By Eduardo Zimmer
We are what we decided to forget
The following article answers the question that Violeta Reys, 7 years old, asked for the series “Children’s questions, answers from science”.
Iván Izquierdo, an Argentine neuroscientist with a naturalized Brazilian, used to say: “We are what we want to forget”. For him, forgetting was the most fascinating biological phenomenon of memory. In fact, we have to forget to remember. I can remember my mother’s date of birth in a millisecond, but I don’t always have to trigger this memory, it is stored in certain places in the brain. But where?
To understand the neurobiological basis of this phenomenon, two concepts are essential. The first is that the brain is divided into regions that perform certain functions but are connected in a way that enables us to perform higher level cognitive functions such as reading, speaking, and thinking. The second relates to the types of memory: there is the short-term memory, which we keep for a few hours (the phone number of a delivery shop) and the long-term memory, which is stored for a long time and can be recalled (which happened last Christmas) and the declarative (” know that “) and not declarative (” know how “). There are also other classifications that differ from a biological point of view, such as semantic and episodic memory. The beginning of the expansion of knowledge about memory deserves … to be remembered.
In 1953, patient Henry Molaison, known as HM, underwent a lobotomy to control epileptic seizures. The epilepsy was contained, but HM was unable to form new declarative memories, although it could form short-term and non-declarative memories. So, HM was having a normal conversation, but once the conversation was over and he started another activity, he completely forgot that the conversation had taken place – he would even forget the person if he was a “new” person. It was as if he were exposed to the “Neuralizer” of the “Men in Black” trilogy, a fictional equipment used to erase people’s memories.
Investigating this case was a turning point. And it was responsible for Brenda Milner, who is considered by many to be the founder of neuropsychology and who introduced him to the scientific community in 1957. (Today, at 102 years old, I am Dr Instituto de Neurology from Montreal, Canada. I myself had the honor of completing part of my doctoral thesis at this institution thanks to the “Science Without Borders” program that has since been discontinued. An unforgettable memory).
The key to understanding the HM case lay in the areas that were removed during the lobotomy, particularly in the hippocampus, the main brain region responsible for short-term and declarative memory. Nowadays neuropsychology suggests that every type of memory is stored in a specific location in the brain. This means that areas other than the hippocampus also have the ability to store memories, such as the cortex.
However, an understanding of an even more fundamental neurobiological process is required. It would be intuitive to think that with each new memory a new neuron would appear or that a neuron could hold a limited number of memories. Now that few neurons are born in adult brains, our “Huntington’s Disease Neural” would already be full of the vast amount of information we receive.
Both hypotheses are wrong. The plasticity of the brain is at stake. Neurons make new connections or even reinforce previous connections with other neurons. This connectivity causes the electrical triggers – the synapses – to be coordinated by a number of neurons to create, retain, “forget” and enable memories to be recalled.
Some readers may long remember this article, others may not remember it ten seconds after reading it. But then the conversation penetrates another region of the brain, the amygdala, which coordinates one of the most beautiful neurobiological phenomena in our lives: emotions. It helps decide which memories to keep. Would you like to take a test? Who doesn’t remember the first kiss? I know there are so many emotions …
Eduardo Zimmer is a biochemist and professor in the Department of Pharmacology at the Federal University of Rio Grande do Sul.
We know children ask the best questions and science can have good answers. The “Children’s Questions, Answers from Science” series invites a scientist each month to answer one of these fundamental questions. Do you have a suggested question? This is how you can work together.