In one study, he and colleagues found that genetics played a significant role in whether a person experiences difficult life events, like the death of a spouse, unemployment and being a victim of crime.

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And contrary to the old dogma that the brain is genetically fixed in form and function, he says, the new understanding of "neuroplasticity" means the brain has the ability to change in significant ways throughout life, not only as a result of experiences but also by our own mental activity.

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