In the brains of cocaine addicts the age-related expansion of white matter is absent.3 Functionally, this means a loss of learning capacity—a diminished ability to make new choices, acquire new information and adapt to new circumstances. It gets worse. Other studies have shown that grey matter density, too, is reduced in the cerebral cortex of cocaine addicts—that is, they have smaller or fewer nerve cells than normal. A diminished volume of grey matter has also been shown in heroin addicts and alcoholics, and this reduction in brain size is correlated with the years of use: the longer the
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