suppressing striosome activity.
In 2017, the same team found — also in rodent models — that stress can influence the performance of striosomes in decision making and lead to bad choices.
Another study published this week — which polled 917 Norwegians about their levels of passion and grit — also concluded that motivation dwindles with age.
Motivation to learn new things and engage with life declines with age due to falling activity in a brain circuit that weighs costs and benefits, a study on mice suggested (stock image)
‘As we age, it’s harder to have a get-up-and-go attitude toward things,’ said neurophysiologist Ann Graybiel of the Massachusetts Institute of Technology.
‘This get-up-and-go, or engagement, is important for our social well-being and for learning — it’s tough to learn if you aren’t attending and engaged.’
In their study, Professor Graybiel and colleagues studied striosomes activity as mice learn to make decisions involving approach-avoidance conflict — and how such brain activity changes as the rodents get older.
To create choices with both positives and drawbacks, the team played mice with two different tones — the first of which was accompanied by the release of sugar water from a spout, and the second with an unpleasantly bright light.
The mice learnt that if they licked the spout more when they heard the first tone, then they would get more sugar water — but that licking less during the second tone would result in the negative stimulus of the light being dulled slightly.
Learning what to do in each situation involves an evaluation of the values of the costs and rewards involved in a given response.
As the mice learned how to approach the experimental task, the researchers found that the striosomes exhibited higher levels of activity than any other part of the striatum — the part of the basal ganglia in which striosomes are found.
Moreover, the team noted that the activity in these cell clusters showed a correlation with the mice’s corresponding response to each of the tones — indicating that the striosomes likely play in role in the brain’s assigning of values to given outcomes.
‘In order to survive, to do whatever you are doing, you constantly need to be able to learn. You need to learn what is good for you, and what is bad for you,’ said paper author and physiologist Alexander Friedman of the University of Texas at El Paso.
‘A person, or this case a mouse, may value a reward so highly that the risk of experiencing a possible cost is overwhelmed,’ added fellow author and neuroscientist Emily Hueske of the Massachusetts Institute of Technology.
Another individual, she added, ‘may wish to avoid the cost to the exclusion of all rewards. And these may result in reward-driven learning in some and cost-driven learning in others.’
To create choices with both positives and drawbacks, the team played mice with two different tones — the first of which was accompanied by the release of sugar water from a spout, and the second with an unpleasantly bright light. The mice learnt that if they licked the spout more when they heard the first tone, then they would get more sugar water — but that licking less during the second tone would result in the negative stimulus of the light being dulled slightly
In the second part of their study, the researchers compared the striosome activity between young mice and their older counterparts — specifically, those between the ages of 13—21 months, or the equivalent of 60+ in ‘human years’.
They found that older mice were less engaged in the experimental task — and that, similarly, the activity in their striosomes was much lower than in younger mice.
A comparable reduction in motivation was also seen in a mouse model of Huntington’s disease — a neurodegenerative disorder that affects the striatum and the striosomes within.
Finally, the researchers found that they could administer genetically targeted drugs to the mice to either boost or suppress striosomal activity — and correspondingly raise or diminish the rodents’ motivation to engage in the experimental task.
US experts have been studying ‘striosomes’ — clusters of cells in the basal ganglia (pictured in red), a brain area linked to habit formation, movement control, emotion and addiction
As the mice learned how to approach the task, the researchers found that the striosomes exhibited higher levels of activity than any other part of the striatum — the part of the basal ganglia where striosomes are found. Pictured, striosomes revealed by different markers
With their initial study complete, the researchers are now working towards potential drug treatments that could help to stimulate activity in the striosomes of humans — and help give people back some of their ‘get-up-and-go’.
In a similar fashion, they added, it may be possible to train patients to enhance striosome activity by means of biofeedback.
‘If you could pinpoint a mechanism which is underlying the subjective evaluation of reward and cost, and use a modern technique that could manipulate it,’ Dr Friedman commented, ‘patients may be able to activate their circuits correctly.’
Such treatments would be relevant outside of combatting the regular effects of aging, as many mental health disorders — such as anxiety, depression and PTSD — can also serve to skew the ability to evaluate the costs and rewards of given actions.
For example, individuals with depression often undervalue potentially rewarding experiences, while those struggling with addiction can end up overvaluing drugs.
The full findings of the study were published in the journal Cell.
This post first appeared on Dailymail.co.uk