"Humans are biologically designed to survive and the single greatest competitive advantage is the ability to learn." from the Introduction to Eric Jensen's The Learning Brain.
The Learning Brain is a nifty little book, laid out in easy to read modules. Chronic stress and stress hormones can damage neurons and axons, especially in the hippocampus. Learning is a way to heal this memory damage and strengthen synaptic connections, plus it gives you a nice shot of dopamine straight from the pleasure center of the brain. Learning is fun-damental as they say. This 1994 booklet is a sharp, early primer of the neuroscience behind learning. I bought my copy (autographed, even) on abebooks.com for only a few bucks.