Seat of Temptation Found in the Brain

By Rachael Rettner, LiveScience Staff Writer

posted: 28 March 2010 02:52 pm ET


Whenever you save money instead of splurging at the mall, or opt for the gym over a relaxing evening on the couch, you might want to thank a region of your brain just above the left ear. This brain area could be responsible for the human ability to resist temptation and wait around to reap rewards, a new study finds.

The results show that when this brain region, called the left lateral prefrontal cortex, is impaired, people are more likely to choose immediate yet smaller rewards over larger rewards that won't come until later.

The findings might one day help researchers to better understand psychiatric disorders like substance abuse and gambling, since alcoholics and gamblers are thought to have problems withstanding the pull of their drug of choice.

And the results could explain why children, adolescents, and even young adults are so impulsive and often give in to temptation, the researchers say.

"The lateral prefrontal cortex really is one of the last brain structures to mature; it matures rather late during puberty and even during adolescence and into young adulthood," said study researcher Bernd Figner of Columbia University in New York. "So this can help explain why adolescents and young adults often seem to have a hard time delaying gratification."

Brain buzzes

To understand more about how we decide whether to resist temptations, Figner and his colleagues enrolled 52 college-aged men to participant in a brain stimulation experiment.

The subjects had short magnet pulses applied to specific regions of their brain, a technique called "transcranial magnetic stimulation," or TMS. The stimulations come from a coil placed on the subjects' head, so the technique is not invasive, and the effect is only temporary.

The subjects received stimulations to either their left or right prefrontal cortex, or they received a "sham stimulation" that wasn’t real.

To resist or not

After brain stimulations, the participants completed several tasks involving choices, answering questions like "Would you prefer $20 dollars today or $30 in two weeks?"

Those who received stimulations to their left lateral prefrontal cortex more often chose the sooner, smaller rewards compared with those who received stimulations to the right prefrontal cortex or the control group. However, if both choices were in the future ($20 in two week vs. $30 in four weeks), there was no real difference between the groups.

This suggests the effect was very specific, and only comes into play when subjects have to exert self-control to resist the tempting, immediate rewards, Figner said.

Once scientists understand the brain mechanisms underlying this type of self-control, they could design interventions to help people make more optimal decisions in the long-term, Figner said.

However, more studies are needed in people of all ages, he added.