How much of the body’s energy does the brain used compared to other organs and why?

The brain consumes a huge amount of energy compared to other organs, 20–25% of total consumption, whether we are resting or physically active, and despite being only 2% of our total weight. Most vertebrates devote 2–8% of total energy to their brain, but in primates the percentage is much higher, with humans using the most. From this we can probably conclude that high energy use is a requirement for intelligence.
How much do we know about this energy use? At the simplest level, as William Halmeck says, energy is needed because the brain uses electrical currents generated by moving sodium, potassium and calcium ions across neuron membranes, which in turn requires energy derived from oxidizing glucose. But this stills begs the question, why so much?
It would be tempting to say that our high energy requirement is due to the activity of the brain’s ‘default mode network’ (DMN), which has been intensely studied since 2007. The DMN is a network of interacting regions which keep busy when we are awake but not focused on any goal-directed task, so correlating with daydreaming, remembering, planning, and also watching a movie or listening to/reading a story. The DMN starts up within a fraction of a second of finishing a specific task. It is probably responsible for much brain activity and energy use in adults, but it is not well defined in children below the age of about 7. Young children’s minds are clearly busy too, so a more accurate comprehensive statement might be simply: “we use a lot of energy because we can’t stop thinking”.

By:-Asst Professor -Safia Hasan
Department of MLT
Uttaranchal (P.G.) College of Biomedical Sciences and Hospital