Sleep study How our brain learns to sleep

Why we can remember some things and not others

Why do you remember some things well and others quickly become forgotten? And what role does sleep play in that? These were the questions a German research team dealt with in a recent study on sleep. The researchers examined how the brain processes and stores previously learned things in their sleep.

A team from the Ruhr-Universität Bochum and the Rheinische Friedrich-Wilhelms-Universität Bonn investigated which activity patterns in the brain occur when people learn new things and which mechanisms in sleep are responsible for whether these things are retained or forgotten. The study results have recently been published in the journal "Nature Communications".

When we learn, our brains react with certain activity patterns. During sleep, the same patterns are run through again. It will decide whether we remember it later or not. (Image: pathdoc / fotolia.com)

Even things we can not remember are stored in the brain

In their research, the researchers documented the brain activity of epilepsy patients. These had been implanted in the brain due to an upcoming surgery electrodes. This allowed the scientists to record the exact activity patterns that occur during both learning and sleeping. It showed that even things that can not be remembered can be retrieved while sleeping.

Course of the study

The participants received small learning tasks before going to bed. You should memorize a series of pictures before nap. Meanwhile, the sleep researchers recorded their brain activity. They were able to discover that the nerve cells in the brain responded in different ways to each individual image. These measurable high-frequency activity fluctuations are referred to as gamma oscillations. After sleep it was determined which pictures the participants could and did not remember.

So previously learned in sleep is retrieved

The respective gamma oscillations that had previously appeared while viewing the motifs occurred again during the sleep phase, the researchers report. In doing so, the brain not only reconstructed the images that the subjects could remember, but also those that they could not remember. "The forgotten pictures do not just disappear from the brain," comments Dr. med. Hui Zhang in a press release on the study results.

How does it decide if we forget something or not??

According to the sleep researchers, not only the reactivation of the gamma oscillations is important for remembering, but also the involvement of the brain region hippocampus, in which the memory is located. Here it comes to extremely fast activity fluctuations, which are called Ripples. When a sleep-coupled activation of gamma oscillations with the ripples occurred during sleep, the image was later recalled, according to the research team. However, this phenomenon only applied to certain sleep phases and not while the participants were awake.

The study results in detail

The team around Dr. Hui Zhang and Professor Nikolai Axmacher was able to recognize even more detailed information. When viewing the pictures, different processing phases were shown. This allowed the researchers to identify a superficial and a deep processing phase. The first phase lasted about half a second. The deep processing followed afterwards. When the above-mentioned ripples were activated in the superficial processing phase, the participants could later no longer remember the image. By contrast, the image remained in memory when the activation of the ripples occurred in the deep processing phase.

Sleep is important for our ability to learn

As early as a year ago, sleep researchers at the University of Zurich discovered that deep sleep is very important for the brain's ability to learn. The scientists were able to establish the first causal link that deep sleep is essentially coupled with human learning ability. These studies showed that the connections between the nerve cells (synapses) during the awake phase are in an active state when environmental impressions are gained. Only in sleep this condition normalizes again. Without a recovery phase, the synapses would remain in an activated state, blocking any learning ability. (Vb)