Neuroscientists suggest that the brain is always firing or using its cells, the neurons, to perform functions. Over the course of a normal day, most people use all of their brain capacity. Previous myths stated that humans only used 10 percent of their brains.
The notion that humans use only 10 percent of their brains may be attributed to American psychologist William James. In his work, "The Energies of Man," James argued that humans use only a very small available portion of their brains. Modern scientists believe a more plausible theory is that during specific activities, such as resting, the brain may use only a smaller portion of its capacities.