I recently overheard a person authoritatively state, “You know, we only use about ten percent of our brain.” I laughed. This wasn’t the first time I’ve heard this outrageous statement and have always wondered where it started. Like a lot of folklore, it’s not true.

Early Greeks realized that a severe depressed skull fracture, say on the left side, could result in paralysis on the right side of the body. But how or where this cross-connectivity between brain and body occurred wasn’t known. For centuries it wasn’t clear that the brain had anything to do with consciousness or thought. The microscope demonstrated neurons and supportive glial tissue, but how they communicated with each other and the rest of the body remained a mystery until a neuroanatomist, Santiago Ramon Cajal, invented a special dye that could demonstrate individual neurons and fiber tracts.

Prior to the last century brain function was localized by carefully correlating obvious brain damage (usually from strokes) with findings from the pre-death neurologic examination. But this only gave anatomists clues to obvious behavior, like movement or speech. Until the mid 20th century there were no methods to measure “silent” brain activities such as memory or solving math problems. The largest lobe of the human brain is the frontal lobe. For centuries anatomists suspected it was important in personality and behavior but there was no methodology to test these hypotheses. Now, with newer imaging techniques, such as Positron Emission Tomography (PET scans) there are elegant ways to visualize brain activity during many subtle functions.

Although we may not be able to ascribe functional labels to every square millimeter of brain, there really are no “unused” areas.