People often find it harder to adapt to new situations as they age and now a new mouse study may have shed light on why.

Key points: A circuit involving neurones in a part of the brain called the striatum deteriorates with age

A circuit involving neurones in a part of the brain called the striatum deteriorates with age Decreased activity in this circuit reduces ability to develop new strategies to meet goals

Decreased activity in this circuit reduces ability to develop new strategies to meet goals Keeping brain active key to healthy ageing

A study published today in the journal Neuron has described, for the first time, how activity in a key brain circuit that allows mammals to adapt to change fades with age.

The circuit is critical to developing new strategies to meet goals, said senior author Dr J. Bertran-Gonzalez, a neuroscientist at the Queensland Brain Institute

He and colleagues hypothesised that older mammals find it harder to adapt because of natural deterioration in this brain circuit involving neurones in the striatum, which is located in the brain's core.

To test their ideas, Dr Bertran-Gonzalez and colleagues set up an experiment in which mice were trained to press levers to obtain food pellets.

One lever gave them access to grain-tasting pellets, while the other gave them access to sweet pellets.

After training, the animals were then given just one type of pellet to eat, before again being given a choice of pellets.

Because mice prefer variety in their diet, after having gorged on one type of pellet they chose the lever that would give them the other type of pellet.

But then the researchers switched the levers so the lever that used to deliver grain-flavoured pellets now delivered sweet pellets and vice versa.

The younger mice in the group quickly learned which lever to press to get the pellets they wanted, but the older mice repeatedly pressed both levers, apparently confused about what to do.

Further experiments showed the brains of the older mice had less activity in the neurones of the striatum previously identified as being critical to the ability to adapt.

Finally, the study found that young mice in which this brain circuit had been deactivated, were just as confused as the older normal mice when the levers were switched.

This confirmed that deterioration in the striatum circuit was responsible for a failure to adapt to change.

Older people 'have difficulty adapting to change'

The striatum is a very ancient part of the brain that is common to all mammals, so the findings could help explain problems with adapting in older humans, Dr Bertran-Gonzalez said.

For example, when a person experiences a big change in life such as acquiring a disability or moving home they must change the way they meet everyday goals.

He said evidence shows that, on average, younger people find it easier than older people to cope with such change by finding new ways of acting to achieve goals.

But if older people stop trying to adapt they run the risk of becoming apathetic, which has been shown in some cases to precede cognitive decline and dementia.

"When an aged person is apathetic, their goal-directed action is reduced to zero," said Dr Bertran-Gonzalez. "They simply do not fulfil any goals anymore.

"There is more and more evidence showing the brain is similar to a muscle. The more you work it the more it responds."