a molecule of motivation

NYTimes | If you’ve ever had a problem with rodents and woken up to find that mice had chewed their way through the Cheerios, the Famous Amos, three packages of Ramen noodles, and even that carton of baker’s yeast you had bought in a fit of “Ladies of the Canyon” wistfulness, you will appreciate just how freakish is the strain of laboratory mouse that lacks all motivation to eat.

The mouse is physically capable of eating. It still likes the taste of food. Put a kibble in its mouth, and it will chew and swallow, all the while wriggling its nose in apparent rodent satisfaction.

Yet left on its own, the mouse will not rouse itself for dinner. The mere thought of walking across the cage and lifting food pellets from the bowl fills it with overwhelming apathy. What is the point, really, of all this ingesting and excreting? Why bother? Days pass, the mouse doesn’t eat, it hardly moves, and within a couple of weeks, it has starved itself to death.

Behind the rodent’s fatal case of ennui is a severe deficit of dopamine, one of the essential signaling molecules in the brain. Dopamine has lately become quite fashionable, today’s “it” neurotransmitter, just as serotonin was “it” in the Prozac-laced ’90s.

People talk of getting their “dopamine rush” from chocolate, music, the stock market, the BlackBerry buzz on the thigh — anything that imparts a small, pleasurable thrill. Familiar agents of vice like cocaine, methamphetamine, alcohol and nicotine are known to stimulate the brain’s dopamine circuits, as do increasingly popular stimulants like Adderall and Ritalin.

In the communal imagination, dopamine is about rewards, and feeling good, and wanting to feel good again, and if you don’t watch out, you’ll be hooked, a slave to the pleasure lines cruising through your brain. Hey, why do you think they call it dopamine?

Yet as new research on dopamine-deficient mice and other studies reveal, the image of dopamine as our little Bacchus in the brain is misleading, just as was the previous caricature of serotonin as a neural happy face.