Hunger for Novelty
A brain-imaging study led by Nora Volkow, at the Brookhaven National Laboratory, sheds light on the mechanism that makes the mere presence of food alluring. When people were allowed to see and smell their favorite chow, a deep-lying brain structure called the dorsal striatum was activated and the subjects reported feeling hungrier. Though it sits right next door to one of the brain’s most important pleasure centers, it is not itself a generator of warm, fuzzy feelings. Indeed, being hungry in the presence of forbidden food is distinctly un-pleasurable.
What this and similar research implies is that the reward of eating is not the sole thing motivating us to eat. The dorsal striatum draws us to food (and other objects of addiction) even when we are not hungry.
This system was once very important for survival,” Volkow says. “It was important to want food whenever you could get it, because you never knew when it was going to be around.”
A structure called the nucleus accumbens lies right beneath the dorsal striatum. Like the dorsal striatum, it is rich in the neurotransmitter dopamine, a brain chemical associated with feelings of satisfaction and reward. But unlike its upstairs partner, the nucleus accumbens is a bona fide pleasure center. It is activated by food, sex, drugs, money, victory, just about anything that feels rewarding. It helps animals to form pleasure-related mental associations and to stay motivated in the pursuit and repetition of positive experience.
The nucleus accumbens also turns out to be crucial to our taste for novelty. “It is very deeply ingrained for us to associate potential reward with things that are new and unexpected,” says Gregory Berns, an Emory University neuroscientist. Tying perceptions of novelty into the reward system makes good evolutionary sense as it’s an excellent way to keep animals attuned to changes in their environment.
One recent brain-imaging study found that the nuclei accumbentes of young heterosexual males were activated by beautiful female faces. Plain female faces and male faces that the subjects rated as extremely good-looking had no effect.
Neuroscientists have made good headway in recent years figuring out why emotionally charged experiences get turned into stronger, more vivid memories than do humdrum and routine events. The key player is another limbic system structure called the amygdala. When revved up by a potent emotion — which a good thrumming in the nucleus accumbens will generate — the amygdala stamps the engendering event firmly into memory. Memories stored by the amygdala are extremely powerful because from then on, whenever you re-encounter that stimulus you will immediately associate it with the pleasure or aversion you first experienced.
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