What’s Going On When Hard Work Seems Impossible?

Here's an unresolved question in science that might surprise you: why do thinking, planning, and calculating take effort?

While physical work requires flexing and unflexing muscles, incurring a direct calorie cost, scientists have measured the metabolic costs of hard thinking and found almost no extra calorie consumption compared to the resting brain state [1][2]. So what gives?! Why can mental work be such a chore?

In a 2016 scientific review article, "Dopamine does double duty in motivating cognitive effort," [3] researchers at Washington University in St. Louis present the hypothesis that cognitive effort is simply a matter of opportunity cost: essentially, it’s nature's jury-rigged mechanism to make us leave some mental capacity available to handle survival needs, by making us averse to sinking too much of that brainpower on extended problem-solving or repeatedly fruitless thoughts. Our ancestors may not have figured out how to protect themselves against rising floodwaters if their brains were always occupied testing better ways to weave a basket.

The article proposes an explanation of how the brain strikes a balance between aversion to effort and the competing experience of motivation—dopamine. Dopamine is popularly known as the feel-good chemical released in the brain by things like exercise, our favorite foods, and sex. But it is also a neurotransmitter that scientists have long known to be intricately involved in regulating cognitive effort. Using evidence from fine-grained experiments and advanced brain imaging techniques, the Washington University researchers lay out a theory of how dopamine works to regulate effort and motivation. Knowing how the brain works in this way may help us understand what’s going on when hard work seems impossible, and even how to make it easier.

Dopamine does “double duty” because it serves at least two key functions in the brain:

In the prefrontal cortex—the logic and planning part of the brain—dopamine directly controls our working memory.
In the midbrain—where reward and motivation centers are found—dopamine systems encode "reward functions" that tell the brain whether something is or isn't worth thinking about.

We’ll deal with each of these in order.

Dopamine in the prefrontal cortex—working memory

In the prefrontal cortex, dopamine signalling acts like knobs on a control panel to our working memory. There’s a steady background level of dopamine in this region, called “dopamine tone,” which increases when we need to maintain more information in our working memory, and decreases when it’s time to get rid of some.

Dopamine can also toggle the prefrontal cortex into a state that allows us to quickly swap new information into working memory. This “phasic dopamine,” which comes in sharp bursts, shows up when we’re done with the current contents of our working memory, helping us to erase it so that new information can replace it.

These two phenomena are all-or-nothing and affect the entire working memory at once, but there is also evidence of a more fine-grained mechanism for dopamine to affect the contents of working memory in a more structured way. This would mean dopamine is involved in keeping the relevant information at the top of your mind and selectively letting no-longer-relevant information go: for example, when you are totalling a bill, you need to figure and remember the sum of the first two prices, and then the sum of that with the third price, and so on, but you can forget the sum of the first two as soon as you’ve figured the following sum.