How Sleep Nurtures Your Brain

Michael Lasalandra Beth Israel Deaconess Medical Center correspondent

SEPTEMBER 01, 2015

Getting the proper amount of sleep each night doesn’t just help us operate at peak efficiency the next day — it also nurtures the brain itself.

A recent study by researchers in England published in Nature Reviews Neuroscience, found that sleep is important to maintaining the health of our brain’s nerve cells, or neurons, in that it allows them to independently rest and repair themselves. If our neurons attempt to rest while we’re awake, they write, it has a negative effect on our brain performance.

“It’s similar to a complex machine with multiple interactive components,” says Dr. Robert Thomas, a sleep medicine physician and co-director of the Sleep Disorders Clinic at Beth Israel Deaconess Medical Center. “If a machine keeps running and running, over time it will experience wear and tear and ultimately, damage.”

The brain has billions of neurons. Neurons transmit information via the thousands of connections each neuron has with other neurons. The connections change in shape and size as the cells serve their purpose. But all that activity during wakefulness leaves debris — byproducts of normal activity.

”As the cells expend energy and perform, they show evidence of stress, energy deficits and accumulate biological junk,” says Dr. Thomas, who is also an Associate Professor of Medicine at Harvard Medical School. “That junk has to be cleaned out. Sleep serves that vital housekeeping function during which the less important new connections are also removed.”

Sleep allows large numbers of neurons to go off-line, so they can more efficiently address this housekeeping task. They shut down and come back on-line again, fluctuating between ‘on’ and ‘off’ periods lasting a little less than a second each during sleep.

Sleep is vital to learning. Ample sleep helps us get ready to form new memories and, process and cement existing memories into the brain’s architecture. While we’re resting, our brains also grow new neurons. And, sleep restores and resets numerous systems, such as metabolic and autonomic systems that in turn play important functions in brain health. Studies have shown that restricted or interrupted sleep can lead directly to health concerns such as obesity, diabetes, heart disease, hypertension, and emotional and cognitive dysfunction.

“Sleep prepares you for your next bout of wakefulness,” says Dr. Thomas. “Without proper sleep, everything starts falling apart.”

When we’re awake for long periods of time, for example, when we pull an ‘all-nighter,’ different parts of the brain will slow down and go intermittently off-line even when we are technically ‘awake.’ Studies show that sleep-deprived people perform as poorly on driving simulators or hand-eye coordination tests as those who are under the influence of alcohol.

“It isn’t known if brain cells will die with sleep deprivation, but formation of new nerve cells is affected,” says Dr. Thomas. “If you mess with sleep, you may not regenerate your brain as well.”

Another recent study, in the Journal of Neuroscience, was conducted in mice that were either allowed to sleep or forced to stay awake. The study, done at the University of Wisconsin, found that sleep or the lack of it affected gene activity of cells called oligodendrocytes, which are involved in the production of myelin. Myelin covers brain and spinal cord nerve cells as a kind of insulation; it is considered essential to the movement of electrical signals from cell to cell.

The study suggests that sleep seems to turn on genes that play a role in the formation of myelin. At the same time, lack of sleep was linked to genes associated with cell stress and death.

Dr. Thomas says most people need seven or eight hours of sleep per night to function efficiently. Teenagers need about nine. Younger children need more. While most people wake up — biologically speaking — several times per night, usually these are for very brief periods and may not even be noticed.

“There is a need for undisturbed sleep. It’s like the difference between highway driving and city driving,” he says. “Highway driving is more efficient. City driving, with all its starts and stops, is less efficient and wears you out. If sleep is excessively interrupted, it cannot perform its function.”

September 2015

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Above content provided by Beth Israel Deaconess Medical Center. For advice about your medical care, consult your doctor.