Controlling memory by triggering specific brain waves during sleep

July 6, 2017, Institute for Basic Science
The electrical fields of groups of neurons in a certain region of the brain give rise to specific patterns of brain waves. Different areas of the brain generate characteristic squiggles of electroencephalogram (EEG) tracings. Peaks (up-states) represent neurons firing at the same time, while minima (down-states) are the sign of neuronal silence. Depending on the origin, frequency and shape, it is possible to distinguish slow oscillations from the cortex, spindles from the thalamus, and ripples from the hippocampus. Credit: IBS, photo modified from Phduet,

Have you ever tried to recall something just before going to sleep and then wake up with the memory fresh in your mind? While we absorb so much information during the day consciously or unconsciously, it is during shut eye that a lot of facts are dispatched to be filed away or fall into oblivion. A good quality sleep is the best way to feel mentally refreshed and memorize new information, but how is the brain working while we sleep? Could we improve such process to remember more, or maybe even use it to forget unwanted memories?

Scientists at the Center for Cognition and Sociality, within the Institute for Basic Science (IBS), enhanced or reduced mouse memorization skills by modulating specific synchronized during deep sleep. This is the first study to show that manipulating sleep oscillations at the right timing affects memory. The full description of the mouse experiments, conducted in collaboration with the University of Tüebingen, is published in the journal Neuron.

The research team concentrated on a non-REM deep sleep phase that generally happens throughout the night, in alternation with the REM phase. It is called slow-wave sleep and it seems to be involved with memory formation, rather than dreaming.

During , groups of neurons firing at the same time generate brain waves with triple rhythms: slow oscillations, spindles, and ripples. Slow oscillations originate from neurons in the cerebral cortex. Spindles come from a structure of the brain called thalamic reticular nucleus and spike around 7-15 per second. Finally, ripples are sharp and quick bursts of electrical energy, produced within the , a brain component with an important role in spatial memory.

The first mouse is a control which did not undergo any stimulation of thalamic spindles overnight. The second mouse had thalamic spindles induced in phase with the slow oscillations. It does not move so much around the cage (freezing, fear response), as it was better able to recall the incident which happened in the same location the day before. Credit: Institute for Basic Science (background image modified from

"Often during the night a regular pattern is manifested, where a slow oscillation from the cortex is immediately followed by a thalamic spindle and while this happens, a hippocampal ripple appears in parallel. We believe that the correct timing of these three rhythms acts like a communication channel between different parts of the brains that facilitates memory consolidation," explains Charles-Francois V. Latchoumane, first co-author of the study.

The researchers focused on spindles because it was shown that the number of spindles is connected with memorization. It has been shown that the number of spindles increases following a day stuffed with learning and declines in the elderly, and in patients with schizophrenia. This is the first study to show that artificial thalamic spindles affect memory, if administered in sync with slow oscillations.

In the experiment, were put in a special cage and given a mild electric shock after hearing a tonal noise. The day after, their memory was tested, by checking their fear reaction in response to either the same noise or the same cage. Latchoumane explains that this could be simplified and compared to the experience of hearing a fire alarm in a certain location, like a cafe. The incident would be followed by either another visit to the same cafe or the sound of the fire alarm in another cafe on the following day.

At nighttime between the two days, scientists introduced artificial thalamic spindles in some of the mice using a light-based technique called optogenetics. The mice were divided into three groups. The first group received the light input just after the slow oscillations, so their spindle could form a triple rhythm (in phase): slow oscillation-spindle-ripples. In the second group the light stimulations were applied later "out of sync". The third group was used as a control and did not receive any light stimulation.

Mice were located in a cage and give a mild electric shock after hearing a noise (left). During the night an optogenetic method (center) was used in some of the mice to induce thalamic spindles artificially. The mice were divided into three groups: in the first group the spindle could form a triple rhythm (IN, red), in the second group the spindle was induced "out of sync" (OUT, green) and in the third group no stimulation was received (NoSTIM, black). The day after, the researchers checked if the mice remembered either the location or the noise (right). If the mice recall the incident, they freeze in fear. If the thalamic spindles were induced in phase with the slow oscillations (IN, red), then the mice were better at remembering the location. If the same noise was presented in a different location, all mice were equally good at remembering it. Credit: IBS, graphics modified from

The day after, mice were placed in the same location and their movement was recorded. The mice of the first group were frozen in fear 40% of the time, even in absence of the noise. On the contrary, mice in the second and third groups only froze up to 20%. Instead, when the mice heard the same tone in a different location, remembered the tone and froze in fear up to 40% of the time, independently from the group they belonged to. The hippocampus is involved in spatial memories which might explain the difference.

The opposite was also true: it was possible to make mice forget. By reducing the number of overnight spindles, the researchers could reduce the memory recall.

The research team thinks that the thalamus is the coordinator of long-term memory consolidation, the process where recently acquired information is transferred from the hippocampus to the cortex to be filed away as long-term memory. The hippocampus is like a hub, where a lot of information comes in and has to be redirected to the correct destination within the brain, especially to the cortex. This study shows that the thalamus seems to mediate the information exchange between hippocampus and cortex. "We think that memorization during has to do with time coordination. If the hippocampus tries to exchange information when the cortex neurons are not ready to receive it, the information could be wasted," describes Latchoumane. "Slow oscillations might be the signal used by the cortex to flag that it is ready to accept information. Then, the thalamus would alert the hippocampus via the spindles."

It is possible to foresee that patients with memory deficiencies could benefit from translation of this research into humans. However, several points need to be clarified: can we manipulate single memories independently? Is the REM phase influencing the outcome? How is stored retrieved? While waiting for the next research outcomes on the science of sleep, sweet dreams... and sweet memories too.

Explore further: Brain consolidates memory with three-step brainwave

More information: Neuron (2017). DOI: 10.1016/j.neuron.2017.06.025

Related Stories

Brain consolidates memory with three-step brainwave

September 22, 2015
Our long-term memory is consolidated when we sleep. Short-term memory traces in the hippocampus, an area deep in the brain, are then relocated to more outer parts of the brain. An international team of neuroscientists, among ...

'Princess Leia' brainwaves help sleeping brain store memories

November 15, 2016
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 ...

How the brain consolidates memory during deep sleep

April 14, 2016
Research strongly suggests that sleep, which constitutes about a third of our lives, is crucial for learning and forming long-term memories. But exactly how such memory is formed is not well understood and remains, despite ...

Entorhinal cortex acts independently of the hippocampus in remembering movement, study finds

January 12, 2017
Until now, the hippocampus was considered the most important brain region for forming and recalling memory, with other regions only contributing as subordinates. But a study published today in Science finds that a brain region ...

Enhanced hippocampal-cortical coupling improves memory

May 18, 2016
For the first time, scientists in the Center for Interdisciplinary Research in Biology (CNRS/INSERM/Collège de France) have produced direct evidence that the long-term storage of memories involves a dialogue between two ...

How sleep deprivation affects memory-making in the brain

April 7, 2017
Scientists have known that a lack of sleep can interfere with the ability to learn and make memories. Now, a group of University of Michigan researchers have found how sleep deprivation affects memory-making in the brain.

Recommended for you

Forty percent of people have a fictional first memory, says study

July 17, 2018
Researchers have conducted one of the largest surveys of people's first memories, finding that nearly 40 per cent of people had a first memory which is fictional.

Protein found to be key component in irregularly excited brain cells

July 17, 2018
In a new study in mice, researchers have identified a key protein involved in the irregular brain cell activity seen in autism spectrum disorders and epilepsy. The protein, p53, is well-known in cancer biology as a tumor ...

Insight without incision: Advances in noninvasive brain imaging offers improvements to epilepsy surgery

July 17, 2018
About a third of epilepsy sufferers require treatment through surgery. To check for severe epilepsy, clinicians use a surgical procedure called electrocorticography (ECoG). An ECoG maps a section of brain tissue to help clinicians ...

New drug target for remyelination in MS is identified

July 17, 2018
Remyelination, the spontaneous regeneration of the fatty insulator in the brain that keeps neurons communicating, has long been seen as crucial to the next big advance in treating multiple sclerosis (MS). However, a lack ...

Artificial neural networks now able to help reveal a brain's structure

July 17, 2018
The function of the brain is based on the connections between nerve cells. In order to map these connections and to create the connectome, the "wiring diagram" of a brain, neurobiologists capture images of the brain with ...

Convergence of synaptic signals is mediated by a protein critical for learning and memory

July 16, 2018
Inside the brain, is a complex symphony of perfectly coordinated signaling. Hundreds of different molecules amplify, modify and carry information from tiny synaptic compartments all the way through the entire length of a ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.