Why do people have messy dreams when they sleep? It turned out to be about memory

Dreaming is a normal physiological activity of human beings, but it is quite mysterious because it is difficult to be observed by people other than themselves, and there are many studies related to dreams. At the end of the 19th century, the Austrian psychologist Sigmund Freud wrote The Interpretation of Dreams, describing dreams as "something that rises from the suppressed subconscious to consciousness."

In 1969, David Fox of Emory University experimented with the idea that people's dreams were related to things they cared about at the moment, such as dreaming about exams because they were anxious or nervous about exams recently.

Later, through computer models, two hypotheses about dreams were proposed: one was proposed by the British psychologist Christopher Evans, who believed that sleep was equivalent to cutting off external signals, and dreams were like a computer terminal being removed and reconstructing the signals left by recent events in the brain; the other hypothesis was that the brain was stimulated by non-specific forms from the brain stem during sleep, resulting in so-called unconscious dreams. Regardless of the research and hypothesis on dreams, dreams have a basic raw material: memory.

The five stages of sleep

Sleep has a biological rhythm, the sleep cycle, and the International Society of Sleep Medicine divides sleep into five phases and two phases. The five stages refer to the sleep period, the light sleep period, the deep sleep period and the deep sleep period, the rapid eye movement period, and some places also divide sleep into four stages, and the deep sleep period and the deep sleep period are collectively referred to as the deep sleep period.

The two phases refer to the non-REM sleep phase and the REM sleep phase, and the non-REM sleep phase is the non-rapid eye movement sleep, or NREM for short. The REM sleep phase is referred to simply as REM. In the normal sleep structure, NREM and REM alternate, alternating once, that is, a sleep cycle, and the cycle is reciprocating.

Sleep cycle stage one of the sleep period, that is, the beginning of sleep, this time people still maintain a part of consciousness, the time is very short, the so-called drowsiness is the state of this stage, at this time the brain wave frequency began to slow down, the amplitude gradually decreased, at this stage is woken up easily awake.

Enter the shallow sleep period of the second stage of the sleep cycle, the temperature of the human body drops, begin formal sleep, the brain waves at this time are irregular, the frequency and amplitude are suddenly large and small, of which the high frequency of large-amplitude brain waves is called "sleep ingots", the low-frequency large-amplitude brain waves are called "K knots", the proportion of submerged sleep in non-REM sleep is relatively large, about half of the whole process, if there is a loud or high-pitched sound at this stage, it is still easier to be woken up.

Sleep cycle stage three and four of the deep sleep period and deep sleep period is the deep sleep stage, at this time the brain wave frequency is only 1-2 weeks per second, the amplitude increase is larger, sleepwalking may occur in this stage, it is not particularly easy to wake up a person in the sleeping stage, and the person who is awakened will also be dizzy and confused.

Stage five of the rapid eye movement period, as the name suggests at this stage of the human eyeball will show rapid beating phenomenon, at this time the person's brain waves change rapidly, the emergence of high-frequency low-amplitude brain waves similar to the brain waves in the waking state, which also has distinctive serrated waves, there will be a situation of turning over, may wake up, if at this stage is woken up, the person who is woken up will usually say that they have just dreamed, so the rapid beating characteristics of the rapid eye movement period are also an important basis for psychologists to study dreaming.

Brain memory

During sleep, non-REM and REM will compete for control of the brain throughout the night, and the beating of the eyeball during the REM phase means that people chase the situation change in the dream, and the human brain at this time shows similar brain waves to the awake state, which means that the brain is as active as when awake.

This is because dreams are inherently an incomplete type of situational memory, and the reality that can support this view is that during rapid eye movement, there will also be a phenomenon of weakening the activity of part of the prefrontal lobe of the brain and increasing the activity of the hippocampus, and the activity of the hippocampus is related to situational memory.

Schematic diagram of the position of the hippocampus in the human brain

According to the way of encoding, storage and extraction and the different length of storage, memory can be divided into four systems: instantaneous memory, short-term memory, long-term memory and permanent memory; according to the classification of memory content, memory can be divided into image memory, logical memory, emotional memory and action memory.

From the perspective of psychology, memory can also be divided into declarative memory and procedural memory, which in turn contains situational memory and semantic memory, and situational memory refers to the memory of personal life experience, including information about life experience and time and place related to it. Whatever kind of memory, it's stored in the brain.

The human brain is a complex tissue weighing about 1.5 kilograms, and with the progress of brain science research, the main memory storage unit of the human brain has gradually been identified as being in the hippocampus region, also known as the hippocampus, which is the structure of the human brain responsible for memory and learning.

In the 1950s, scientists discovered the association between the hippocampus and memory by removing part of the memory in the human brain after the excision of the hippocampus, and the older memories after the removal of the hippocampus will not disappear together, and found that the hippocampus is responsible for short-term memory, including the knowledge points of the instantaneous memory before the exam, the telephone number written temporarily, the perceptual information that is accidentally contacted, etc. These short-term memories that need to be temporarily stored in the short term are processed by the hippocampus.

Some people compare the hippocampus to the memory of the computer, the recent memory is vividly retained for easy access, if these short-term memories want to become long-term memories, the relevant information needs to be repeated continuously, the hippocampus will "permanently" store it in the cerebral cortex. However, the "permanent memory" in the human brain is not forever gone, and although the hippocampus is mainly responsible for short-term memory, if the hippocampus suffers major damage, it will completely lose its role.

Then the information stored in the cerebral cortex can not be used for a long time, then the so-called permanent memory will also be deleted, if the hippocampus is only partially damaged, then it can continue to perform its functions with partial functions.

With the deepening of the study of the hippocampus, scientists have found that the damage to the hippocampus can also affect the imagination, and a patient with a damaged hippocampus will not be able to form a specific picture in the brain when exposed to some words describing the scene, because the hippocampus provides the brain with an environment to construct various images, which is achieved through nerve cell activity.

On this basis, scientists found that by artificially simulating neural signal activities, artificial memory can be implanted into the hippocampus slice of the brain of the laboratory mouse, and in the subsequent study of how the hippocampus encodes and stores the human experience as a memory, the experimenter successfully affects the dream of the laboratory mouse by playing the ambient sound it has encountered, which also proves that the appearance of the dream is related to the coding and storage process of memory in the hippocampus.

Dreams of different scenes

Memory usually has logic and clues, when we recall an event, if it exists in our minds as an instantaneous memory, we may only be able to think of some key words or key scenes, and then slowly get the complete information. For example, recalling a friend's birthday date may first recall the scene of talking with a friend about age or expected birthday gifts, and then think of specific numbers; if it becomes a long-term memory, such as the basic theory related to personal majors, it is almost a state that can be blurted out during the speech.

No matter what kind of memory, any scene in the process of recall is in line with the logic of reality, will not make people feel too chaotic and weird, but the situation of the dream is different, many times our dream logic chaos clues are complicated, sometimes even because it is too senseless and let their consciousness find themselves in the dream, and the scene in the dream is not controlled by logic and often brings us into the scene that we do not want to stay, which is a nightmare.

As the saying goes, "day and night have dreams", dreaming of exams is a common experience of many students, and even some people will return to the university high-number examination room in their dreams after graduating for many years, facing unsolvable problems like numbness, and when they wake up in the morning, they cannot escape the emotions that were once dominated by the exam.

There are also people who dream of encountering Waterloo at the interview site on the eve of the upcoming interview, dreaming of being rejected or being snatched by a knife on the eve of the marriage proposal, these dreams that are closely related to reality are the brain's re-encoding and re-creation of the situation constructed by the individual subconscious in the future, and invade the thinking field after the person falls asleep.

The sources of these situations are human experience and memory: fear and anxiety about exams are emotional memories that were deeply rooted in the brain many years ago; in "precognitive dreams" or "reverse precognitive dreams" of what is going to happen in the future, the imagination of specific situations in life or pessimistic or optimistic situations comes from the reuse of memories of real-life experiences of others or constructed scenes in film and television works.

And those strange dreams may come from very vague instantaneous memories, they have lost the logical connection around themselves, more in a less clear and clear figure exists in the subconscious, and in the night of poor sleep quality is shaped by the brain into a variety of logically chaotic nonsense scenes, in the past human imagination of some unknown things may also come from a brain to release the dream of the self.

Sleep, memory and dreams

There are also some special molecules in dreams, such as continuous dreams night after night, such as dreams that really confuse reality, and these dreams are characterized by smooth logical lines. Infinitely close to reality, they are usually the most vivid dreams remembered after a person is awakened from deep sleep, and some people may even think that they are really happening, and they are remembered so clearly by the brain because the brain has been awakened to some extent during the process of being awakened and has begun to send instructions to various parts of the body.

The two most common situations are either the gradually awake brain intervenes in the dream to clear up more of the logic in the memory, making the dream more "normal", or the dream that is inconsistent with the actual situation leaves a deep impression on the brain.

Years later, when encountering similar scenes or recalling scenes that have actually happened, the situation in the dream may be confused with the actual situation, and the brain may even replace the dream with the memory, such as someone recalling that he did not get a place at a sports meeting in his childhood, which is actually the result of a pessimistic dream, and the reality is that his award certificate is still hanging on the wall of the room when he was a child.

These dreams can have such a big impact and even change memory, mainly due to poor sleep quality or lack of sleep, and people who wake up naturally after a normal sleep cycle usually do not remember what is in the dream. Those brains' free creation in the middle of the night are abandoned in a long break, becoming an obstacle to sleep for the next day's life, study and work.

And the poor quality of sleep at night may also be accompanied by a dream that magnifies the anxiety and worry of reality, long-term lack of sleep can even lead to memory decline, when the memory ability becomes poor, those fragments of life situations that are free between instantaneous memory and long-term memory will become the best raw material for creating dreams.

In writing The Interpretation of Dreams, Freud reviewed past scientific works on dreams and expounded many of his own and his patients' dreams to justify his theories. He believes that dreams are a true dialogue with his heart, a process of learning from himself, and another life that is closely related to himself.

Although dreams sometimes make people feel chaotic and do not know what to call it, from a certain point of view, dreams are also a reproduction of their own lives, and the situations and emotions of life are reprocessed, reflecting some secret thoughts, which is also one of the values of "dream interpretation" outside the superstitious circle.