In The Loom: 10% Myth, 1% Fact? Carl Zimmer explains the old “you only use 10% of your brain” myth:
In a nutshell, in the 1930s neurologists figured out that only 10% of the human cortex becomes active during sensory stimulation or the motor control of the body. So the other 90% was referred to as ‘silent cortex.’ This technical term doesn’t mean that that 90% is useless, only that it is silent in these particular tasks, like walking and smelling. In fact, these other regions become active in other kinds of thought — such as making decisions and recalling memories. But that didn’t stop the 10% figure from taking on a life of its own.
It turns out that that 10% figure is actually an overestimate:
By coincidence, the 10% story has been on my mind again recently. Over the summer I came across a fascinating paper in Current Biology by Peter Lennie of New York University. Lennie takes a look at how much energy the cortex uses to think. First, he calculates the total amount of energy used by the human cortex, based on recent neuroimaging studies. Then he calculates how much energy a single neuron in the cortex uses when it generates an electric impulse. And finally, he uses these figures to estimate how many neurons in the cortex can be active at any one time. His estimate? Around one percent.