The idea that humans use only a fraction of their brain is a long-debunked myth. Modern neuroimaging — including functional MRI (fMRI) and positron emission tomography (PET) scans — reveals widespread activity across all brain regions, not just a small slice. Britannica notes that these imaging tools allow scientists to observe the brain in real time, consistently showing whole-brain engagement during everyday tasks.
One of the strongest pieces of evidence against the 10% myth comes from the brain's energy demands. As MIT's McGovern Institute points out, the brain consumes roughly 20% of the body's total caloric intake. Maintaining that level of energy expenditure for an organ that was 90% idle would make no biological sense — evolution would have eliminated such waste.
Medical News Today cites a study published in Frontiers that further dismantled the myth, while Harvard Health has called the 10% claim "100% fiction." Johns Hopkins Medicine reinforces this by explaining that all parts of the brain work together to control the body's functions — there is no dormant 90% waiting to be unlocked.