Question: Why do we only use 10% of our brain?

Helen O'Connor answered on 15 Jun 2011:

Over thousands of years, our brains have grown in size to cope with the additional complex things we have evolved to do, like language. If 90% of the brain wasn’t being used, it seems unlikely that we would have needed to grow larger brains.
Brain scans show us that we do actually use all parts of the brain although some parts are more active at different times or when we are doing different things. But so far we aren’t seeing any part of the brain that is totally unused, and certainly not 90%.
There are certainly ways to improve HOW our brains work: we can practice techniques that help us store information in memory and retrieve it better when we need it; and through practice we can improve our reflexes and response times. This is what a lot of the ‘brain-training’ console or DS games do.
In psychology we use the Stroop Test to test people’s cognitive flexibility and brain processing speed. Try doing a Stroop Test a few times and see if after practice you get better at it: http://faculty.washington.edu/chudler/java/ready.html