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Did you know that when dolphins sleep they shut down only one half of their brain? The other half stays awake just in case a shark or other predator comes around.

While none of us are likely to have perfected what the dolphins can do, did you know that when we get really over tired, parts of our brain has little micro-naps while the rest of our brain is still awake?

These micro-naps are thought to be responsible for those episodes such as when someone falls asleep at the wheel while driving a car.

When we get dog-tired it is much harder to pay attention, we make more mistakes and we are far less aware of our surroundings. Have you ever had that experience when all your remaining focus is on trying to keep your eyelids open and both eyeballs focussed in the same direction? Or when you realise you have become the nodding donkey in a particularly sleep inducing presentation, and just hope that when you came too again, it’s not with a loud snort?

Some brain cells take themselves off to bed before the rest of our brain.

A new study suggests that even before we get to this stage of nodding off, certain brain cells are already in shut down mode. This means parts of our brain are already asleep while the rest is still functioning. A bit like closing down one window on your computer screen while the others remain active.

Actually, it may be that certain neurons are more affected than others when we get tired, and these are the ones that go “off-line” even when the brain on EEG is still showing a wakeful pattern.
The problem is that if certain groups of brain cells or areas are dozing wile the rest of us is still awake, this is still likely to impair our performance.

Researchers at the University of Winsconsin-Madison monitored 20 brain cells in rats to see which brain cells stayed awake when the rats were tired. Of the 20 brain cells, 18 stayed awake, but two showed signs of being asleep, with brief periods of EEG activity alternating with periods of neural silence. Plus the rats were noticed to be making mistakes. They were noticed to be less able to manouevre their paws accurately to pick up a food pellet or dropped the food pellet more frequently.

Why does our brain do this?

Why parts of our brains should take these micro-naps when we are still awake but tired has yet to be explained. Maybe it is a protective mode the brain has developed to allow those especially fatigued neurons to get the rest they need.
Maybe too it could explain why some of those more aberrant events occur when we are tired, such as when I found myself holding the dog lead and opening the fridge to put it away the other night. Or maybe there’s another reason for that!

Vladyslav V. Vyazovskiy, Umberto Olcese, Erin C. Hanlon, Yuval Nir, Chiara Cirelli, Giulio Tononi. Local sleep in awake rats. Nature, 2011; 472 (7344): 443 DOI: 10.1038/nature10009

Dr Jenny Brockis

Dr Jenny Brockis is a medical practitioner and internationally board-certified lifestyle medicine physician, workplace health and wellbeing consultant, podcaster, keynote speaker and best-selling author. Her new book 'Thriving Mind: How to Cultivate a Good Life' (Wiley) is available online and at all good bookstores.

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