Scientists still haven’t figured out why we spend a third of our lives sleeping. But, for the first time, research into the impact of sleepless nights on brain function has revealed what happens when we sleep, and may lead to new treatments for depression.
Sleep resets the steady build-up of connectivity in the human brain which takes place in waking hours. This appears to be crucial for brains to remember and learn so we can adapt to the world around us.
Christoph Nissen, a psychiatrist who led the study at the University of Freiburg described his experiments and findings in the journal Nature Communications this week.
Some 11 men and nine women aged 19 to 25 took part in tests after a good night’s sleep or a night without sleep.
On the sleepless night, participants played games, went for walks and cooked food but were not allowed caffeine. Staff watched to make sure they stayed awake.
In the first round of experiments, Nissen used magnetic pulses to make neurons fire in the volunteers’ brains and cause a muscle in the left hand to twitch. When sleep-deprived, far weaker pulses were enough to make the muscles move. This implied that sleepless brains are in a more excitable state, their neurons more strongly connected than after a good sleep.
In the second round, using a simple memory test, Nissen found it harder to get the neurons to respond in sleep-deprived people, a sign that the process of writing memories was impaired by sleep loss.
The results suggest sleep allows the brain to calm its activity so memories can be written down.
But the sleep-deprived brain becomes noisy with electrical activity and so feeble at laying down memories that the process is all but blocked.
Understanding how sleep affects brain connections could do more than answer why we snooze so much. Shift workers and military personnel who have to cope with sleep deprivation could benefit from new drugs or countermeasures that restore normal brain connectivity.
Nissen is particularly excited about its potential for helping people with mental health disorders.
One radical treatment for major depression is therapeutic sleep deprivation. The new research offers a deeper understanding of the phenomenon which could be adapted to produce more practical treatments.
“Why we sleep is a fundamental question. Why do we spend so much of our lives in this brain state? This work shows us that sleep is a highly active brain process and not a waste of time. It’s required for healthy brain function,” said Nissen.
“If you deprive people with major depression of sleep for one night, about 60% show a substantial improvement in mood, motivation and cognitive function. We think it works by shifting these patients into a more favourable state.
Therapeutic sleep deprivation is not much use because many patients relapse after the next night’s sleep. But that is not the point, Nissen says.
“It proves that it’s possible to shift a person’s mood from one state to another within hours. The idea is that we use sleep and sleep deprivation to understand the brain and develop new treatments. If you think about antidepressants or psychotherapy, it can take weeks or months to see any effects.”