Why did your memories before the age of three "disappear"?

Do you remember what you did before the age of three?

In fact, many of us may only have a very vague memory of things that happened when we were very young. Maybe your parents will tell you some things, but no matter how hard you try, you can't remember whether you really experienced those things.

So why is it that all memories before the age of three seem to have disappeared?

Today, let Professor Ye Sheng from Beijing University of Aeronautics and Astronautics talk about our childhood memories.

In fact, the disappearance of childhood memories has attracted the attention of psychologists for a long time. Before the advent of modern science, many psychologists have given various explanations. Today we will not go into details about these explanations because they are really unscientific and we will not spread these unscientific ideas here.

Today, based on the knowledge framework of modern biology, neuroscience and psychology, we can look at why all memories before the age of three have disappeared.

There are probably three reasons for this.

The first reason is that the neural network of our entire brain is not fully developed before the age of three.

We know that humans actually have the most complex brain neural network among all animals. Our brain has about 100 billion neurons, which is super complex. In fact, there is no computer on earth that can compare with the complexity of our brain.

Such a complex brain does not develop all at once. In fact, the brain continues to develop after we are born, and the entire development process reaches a peak of complexity when we are about three years old. Before the age of three, as our brain continues to develop, the physical connection between these neurons is also changing. At this time, some memories are likely to disappear. This is the first reason.

The second reason is that at the age of three, after our brains mature, we begin a new stage of change - our brains begin to remove some unnecessary neural connections .

Why does this happen? Let me give you an example:

I don't know if you have heard of the word "synaesthesia". Only a small number of people have this ability of synaesthesia. What is synaesthesia? For example, some people may see a number with a special color when they see it; for example, some people may hear a unique melody in their ears when they see a certain letter. In other words, the signal from one sense organ stimulates us to produce the reception of another sense organ, which is a synaesthesia effect.

The cause of synaesthesia is not complicated. It is actually a neural connection between two brain areas. However, when scientists were studying this matter, they found that many children have synaesthesia, and the proportion of synaesthesia in children is much higher than that in adults.

So why do these children lose their synaesthesia when they grow up? What happened in between?

One view is that one of the neurons in these special neural links may have died . Because the neuron died, the link was broken, so the synaesthesia disappeared. Another view is that these neurons are still in place, but the connection between them has become weaker . Because this connection is weakened, they cannot effectively form signal transmission, so the synaesthesia disappears.

So which opinion is right? Later, scientists accidentally discovered a hallucinogen called LSD. Because the use of this hallucinogen can produce a large number of rich synaesthesia effects in users, scientists know that those neurons have not disappeared, they have always been on the neural links, but these connections have become weaker . When hallucinogens enter our brains and strengthen these connections, synaesthesia returns.

By extension, we know that in fact, as we grow up, many neural links in our brain that are considered useless by the brain will gradually disconnect . When these connections are disconnected, our corresponding memories will disappear. Because all our memories are actually stored in the connections between these neurons. The above is the second reason.

The third reason is that our memory needs to be constantly reread by us .

Why do you remember something? It is not because you have really experienced it and you will remember it forever, but because in the years that follow, your brain will constantly retrieve it and review it. In fact, our brain not only reviews the memory, we also reprocess it and then store it back, so everyone knows that our human memory is very unreliable. What is the source of this unreliability? It is because we will constantly retrieve, review, and reprocess memories from a long time ago, and at this time our brain has the opportunity to tamper with the memory .

Of course, the memory we are talking about here refers to experiential memory , which is related to our experience and our situation, rather than to knowledge memory such as "1+1=2". This kind of situational memory must be constantly reviewed in order to be remembered for a long time.

But think about what happened before you were three years old. What were the things that were very important to you and needed you to constantly review? I am afraid that this habit of constantly reviewing situational memories will only be gradually developed after we become adults. This is also a very important reason why we lose memories before the age of three.

All in all, no matter what the reason is, there is no need to feel sorry. Since we have obtained such a result in evolution, it must make sense, and the memories before the age of three may not be so important to our lives.

This video is produced by the Science Popularization China Creation Cultivation Program.

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