All that changed after a snippet of DNA known as an "anti-sense expression vector" was injected into a part of the brain known as the rhinal cortex. The vector suppressed the expression of the D2 gene for several weeks, hampering the ability of the rhinal cortex to detect dopamine.

Dopamine is related to the reward pathways in the brain. The rhinal cortex is a part of the brain where meaning is attached to recognized objects. The hardworking monkeys acted as if their rhinal cortexes had been removed.

Other illnesses are linked to some fault in the reward circuitry of the brain. Manic people work even when the rewards are insignificant. In depression, no amount of work seems worth the reward. In obsessive compulsive disorder, the rewards never seem to register. Drug abusers risk danger for their reward.