The following article is from NeuroReality, author M. R. O’Connor.
When it comes to memories of the first years of life, we are all amnesiacs | Source: pexels.com
Introduction
The existence of the hippocampus Not only does it allow us to build a cognitive map of space, it also shows that our memories of the past are based on cognitive maps.
Writing | M. R. O'Connor
Translation | M.W.
Proofreading | Lyon
Editor | Orange Soda
Jon was a premature baby born at 26 weeks, weighing only 0.91 kilograms at birth and unable to breathe on his own. He was kept in an incubator for the first two months, but he eventually made it through infancy and early childhood. At age four, he had two seizures. After about a year, his parents began to notice that Jon was unable to remember events in his daily life. He could not remember what he had watched on television, what happened at school, or what books he had read. Jon's IQ is normal, he can read and write, and he's doing well in school. He can remember facts, but not past situations.
By the time Jon was 19, he couldn't find his way anywhere, and he couldn't remember familiar surroundings, where he put his things, or the route between the two places.
It wasn't until neuroscientists used magnetic resonance imaging to probe his brain that the cause of those strange behaviors was finally revealed. They found that Jon's hippocampus (a bilateral brain region deep in the temporal lobe) was unusually small, about half the size of a healthy hippocampus. This seems to be due to brain hypoxia (hypoxia) in infancy and the accompanying convulsion* (convulsion), which causes severe damage to hippocampal cells and seriously hinders the normal development of the hippocampus.
*Translator's Note
Convulsion is a medical condition in which the body's muscles rapidly and repeatedly contract and relax, causing the body to shake uncontrollably. Because convulsions are often a symptom of epileptic seizures, the term "convulsions" is often used interchangeably with seizures.
Hippocampus - critical for spatial cognition and memory, influenced by children's experience of exploring the environment and navigating in space | Source: Wikipedia
Since 1990 Jon has been the subject of numerous research papers since the 1990s, but his real name has not been made public to protect his privacy. His case illustrates the crucial role the hippocampus plays in the human body. The existence of the hippocampus not only allows us to build a cognitive map of space*, helping us remember locations and find the correct route, but also shows that our memories of the past, that is, episodic memory, are built on cognitive maps.
*Translator's Note
Cognitive map, also known as mental map or mental model, is a mental representation that serves individuals to acquire, encode, store, Recall and decode information about the relative position and properties of phenomena in their everyday or metaphorical spatial context.
Nora S. Newcombe, a professor of psychology at Temple University, explained, "The hippocampus evolved a function of spatial navigation. One of our guesses is that in our In the long history of evolution, because the neural structure of the hippocampus is very suitable for episodic memory, it has been 'hijacked' by evolution."
The significance of spatial cognition and memory to humans goes far beyond daily survival: they are. forms our sense of self.
Memories of the past are like the backbone of our individual identities; we use them to forge unique narratives in our lives. It is these stories that shape our actions and decisions and provide the framework for our imaginations about the future.
Recent research has revealed how the hippocampus develops in infancy and childhood, when neural circuits are maturing and new cells fire to encode space into cognitive maps. The child's experience of exploring the environment, navigating in space, and self-locomotion will all affect the development of the hippocampus.
Alessio Travaglia, a researcher at the New York University Neuroscience Center, said: "This is a very exciting finding because we generally think that brain maturation depends only on Time and genetic programming. But what we're trying to say is that brain development is not a program, it's about experience. A baby growing up in New York will definitely have different experiences than a baby growing up in a desert or a forest."
This discovery about neuroplasticity is fascinating, but also a wake-up call. Pediatricians have long warned that children are spending less time playing and having less free time, and they are spending more sedentary time than ever before.
For more than a century, people with memory loss like Jon's have given scientists a new way to study memory. Perhaps the most famous case of amnesia in the scientific literature is that of H.M. He was first an epileptic, and later in the 1950s, when he was 27, part of his temporal lobe was surgically removed, and he lost the ability to access and retrieve episodic memories. It was H.M.'s case that led scientists to discover that the hippocampus is the source of episodic memory.
The funny thing is, we are all just like H.M. and Jon. When it comes to memories of the first years of our lives, we are all amnesiacs. We cannot recall events before the age of 2, and memories up to the age of 6 are sketchy and unreliable. This strange phenomenon is called infantile amnesia, which is followed by childhood amnesia. Their ubiquity in humans and other species, from rats to primates, has been a mystery for decades.
Newcomb, principal researcher at Temple University's Center for Spatial Intelligence and Learning, said, "Everyone thinks the first two years of life are so important. But 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 simple answer, it means that we still know too little about the brain."
Sigmund Freud named infantile amnesia and explained it as a form of repression: the brain prevents infantile desires and emotions from entering the adult mind, and psychotherapy can open up access to those again Desires and emotions. Later explanations for amnesia in infancy have attempted to refute Freud's view and propose an alternative hypothesis: language acquisition provides children with the ability to remember long-term memories. But there are other species that show infantile amnesia that never develop language at all, so the validity of this idea remains in doubt.
In 1978, neuroscientists Lynn Nadel and John O'Keefe published a landmark book, "The Hippocampus as a Cognitive Map" ( The Hippocampus as a Cognitive Map). It theorizes that this hippocampus-shaped brain structure is where rats, humans and other animals represent their environment. These cognitive maps provide the basis for spatial memory, orientation, and navigation. It is worth noting that the spatial memory system extracts the material used to store situations and narratives from our autobiographical memories. Indeed, our memories of experiences are always imbued with a temporal-spatial context.
When we recall something that happened long ago, we enter a mental time travel, visualizing in our minds the time and place where past events occurred.
An early discovery by O'Keefe supports this theory: There is a type of neuron in the hippocampus of rats that he called place cells. When the animal is in a strange or familiar environment, these neurons Neurons all fire. Different place cells are active in different places in an environment and jointly form a cognitive map. This discovery earned O'Keefe the 2014 Nobel Prize*. After him, other scientists discovered other cells in the hippocampus that are important for spatial memory and navigation. These include head-direction cells, which fire depending on where our head is facing on the horizontal plane, and grid cells, which fire and establish a coordinate system as we walk through an environment. **.
Movement, exploration, and experiences in unfamiliar or familiar environments cause these cells to fire. There is evidence that the richness and complexity of the environment affects the number of neurons and therefore the size of the hippocampus. For example, in 1997, researchers found that mice that explored an enriched environment (paper tubes, nesting strips, rollers, and plastic tubes that could be rearranged) grew 4 longer than the control group. Thousands of neurons. These new neurons increased the size of their hippocampus by 15% and significantly improved their performance on spatial learning tests. The researchers concluded that it was a combination of increased numbers of neurons, synapses and dendrites that greatly improved the animals' performance in the test.
*Translator's Note
*Scientists John O'Keefe, May-Britt Moser, and Edvard I. Mosel were recognized for their discovery in 2014 of the special cells that make up the brain's positioning system (GPS). The research results won him the Nobel Prize in Physiology or Medicine.
**Head-direction cells are neurons found in many brain areas that increase their firing rate above baseline level.
Grid cells are neurons found in the entorhinal cortex of the animal brain. It is similar to place cells in that when an animal passes through a small area in a given environment, both will fire strongly; but unlike place cells, each grid cell will fire in a given environment. Multiple locations are discharged, and the discharge location nodes are spread throughout the environment and form a hexagonal grid.
***Enriched environment stimulus refers to the stimulation of the physical and social environment provided to the brain due to the surrounding complex environment. The brain has a higher rate of synapses and more complex dendrites in a richer, more stimulating environment, resulting in increased brain activity.
Nadel said that while writing the book, he became interested in the development of the hippocampus. While other brain regions are relatively mature at birth, this is not the case with the hippocampus - the timing of hippocampal maturation varies between animals. He said, "We now have theories about the function of the hippocampus. But what happens if the hippocampus fails? Simply put, it is amnesia." Nadel's line of thinking led him to think about the problem of infants. Neurobiological explanations for early forgetting. Essentially, children like Jon are unable to store memories because their hippocampus is not fully developed.
Nadel formulated this hypothesis in a paper published in 1984.
Together with fellow author Stuart Zola-Morgan, he proposed that episodic memory is possible only when an organism's brain is able to learn places, and that infantile amnesia is occurring Before the spatial hippocampal memory system emerged.
Now, Nadel believes that in this hypothesis, both the definition of forgetting in infancy and the description of the hippocampal maturation process are too simplistic. But development itself and its relationship to memory have become a key issue in neuroscience over the past 30 years. Is the brain hardwired to develop spatial and episodic memory systems? Or does this process require experienced participation?
Kate Jeffery, a behavioral neuroscientist who worked with O'Keefe as a postdoctoral fellow studying hippocampal neurons, said, "I think the field is still struggling. address these questions, but we don’t have firm answers yet”. However, she also explained that research so far has revealed a magical process: head cells are the first to become active, then place cells, and finally grid cells. Therefore, although these components of the cognitive map are innate to the mammalian brain, the mammalian brain still has a period of acquiring spatial knowledge, and this period may affect the subsequent functions of the hippocampus. .
In 2010, two different research teams both revealed how this development occurs. They placed electrodes in the brains of unweaned rats and recorded the firing of individual neurons in the hippocampus as they moved freely. The two teams, one from the Norwegian University of Science and Technology and the other from University College London, both recorded hundreds of head-direction cells, place cells and grid cells starting on day 16 of the rat's life.
The researchers found that all three types of cells appeared in the young rats a few days after they opened their eyes and before they began to leave the nest and explore their environment. But among these three types of cells, only the head-directed cells are fully mature. Young mice need several weeks to explore their environment before place and grid cells mature. From these data, the two teams concluded that spatial learning continues to improve even after the "pieces" that form the cognitive map are in place.
Neuroscientists combined 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 around the age of two, the hippocampus CA1 is responsible for distinguishing objects in long-term memory. Zones begin to mature and struggle with infantile amnesia. From the following years of childhood until adulthood, the highly plastic dentate gyrus still undergoes neurogenesis (the process of forming new neurons), gradually matures and begins to support the formation of new memories.
Before the age of 7, there is a strong relationship between children's hippocampus volume and their episodic memory ability - the larger the hippocampus, the stronger their ability to recall event details, which is also the key to childhood The age when forgetting completely fades away.
"The hippocampus didn't suddenly appear one day," Nadel said. "But its function does come about slowly; it's this network and the connections within the various parts of the hippocampus that give you the long-term context." Memory."
In the summer of 2016, a research team at the New York University Neuroscience Center mentioned in an article that they found that the development of the hippocampus is extremely susceptible to learning. The team selected two stages of juvenile rats for study, one on the 17th day after birth, which roughly corresponds to the 2-year-old human age, and the other on the 24th day after birth, which roughly corresponds to the period from 6 to 10 years old. .
By measuring levels of hippocampal molecular markers, they discovered how environmental experience positively affects hippocampal maturation.
In addition, they manipulated the rats' hippocampus to fast-forward to a stage of memory retention or prolong forgetfulness in infancy by increasing or decreasing levels of these molecules.
Researchers also believe that amnesia in infancy is related to the critical period, which is a period when environmental stimulation has 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 does not receive the correct stimulation at this time, the normal development of the brain will be hindered. Our hypothesis now is, The human brain also needs the right stimulation during a critical period of development. A lack of appropriate stimulation can lead to cognitive and memory deficiencies.
In addition to the environment itself, A very important stimulus for the hippocampus may be self-motion. In early 2016, Arthur Glenberg, a psychology professor at Arizona State University, proposed a hypothesis: Infantile amnesia begins to fade when children begin to crawl and walk. Grunberg and co-author Justin Hayes proposed that once babies are out of the arms of an adult and begin to explore space on their own, the place cells and grid cells in their brains begin to fire. , respond to the environment, and encode the environment that the baby explores, ultimately forming a framework for episodic memory.
Grunberg’s research in the past 20 years has focused on the theory of embodied cognition, which believes that cognitive processes, whether conscious or unconscious, are inseparable from our bodies, just like the flute. That's what Carl said. Our experience of the world and our thinking are inseparable from the existence of our legs, arms, eyes, ears, motor systems, and emotional systems. Grunberg said, "It would be unreasonable if the body did not influence the evolution of abilities such as cognition. We are not computers, we are biological systems. We are not programmed, but products of evolution. We should treat Human cognition is seen as an extension of the cognitive abilities of other animals.”
During an academic conference on child development, Grunberg had the idea that embodiment might help. He solved the mystery of infancy's amnesia, and found some very interesting evidence to support his hypothesis. In 2007, a British research team found that the beginning of crawling in 9-month-old babies was closely related to a huge leap in their cognitive level: their memory retrieval ability became more flexible and mature. The researchers also found that exercise and self-movement can improve spatial learning and neurogenesis in mice.
However, the sooner or later the self-movement begins seems to be far less important than the degree to which children explore the environment; in 2014, Dutch researchers found that before the age of 4, children who had a higher degree of exploring the environment in childhood had stronger Spatial memory ability and fluid intelligence, that is, the ability to solve problems, summarize rules and logic.
But Grünberg's idea doesn't explain why it takes so long for children to have stable memory abilities from the time they begin to move on their own at the beginning of life to the age of six. He suggested that this may be because children need rich enough experience in spatial exploration and complex cognitive map building to develop a fully functioning hippocampal memory system like adults.
"A 10-month-old baby may know the way around his home, but it's unlikely that he'll be able to walk from home to the park," Grunberg said. "They need a lot of walking experience to do that." A series of neurons develops that are complex and interconnected enough to support memory. ”
Newcomb’s lecture at an academic conference inspired Grunberg’s hypothesis; Grunberg's idea is still just speculation, but it is pushing the scientific community in the right direction. To her, what's most fascinating about hippocampal plasticity is that our improved understanding of it is likely to guide advances in treatments for children with disabilities with limited movement.
If we provided children with equipment to assist their movement during critical periods, would that help them acquire cognitive skills? A 2012 study showed that babies with severe motor deficits who were trained to move using a custom-made stroller scored higher on cognitive and language tests compared with a control group. In the study, a 7-month-old baby with spina bifida improved his cognitive and language skills faster than he should have for his age.
Compared with the previous generation, children today have much less time for free activities and outdoor sports. One study found that children's free play time decreased by 25 percent between 1981 and 1997; another study focusing on preschoolers in Seattle found that children spent 70 percent of their day sitting. Therefore, although the American Academy of Pediatrics recommends at least 2 hours of physical activity per day, most children do not have that much time to play.
Based on our latest understanding of the relationship between hippocampal development, amnesia in infancy, and spatial cognition, in addition to combating obesity and ADHD, we must also allow children to explore and build knowledge. opportunities to map themselves, because their cognitive health, that part of the brain that continues to influence self-perception in various ways, depends on these opportunities to develop properly. A large body of data suggests that addiction, post-traumatic stress disorder, schizophrenia, and Alzheimer's disease are all associated with decreased hippocampal volume.
There is also some interesting evidence that the brain's spatial cognitive ability contains the secret of intelligence. In the September 2016 issue of Nature, a 45-year study of 5,000 "mathematically gifted young people" found that the number of patents and peer-reviewed journal articles they had was associated with their performance on spatial ability tests. scores are related. David Lubinski, one of the leaders of the study, told the journal Nature, "I think [spatial ability] is probably the most unknown and untapped human potential."
It now appears that forgetting in infancy and childhood is actually our brains laying the foundation for experiential learning. Although we cannot remember those early experiences, they ultimately shape us into the “people” we truly are. Newcomb said, "This is an important part of our huge undertaking to understand the human mind and brain and its development. It is of great significance."
The translation of this article was originally published in "NeuroReality", "Knowledge" Molecules" is authorized to reprint the translation.
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