An article published in the November issue of the American Journal of Psychiatry and cited by the NIH News on November 6 describes an interesting study of incentive-based therapy for methamphetamine abusers.

No, you haven’t stumbled onto the wrong blog. This study is of great significance for people struggling to lose or maintain body weight and to community and medical groups involved in issues of obesity and metabolic syndrome.

The lead scientist, Dr. John Roll of Washington State University, and his colleagues observed that participants who received Contingency Management (CM, also known as Motivational Incentives) along with psychosocial therapy did better than participants who only received psychosocial therapy.

CM is a program that applies rules and consequences to help people change their behavior. In this study, for example, participants in the CM-based drug abuse program were told they have to produce drug-free urine samples on a regular basis. When they were successful at doing this, they received plastic chips that could be exchanged for a variety of prizes.


Matrix model psychosocial therapy

The psychosocial therapy in this study consisted mostly of the Matrix Model; this is a comprehensive treatment approach including the following:

  • individual counseling
  • cognitive behavioral treatment (a mode of treatment that seeks to identify distorted thinking that influences mood and behavior and to replace it with more rational, adaptive thoughts and actions)
  • family education, and
  • self-help programs

Participants of the study that received psychosocial therapy plus CM were drug-free for a period 60% longer than those who received psychosocial treatment alone.

This is a well designed clinical trial:

  • The study was controlled (the psychosocial without CM participant group served as the comparison or control group)
  • It was randomized (participants were randomly assigned to the treatment group or the control group) and,
  • The end-point was an objective measure (drug-free urine).

I believe that the results of this study are significant beyond the treatment of methamphetamine addiction, and may, in fact, have relevance specifically to weight control.


Incentivize, don’t demonize

A few days ago (October 29, 2006), the New York Times published a front-page article by Gina Kolata decrying the fact that there is an increasing tendency to demonize obese people. A few days later the New England Journal of Medicine published a study that demonstrated that indeed demonization does not work as a motivational force. Fair enough!

Kolata makes the point that obesity is in large measure controlled by our genes. This, too, is correct, but to a scientist, this statement is not helpful. What genes? What functions are controlled by those genes? How much leeway is there for environmental/behavioral factors to modify the genetic influence?

We hear a lot about obese people having a more efficient metabolism, namely that they store more energy (calories) as fat, whereas the inefficient metabolizers have a more “leaky” energy metabolism, a lot of calories are “blown off” as heat. But even this is not a satisfactory answer; a scientist would demand a mechanism to explain this “leakiness”, and data to back it up.

There is, however, another way to approach this problem. From studies of the brain of addicted animals and humans, we know that addiction to alcohol, for instance, is genetically determined. And we have a pretty good idea how it works. The brain has centers that are specialized for coupling our actions to reward.

What purpose do these reward responses have? We know from imaging studies of the brain that reward/pleasure centers are located deep in the mid-brain, which means that they are quite ancient in evolutionary timescale. Even mice have them, so they must be hard-wired in the brain, and must have some function basic to survival.

Indeed, let’s consider a basic drive like hunger. If finding food was not coupled to the sensation of pleasure (think of the term “comfort food”), we, or the mice, probably wouldn’t be seeking it so actively under conditions of scarcity. In other words, it is an adaptive response that gives its owner a survival advantage.

But what happens when environmental conditions change abruptly? Again, let’s consider food supply. Food became more abundant when humans started domesticating plant and animals and gradually became farmers rather than hunter-gatherers. This happened about 10,000 years ago. But the real explosive increase in food supply happened only about 100 years ago—a mere nanosecond on the evolutionary clock. No gene could mutate and adapt to the new situation in this time period. So here we are blessed with an abundance of food as well as with multiple systems, some metabolic, some neurological, all designed to maximize the hunger drive. Hence overeating and obesity.

Let’s go back to our addiction model. When a person takes a drug, be it a narcotic administered in the hospital to treat pain or a kid experimenting with a street drug for recreational purposes, the sensation is that of pleasure. What happens on the cellular level is that the drug will bind to a receptor on the membrane of a neuron (nerve cell) in the reward center. That receptor then transmits a message to the inside of the cell through a process called “signal transduction”. This particular neuron will then fire off a signal to an adjacent neuron in the same reward center, and very quickly thousands of neurons get activated resulting in the sensation of pleasure.

What happens when this stimulus (the drug) is repeated chronically, over a prolonged period of time? The cellular response becomes attenuated and, accordingly, the reward response is unfulfilled. To keep the reward/pleasure response the cell increases the number of receptors on its surface, the signal becomes “loud” again and the “hunger” for reward is satisfied again. This process repeats itself again and again and the result is addictive behavior.

The experiment described in the Journal of Psychiatry showed in a rigorous scientific way what we all knew intuitively: reward works. It doesn’t matter how trivial the reward looks to us—what is important is what it means to the recipient. (I still remember how I worked myself to exhaustion in elementary school doing my homework so that I would win a ridiculous paper gold star; I can still taste the pleasure of this reward.) But from a neurobiological perspective, this experiment is quite instructive. What it may tell us is that we can set up an alternative reward pathway, to compete with original “addictive” one.

But will it work in weight loss? Can we counteract the pleasure pathway of feeling “full” and contented? I think that if we couple psychosocial treatment with a reward, we could more effectively counteract the urge to overeat. What kind of reward? Here is one. The simple pleasure of standing on the scale and realizing that you are making progress, pound by painful pound, is a self-reinforcing reward. Hence the recommendation of frequent weighing; the immediate feedback allows self-correction before things get out of hand. And the pleasure of seeing progress is reinforcing and strengthening the resolve to continue.

Everyone who has tried to lose weight knows that daily weighing is important, but the pleasure from the reward may not be enough to sustain weight loss or weight loss maintenance over the long run. It would be great to see CM applied to weight loss in a variety of ways and be rigorously studied to determine its effectiveness. It would be one more tool in the toolbox that could help people achieve a healthy weight.

Dov Michaeli, MD, PhD
Dov Michaeli, MD, PhD loves to write about the brain and human behavior as well as translate complicated basic science concepts into entertainment for the rest of us. He was a professor at the University of California San Francisco before leaving to enter the world of biotech. He served as the Chief Medical Officer of biotech companies, including Aphton Corporation. He also founded and served as the CEO of Madah Medica, an early stage biotech company developing products to improve post-surgical pain control. He is now retired and enjoys working out, following the stock market, travelling the world, and, of course, writing for TDWI.