Aubusson, K. Brain Reboot: How One Sleepless Night May Affect Memory & Learning, Study Finds

The Sydney Morning Herald
August 24,2016

Kate Aubusson

One-third of a life span is a massive slice of time to spend with our eyes closed, but there’s a very good reason humans need so much sleep. We just don’t know what it is.

What does sleep do to our brains? Like a sleep-deprived student trying to muddle through a morning exam, scientists trying to unravel this enduring mystery have been labouring in a heavy fog.

But a new study could help answer this fundamental question, suggesting those hours of slumber allow the brain to rewire the crucial connections between the brain’s neurons that clog up when we’re awake.

This nightly reset is vital for building and preserving memory, as well as our ability to learn new skills and engage with our waking realities, according to the German researchers.

But just one sleepless night may be all it takes to stop the brain’s ability to recalibrate its connections, overloading its synaptic activity and ultimately hampering its ability to form and retain new memories, according to the research paper published Wednesday in Nature Communications.

The researchers set out to test the “synaptic homeostasis hypothesis” that a good night’s sleep allows the brain’s neuron signals to cut through the chaotic “noise” and improve its capacity to encode, or remember, new information.

It is virtually impossible directly test this theory in humans.

Using non-invasive transcranial magnetic stimulation (TMS), the research team was able to indirectly compare the synaptic activity in the brains of 20 individuals (aged between 19 and 25) after one night’s sleep or after one night of sleep deprivation.

The research team used small magnetic pulses to zap the motor cortex – the region responsible for movement – to trigger a muscle twitch in participant’s left hands.

After their sleepless night, participants needed a much lower pulse to activate the hand muscles compared their well-rested counterparts, suggesting their sleep-deprived brains were more excitable, said the researchers lead by psychiatrists Dr Christoph Nissen at Freiburg University, Germany.

The researchers then used the magnetic pulses to imitate the brain activity used to encode new memories. The sleep-deprived participants showed a weaker synaptic response and performed worse in a word-pair memory exercise.

Their blood samples also showed reduced BDNF, a molecule that regulates synaptic plasticity needed for memory and learning.

“Our study provides the first evidence for sleep-wake-dependent dissociation of associative and homeostatic synaptic plasticity in humans,” the researchers concluded.

The results may pave the way for effective treatments for neuropsychiatric disorders.

There is some evidence the experimental treatment – therapeutic sleep deprivation – can improve mood among people with major depression.

The findings suggest the therapy shifts the brain of a depressed patient “into a more favourable window of associative plasticity”, the authors suggested.

Overall, “the findings were a significant step towards a better understanding of basic mechanisms for health performance and potential alterations in neuropsychiatric disorders,” they concluded.

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