University of Wisconsin-Madison researchers have discovered that the same brain pathways involved in rewarding addictive drug use appear to reward compulsive running behavior.
The researchers studied changes in brain activity in two groups of rodents: typical laboratory mice and a special breed of mice selected over 29 generations for their affinity for voluntary wheel running.
"All mice run on wheels, and, therefore, have a motivation to run," says Justin Rhodes, a postdoctoral fellow at Oregon Health & Science University who completed the study while a graduate student at UW-Madison. But he adds that the specially bred mice have a genetic predisposition to run longer distances.
"They represent those few extreme individuals in the population with an intense desire or compulsion to run," he says.
To understand what drives these mice to run faster and farther than the average mouse, Rhodes and his colleagues at UW-Madison designed a study to measure changes in brain activity when both groups of mice were granted or denied access to the running wheel. For six days, they let all mice run as long as they wanted, and they recorded their distances. By and large, the high wheel running mice, compared to the other group, covered more ground in the same amount of time on their spinning treadmills. On the sixth day, for example, these mice averaged about six miles, compared to about two miles among the controls.
On the seventh day, the researchers blocked half the mice in each group from the wheel while giving free access to the other half. Five hours later, when the mice usually reach their running peak, the researchers compared brain activity in each mouse by measuring levels of Fos, a gene that's expressed in response to neuronal excitement.
"We thought we'd see more activity in the mice doing the running, but that's not what we saw at all," says Stephen Gammie, assistant professor of zoology at UW-Madison and senior author of the recent paper.
Instead, Gammie, Rhodes and their Wisconsin colleague Theodore Garland, Jr., (now at the University of California, Riverside) found that all the mice denied access showed higher levels of neuronal stimulation in 16 out of 25 brain regions.
Stimulation was even greater in mice that typically ran longer distances, showing a correlation between brain activity levels and average amount of wheel running.
"In the high-running mice, certain brain regions displayed extremely high levels of activity, more than normal," says Rhodes. "These were the same brain regions that become activated when you prevent rats from getting their daily fix of cocaine, morphine, alcohol or nicotine."
The researchers explain that blocking the running behavior in the mice bred to do more voluntary wheel spinning triggers a neuronal response - activation of brain regions involved in reward circuitry - that drives them to run. Explains Gammie, "These mice have run for six days. They want to run, and they're ready to run, but they can't. Change in brain activity is an indication of their motivation to run."
These findings then would suggest that all mice have the motivation to run, since each blocked mouse showed neuronal stimulation, but that some mice may actually crave it. After all, abstaining from their running regimen signals the same pathways involved in the craving for drugs of abuse, says Rhodes.
Whether these findings on exercise motivation hold true for humans remains to be studied. If it does, anecdotal evidence from Rhodes and Gammie would suggest that they've got more in common with the study's control mice: While they bike or play ultimate Frisbee, neither one says he feels the compulsion to do it on a regular basis.
One big reason cited for pursuing research into addiction is that such research may eventually point the way toward way to treat and stop addictions. Also, since addiction shows up as a form of compulsion the study of addiction may lead to better treatments of Obsessive Compulsive Disorders (OCDs). But isn't it easy to imagine all sorts of Obsessive Compulsive Adaptations (let's call them OCAs) where the compulsion is to do things that you really think you ought to do? The most obvious example for this is running. But suppose you want to study math or clean the house but never seem to get a strong enough urge to do it. Wouldn't it be handy to be able to flip a neural switch to engage a compulsive desire for, say, 30 minutes and then have the desire automatically shut down?
Our real problem is not that we have addictions or compulsions. Our problem is that we have compulsions that are counterproductive and harmful. What we need is the ability to shape our compulsions to make our compulsions more adaptive. It would be very handy to be able to do some behavior and while doing it send a signal to one's brain to reward that behavior and to record that as reward should be delivered when that behavior is done. One could set that up when faced with the need to do a large amount of fairly repetitive and boring but necessary work. This would probably dramatically enhance productivity for many tasks. Though it would also be necessary to be able to turn off a compulsion so that in situations where it is not appropriate one could turn one's attention to other activities.
Of course, with any new capability comes new ways for it to be abused. The ability to program in compulsions would open up the potential for both self-abuse (imagine a really depressed person with low self-esteem programming in a compulsion to commit physical self-torture) or a military programming in a compulsion to obey a particular person or a pimp programming young girls to have the desire to be a prostitute. When technologies are developed that make the mind more reprogrammable the issue of who does the programming and for what purposes may become one that wars are fought over. Still, I'd like to be able to shape and control the intensity of my compulsions in order to make myself more productive.
|Share |||Randall Parker, 2003 December 03 01:58 PM Brain Addiction|