Cerebral oxygen sensing and the integrated regulation of hypoxic vasodilatation

Modern humans are the most encephalised of all species, with a brain that has more than tripled in size over the last 3 million years, much thanks to a dramatically enlarged neocortex. Yet being so big doesn’t come cheap and fuelling the brain is energetically expensive. Indeed, despite weighing less than 2 % body mass, we allocate a disproportionate 20 % of the body’s resting basal oxygen (O2) budget to maintaining its “dark energy”, equating to a cerebral metabolic rate of oxygen (CMRO2) of
~3 mL/min/100g, more than 10 times that expected from its mass alone. Any interruption in the continuous supply of precious O2 can spell disaster for the brain given its almost exclusive reliance on aerobic metabolism and baffling lack of energy reserve (Bailey, 2019).