Apathy may be down to specific differences in the pre-motor cortex, according to the new study.
The study, led by Prof. Masud Husain and funded by The Wellcome Trust, is published in the journal Cerebral Cortex.
Though apathy is traditionally viewed as an attitude or outlook, the neuroscientists say their results suggest it is actually biology that may be to blame.
They wanted to study young, healthy people to see if there were any observable brain differences in those classed as "motivated," versus those who are apathetic.
"Many such patients can be physically capable," he says. "Yet they can become so demotivated they won't be bothered to care for themselves, even though they're not depressed."
He and his team decided to study healthy people to determine whether there were any brain differences that could underpin apathy.
For their study, a total of 40 volunteers completed a questionnaire that the researchers used to score their motivation. Then, the participants played a game where they were made offers with different reward levels and physical effort involved in winning the reward.
'Apathetic brains have to make more effort'
The researchers explain that, as predicted, the participants usually accepted the offers with high rewards and low effort. However, the low rewards requiring high effort were not accepted as often.
Next, the study participants played the game in an MRI machine while the researchers analyzed their brains.
Interestingly, although the apathetic people were less likely to accept the offers requiring a lot of effort, one brain area in particular showed more activity than in the motivated participants: the pre-motor cortex. This brain area is involved in taking actions and activates just before other brain areas that control movement do.
The brain scans revealed that in more apathetic people, the pre-motor cortex was more active when they chose to take an offer than it was in the motivated participants.
Prof. Husain explains that this was the opposite of what he and his team expected; they anticipated less activity in apathetic people since they were less likely to accept the choices requiring effort, but this was not the case.
"We thought that this might be because their brain structure is less efficient, so it's more of an effort for apathetic people to turn decisions into actions," he says, adding:
"Using our brain scanning techniques, we found that connections in the front part of the brains of apathetic people are less effective. The brain uses around a fifth of the energy you're burning each day. If it takes more energy to plan an action, it becomes more costly for apathetic people to make actions. Their brains have to make more effort."
He and his team say that to their knowledge, this is the first evidence of a biological basis for apathy. However, they add that their findings do not account for apathy in everyone, but rather, they provide more information about brain processes involved in "normal motivation."
The findings also shed light on how patients with "pathological conditions of extreme apathy" may be helped.
"These findings reveal that effort sensitivity and translations of intentions into actions might make a critical contribution to behavioral apathy," the researchers conclude.
If you are an apathetic person and have made it to the end of this article, well done. As a reward for your effort, here is an article on the scientific explanation of puppy dog eyes.