Surrounded by computers and handheld devices at work and at home, people are accustomed to having e-mail within reach nearly all day, making it hard to shift gears on vacation, says Kate Muller, director of psychology training at Montefiore Medical Center in the Bronx, New York.

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According to Mr Shamdasani, an eminent historian of psychology and psychiatry at the Wellcome Trust Centre for the History of Medicine at University College London, these included medical psychology, philology, anthropology, history, philosophy, theology and biology.

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"The brains of children are far more plastic and amenable to change, " says Candice Alfano, assistant professor of psychology and pediatrics at Children's National Medical Center in Washington, D.

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