It's late at night and you're watching TV when an infomercial comes on. You don't need a food dehydrator, but there's a part of you that wants it anyway. You look at your phone.
What happens next may come down to how impulsive you are. Impulsiveness is about more than shopping -- impulsive people are vulnerable to substance abuse and some forms of mental illness.
Joshua Buckholtz, a researcher at Vanderbilt University in Nashville, Tenn., thinks that the brains of impulsive people have too much dopamine. Dopamine is a chemical involved with many different brain functions, but in this case researchers are interested in drive. They believe high levels of dopamine are causing some individuals to behave rashly, perhaps by buying a food dehydrator they don't need.
To understand how dopamine could lead to impulsive behavior, Buckholtz and the Vanderbilt group looked at the midbrain, the lower-middle bit of the brain. The midbrain produces dopamine and pipes it out to other regions, where it creates the drive to get the things you want. Normally, sensors in the midbrain called autoreceptors keep dopamine at the right level.
"You can think of it as very similar to how a thermostat works," Buckholz says. In your house, the thermostat will tell your furnace to produce more heat or shut off, depending on the temperature. Similarly, the autoreceptors tell the midbrain to start pumping dopamine or stop, depending on how much of the chemical is already around.
The Vanderbilt researchers suspected that the dopamine thermostats of highly impulsive people are broken. To find out, they took 32 healthy volunteers with varying levels of impulsivity. They scanned their heads and found that on average, impulsive people had fewer thermostats. To test the idea still further, the team gave volunteers a drug that releases dopamine, then scanned their brains again.
"The people who scored highest on our trait measure of impulsivity had upwards of four times the amount of dopamine released," Buckholtz says.
But some researchers believe that there's more to impulsiveness than the dopamine thermostat. "This is not a very huge effect," says Ahmad Hariri, a professor of psychology and neuroscience at Duke University. He thinks that other brain chemicals with their own thermostats also play a role.
"I think that there is a circuitry of self-control that's fundamental to many, many aspects of living," agrees Edythe London, a psychiatrist at UCLA. London says that understanding the dopamine thermostat and others may eventually lead to treatments for addiction and attention-deficit hyperactivity disorder. Those treatments might be drugs, or they might be new therapies that reinforce the thermostats and improve their performance.
London adds that the goal isn't to get rid of impulsiveness all together. "Too much self-control thwarts creativity," she says.
The work is published this week in the journal Science.