A woman asleep in the driver's seat of her car.
(photo credit: INGIMAGE)
You haven’t been imagining it: When you’re exhausted and haven’t had enough sleep, individual neurons in the brain actually slow down, according to a joint Israeli-American research team.
Their study was recently published in the Nature Medicine journal.
Sleep rhythms can disrupt normal activity in specific regions of the brain, said researchers from Tel Aviv University
, the University of California at Los Angeles and the University of Wisconsin-Madison.
It’s already been proven that sleep deprivation slows down our reaction time, but it has been unclear how exactly the lack of sleep affects brain activity and subsequent behavior.
The team was led by Dr. Yuval Nir of Tel Aviv University’s Sackler Faculty of Medicine and Sagol School of Neuroscience; and Prof. Itzhak Fried of UCLA, TAU and Tel Aviv Sourasky Medical Center, together with sleep experts Prof. Chiara Cirelli and Prof. Giulio Tononi in Wisconsin.
The researchers found that individual neurons slow down when we are sleep deprived, leading to delayed behavioral responses to events taking place around us. The neural lapse – or slowdown – affects the brain’s visual perception and memory associations.
“Since drowsy driving can be as dangerous as drunk driving, we hope to one day translate these results into a practical way of measuring drowsiness in tired individuals before they pose a threat to anyone or anything,” Nir said.
“When a cat jumps into the path of our car at night, the very process of seeing the cat slows down. We’re therefore slow to hit the brakes, even when we’re wide awake.
“When we’re sleep-deprived, a local intrusion of sleep-like waves disrupts normal brain activity while we’re performing tasks,” he explained.
Researchers recorded brain activity of 12 epileptic patients who 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.
During their hospitalization, their neuron activity was continuously recorded.
After being kept awake all night to accelerate their medical diagnosis, the patients were presented with images of famous people and places that they were asked to identify as fast as possible.
“Performing this task is difficult when we’re tired and especially after pulling an all-nighter,” noted 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 response of individual neurons, leading to behavioral lapses.”
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 responses of individual neurons in the temporal lobe – the region associated with visual perception and memory – changed when sleep-deprived subjects were slow to respond to a task.
“During such behavioral lapses, the neurons gave way to neuronal lapses – slow, weak and sluggish responses,” added Fried.
“These lapses occurred when the patients were staring at the images before them, while neurons in other regions of the brain
were functioning as usual.”
The team then examined the dominant brain rhythms in the same circuits by studying the local electrical fields measured during lapses.
“We found that neuronal lapses co-occurred with slow brain waves in the same regions,” Nir said. “As the pressure for sleep mounted, specific regions ‘caught some sleep’ locally. Most of the brain was up and running, but temporal lobe neurons happened to be in slumber, and lapses subsequently followed.”