Run for your mind

Scientists used to think that humans were born with a lifetime supply of brain neurons. Then, in the 90s, research showed that wasn’t so. Even old brains can crank out new neurons. Thank goodness. Scientists discovered that exercise accelerates neuron genesis, but weren’t quite sure why. David A. Raichlen, a biologist, and Gene E. Alexander, a psychologist, think they know. It has to do with how we evolved to carve out our place in the world, and made ourselves unique among primates. They discuss their ideas in the January 2020 issue of Scientific American. They also speculate on how we might give our daily exercise routines a boost to ward off mental decline as we age.

Most primates move about on all four legs. Many also forage exclusively on plants. At some point, two million years ago or so, the hominids that would ultimately become us adopted bipedalism: the art of walking on two legs. It ain’t all that easy, as many a toddler can testify. It requires learning the art of balancing one’s weight over the hips while throwing it forward in a coordinated way. A hefty change in African climate may have provided the initial push to making humans two-legged omnivores always on the search for anything edible. Some of those gustatory treasures consisted of animal protein—high-energy food good for growing brains. And clever brains make an all-purpose hunter-gatherer’s life much easier. A feedback loop started that helped make us the big-headed primates we are.

Humans became endurance hunters who could run after faster animals with too much hair and too few sweat glands until they fell to the ground and begged for mercy—which we declined to dispense. Physical activity apparently helps neurons increase in number and connectivity with other neurons through the production of a protein called BDNF: brain-derived neurotrophic factor. Raichlen and Alexander believe that the niche humans carved for themselves as omnivores always looking for suitable salad to go with their steaks helped forge the connection between physical activity and brain growth.

What clues might this provide for 21st century overfed humans who never need to run down hot dogs until they droop with exhaustion, and can always find onions in the produce section of King Soopers? We spend much of our day lounging behind mesmerizing images on a screen. When we do exercise, we often choose to run like hamsters on a wheel with no destination to achieve, and nothing to challenge our supersized brains. Raichlen and Alexander suggest that exercising while playing video or other brain-stretching games might help boost our supply of BDNFs more than plain vanilla exercise alone.

Evidence shows that exercising for at least 150 minutes a week at moderate intensity or at least 75 minutes a week at vigorous intensity helps both the body and the mind. Perhaps adding some mental challenges to those minimums will do even better in keeping our brains in shape for a lifetime. Perhaps we can help run Alzheimer’s and other forms of dementia to ground—and out of our lives.

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