Brain: Forgetting is not lost

Connections between nerve cells remain, even if they are not needed

Memory for future learning: Nerve cells retain many of their newly formed connections and inactivate, if necessary, only the data transmission. This makes relearning easier. © MPI for Neurobiology / Hofer
Read out

Scientists are beginning to understand what happens in the brain when it learns or forgets. What is certain is that changes in the contacts between nerve cells play a major role in this. But can such structural changes also explain the well-known phenomenon that it is much easier to learn something forgotten than to learn something new? Apparently yes. Because researchers have now shown that many of the grown during a learning process cell contacts probably only inactivated, but not degraded when they are no longer needed.

The reactivation of these "contacts in stock" allows the faster re-learning of forgotten memory content, the scientists in the current issue of "Nature".

Unlike an insect that bounces against the window even with the tenth attempt, our brain is able to learn very complex relationships and motor processes. This not only allows us to avoid glass doors accident-free, but also to learn different things such as cycling or skiing, speaking different languages, or playing a musical instrument.

The juvenile brain learns more easily, but the ability to learn remains intact until old age. Scientists have long been trying to understand what happens in learning or forgetting in the brain.

Flexible information connections

In order to learn something, ie to be able to process new information, nerve cells enter into new connections with each other. If information is available for which there is still no processing path, grow from the corresponding nerve cell fine processes to their neighboring cells. If a special contact point, a synapse, forms at the end of an extension, the exchange of information between the cells is possible - the new information is learned. If the contact dissolves again, the learned is forgotten. display

Learning and re-learning - a fine difference

The observation that learning and memory are associated with such structural changes in the brain is relatively new, and many questions remain open. For example, what happens when the brain learns something, forgets it, and then has to learn again? Experience shows that once you have learned cycling, it will come back quickly, no matter how long it was not practiced. In other things too, a "relearning" is usually easier than a "learning". Does this subtle difference also have its origin in the structure of nerve cells?

Cell fortunes: What you have, you have

Scientists at the Max Planck Institute of Neurobiology have now been able to show that there are indeed clear differences in the outgrowth of cell contacts - depending on whether information is being re-learned or re-learned. For example, nerve cells responsible for the processing of visual information showed a significantly increased outgrowth of new cell contacts when they no longer received information from their eyes.

After about five days, the nerve cells had reconnected so far that they could now respond to information from the other eye - the brain had learned to cope with only one eye. Once again information from the now inactive eye, the nerve cells quickly resumed their original work and hardly responded to signals from the other eye.

"However, it was completely unexpected that a large proportion of the newly created extensions remained, " explains Mark H bener, head of the study. All observations indicate that frequently only the synapses are deactivated and thus the information transmissions are interrupted.

"Once a past experience is needed later, the brain seems to be keeping some of its" up-to-date ", so H bener. And in fact, when the same eye was inactivated again at a later time, the reorganization of the nerve cells was much faster - even though no new extensions were made.

Useful reactivation

Many of the once formed extensions between nerve cells thus remain and facilitate a later relearning. An important insight in understanding the basic processes of learning and remembering. After only a few years without skiing, after only a short period of practice, we are safely back on the boards, even after we have learned it.

(MPG, 13.11.2008 - DLO)