This book is strongly recommended reading for anyone who uses their brain.
This book starts with the assertion that conditioning the body is just a side effect of exercise, and the real benefit is the changes that exercise causes in and on the brain. Many people have made the case that our current lifestyle doesn't match the conditions we evolved for, but the assumption is that too many caleries and not enough running only effects the heart and lungs. Ratey argues that part of what we evolved for was hunting and gathering that required speed, stamina, cunning and fine motor control. We lose all of that when we're sedentary.
In a Chicago High School gym class was transformed into exercise class, with emphasis on effort as measured by heart rate monitors. This allowed even unfit kids to succeed, by working enough to elevate their heart rate. This school's obesity rate is now 3% compared to the national average of 30%. They are also setting records for academic performance.
This book has a lot of chemical names in it and one of the most important is brain-derived neurotrophic factor (BDNF). BDNF causes an increase in synaptic connections which is how we learn. This molecule is produced in the hippocampus and studies show the exercise causes an increase in its production. Ratey calls BDNF "miracle grow" for the brain. BDNF doesn't make you smarter but it creates an environment conducive to forming new connections. So, if exercise and then learn something its easier for the brain to encode the learning.
We used to think that we were born with all the brain cells we'd ever get, but we now know the neurogenisis occurs all the time. New neurons are born and then have 28 days to get connected into a network. If they don't they die. Exercise increases both the rate of nerurogenisis, and the ability of new neurons to make the connections they need to survive.
Ratey goes on to say that the benefit can be enhanced by combining aerobic exercise with complex activity such as Tai Chi. "The more complex the motions, the more complex the synaptic connections". Although these neurons are associated with exercise they can be recruited for other tasks (such as learning)
When under stress we produce cortisol which tells the hippocampus to selectively process data and memories (so as to focus on the stressor). While beneficial in the short term, in the long run it actually causes the non-stressor related nerves to degenerate and lose connections. This makes it harder for the non-stressor memories to be accessed, which can lead to more perceived stress. Exercise on the other hand causes a reduction in the production of cortisol, which can break the cycle.
The book does get somewhat repetitive as it explains the positive effect exercise has on the neurochemistry of anxiety, depression, ADHD, addition and aging. On the other hand you really can’t fault the author for providing so much good news. Each of these conditions represents a deviation from normal brain chemistry and exercise is a strong force for bringing the brain back into its normal condition of plasticity. Which is to say, that our brains were designed to be adaptable and exercise creates the right chemical soup for the brain to swim in to enhance the flexibility.