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Gambling monkeys get dopamine rush Neurons of the midbrain that release the neurotransmitter dopamine are known to be involved in drug addiction. Now, Christopher D. Fiorillo and colleagues at the University of Fribourg, Switzerland, and the University of Cambridge suggest that they may be involved in gambling as well [Science, 299, 1898 (2003)]. The researchers measured the activity of dopamine neurons in monkeys that had been conditioned to get a reward after receiving a stimulus. Earlier work had shown that an unexpected reward is accompanied by a burst of dopamine release, but that once the monkeys learn to expect the reward, the dopamine release no longer occurs. In the new work, the researchers find a second pattern of dopamine release that seems to correlate with uncertainty. They find dopamine release is greatest when the reward occurs only 50% of the time, and falls off as the probability of getting the reward either increases or decreases. Furthermore, dopamine release increases as the time from stimulus to reward increases, and it increases when the size of the anticipated reward is greatest. Thus, increased release of dopamine may reinforce risk-taking behavior, and it could be what makes gambling exciting. |
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