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NEUROSCIENCE
Neuroscientists are learning how to repair neural circuits damaged by addiction.
Neuroscientist Woody Hopf opens a cabinet in his alcohol research laboratory at the University of San Francisco, California. Inside is a cage containing a rat that is being taught addictive behaviours. The rat has been conditioned to press a lever to release a squirt of alcohol when it hears a beep. Hopf closes the cabinet so that the rat will not be distracted by the sights and sounds of human visitors. Just as it takes time for people to undergo the characteristic brain changes that enforce addiction, he says, it will take time for his rat to become dependent on alcohol.
Researchers such as Hopf view addiction as a disease of the brain circuits responsible for pleasure, stress and decision-making. "Addictive substances come at the brain in different ways," says George Koob, director of the US National Institute on Alcohol Abuse and Alcoholism (NIAAA) in Bethesda, Maryland. "But in the end, they're activating some of the same circuitry and patterns of behaviour."
For decades, researchers have been mapping the electrical and chemical circuits that underlie addiction. Now they are working on strategies for healing these neural pathways. Imaging studies show how the brain rewires during recovery from addiction. When combined with studies of how the brain develops during adolescence, the work could help researchers to understand how the brain changes that are characteristic of addiction occur, as well as who is most vulnerable and why. This work is rapidly being translated into treatments. By using electrodes and fibre-optic cables, researchers can intervene in neural circuits with great precision, causing animals to lose their taste for alcohol or their interest in cocaine, not just for days but for weeks or months. This work is now being tested in people. Researchers hope that therapies to heal damaged brain circuits will improve the odds of people overcoming addictions.
CROSSED WIRES
Koob divides addiction into three stages, each with its own brain circuit - groups of neurons or larger structures that interact in a characteristic way (see page S46). Addiction starts with the feel-good binge stage, which is fuelled by the brain's reward circuit, particularly at the nucleus accumbens. Withdrawal brings stress, centred in the emotional...