It has cell metabolism but no brain metabolism.
Function is concentrated in the brain stem and in villages in the cortex known as centres.
In childhood there is enough blood in the brain for all centres to be able to function when required. However, when the capillary volume decreases at adulthood, fewer centres can function simultaneously. The diminished quantity of blood must now be rationed so that those centres on whose function survival depends have enough. The centres that, through conditioning, have come to dominate the co-ordination of the brain functions are the word communication centres. Since the centres of the speech system are the latest centres to evolve, they are the least economical in their use of energy.