The researchers compared the effectiveness of willpower versus voluntarily restricting access to temptations, called 'precommitment'. (Examples of precommitment include avoiding purchasing unhealthy food and putting money in savings accounts with hefty withdrawal fees.) They also examined the mechanisms in the brain that play a role in precommitment to better understand why it is so effective.

Molly Crockett, who undertook the research while at the University of Cambridge and is currently a Sir Henry Wellcome Postdoctoral Fellow at UCL, said: "Our research suggests that the most effective way to beat temptations is to avoid facing them in the first place."

For the study, the researchers recruited healthy male volunteers and gave them a series of choices: they had to decide between a tempting "small reward" available immediately, or a "large reward" available after a delay. Small rewards were mildly enjoyable erotic pictures and large rewards were extremely enjoyable erotic pictures. Since erotic pictures are immediately rewarding at the time of viewing, the researchers were able to probe the mechanisms of self-control as they unfolded in real-time. (The scientists could not use money, for example, since subjects could only reap the rewards of money once they left the lab.)

For some of the choices, the small reward was continuously available, and subjects had to exert willpower to resist choosing it until the large reward became available. But for other choices, subjects were given the opportunity to precommit: before the tempting option became available, they had the ability to prevent themselves from ever encountering the temptation.

The scientists measured people's choices and brain activity as they made these decisions. They found that precommitment was a more effective self-control strategy than willpower -- subjects were more likely to get the large reward when they had the opportunity to precommit. They also found that the most impulsive people (those with the weakest willpower) benefited the most from precommitment.

The scientists were also able to identify the regions of the brain that play a role in willpower and precommitment. They found that precommitment specifically activates the frontopolar cortex, a region that is involved in thinking about the future. Additionally, when the frontopolar cortex is engaged during precommitment, it increases its communication with a region that plays an important role in willpower, the dorsolateral prefrontal cortex. By identifying the brain networks involved in willpower and precommitment, the research opens new avenues for understanding failures of self-control.

Tobias Kalenscher, co-author on the paper from University of Dusseldorf, said: "The brain data is exciting because it hints at a mechanism for how precommitment works: thinking about the future may engage frontopolar regions, which by virtue of their connections with the dorsolateral prefrontal cortex are able to guide behaviour toward precommitment."