Sleep Is Local
Think globally, act locally. That old political mantra also is true of the brain – including sleep.
The American model of sleep is relatively simple – light switch on, light switch off. We go out “like a light,” or as others put it, “lie down and die.” Then the light switch goes on and just like our computer, we’re on again.
Except that’s not what happens. Getting the brain to go into sleep is a symphonic process where tens of millions of neurons must coordinate – with superb accuracy – so that everything comes together. It’s rather like trying to get a dozen separate orchestras simultaneously play the Star Spangled Banner. Only two of the orchestras are in the concert hall – one one stage and the other in the balcony. Other orchestras are seated out in the parking lot and several different bus stops, while several more are playing clear across town. If they don’t work together, or the phenomenon we call “sleep” doesn’t happen.
And just like the different orchestras, sleep operates locally. Many a severely sleep deprived individual has described feeling that their shoulder or their arms were asleep, while other parts were fully “awake.” Could it be that sleep in animals really is bit by bit and piece by piece, with some parts sleeping and others awake?
It sure could.
Science Follows Technology
It was a coup when Giulio Tononi and Chiara Cirelli and cohorts were lured from Italy to the University of Wisconsin. They had long worked on new technology that allowed studying brain electrical activity in much more detail – and greater speed – that standard electroencephalographic leads. As all of clinical sleep research depends on standard application of those leads, it was expected that Tononi and Cirelli’s research would shake up the world of sleep.
The technology is so good it allows you to accurately study sleep in fruit flies. It also makes it easier to drill down, neuron group by neuron group, to what is happening in the brains of small mammals.
In one of their latest studies, Tononi and Cirelli looked carefully at rats that had been kept awake longer than usual. The rats looked fine. They ran around normally. They performed their usual tasks.
Yet parts of their brain were asleep.
Not just “offline,” as many neurons go when they are not actively engaged. Offline neurons are far from passive, actively remaking themselves even when not engaged in specific tasks.
No, in the kept awake rats, different groups of neurons in areas required for decision making went to sleep, while the neurons around them remained alert. Here were islands of sleep in a sea of wakefulness.
With interesting consequences. For in the rats with pockets of sleeping neurons, decision making was clearly impaired.
Though they looked completely awake.
Implications for People
If people are sleep deprived, they eventually perform less well on cognitive tests. A major question has always been why.
Tononi’s and Cirelli’s study may provide one partial answer. Sleep in rats and in humans appears somewhat similar when it comes to making executive decisions. Keep an animal, including a human being, awake for longer and longer periods of time, and its ability to makes decisions intelligently slowly breaks down.
Perhaps because parts of its brain are asleep.
People can be asleep with their eyes wide open, as Torbjorn Akerstedt showed in Swedish train drivers. The conductors’ brains were clearly fully asleep, even though they were standing up and staring straight ahead.
And if this recent research can generalize like other mammalian work, it probably means humans “fall asleep” bit by bit. For air traffic controllers and bus drivers, airline pilots and medical interns, the longer they’re awake, the worse the decisions they will make. As more groups of neurons go to sleep, less is available to keep us focused, alert, and aware.
So we’ll make more errors. And sometimes, as so commonly occurs with microscleeps, not be aware we’re impaired and making errors.
Because lack of rest really does lead to brain impairment. Which is something to think about the next time you do an all nighter, or drive cross country during the wee hours.
Don’t expect all of your brain to remain awake those nights – especially some parts you really want to use.
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