Rats Compulsively Gamble for Same Reason Humans Do: Lack of Serotonin

Rats in laboratory tests learned to gamble based on a system of punishments and rewards, strategizing like human gamblers. And when researchers tweaked the animals' brain chemistry to mimic that of humans with a gambling addiction, the mice began taking risks like pathological gamblers, according to a study published in the journal Neuropsychopharmacology. To create this animal model of gambling addiction, researchers created a system in which options that could bring greater rewards also could yield stronger punishment. In this case, however, instead of gambling for money, the rats aimed to get as many sugar pellets as possible. The rodents were placed in specially built boxes whose walls incorporated four "response holes." Each opening was associated with a possibility of earning treats - from one up to four, depending on the aperture chosen. When an animal poked its snout into a hole, the movement would break an infra-red light across the opening, signaling a computer with a "probabilistic" reward-punishment schedule to assign a pellet win or a "timeout" loss. Playing against the clock, the rats had only 30 minutes to accumulate as many sugar pellets as they could