Pubdate: Aug 5, 1999 Source: Guardian Weekly, The (UK) Copyright: 1999 The Guardian Weekly Contact: 75 Farringdon Road London U.K EC1M 3HQ Fax: 44-171-242-0985 Website: http://www.guardianunlimited.co.uk/GWeekly/ Author: Tim Radford HOW RISK AFFECTS THE BRAIN Connoisseurs of risk talk of danger as an addiction, a drug. Absolutely, says Professor Colin Blakemore, the Oxford neuroscientist, but there is a lot more to it than just the empty thrill of a pounding heart. Risk makes sense in biological terms: how else would animals discover any new activity? Too great a risk has its obvious downside. Driving a motorcycle over a cliff for the hell of it could be an unrepeatable experience. So thrill-seeking and exploration are intertwined: the accelerators of evolutionary advantage. The risk-taker who survives gets something out of it. "The notion of building in a drive for exploration and even risk-taking is obvious, but it has to be controlled on the basis of success," says Blakemore. The instant reward comes in the form of dopamine, the chemical transmitter that pushes the neurological levers marked "gratification". Drugs play on the mesolimbic reward system of the brain: the consensus among brain scientists is that such pleasures are dependent on dopamine signals into parts of the hypothalamus and the limbic system involved in reinforcement. But although dopamine signals are involved in almost every aspect of pleasure, no one knows why one form of behaviour manifests itself as one kind of pleasure, while a different set of actions fires off a different burst of reward. "Presumably you have particular pathways for each particular activity," says Blakemore. "It wouldn't make sense to have only one reward system, otherwise you wouldn't be able to sort out which behaviour was generating the real reward and which wasn't. They can habituate or sensitise separately, so you could get addicted to one drug, but that wouldn't mean you could get addicted to all drugs. Someone addicted to bungee-jumping wouldn't dream of jumping across the Colorado river on a motorcycle." - --- MAP posted-by: manemez j lovitto