Welcome to EvC! It's a good place to learn if you can learn.
It's a myth.
It gets bandied about because most people can't be arsed to look it up or like to think that that 'extra' 90% can be used for ESP or some such.
Brain cells such as schwann cells or glial cells don't do the business of 'thinking' as such and yet they are a big, big part of the brain; so physically they make up non neuronal mass.
In other terms, balance, homeostasis, and perception take up a massive amount of 'thinking power' that does not require conscious thought.
Maybe, if you clutch at as many straws as you can find in a straw filled straw factory you could say that 10% of our brain goes towards conscious thought and decision making but that's about it.
There's tons going on 'under the bonnet'.
How do we know this? It's been proved in tests: Google them.
ABE: Sorry about the tone and the use of the word proved, I'm terribly hung over and I have to go and play Warhammer soon; good grief.
ABE: and it seems I have been slow ninja'd by bluegenes
Edited by Larni, : Acknowledging being slow ninja'd.
Edited by Larni, : Welcome note.