Why we can remember some things and not others
Why do you remember some things well and others are quickly forgotten? And what role does sleep play in this? A German research team dealt with these questions in a current sleep study. The researchers investigated how the brain processes and stores what it has learned in sleep.
A team from the Ruhr-Universität Bochum and the Rheinische Friedrich-Wilhelms-Universität Bonn examined which activity patterns occur in the brain when people learn new things and which mechanisms are responsible for whether these things are kept or forgotten during sleep. The study results were recently published in the journal "Nature Communications".
Things that we cannot remember are also stored in the brain
In their investigations, the researchers documented the brain activity of epilepsy patients. Due to an upcoming operation, they had electrodes implanted in the brain. In this way, the scientists were able to record the precise activity patterns that take place during both learning and sleeping. It turned out that even things that you can no longer remember can be called up during sleep.
Course of the study
The participants were given small learning tasks before going to bed. You should memorize a series of pictures before taking a nap. The sleep researchers meanwhile recorded their brain activities. In this way, they were able to determine that the nerve cells in the brain reacted to each individual image in different ways. These measurable high-frequency activity fluctuations are called gamma oscillations. After sleep, it was then determined which pictures the participants could remember and which they could not.
In this way, previously learned information is recalled during sleep
The respective gamma oscillations, which had previously been shown when looking at the motifs, occurred again during the sleep phase, the researchers report. The brain not only reconstructed the images that the test subjects could remember, but also those that they could not remember. "So the forgotten pictures don't just disappear from the brain," comments Dr. Hui Zhang in a press release on the study results.
How is it decided whether we forget something or not?
According to the sleep researchers, it is not only the reactivation of the gamma oscillations that is important for remembering, but also the involvement of the brain region hippocampus, in which the memory is located. This leads to extremely rapid activity fluctuations, which are referred to as ripples. If the gamma oscillations were activated in time with the Ripples during sleep, the picture was recalled later, according to the result of the research team. However, this phenomenon only applied to certain phases of sleep and not while the participants were awake.
The study results in detail
The team around Dr. Hui Zhang and Professor Dr. Nikolai Axmacher could see even more detailed information. When looking at the pictures, different processing phases were shown. This enabled the researchers to identify a superficial and a deep processing phase. The first phase lasted about half a second. The deep processing followed. If the above-mentioned ripples were activated in the superficial processing phase, the participants could not remember the picture later. In contrast, the picture remained in memory when the activation of the Ripples took place in the deep processing phase.
Sleep is important to our ability to learn
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 connection that deep sleep is essentially linked to human learning ability. It emerged from these studies that the connections between the nerve cells (synapses) are in an active state during the waking phase when impressions are obtained from the environment. This state only normalizes again during sleep. Without a recovery phase, the synapses would remain in an activated state and thus block any ability to learn. (vb)