Why you're jittery after a bad night's sleep


Gaps between brain cells suffer with you don't get enough shut-eye. Amy Middleton reports.


OK, an air horn would be enough to startle a well-rested person. But when you're extra-tired, you're jumpier, and neuroscientists have figured out why that may be.
Tara Moore / Getty Images

Ever wondered why you’re particularly twitchy after a bad night’s sleep, even though your brain feels like cotton wool?

Experts have long theorised that we have a foggy brain when we’re tired because sleep deprivation affects the connections between our neurons, effectively interrupting the brain’s messaging system, like bad mobile phone reception.

A new study, published in Nature Communications, set out to find evidence to support this theory. And the results offer some science behind the twitches that cause us to spill our coffee on sleepy mornings.

The European research team, led by Christoph Nessen at University Medical Centre in Freiburg, Germany, focused on homeostatic plasticity – that is, the ability of our neurons to contain their excitement and consistently receive and deliver messages properly.

This process centres on the performance of gaps between brain cells that allow messages to travel between neurons called synapses.

During the study, the team analysed brain activity of 20 adult participants after a night of normal sleep, and after a night of interrupted sleep.

In both contexts, they used magnetic pulses to activate neurons in the motor cortex – part of the brain responsible for movement – to make a subject move his or her left hand.

They found sleep-deprived brains required significantly less magnetic pulse to instigate movement. This suggested the tired neurons were overly excitable, possibly because their strength had not been regulated by sleep.

Sleep-deprived brains also showed reduced levels of brain-derived neurotrophic factor, the molecule responsible for regulating the strength of synapses in response to varying levels of activity. This process helps facilitate learning and memory.

So it was no surprise that when participants were asked to recall words in a particular series, after just one sleepless night, the subjects did poorly compared to being fresh and well-rested.

This combination of results, the researchers say, goes some way to illustrating how neural connectivity is interrupted by sleeplessness.

  1. http://nature.com/articles/doi:10.1038/ncomms12455
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