Medina opens by marveling at the capacity of the human brain. Humans can do amazing things, including translating black marks on a page into something meaningful and powerful (reading). Medina hopes to shed light on what the brain does and how it affects everyday life in the form of 12 brain rules. These statutes indicate basic truth statements about the brain. As Medina explores each rule, he provides practical applications for how the rule be harnessed. For example, he proposes that humans are not used to sitting at a desk all day and instead evolved to walk approximately 12 miles a day. He emphasizes the importance of incorporating exercise into one’s daily routine to improve cognitive functioning.

Each rule undergoes rigorous scrutiny. Medina describes himself as “a grumpy scientist” who requires all his rules to pass what he refers to as the “Medina Grump Factor” (3). This means that the ideas supporting the rules must be published in peer-reviewed journals and the results replicated by other scientists. He warns against pop science that latches onto unsubstantiated brain research. Ideas like left-brain and right-brain individuals or the impact of playing Mozart for a baby on intelligence have permeated society and become accepted as truth, but Medina explains that these are only myths.