When it comes to memories of the first few years of life, we are all amnesiacs | Source: pexels.com.

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The existence of hippocampus not only allows us to establish a cognitive map about space, but also shows that our memory of the past is based on the cognitive map.

Write | Mr. O 'Connor

Translation | Chinese

Proofreading | Lyon

Edit | Orange Soda

Jon, a 26-week-old premature baby, weighed only 0.9 1 kg at birth and could not breathe spontaneously. In the first two months, he was put in an incubator, but in the end he passed his infancy and childhood smoothly. At the age of four, he had two seizures. About a year later, his parents began to notice that Jon couldn't remember what happened in his daily life. He doesn't remember watching TV, what happened at school or what books he read. Jon has a normal IQ, can read and write, and does well in school. He can remember the facts, but not the past.

By the time Jon 19 arrived, he couldn't find the way to anywhere, and he didn't remember the familiar environment, where he put his things or the route between the two places.

It was not until neuroscientists explored his brain with magnetic resonance imaging technology that the reasons for those strange performances were finally uncovered. They found that Jon's hippocampus (bilateral brain regions deep in the temporal lobe) was unusually small, about half the size of a healthy hippocampus. This seems to be due to the brain hypoxia in infancy and the convulsions that followed, which caused serious damage to hippocampal cells and seriously hindered the normal development of hippocampus.

* Translator's note

Convulsion is a medical condition, that is, the muscles of the body contract and relax rapidly and repeatedly, resulting in uncontrolled shaking of the body. Because convulsions are usually symptoms of seizures, the word "convulsions" is often confused with seizures.

Hippocampus is very important for spatial cognition and memory, and it is influenced by children's experience in exploring environment and spatial navigation | Source: Wikipedia.

Jon has been the subject of many research papers since 1990, but his real name has not been made public to protect privacy. His case shows that the hippocampus plays a vital role in the human body. The existence of hippocampus not only allows us to build a cognitive map about space, helps us remember the position and find the correct route, but also shows that our memory of the past, that is, situational memory, is based on the cognitive map.

* Translator's note

Cognitive map, also known as mental map or mental model, is a mental representation, which serves individuals to acquire, encode, store, recall and decode information about the relative position and attributes of phenomena in their daily or metaphorical spatial environment.

Nora S. Newcombe, a professor of psychology at Temple University, explained, "The hippocampus has evolved the function of spatial navigation. One of our guesses is that in our long evolutionary history, because the neural structure of hippocampus is very suitable for situational memory, it was hijacked by evolution. "

Spatial cognition and memory have far more significance to human beings than daily life: they form our self-perception. Memories of the past are like the pillars of our personal identity; We use it to create unique stories in life. It is these stories that shape our actions and decisions, and also draw a framework for our reverie about the future.

Recent studies have revealed how the hippocampus develops in childhood and childhood, when neural circuits gradually mature and new cells encode space into cognitive maps through discharge. Children's experiences of exploring environment, spatial navigation and self-movement will all affect the development of hippocampus.

Alessio Travaglia, a researcher at the Center for Neuroscience of new york University, said: "This is a very exciting discovery, because we usually think that the maturity of the brain depends only on time and genetic programming. But what we want to explain is that the development of the brain is not a procedure, it is related to experience. Babies growing up in new york and babies growing up in deserts or forests will definitely have different experiences. "

This discovery about neuroplasticity is fascinating, but it also sounds an alarm. Pediatricians have long warned that children have less and less time to play and their free time, and their sedentary time has become longer than ever before.

For more than a century, amnesiacs like Jon have provided scientists with a new way to study memory. Perhaps the most famous case of amnesia in scientific literature is H.M. He is first and foremost an epileptic. Later, in the 1950 s, when he was 27 years old, a part of his temporal lobe was surgically removed, and he lost the ability to acquire and extract situational memories. It is the case of H.M. that makes scientists discover that hippocampus is the source of situational memory.

Interestingly, we are all like H.M. and Jon. When it comes to the memory of the first few years of life, we are all amnesiacs. We can't remember anything before the age of 2, and the memory before the age of 6 is rough and unreliable. This strange phenomenon is called infantile amnesia, followed by childhood amnesia. Their ubiquity in humans and other species (from mice to primates) has been a mystery for decades.

Newcomb, chief researcher of the Center for Space Intelligence and Learning at Temple University, said, "Everyone thinks that the first two years of life are too important. However, if we can't remember these two years, how important are they? We do have some answers to this question. But if we don't have a clear and crisp answer, it means that we still know too little about the brain. "

Sigmund freud gave a name to infantile amnesia and explained it as a kind of depression: the brain will prevent the desires and emotions of infancy from entering the hearts of adults, and psychotherapy can make those desires and emotions reappear. Later, some explanations about forgetting in infancy tried to refute Freud's point of view and put forward another hypothesis: language acquisition gave children the ability to remember for a long time. However, there are other species that have forgotten in infancy and have not developed language at all, so the correctness of this view is still in doubt.

1978, neuroscientists Lynn Nadel and John O'Keefe published a landmark book, Hippocampus as a Cognitive Map. It puts forward a theory that this hippocampus-like brain structure is the place where rats, humans and other animals represent the environment. These cognitive maps provide a basis for spatial memory, orientation and navigation. It is worth noting that the spatial memory system is a material that extracts and stores scenes and narrative methods from our autobiographical memory. Indeed, our memory of experience is always infused with the background of time and space. When we recall what happened a long time ago, we will enter a spiritual time travel and imagine the time and place of the past events in our minds.

One of O'Keefe's early discoveries supports this theory: there is a neuron in the hippocampus of mice, which he called positional cell. These neurons all discharge when animals are in unfamiliar or familiar environments. Cells in different locations move in different places in an environment to form a cognitive map together. This discovery won O'Keefe the Nobel Prize in 20 14 years. After him, other scientists discovered other important cells in the hippocampus for spatial memory and navigation. These cells include head direction cells that discharge according to the position of our head facing the horizontal plane, and grid cells that discharge when we walk in the environment and establish a coordinate system.

Moving, exploring and experiencing in an unfamiliar or familiar environment will lead to the discharge of these cells. There is evidence that the richness and complexity of the environment will affect the number of neurons, and then affect the volume of hippocampus. For example, in 1997, some researchers found that mice explored in rich environments (paper tubes, paper strips for nesting, rollers and plastic tubes that can be rearranged) grew more than 40,000 neurons than the control group. These newly added neurons increased the volume of hippocampus by 15%, and significantly improved its performance in spatial learning test. The researchers concluded that it was the increase in the number of neurons, synapses and dendrites that greatly improved the performance of these animals in the test.

* Translator's note

* Scientists John O'Keefe, May-Britt Moser and Edward I Morsel won the 20 14 Nobel Prize in Physiology or Medicine for their research achievements in finding special cells that make up the brain positioning system (GPS).

* * Headward cells are neurons found in many brain regions. Only when the animals' heads are pointed in a specific direction will their discharge rate increase above the baseline level.

Grid cells are neurons found in the entorhinal cortex of animal brains. It is similar to positional cells. When animals pass through a small area in a given environment, both of them will have strong discharge. However, different from location units, each grid unit will discharge at multiple locations in a given environment, and the nodes of discharge locations will spread all over the environment and form a hexagonal grid.

* * * Rich environmental stimuli refer to the physical and social environmental stimuli provided to the brain due to the complex surrounding environment. In a richer and more exciting environment, the incidence of synapses is higher and the dendrites are more complex, which leads to an increase in brain activity.

Nadel said that in the process of writing a book, he became interested in the development of hippocampus. Other brain regions are relatively mature at birth, but the hippocampus is not-different animals have different mature time in hippocampus. He said, "We now have a theory about the function of hippocampus. But what happens if the hippocampus fails? Simply put, it is amnesia. " Nadel's thinking reminds him of the neurobiological explanation of forgetting in infancy. Essentially, children like Jon can't store memories because the hippocampus is not fully developed.

Nadel expressed this hypothesis in a paper published in 1984. He and Stuart Zola-Morgan, the co-author of "* * * *", suggested that an organism's brain can only have situational memory when it can learn places, and infant forgetting occurred before the hippocampus memory system for space appeared.

But now, Nadel thinks that in this hypothesis, both the definition of infantile amnesia and the description of hippocampal maturity are too simplistic. However, development itself and its relationship with memory have become a key link in the theme of neuroscience in the past 30 years. Is the brain born to develop spatial and situational memory systems? Or does this process require experience?

Kate Jeffery, a behavioral neuroscientist, worked with O'Keefe during her postdoctoral period, mainly studying hippocampal neurons. She said, "I think the field is still trying to solve these problems, but we haven't got the exact answer yet." However, she also explained that the research so far has revealed a magical process: first, the directional cells in the head are active, then the positional cells, and finally the grid cells. Therefore, although these components of cognitive map are inherent in mammalian brain, mammalian brain still has a period of acquiring spatial knowledge, which may affect the function of hippocampus.

In 20 10, two different research teams revealed how this development process happened. They placed electrodes in the brains of weaned rats and recorded the discharges of individual neurons in the hippocampus during free movement. The two teams, one from the Norwegian University of Science and Technology and the other from University College London, recorded hundreds of head cells, positional cells and grid cells after birth 16 days.

The researchers found that all three kinds of cells appeared a few days after the young mice opened their eyes and before they began to leave the nest to explore the environment. But among these three kinds of cells, only the head cell is fully mature. Young mice need to explore the environment for several weeks, and then the positional cells and grid cells will mature. From these data, the two teams concluded that the ability of spatial learning will continue to improve even after the "part" of the cognitive map is in place.

Neuroscientists combine these findings with the behavior of primates and children to explore how this process occurs in children's brains. Swiss neuroscientists Pierre Lavenex and Pamela Banta Lavenex proposed that at about two years old, the hippocampal CA 1 area is responsible for distinguishing objects in long-term memory, starting to mature, and fighting amnesia in infancy. However, from childhood to adulthood in the next few years, the highly plastic dentate gyrus will still undergo neurogenesis, gradually mature and begin to support the formation of new memories.

Before the age of 7, the size of children's hippocampus has a strong relationship with their situational memory ability-the bigger the hippocampus, the stronger their ability to recall the details of events, which is the age when childhood forgetfulness completely disappears.

Nadel said, "The hippocampus didn't suddenly appear one day. But its function is really realized slowly; It is the internal connection between this network and various parts of the hippocampus that gives you long-term situational memory. "

In the summer of 20 16, a research team from the Center for Neuroscience of new york University mentioned in an article that they found that the development of hippocampus was easily influenced by learning. The research team selected two stages of young mice for research, one is 17 days after birth, which roughly corresponds to a 2-year-old human, and the other is 24 days after birth, which roughly corresponds to a human aged 6 to 10.

By measuring the level of molecular markers in the hippocampus, they found out how environmental experiences positively affect the maturation of the hippocampus. In addition, by increasing or decreasing the level of these molecules, they can control the hippocampus of rats to fast-forward to the memory retention stage or prolong amnesia in infancy.

The researchers also believe that amnesia in infancy is related to the critical period, which is the stage when environmental stimuli have a particularly active impact on brain plasticity. Travaglia, one of the authors of the above study, said, "The critical period is the most sensitive stage of the nervous system. If it is not stimulated correctly at this time, the normal development of the brain will be hindered. Now our hypothesis is that the human brain also needs appropriate stimulation during the critical period. This is a particularly critical development period for acquiring memory. Lack of proper stimulation can lead to cognitive and memory defects. "

In addition to the environment itself, another very important stimulus to the hippocampus may be its own movement. 2065438+At the beginning of 2006, Arthur Glenberg, a professor of psychology at Arizona State University, put forward a hypothesis that childhood forgetfulness began to fade when children started crawling and walking. Gruenberg and Justin Hayes, the co-author of * * *, proposed that once babies leave the arms of adults and start exploring in space by themselves, the positional cells and grid cells in their brains will start to discharge and respond to the environment, and the environment that babies explore will be coded, eventually forming a framework of situational memory.

Gruenberg's research in the past 20 years has mainly focused on the theory of embodied cognition, which holds that both conscious and unconscious cognitive processes are inseparable from our bodies, just as Descartes said. Our experience and thinking about the world are closely related to the existence of our legs, arms, eyes, ears, sports system and emotional system. Gruenberg said, "It is unreasonable if the body does not affect the evolution of cognitive ability. We are not computers, we are biological systems. We are not programmed, but the product of evolution. We should regard human cognition as an extension of the cognitive ability of other animals. "

At an academic conference on children's development, Gruenberg had a brainwave and made it concrete, which may help him solve the problem he forgot in infancy, and some very interesting evidence just supported his hypothesis. In 2007, a British research team found that 9-month-old babies began to crawl closely related to their great leap in cognitive level: their memory retrieval ability was more flexible and mature. The researchers also found that exercise and self-exercise can improve spatial learning and neurogenesis in mice.

However, it seems that the starting time of one's own sports is far less important than the degree to which children explore the environment; 20 14 Dutch researchers found that before the age of 4, children who had a high degree of environmental exploration in childhood had stronger spatial memory ability and fluid intelligence, that is, the ability to solve problems and summarize laws and logic.

However, Gruenberg's idea can't explain why it takes so long for children to have stable memory ability from the beginning of life to the age of 6. He suggested that this may be because children need enough experience in space exploration and complex cognitive mapping to develop a fully functional hippocampus memory system like adults.

Gruenberg said, "A baby of 10 months may know the way near his home, but he can't walk from home to the park. They need a lot of walking experience to develop a series of complex and interrelated neurons to support memory. "

Newcomb's speech at an academic conference inspired Gruenberg's hypothesis, while the former thought that although Gruenberg's idea was just speculation, it was urging the scientific community to develop in the right direction. For her, the most attractive thing about hippocampal plasticity is that our further understanding of it is likely to guide the treatment progress of disabled children with limited mobility. If we provide children with devices that can help them exercise during the critical period, will it help them acquire cognitive ability? A study of 20 12 showed that infants with severe dyskinesia scored higher in cognitive and language tests than the control group after using customized wheelbarrows for mobile training. In this study, a 7-month-old spina bifida baby's cognitive and language skills improved even faster than his age.

Compared with the previous generation, today's children have less time for free activities and outdoor sports. A study found that between 198 1 and 1997, children's free play time decreased by 25%; Another study on preschool children in Seattle found that children spend 70% of their day sitting. Therefore, although the American Academy of Pediatrics recommends at least 2 hours of physical activity every day, most children don't have that much time to play.

According to our latest understanding of the relationship among hippocampus development, infantile amnesia and spatial cognition, in addition to fighting obesity and ADHD, we should also give children opportunities to explore and build cognitive maps, because their cognitive health, that is, the part of the brain that constantly affects self-perception in various ways, depends on these opportunities to develop normally. A large number of data show that addiction, post-traumatic stress disorder, schizophrenia and Alzheimer's disease are all related to the decrease of hippocampal volume.

There is also some interesting evidence that the spatial cognitive ability of the brain contains the mystery of intelligence. From September 2065438 to September 2006, Nature conducted a 45-year study on 5,000 "young people with extraordinary mathematical ability", and found that the number of patents and peer-reviewed journal articles of these people were related to their scores in the space ability test. David Lubinski, one of the leaders of this research, told Nature, "I think (space capability) is probably the most unknown and undeveloped human potential."

Now it seems that the forgetting of infancy and childhood is actually our brain laying the foundation for experiential learning. Although we can't remember those earlier experiences, they finally shaped us into real "people" Newcomb said, "This is an important link in our great cause of understanding the human mind and brain and its development. It is of great significance. "

The translation of this article was originally published in Neuroreality, and intellectuals were authorized to reprint the translation.

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Original link:

https://nautil . us/issue/40/learning/for-kids-learning-is-moving