How much brain do we use ?

You no more use 90% of your brain potential than you use 90% of your muscle potential all 
of the time. 

To say that we use all of our brain, would be like saying Arnold Schwarzenegger or Lou Firigno  had as 90 pound teenagers reached the pinnacle of their muscular development.

You no more use all of your brain all of the time than you use 100% of your lung capacity sitting at your computer keyboard.

You no more use all of your brain all of the time than you use all of your car all of the time; that you always drive at the full potential of your Honda; that you always drive at the top speed of your car; that your trunk and seats are always filled to capacity; that you have even figured out and daily employ every single way in which you could use your car.

To say that we use all of our brain ignores the fact that you keep losing your car keys all the time.

To say that we use all of our brain ignores the fact that you couldn't remember where you left your car in the parking garage- even though this is well within your brain potential.