Brain Rules: 12 Principles for Surviving and Thriving at Work, Home, and School

Brain Rule #2 states, “Exercise boosts brain power” (17). Historically, humans were designed to move. When human ancestors began to stand upright, they began to travel long distances. All humans come from ancestors in Africa, proving the power of migration and exercise. Anthropologists estimate that early human males walked approximately 10 to 20 kilometers (about 12.43 miles) per day. Human brains evolved in a climate of exercise. Scientists have touted the benefits of exercise for centuries.

A sedentary lifestyle has been proven to contribute to bodily decline in old age, but Medina observes that older individuals who are more physically fit are also more mentally alert. Multiple studies show that those who exercise throughout their life have better cognitive performance when they are elderly. The same is true for people of all ages; exercise leads to better cognitive functioning. Medina explains that studies also show that people can shape their brains with exercise; elderly individuals who lived sedentary lifestyles throughout their youth show improvement in cognitive functioning as they engage with physical activity. Walking a few times a week can improve brain performance; however, aerobic exercise is even more effective. The risk of dementia or Alzheimer’s disease is cut in half when an individual engages in regular aerobic exercise. This may be because exercise regulates the release of chemicals that contribute to mental well-being.

Exercise also benefits children. One study shows that children who are physically fit have better concentration and mental stamina. They also have better psychological health. Medina illustrates how exercise assists the brain with the example of competitive eating. The brain utilizes about 20% of the body’s energy; it requires so much energy that it cannot utilize more than 2% of its neurons at any point in time. This energy comes from glucose, which is absorbed into the bloodstream from food. As the body breaks down glucose for energy, it leaves behind electrons that can become toxic if they are not properly disposed of. These electrons are absorbed by oxygen and converted into carbon dioxide to be expelled through the lungs. Exercise increases the body’s access to oxygen and glucose by increasing blood flow and creating new blood vessels.

Medina suggests that people can improve their cognitive functioning by spending 20-30 minutes in the morning three times a week participating in aerobic exercise and the same amount of time each afternoon in strengthening exercise. He reimagines a school in which students are encouraged to follow this regime and classrooms include treadmills and stationary bikes to encourage movement.

Brain Rule #3 states, “Sleep well, think well” (37). When humans do not sleep, their brains and bodies betray them. One rare disorder that renders the individual incapable of sleep leads to coma and then death. However, Medina questions the evolutionary function of sleep. When humans are sleeping, they are more vulnerable to attack from predators. He suggests that there must be a reason for sleep, and the answer lies in the brain.

During rest, the brain is extremely active. However, those who sleep well report feeling restored and rejuvenated. The human body is continuously engaged in the sleep/wake cycle. In each part of the cycle, all parts of the body—including neurons and hormones—battle to maintain their hold. The wake part of the cycle is the circadian arousal system, and the sleep part is the homeostatic sleep drive. These two processes are in constant war with one another; the longer one lasts, the weaker it becomes before surrendering. In one experiment, a researcher went underground in a cave in Kentucky for an entire month to determine whether the circadian rhythms would work themselves out when devoid of sunlight or clocks. The researcher discovered that his body did fall into a natural rhythm, even without the usual ways of monitoring the sleep/wake cycle. Both processes reach “a climactic stalemate” in the afternoon, which means that a short afternoon nap can be extremely beneficial (46).

While almost all humans have an internal clock, their clocks may work differently. Medina divides people into categories based upon their internal clocks. Larks are most alert a few hours before lunch and hit their peak at noon. They typically do not need an alarm clock and easily wake up early. Larks represent approximately one in 10 humans. Another small portion of the population can be categorized as owls. They are most alert at 6:00pm and are most productive in the evening. Owls go to bed late and struggle to wake up in the morning. The rest of the population falls along a spectrum between these two points. These patterns are apparent from early childhood.

Humans can benefit from an afternoon nap. However, the question of how much sleep humans need varies on an individual basis. Sleep needs and cycles also change over time and by experience. Scientists know that not enough sleep contributes to cognitive decline and can have lasting effects on both the brain and body. Medina suggests creating work schedules and educational systems that reflect variances in chronotypes (natural predilection to sleep/wake cycles).