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Which brain circuits do food and drugs activate in common?

The system in the brain that both food and drugs activate is basically the circuitry that evolved to reward behavior essential to our survival. One reason humans are attracted to food is because it is rewarding and pleasurable. When we experience pleasure, our brains learn to associate the sensation with the conditions that predict it. That memory strengthens as the cycle of predicting, seeking and obtaining pleasure becomes more reliable. In scientific terms, we call this process conditioning.

Drugs are particularly effective as conditioning stimuli, primarily by virtue of their chemical properties. Natural reinforcers, such as food or sex, take longer to activate the reward pathway. Important for both, however, conditioning links a memory not just to a stimulus but to the environment in which it is found and other related cues. That’s exactly what nature intended: if the action needed to attain a pleasurable experience were triggered exclusively by the stimulus in question, the conditioned response would be very ineffective indeed. Once you create a conditioned memory, it’s just like Pavlov’s dogs; the response becomes a reflex. This conditioned response underlies the drive both in drug addiction and compulsive eating.