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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.