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."