The very word ‘willpower’ implies a metaphor: that actions (and inhibition of actions) are a matter of conscious will and that they require the use of a resource or source of power. What powers the will is willpower. This is a sort of folk psychology – it takes a special sort of effort to have self-control, make a decision, solve a problem or resolve conflict. People vary in how much of this special effort they can sustain and it is limited. Will is like a muscle and it can tire, but if ‘exercised’ it can become stronger. Baumeister and others investigated this view of willpower experimentally. This metaphor is supported by showing that different tasks that were thought to require willpower interfered with one another. This phenomenon was called “ego depletion”. (I find that name hints at a Freudian picture.) It also appeared that tasks associated with willpower required glucose and this might be the limited fuel. This was a nice clear picture – the metaphor was holding up. But - this is one of those metaphors that is true if you believe it. If you believe that willpower is required to do hard mental work, that it is limited and can be used up, then that is what you will find.
But then the doubts came. Job and others showed the ego depletion works only if the subject believes the theory and Clarkson and others showed that the subject had to believe that they were short of energy for sugar to be limiting. It seems that gargling sugar water is as effective swallowing it. Some people think that physical exercise depletes willpower and for them it does. Others believe that exercise is mentally invigorating and surprise, it is. This history is reviewed by Brass (see citation below).
Doubts have also been shown in the area of conscious will as opposed to decisions and other ‘will’-requiring tasks having to be conscious. So both the will and the power in willpower are now suspect.
Brass and others also outline another way to look at willpower. The brain compares the predicted reward of doing something with the predicted effort. This is what affects what people decide to do, manage to do, and manage not to do. So instead of calling it willpower, we now can call it self-control and leave the old baggage behind. People vary in what they bring to the table when making the comparison of reward to effort. That is really what is involved in some people being able to resist temptation and others not. They include different values in the assessment of reward versus effort. The interference between tasks is thought to be due to the tasks requiring the same set of brain regions, and those areas not being good at doing two things at the same time.
Interestingly, most of the tasks that are described as drawing on willpower are tasks that involve the mPFC (medial pre-frontal cortex), and in particular the ACC (anterior cingulate cortex) . … The research outlined here suggests that the mPFC, and in particular the ACC, might be a central node in the neural circuit related to willpower. From what we know about the ACC, however, it is not plausible to assume that it provides a common resource, but rather that it has a kind of regulatory function determining the level of effort that is invested in a task. In a recent position paper, Holroyd and Yeung argued that the ACC is involved in choosing between different behavioural options and determining the level of effort that is invested in executing the chosen behavioural option. This description is consistent with the idea that the ACC implements a regulatory mechanism that determines the intentional investment in a specific response option or task. Accordingly, there is strong evidence for construing willpower as a regulatory function that can be related to specific brain structures in the mPFC. While such a regulatory mechanism is evidently required in situations of self-control and complex choice, we argue that any kind of intentional decision draws to some degree on this mechanism.
I feel for the people who are gritting their teeth and trying to muster willpower as if by magic, when it is cultivating a fuller value system that might serve them better.
Brass M, Lynn MT, Demanet J, & Rigoni D (2013). Imaging volition: what the brain can tell us about the will. Experimental brain research. Experimentelle Hirnforschung. Experimentation cerebrale, 229 (3), 301-12 PMID: 23515626