But the neurons, which use a lot of energy, aren’t in direct contact with the blood vessels. What we found was that in REM sleep, the blood vessels expand, so more energy is being provided. One is that the neurons are consuming so much energy in dreaming that the total energy in the system decreases. The third is that even though the astrocytes are supplying energy to the neurons, the neurons’ mitochondria, the engine of the cell, stop converting this energy into ATP. AdvertisementRead more: “Dreaming Is Like Taking LSD”How do the energy supply needs of REM sleep compare to those of waking-life activities, like reading a book or watching a movie?