Shopping. Gambling. Facebook. Cookies. Meth.  What do they have in common? In my life, addictive urges center on certain foods.  Irrational, compulsive behavior also emerges when I check e-mail or Facebook every few minutes while doing something else on the computer.   Even if the behavior is not life-threatening, it doesn't feel good to spin out of control.

This week, we continue our sampling of insights from Spark by Dr. John Ratey, turning to  "Addiction:  the Biology of Self-Control."  In that chapter, we learn about the chemical and structural elements of addiction in the brain.  Why is it so darned hard to stop a behavior that we know is bad for us, and that we don't even enjoy all that much?

The answer comes back to our old friend dopamine (no wonder we call drugs "dope").   Dopamine functions in the reward center of the brain, reinforcing behaviors that trigger its release.  First, it grabs our attention, then it imprints a behavioral pattern by "hard-wiring" the connection between stimulus and response.  That wiring is the pathway in the brain that develops when nerve endings form synapses.  The wiring is strengthened with every use.  We are driving down the street, and our car turns into the Dairy Queen without our having the experience of making a decision. 

Addictive behaviors bypass the rational part of the brain.  They are automatic.  They resist rational approaches to change; and the underlying brain structure persists, even after long periods of abstinence.  Relapse is a familiar threat to drug addicts and dieters alike.    

So, how does exercise work in this picture?  Physical activity also triggers the release of dopamine.  Dopamine acts on the reward center of the brain.  The brain forms neural pathways that pull us toward taking a walk as they pull us toward eating a sweet.  It doesn't happen immediately (only a few drugs trigger addiction on the first try).  But it does build. It becomes powerful.  And it competes with other urges. 

We know that exercise helps with weight loss.  We know that it burns off the calories we ingest.  However, exercise also helps us control automatic eating.  It is especially helpful as we gradually hard-wire the urge to be active, offsetting the pull toward unhealthy relapse.