The experiment, by Stanford University professor Baba Shiv was simple: collect several dozen undergraduates and divide into two groups. Give one group a two-digit number to remember and the other group a seven digit number. Instruct them to walk down the hall. In the hall give each person an option for a snack, either a slice of chocolate cake or a bowl of fruit salad.
As reported by Jonah Lehrer, whose books How We Decide and Proust Was a Neuroscientist I have sitting in my too large pile of books to read, in an article in the Wall Street Journal:
Here's where the results get weird. The students with seven digits to remember were nearly twice as likely to choose the cake as students given two digits. The reason, according to Prof. Shiv, is that those extra numbers took up valuable space in the brain—they were a "cognitive load"—making it that much harder to resist a decadent dessert. In other words, willpower is so weak, and the prefrontal cortex is so overtaxed, that all it takes is five extra bits of information before the brain starts to give in to temptation.
Everybody knows that the bicep has practical limitations: If we ask the muscle to hold too much, it will give out and drop everything on the floor. And just as our muscles get tired after a tough workout, and require a rest to recuperate, so does the poor prefrontal cortex need some time off.
I totally get this – I understand lack of will power.
There is something about this view of the brain that undermines the modern view of the mind as rational and self-controlled; that character, not nature, is why we fail in self control. The research clearly suggests otherwise.
To understand ourselves we must look beyond the rational, which is only a recent and thin overlay in our brain.
I see this in nearly every negotiation I mediate. Strong emotions appear in place of rational discourse, even when rational discourse would be more effective.
We might think of ourselves as rational beings, but the cognitive load in our frontal cortex when we are at the table trying to keep track all of the information and arguments is a lot for our brain to handle. So we become emotional; we have a hard time managing our impulses.
According to Lehrer, “This helps explain why, after a long day at the office, we’re more likely to indulge in a pint of ice cream, or eat one too many slices of leftover pizza.” Our willpower fails in large part “because the brain wasn't built for success.”