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Two extremely well respected reseachers in biology/psychology
Richard Davidson professor of psychology at University of Wisconsin-Madison and Bruce McEwen of Rockefeller University.

Begins by considering how social stressors can harm the brain. The massive neglect of children in orphanages in Romania did not just have psychological impacts; it created measurable changes in their brains, Davidson says. "Such studies provide an important foundation for understanding the opposite effects of interventions designed to promote wellbeing."
Practices like physical exercise, certain forms of psychological counseling and meditation can all change brains for the better, and these changes can be measured with the tools of modern neuroscience...