There is a common misperception, and pervasive urban legend that we only use a fraction of our brains. The fraction of our brains we supposedly use is 10% or one tenth. This belief is often followed by the theory if we were to make use of the remaining 90% of our brains not in use, we would have amazing potential for intelligence, perhaps extra-sensory perception, and other sixth sense abilities.

A fraction of our brains, about 10% is composed of neurons, which on brain scans can be shown to be active. 90% of the human brain is made up of glial cells, which have very different functions than neurons. Through the use of brain mapping, it has been observed that in normal thought processes, the brain is in constant activity, no matter if we are sleeping or awake. It is important to note that we don't use the entire portion, or fraction of our brains that have neurons at the same time.

Firing of all neurons at once would cause seizures and possibly brain death. In this sense, we are not using all 10% of the supposed fraction of our brains we do use. But we are using glial cells as well as neurons in order to think, act, feel and move. Therefore, we’re using much more than a one tenth fraction of our brains at any given time. Not all of it can be mapped in the same way that neurons can be.

This doesn’t mean that all human beings reach their maximum “thinking” or cognitive abilities. In this metaphoric sense, we are only using a fraction of our brains, because we may not the smartest, most educated or most brilliant people we can be. Various things can influence ability to maximize cognition. These include diet, genetics, nurture, education, and socio-economic level. Even still, some people who seem to have little in the way of nurturance appear to have genius or a savant skill, which makes people wonder if we all could have genius potential. It does seem that genius abilities are exceptional, rather than the norm, and these abilities may not be able to be nurtured or fostered into existence.

People who are classed as genius may show a correspondingly higher level of neuron activity when their brains are scanned and examined. But they still do not have total neural activity. Some illnesses and diseases also show higher levels of neuron engagement, but the results are not uniformly positive. What can be said of the brain is that it is constantly working and active. We use much more than a fraction of our brains — we use the whole organ consistently.