Researchers have long wished to understand the connection between sleep and memory, especially how the brain encodes long-term memories during slow-wave sleep (while discarding others), or the deep sleep that occurs during the initial hours of one’s rest. Recent research sheds fascinating new light on the issue, but to understand how this works, scientists had to literally take brain samples from living people. The results could help us develop technologies that could one day improve our ability to form deep, long memories.
The 45 patients who donated their brains to science had to undergo neurosurgery for preexisting conditions (33 for drug-resistant epilepsy and 12 for brain tumors) and gave prior written consent. Franz Xaver Mittermaier, the first author of a study in the journal Nature Communications that examined those brain samples, told Salon that the patients’ participation was crucial to the scientists’ success.
“The reason why we were able to address these questions for the first time at a mechanistic level, is because we received very rare alive brain tissue samples from patients who underwent surgery for drug-resistant epilepsy or brain tumors,” Mittermaier said, adding that they strictly adhered to ethical requirements and are “deeply thankful” to the patients for making their sacrifice.
Prior to this research, scientists already understood that each night, memories transfer from short-term storage in the hippocampus to long-term storage in the neocortex during slow-wave sleep. Thanks to electroencephalography, researchers can even link slow-wave sleep to a process of synchronous changes in electrical voltages in thousands of neurons, known as up and down states.
“We, for the first time, show that these up and down states affect how human brain cells communicate with each other,” Mittermaier said. In addition to learning more about the strength of the connections between neurons, or synapses, they also broke down the cellular mechanisms behind how synapses perform these basic functions. “The results that our experiments generated are crucial because they deepen our understanding of how the brain achieves long-term memory storage and form the basis that will allow us to understand what goes wrong in disorders where memory is impaired.”
He also stressed the indispensable contributions of the patients. By giving tissues that would otherwise have been discarded — 38 samples from the temporal cortex, five from the frontal cortex and two from the parietal association cortices — they provided the doctors with an invaluable tool. The professionals had to work quickly too, as they had less than thirty minutes to deliver the tissues from the operating room to the laboratory.
“After neurosurgical resection, tissue samples were immediately submerged in a sterile bottle containing ice-cold, carbogen-gassed (95/5% O2/CO2) sucrose-containing artificial cerebrospinal fluid,” the study authors write. “The bottle was sealed gas-tight and placed in a styrofoam box with ice for transport to the laboratory.”
That was the only way to study the brain tissue samples while they were technically still alive. One major drawback to the study is a lack of control subjects. But all of the patients had legitimate reasons for wanting a part of their brain removed: they were sick. “While disease effects cannot be ruled out entirely, neurosurgical resections ultimately represent the only opportunity to investigate human synapses,” the authors explain in their paper.
If you want to improve your own sleep health, you don’t need an Apple Watch or other tech to monitor your sleep, according to Mittermaier. While smartwatches can help optimize one’s sleep hygiene and are therefore “probably useful,” he argues there are much simpler ways to improve one’s sleep health.
“It is not just the duration of deep sleep stages but also an intact structure of our sleep,” Mittermaier said. “A ballpark number would be that 10% to 25% of the entire seven to eight hours of sleep should be in NREM sleep 3. During childhood and adolescence, it should be more (20 to 40%).”
Mittermaier hopes that ordinary people will realize, as a result of their study, that sleep is important to their overall health. Even though we live in a culture that values hustling over rest, sleep is not merely a period of inactivity. The body undergoes complex processes of self-repair that are crucial to a person’s optimal performance in all areas of their life.
“Sleep is a fascinating phenomenon,” Mittermaier said. “It is highly conserved across species — believe it or not, but even fruit flies sleep.”
Humans spend between one-quarter and one-third of their lives asleep, and they suffer serious health problems when it is interrupted, disturbed or otherwise lacking.
“Depriving humans of sleep leads to all sorts of problems and can cause serious harm,” Mittermaier said. “To me, it felt like a great privilege being put in a position where I get to study this fascinating topic.”
