Brain consolidates memory with three-step brainwave

September 22, 2015, Radboud University
Brain consolidates memory with three-step brainwave

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 who Mathilde Bonnefond and Til Ole Bergmann from the Donders Institute at Radboud Universiy, now shows how a three-step brain oscillation plays an important part in that process. Nature Neurosciences publishes the results on September 21st.

Bonnefond and Bergmann specialize in research on oscillations: waves of activity. 'Non-rapid eye movement (NREM) sleep is responsible for the consolidation during our sleep', Bonnefond explains. 'NREM is known for its very slow oscillations (SOs). Other types of oscillations are hidden inside these SOs. We discovered that three types of oscillations are nested inside each other in the hippocampus and have a joint function.'

Slow waves, spindles and ripples

Slow oscillations only happen about once per second (~0.75 Hz). In a specific time frame within these SOs, Bergmann, Bonnefond and their colleagues found clusters of oscillations of an intermediate speed: the so called spindles which happen about 15 times per second (12 – 16 Hz). And within these spindles, they found clusters of superfast oscillations called ripples, which happen about 90 times per second (80 – 100 Hz), and which reflect the local reactivation of the memory trace to be shuttled to the cortex.

To summarize: SOs contain spindles, which in their turn contain ripples (see figure 'Bonnefond'). 'Earlier studies only coupled these oscillation types in pairs', Bonnefond explains. 'But now, we see that SOs, spindles and ripples are functionally coupled in the hippocampus. And we hypothesize that they provide fine-tuned temporal frames for the transfer of memory traces to the neocortex.'

Epilepsy

The group of researchers investigated the process in human epilepsy patients during natural sleep. Doctors were looking for the brain areas responsible for their epilepsy, and the current research was done at the same time: with special electrodes, the researchers recorded oscillations from inside the brain. Bonnefond: 'This was a great opportunity to investigate the hippocampus, since it's difficult to measure deep brain regions with classical electrophysiological techniques.'

The patients did not have to remember any specific information. 'You're consolidating memories every night, so we investigated the process in general. The next step would be to link these clustered to specific memories.'

Explore further: Researchers identify potential cause of schizophrenic symptoms

More information: "Hierarchical nesting of slow oscillations, spindles and ripples in the human hippocampus during sleep." Nature Neuroscience DOI: 10.1038/nn.4119

Related Stories

Researchers identify potential cause of schizophrenic symptoms

May 7, 2015
Schizophrenia affects millions of people worldwide but the cause of its wide-ranging symptoms remains largely unknown.

Sound stimulation during sleep can enhance memory

April 11, 2013
Slow oscillations in brain activity, which occur during so-called slow-wave sleep, are critical for retaining memories. Researchers reporting online April 11 in the Cell Press journal Neuron have found that playing sounds ...

Fast ripples confirmed to be valuable biomarker of area responsible for seizure activity in children

July 29, 2011
New research focusing on high-frequency oscillations, termed ripples and fast ripples, recorded by intracranial electroencephalography (EEG), may provide an important marker for the localization of the brain region responsible ...

Scientists have decoded the functioning of the short-term memory

September 26, 2014
School children and university students are often big fans of the short-term memory – not least when they have to cram large volumes of information on the eve of an exam. Although its duration is brief, short term memory ...

Brain training instead of medication to counter insomnia

April 13, 2015
The ability to finally enjoy a good night's sleep is something that can be learned. An Austrian Science Fund FWF project has investigated how this can best be learned and who responds best to such "brain training".

Fluctuations in size of brain waves contribute to information processing

February 8, 2013
Cyclical variations in the size of brain wave rhythms may participate in the encoding of information by the brain, according to a new study led by Colin Molter of the Neuroinformatics Japan Center, RIKEN Brain Science Institute.

Recommended for you

Brainwaves show how exercising to music bends your mind

February 18, 2018
Headphones are a standard sight in gyms and we've long known research shows listening to tunes can be a game-changer for your run or workout.

To sleep, perchance to forget

February 17, 2018
The debate in sleep science has gone on for a generation. People and other animals sicken and die if they are deprived of sleep, but why is sleep so essential?

Lab-grown human cerebellar cells yield clues to autism

February 16, 2018
Increasing evidence has linked autism spectrum disorder (ASD) with dysfunction of the brain's cerebellum, but the details have been unclear. In a new study, researchers at Boston Children's Hospital used stem cell technology ...

Fragile X syndrome neurons can be restored, study shows

February 16, 2018
Fragile X syndrome is the most frequent cause of intellectual disability in males, affecting one out of every 3,600 boys born. The syndrome can also cause autistic traits, such as social and communication deficits, as well ...

Brain-machine interface study suggests how brains prepare for action

February 16, 2018
Somewhere right now in Pyeongchang, South Korea, an Olympic skier is thinking through the twists and spins she'll make in the aerial competition, a speed skater is visualizing how he'll sneak past a competitor on the inside ...

Humans blink strategically in response to environmental demands

February 16, 2018
If a brief event in our surroundings is about to happen, it is probably better not to blink during that moment. A team of researchers at the Centre for Cognitive Science from Technische Universität Darmstadt published a ...

0 comments

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.