Danielle is trying a trial subscription to Seed magazine, and she showed me an article she thought fit into Ecojoy: The Reinvention of the Self. Its about Dr. Elizabeth Gould's work with marmoset monkeys, and about her discovery of neurogenesis. Prior to Dr. Gould's work, scientific and medical knowledge about brains was that they didn't grow new cells (neurons). Dr. Gould discovered that the conditions under which the animals are kept affect growth of new neurons. Animals kept in supportive, non-stressful conditions can grow new neurons.
We didn't have previous evidence of this because researchers didn't think the conditions under which animals were kept were related to neurogenesis. And Dr. Gould has a tangible, medical way to measure stress. I highly recommend the article and Dr. Gould's papers.
From this work, it is becoming clear that there is a medical, scientific foundation to the theory that joy is a more powerful motivator than fear.