You may be staying up way too late every night scrolling through Facebook, but your brain cells aren’t necessarily along for the ride.
Researchers at Tel Aviv University (TAU) together with University of California, Los Angeles (UCLA) and the University of Wisconsin-Madison, say that when we are sleep-deprived, the activity of our brain is affected because individual neurons slow down, damaging the brain’s visual perception and memory associations.
Much has been written about the adverse effects of lack of sleep in humans: we become grumpy and foggy, and see damage to our memory, health, looks and sex lives too. It has been established, too, that sleep deprivation slows down our reaction time, but what was still unclear was exactly how lack of sleep affects brain activity and subsequent behavior.
Enter the new study, which found that when they are deprived of sleep, neurons in the temporal lobe of the brain — the region associated with visual perception and memory — take a figurative nap, having been overcome by slow brainwaves, the kind that are typically found in our brains while we sleep.
Neurons are nerve cells that transmit signals to and from the brain at up to 200 mph. They are in the part of the brain that deals with stimuli, and are responsible for processing information.
It is this slowdown of individual neurons, when we are sleep-deprived, that leads to delayed behavioral responses to events taking place around us, the new study, published in Nature Medicine, reveals.
“When we’re sleep-deprived, a local intrusion of sleep-like waves disrupts normal brain activity while we’re performing tasks,” said Yuval Nir of TAU’s Sackler Faculty of Medicine and Sagol School of Neuroscience who led the study.
The study was an international collaboration led by TAU’s Nir; Prof. Itzhak Fried of UCLA, TAU and Tel Aviv Medical Center; and sleep experts Profs. Chiara Cirelli and Giulio Tononi at the University of Wisconsin-Madison.
During the study, investigators recorded the neuron activity in the brains of 12 epilepsy patients who were the subjects of a study to find out why they had previously shown no or little response to drug interventions at UCLA.
The patients were hospitalized for a week and implanted with electrodes to pinpoint the place in the brain where their seizures originated.
After being kept awake all night to accelerate their medical diagnosis, the patients were presented with images of famous people and places, which they were asked to identify as quickly as possible.
In over 30 image experiments, the research team recorded the electrical activity of nearly 1,500 neurons, 150 of which clearly responded to the images. The scientists examined how the responses of individual neurons in the temporal lobe changed when sleep-deprived subjects were slow to respond to a task.
“Performing this task is difficult when we’re tired and especially after pulling an all-nighter,” says Nir. “The data gleaned from the experiment afforded us a unique glimpse into the inner workings of the human brain. It revealed that sleepiness slows down the responses of individual neurons, leading to behavioral lapses.”
“The study showed that what we can measure behaviorally — a slowing down of responses — goes down to the level of the neurons,” said UCLA’s Fried by phone. The nerve cells of those who were sleep-deprived were “slower and more sluggish,” he said. And slow brainwaves, characteristic of when we sleep, “were intruding into these areas.”
As the pressure for sleep mounted, specific regions of the brain “caught some sleep,” explained Nir. “Most of the brain was up and running, but temporal lobe neurons happened to be in slumber,” and behavioral lapses subsequently followed, he said.
Nir said he hopes the results of the study will translate into practical ways to measure drowsiness in tired individuals before they pose a threat to anyone or anything, “since drowsy driving can be as dangerous as drunk driving.”