Jessa Gamble in Aeon:
Human sleep comprises several 90-minute cycles of brain activity. In a person who is awake, electroencephalogram (EEG) readings are very complex, but as sleep sets in, the brain waves get slower, descending through Stage 1 (relaxation) and Stage 2 (light sleep) down to Stage 3 and slow-wave deep sleep. After this restorative phase, the brain has a spurt of rapid eye movement (REM) sleep, which in many ways resembles the waking brain. Woken from this phase, sleepers are likely to report dreaming.
One of the most valuable outcomes of work on sleep deprivation is the emergence of clear individual differences — groups of people who reliably perform better after sleepless nights, as well as those who suffer disproportionately. The division is quite stark and seems based on a few gene variants that code for neurotransmitter receptors, opening the possibility that it will soon be possible to tailor stimulant variety and dosage to genetic type.
Around the turn of this millennium, the biological imperative to sleep for a third of every 24-hour period began to seem quaint and unnecessary. Just as the birth control pill had uncoupled sex from reproduction, designer stimulants seemed poised to remove us yet further from the archaic requirements of the animal kingdom.
Any remedy for sleepiness must target the brain’s prefrontal cortex. The executive functions of the brain are particularly vulnerable to sleep deprivation, and people who are sleep-deprived are both more likely to take risks, and less likely to be able to make novel or imaginative decisions, or to plan a course of action. Designer stimulants such as modafinil and armodafinil (marketed as Provigil and Nuvigil) bring these areas back online and are highly effective at countering the negative effects of sleep loss. Over the course of 60 hours awake, a 400mg dose of modafinil every eight hours reinstates rested performance levels in everything from stamina for boring tasks to originality for complex ones. It staves off the risk propensity that accompanies sleepiness and brings both declarative memory (facts or personal experiences) and non-declarative memory (learned skills or unconscious associations) back up to snuff.