Summary: Newly discovered rotating waves of brain activity that repeat during the night are responsible for forming associations between different aspects of a day’s memories, a new study reports.
Source: Salk Institute.
Salk researchers discover rotating waves of brain activity that repeat during night.
Every night while you sleep, electrical waves of brain activity circle around each side of your brain, tracing a pattern that, were it on the surface of your head, might look like the twin hair buns of Star Wars’ Princess Leia. The Salk Institute scientists who discovered these circular “Princess Leia” oscillations, which are described in the journal eLife, think the waves are responsible each night for forming associations between different aspects of a day’s memories.
“The scale and speed of Princess Leia waves in the cortex is unprecedented, a discovery that advances the Brain Research through Advancing Innovative Neurotechnologies (BRAIN) Initiative,” says Terrence Sejnowski, head of Salk’s Computational Neurobiology Laboratory.
Short-term memory of events is stored in an area of the brain called the hippocampus. Long-term memories, however, are encoded in the neocortex. The transfer of memories from the hippocampus to the neocortex is called memory consolidation, and happens while we sleep.
Sleep spindles—a type of brain wave pattern known to occur in the earliest stages of non-REM sleep—are associated with memory consolidation. Previous studies showed that the more sleep spindles a human brain exhibits overnight, the more numbers one would remember the next day. But exactly how these sleep spindles related to memory was unclear, and scientists were limited by the fact that electrodes could only detect these spindles at one place in the brain at a time.
“For a long time, neuroscience researchers had to record activity at one point in the brain at a time and put many data points together without seeing the whole picture simultaneously,” says Lyle Muller, a Salk research associate and first author of the new work. Scientists had long believed that each sleep spindle oscillation peaked at the same time everywhere in the neocortex of the brain.
Sejnowski and Muller wanted to see the broader picture, however, and turned to large-scale recordings, called intracranial electrocorticograms (ECoGs), that can measure activity in many areas of the brain at once. Patients with epilepsy often have ECoG arrays temporarily implanted in their brains to determine the location in the brain of epileptic seizures, so the scientists were able to study all the data collected from five such patients on healthy, seizure-free nights.
When they crunched the ECoG data from each night, the researchers were in for a surprise: the sleep spindles weren’t peaking simultaneously everywhere in the cortex. Instead, the oscillations were sweeping in circular patterns around and around the neocortex, peaking in one area, and then—a few milliseconds later—an adjacent area.
“We think that this brain activity organization is letting neurons talk to neurons in other areas,” says Muller. “The time scale that these waves travel at is the same speed it takes for neurons to communicate with each other.”
Throughout the night, the researchers observed the same rotating patterns, each lasting about 70 milliseconds but repeating hundreds and hundreds of times over a matter of hours.
This video illustrates five oscillation cycles during which potential measured from the surface of the cortex exhibits stereotyped rotating patterns.
Why would different areas of the neocortex need to communicate to store memories? One single memory is composed of different components (smell, sound, visuals) that are stored in different areas of the cortex. As a memory is being consolidated, Muller and Sejnowski hypothesize, circular sleep spindle waves help form the links between these different aspects of a single memory.
“If we understand how memories are being linked up like this in the brain, we could potentially come up with methods for disrupting memories after trauma,” says Sejnowski. “There are also disorders including schizophrenia that affect sleep spindles, so this is really an interesting topic to keep studying.”
Other researchers on the study were Dominik Koller of the Salk Institute; Giovanni Piantoni and Sydney S. Cash of Massachusetts General Hospital; and Eric Halgren of the University of California San Diego.
Funding: The work and the researchers involved were supported by grants from the National Institutes of Health, Howard Hughes Medical Institute, the Swartz Foundation and the Office of Naval Research.
Source: Salk Institute
Image Source: This NeuroscienceNews.com image is adapted from the Salk Institute video.
Video Source: The video is credited to Salk Institute.
Original Research: Full open access research for “Rotating waves during human sleep spindles organize global patterns of activity that repeat precisely through the night” by Lyle Muller, Giovanni Piantoni, Dominik Koller, Sydney S Cash, Eric Halgren, and Terrence J Sejnowski in eLife. Published online November 15 2016 doi:10.7554/eLife.17267
The researchers will present their findings at Neuroscience 2016 in San Diego between November 12 – 16, 2016.
[cbtabs][cbtab title=”MLA”]Salk Institute. “”Princess Leia” Brainwaves Help Sleeping Brain Store Memories.” NeuroscienceNews. NeuroscienceNews, 15 November 2016.
<https://neurosciencenews.com/memory-sleep-princess-leia-5520/>.[/cbtab][cbtab title=”APA”]Salk Institute. (2016, November 15). “Princess Leia” Brainwaves Help Sleeping Brain Store Memories. NeuroscienceNews. Retrieved November 15, 2016 from https://neurosciencenews.com/memory-sleep-princess-leia-5520/[/cbtab][cbtab title=”Chicago”]Salk Institute. “”Princess Leia” Brainwaves Help Sleeping Brain Store Memories.” https://neurosciencenews.com/memory-sleep-princess-leia-5520/ (accessed November 15, 2016).[/cbtab][/cbtabs]
Abstract
Rotating waves during human sleep spindles organize global patterns of activity that repeat precisely through the night
During sleep, the thalamus generates a characteristic pattern of transient, 11-15 Hz sleep spindle oscillations, which synchronize the cortex through large-scale thalamocortical loops. Spindles have been increasingly demonstrated to be critical for sleep-dependent consolidation of memory, but the specific neural mechanism for this process remains unclear. We show here that cortical spindles are spatiotemporally organized into circular wave-like patterns, organizing neuronal activity over tens of milliseconds, within the timescale for storing memories in large-scale networks across the cortex via spike-time dependent plasticity. These circular patterns repeat over hours of sleep with millisecond temporal precision, allowing reinforcement of the activity patterns through hundreds of reverberations. These results provide a novel mechanistic account for how global sleep oscillations and synaptic plasticity could strengthen networks distributed across the cortex to store coherent and integrated memories.
“Rotating waves during human sleep spindles organize global patterns of activity that repeat precisely through the night” by Lyle Muller, Giovanni Piantoni, Dominik Koller, Sydney S Cash, Eric Halgren, and Terrence J Sejnowski in eLife. Published online November 15 2016 doi:10.7554/eLife.17267
