by KELLY CLANCY
IMAGE/Basic Knowledge 101
The brilliant compromise between efficiency and ability in your head.
You’ve probably heard the myth that the average person uses only 10 percent of their brain. It’s a seductive lie because it suggests that we could be more than we are. Sci-fi movies like Limitless and Lucy, whose protagonists gain super-human abilities by accessing latent mental capacities, have exploited the myth. Neuroscientists, on the other hand, have long loathed it. Eighty years of studies confirm that every part of the brain is active throughout the course of a day. Save those who have suffered serious brain injury, we use all of our brains, all of the time.
But, like many legends, the 10 percent myth also carries a grain of truth. In the last 20 years, scientists have discovered that our cortex follows a strangely familiar pattern: A small minority of neurons output the vast majority of activity. It’s not that we don’t use 90 percent of our brain, but that many neurons remain eerily quiet even during use. The story behind this silence is more profound than the boosted IQs and temporary clairvoyance from the movies. It speaks to the basic principles of how our minds represent reality in the first place.
Neurons communicate with electrical impulses called spikes. In the 1930s, scientists began to record spikes from individual neurons using small metal electrodes inserted into the brain. They observed neurons with activity rates of tens to hundreds of spikes per second, with each spike lasting a few milliseconds.1 The brain seemed to be buzzing with communication. Then in a 1968 review of microelectrode technology, the biomedical engineer David Robinson brought an important discrepancy to light. As electrodes are lowered into the brain, they should detect activity from any cell they come close to. In a typical recoding, this would theoretically amount to about 200 cells. Yet researchers were lucky to record from five cells per electrode insertion. Where were the rest of the neurons?
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