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It is now proved that the human brain utilizes more energy than whatever other human organ, representing up to 20 percent of the body's aggregate pull. Up to this point, most researchers trusted that it utilized the main part of that vitality to fuel electrical impulses that neurons utilize to communicate with one another.

reference :

https://www.scientificamerican.com/article/why-does-the-brain-need-s/http://todayilearned.co.uk/2013/09/28/human-brain-consumes-20-of-the-bodys-energy/