When you sleep, your brain’s electrical waves circle around to either side of your head, making a pattern resembling the twin buns of Princess Leia in ‘Star Wars.’ Salk Institute scientists discovered these oscillations in electrical activity and described them in the journal, eLife. They believe the waves are responsible for the memory associations that are formed during the day.
Head of the Computational Neurobiology Laboratory at Salk Institute, Terrence Sejnowski, noted that the speed and scale of these electrical waves in the brain is unheard of, which will help to advance the Brain Research through the Advancing Innovative Neurotechnologies Initiative.
The hippocampus stores all short-term memories and events; however, the long-term memories reside within the neocortex and are encoded like secret messages. Memory transfers from hippocampus to neocortex are what is known as memory consolidation, which happens during sleep.
Sleep spindles are involved in memory consolidation, and these spindles happen in the earlier stages of non-REM sleep. Studies in the past have found that people who had more sleep spindles overnight were able to remember more numbers the next day; however, the exact nature of how these sleep spindles relate to memory was unclear. This limited the research because the electrodes used to identify sleep spindles could only find them in one area of the brain at a time.
One of the authors of this study, Lyle Muller, notes that previous neuroscience research had to record activity in one area of the brain at a time, and then put all the data points together later, without looking at the whole picture. Many scientists believed the oscillating spindles were peaking at the same time all within the neocortex.
The lead authors of the study wanted the broader picture, though, so they turned their attention to large-scale recordings. This is known as intracranial electrocorticograms, or ECoGs. This study measures brain activity in multiple areas at the same time. ECoG arrays are often implanted into the brains of epileptic patients to try and identify the exact origin of their seizures. In this way, scientists were able to look at all the data at once from five different patients on those seizure-free nights.
It was a surprise to find the results after putting in all the ECoG data for each night. The theory that spindles peaked simultaneously throughout the cortex was proven wrong. The oscillations swept in circular patterns on either side of the brain around the neocortex, peaking in specific areas and then again in an adjacent area just milliseconds later.
Mr. Muller stated that they believe the activity is the result of neurons talking to other neurons in various areas of the brain. The time it takes the waves to travel is the same speed it would take for communication between different neurons.
These same swirling patterns were noted all throughout the night, and each one lasted for approximately 70 milliseconds. They repeated hundreds of times in a matter of hours.
A single memory has various components that are obtained through each of our senses, and each component is stored in a different area of the cortex. This is why parts of the neocortex need to be able to communicate with each other in order to store and transfer memories. The oscillating spindle waves are thought to help form links between the different components of each memory.
These findings may help determine new methods for disrupting memories after a trauma. The results open the door to new treatments for other brain diseases that affect sleep spindles as well, such as schizophrenia, so researchers in this study believe further study is warranted.
Rachael Herman is a professional writer with an extensive background in medical writing, research, and language development. Her hobbies include hiking in the Rockies, cooking, and reading.
© 2021 American Sleep Association.