Maximizing Your Brain’s Potential

It was 1962 when a group of neuroscientists led by psychologist Mark Rosenzweig published the unexpected finding that the brains of rats raised in enriched environments were significantly different from the brains of rats raised in impoverished environments.

For lab rats, an enriched environment is spacious, houses several rats, and has assorted wheels, ladders, tunnels, and objects to explore. The environment is also regularly changed for further variety. Some enriched environments have been designed to mimic an animal’s natural environment (see Heyman, 2003). In the impoverished environment, a solitary rat lives in a small, bare laboratory cage with only a water bottle and food tray to keep it company.

Decades of research have shown that enrichment increases the number and length of dendrites and dendritic branches, increases the number of glial cells, and enlarges the size of neurons (Cohen, 2003). Enrichment produces more synaptic connections between brain neurons, while impoverishment decreases synaptic connections. With more synapses, the brain has a greater capacity to integrate and process information and to do so more quickly. In young rats, enrichment increases the number of synapses in the cortex by as much as 20 percent. But even the brains of extremely old rats respond to enriched environments. In fact, no matter what the age of the rats studied, environmental enrichment or impoverishment had a significant impact on brain structure (Kempermann & others, 1998).

Enrichment has also been shown to increase the rate of neurogenesis in many different species, from rodents to monkeys (Fan & others, 2007; Nithianantharajah & Hannan, 2006). Both the number and the survival time of new neurons increase in response to enrichment (Gould & Gross, 2002; van Praag & others, 2000). Interestingly, while enriched environments can increase neurogenesis, social isolation and a stressful environment decrease neurogenesis (Ming & Song, 2005).

Collectively, these changes result in increased processing and communication capacity in the brain. Behaviorally, enrichment has been shown to enhance performance on tasks designed to measure learning and memory, such as performance in different types of mazes (van Praag & others, 2000).

Who Moved My Exercise Wheel?

Neuroscientists have identified an additional factor that improves brain function, even in aging mammals: exercise (Hillman & others, 2008). In one study, just a month of daily exercise helped reverse cognitive declines associated with aging in previously sedentary, elderly mice (van Praag & others, 2005). After having access to an exercise wheel for 30 days, mice that were the rodent equivalent of 70 years old learned to navigate a maze much faster than mice of the same age that did not exercise. They also had better memories of maze locations. Finally, the physically active elderly mice had a greatly increased rate of neurogenesis, and the new neurons functioned as well as new neurons generated in the brains of young mice. As study coauthor Henriette van Praag (2005) points out, “Our findings show that it is never too late in life to start to exercise, and that doing so will likely delay the onset of aging-associated memory loss.”

From Animal Studies to Humans

Enrichment studies have been carried out with many other species, including monkeys, cats, birds, honeybees, and even fruit flies. In all cases, enriched environments are associated with striking changes in the brain, however primitive.

Can the conclusions drawn from studies on rats, monkeys, and other animals be applied to human brains? Obviously, researchers cannot directly study the effects of enriched or impoverished environments on human brain tissue as they can with rats.

However, consider a study conducted by Ana Pereira and her colleagues (2007). Male and female participants, aged 21 to 45, were assessed for their overall level of fitness. Using MRI scans, each participant’s brain was also mapped for amount of blood flowing into the hippocampus. Over the next three months, the participants worked out for one hour four times a week. Finally, the same physical and brain measurements were taken again.

As you probably anticipated, all of the participants had significantly improved their overall level of aerobic fitness. More importantly, they had also substantially increased the blood flow to their hippocampuses, in some cases doubling the blood flow as measured prior to the exercise program. In general, the greater the increase in a participant’s aerobic fitness, the greater the increase in blood flow to the hippocampus.

Now for the key finding of the study: Along with the human subjects, a group of mice followed a comparable exercise program. In the mice, the exercise program resulted in increased blood flow in the same hippocampus regions as the humans. However, the researchers were able to directly examine brain changes in the mice. They found that the increased blood flow to the hippocampus in the mice was directly correlated to the birth of new neurons in the same region of the hippocampus. Although neuroscientists tend to be cautious in drawing conclusions, the implication of Pereira’s study is obvious: Exercise promotes neurogenesis in the adult human brain just as it does in other mammals. A footnote: The participants in Pereira’s study also improved their scores on several tests of mental abilities. Later studies have extended and confirmed these findings (Kobilo & others, 2011; Kuzumaki & others, 2011). And, recent research has shown that even moderate exercise can increase brain volume in previously sedentary, older adults (Erickson & others, 2011). We describe this study in more depth in Chapter 9.

Neuroscientists have also amassed an impressive array of correlational evidence showing the human benefits from enriched, stimulating environments. For example, several studies have compared symptoms of Alzheimer’s disease in elderly individuals with different levels of education (Bennett & others, 2003). Autopsies showed that the more educated individuals had just as much damage to their brain cells as did the poorly educated individuals. However, because the better-educated people had more synaptic connections, their symptoms were much less severe than those experienced by the less educated people (Melton, 2005).

The results of this study echo earlier research on intellectual enrichment: A mentally stimulating, intellectually challenging environment is associated with enhanced cognitive functioning. Just as physical activity strengthens the heart and muscles, mental activity strengthens the brain. Even in late adulthood, remaining mentally and physically active can help prevent or lessen mental decline (Hertzog & others, 2009; Hillman & others, 2008; Kramer & Erickson, 2007).

Pumping Neurons: Exercising Your Brain

So, here’s the critical question: Are you a mental athlete—or a cerebral couch potato? Whatever your age, there seems to be a simple prescription for keeping your brain fit. Along with regular physical activity, engaging in any kind of intellectually challenging pursuits will keep those dendrites developing. Enrichment need not involve exotic or expensive pursuits. Novelty and complexity can be as close as your college campus or library. Here are just a few suggestions:

Better yet, take a few minutes and generate your own list of mind-expanding opportunities!