You spend nearly 1/3 of your life asleep. Or you should (somehow I never get there). As an insomniac (or at least social insomniac – too busy to sleep) I am regularly grumpy, headachey and very vague with lack of sleep.
Not only can I not sleep, I resent the amount of time I have to spend virtually unconscious. Think how much more I could do with an extra 6 or 7 hours a day. But lack of sleep can be dangerous (and not just from falling asleep at the wheel).
Sleep seems to be essential for humans – a time for the brain to re-organise and regroup. It plays a part in learning, memory and development. It promotes cell regrowth and restoration. Sleep may also be important in regulating temperature, with brain and body temperature fluctuating during the different stages of sleep.
Humans are not unique in their sleep – many animals (including mammals, fish and invertebrates) also sleep, but if you think about it, sleep does have serious evolutionary disadvantages. When asleep, you are vulnerable to predation and to sudden environmental changes. Senses reduce or even switch off during sleep. Even the need for smoke alarms is due to the inability of sleeping people to smell smoke. You cannot look after young whilst asleep. Sleeping for nearly a third of your life reduces the amount of food and water you can collect and reduces the time available for procreation. So any benefits come at a high cost.
So could humans reduce or remove the need for sleep?
Many animals have avoided some of the problems associated with sleep by replacing some, or all, of their sleep with unihemispheric sleep. That is, they sleep one brain hemisphere at a time. This means that they can continue to function while resting the brain. Animals which practice this type of sleep include many birds and cetaceans including dolphins. Immediately you can see the advatange. By sleeping with only a single hemisphere at a time, the other hemisphere can continue to work allowing you to fly or swim at the same time. Migratory flights are long enough without stopping every couple of hours for a nap.
Buddhist monks claim to be able to meditate with a single brain hemisphere at a time. If we could all learn to do this, could we gain the ability to turn off one hemisphere while using the other?
Sleep consists of two distinct types. REM (rapid eye movement) sleep – a small proportion of sleep time in which the brain appears aroused – and non REM sleep which is characterised by desynchronous brain activity. Non REM sleep is the type of sleep animals can do unihemispherically. However, it appears that animals can only undergo REM sleep with both hemispheres. Humans spend 20 – 25% of their sleep time in REM sleep. This suggests that not all sleep could be replaced even if we could isolate brain hemispheres. But even reducing the hours of sleep by 80% would be of benefit.
Another possibility is transcranial magnetic stimulation (TMS). This creates small electrical currents in the brains of volunteers. Drs Stern and Lisanby of Columbia University have used TMS to stimulate the brains of people who have been deprived of a night of sleep. Volunteers given TMS performed better on tricky problems than their equally sleep-deprived but not stimulated peers. Furthermore, they could refuse the lure of a darkened room and remain awake longer. Perhaps in the future, electrical stimulation will have the power to “reset” the brain, reducing or even eliminating the need for sleep.
Chemicals could also solve our needs. Stimulants such as Provigil, a drug created by Cephalon and used by the US military claims to permit people to stay alert and active for 48 hours without side effects. Other drugs aim to make sleep time more efficient by forcing the body into the most effective sleep rhythms thus reducing the total number of hours of sleep required.
Whatever the solution turns out to be, I can imagine a child of the future coming home from school and saying “Mum, did you know that hundreds of years ago people spent 8 hours a day unconscious? How did they get anything done?”
References
Caldwell J.A. (2001) Efficacy of stimulants for fatigue management: the effects of Provigil(R) and Dexedrine(R) on sleep-deprived aviators, Transportation Research, Part F, Traffic Psychology and Behaviour, 4(1):19-37
Marks G, Shaffery J, Oksenberg A, Speciale S, Roffwarg H (1995). “A functional role for REM sleep in brain maturation.”. Behav Brain Res 69: 1-11.
Rattenborg NC, Amlaner CJ, Lima SL. (2000) Behavioral, neurophysiological and evolutionary perspectives on unihemispheric sleep. Neurosci Biobehav Rev. 24(8):817-42.
