The brain is a real miracle. A seemingly endless library whose shelves hold our most precious memories and knowledge of our lives. Is there a moment when it reaches its limit? In other words, can our brain be "full"?
The answer will sound like no, but explaining it will take time, because the brain is a little more complex than just a piggy bank. A study published in Nature Neuroscience found that instead of just accumulating, old information is sometimes pushed out of the brain, making room for new memories.
Previous behavioral research has shown that learning new information can lead to forgetfulness. However, in this study, scientists used new neuroimaging techniques to demonstrate for the first time how this effect manifests itself in the brain.
The authors of the work set themselves the task of finding out what happens in the brain when we try to remember information similar to what we already know. This is important because similar information is likely to mix with existing knowledge and crowd out similar information.
To do this, scientists studied how the activity of the brain changes when we try to remember "target" information, that is, we try to remember something specific, while simultaneously trying to assimilate something similar ("competing" memory). Participants were taught to associate one word (say, the word "sand") with two different images - Marilyn Monroe and hats.
It turned out that as the target information was recalled more often, the brain activity for it increased. Meanwhile, the activity of the brain for competing information simultaneously decreased. This change was particularly noticeable in areas near the frontal part of the brain like the prefrontal cortex, compared to key memory structures in the middle of the brain like the hippocampus that are commonly associated with memory loss.
The prefrontal cortex is involved in a number of complex cognitive processes like planning, decision making, and selective retrieval of memories. Extensive research shows that this part of the brain works in conjunction with the hippocampus to retrieve specific memories.
If the hippocampus is a search engine, the prefrontal cortex is the filter that determines which memory is more relevant. This suggests that information storage alone is not enough for good memory. The brain must also be able to access relevant information without being distracted by similar competing pieces of information.
In everyday life, forgetting has obvious benefits. Imagine, for example, that you have lost your bank card. The new card you receive will come with a new PIN. Research shows that whenever you remember a new PIN, you gradually forget your old one. This process improves access to relevant information and old information does not get in the way.
And most of us are familiar with this feeling when old memories mix with new, relevant ones. Let's say you're trying to remember where you parked your car in the same fleet where you were a week ago. This type of memory (when you are trying to recall new but similar information) is particularly susceptible to interference.
When we receive new information, the brain automatically tries to incorporate it into existing information, forming associations. And when we receive information, at the same time associative, but irrelevant information pops up.
Most of the previous research has focused on how we learn and remember new information. But modern research is starting to pay more attention to the conditions under which we forget, their importance is starting to grow.
Curse of Memory
Very few people are able to remember almost every detail of their lives in great detail; they have hyperthymic syndrome. Give a date and they will tell you where they were and what they did that day. While this may sound like a boon to many people, those gifted with this ability often find it burdensome.
Some report an inability to think about the present or the future, as if they are constantly living in the past, caught in their own memories. All of us, in principle, could suffer from this if our brains did not have a mechanism for updating information that no longer meets the relevance and is considered unnecessary.
At the other end of the spectrum is what is called “accelerated long-term forgetfulness, ” and is often seen in epilepsy and stroke. As the name suggests, people forget the information they just received at a much faster rate, sometimes within hours; it is not normal.
It is believed to be based on a refusal to "consolidate" or transfer new memories into long-term memory. But the processes and effects of this form of forgetfulness remain largely unexplored.
Research in this area demonstrates that remembering and forgetting are two sides of the same coin. In a sense, forgetting is a mechanism for sorting our brain's memories so that the most relevant memories are at hand. Normal forgetfulness can be a safety mechanism that keeps our brains from getting overwhelmed.