Sleep has a preventive and prophylactic function, because when we sleep, neurons produce proteins and other molecules that help them recover from the wear and tear suffered during the day and maintain their normal functions. But, in addition, sleep enhances learning and memory, because in the same way that every time we remember something we reactivate its memory and make it stronger and more stable, the cerebral reactivation of what has been learned also occurs unconsciously when we sleep. During sleep, neurons in the hippocampus, a region of the brain closely related to memory formation, spontaneously repeat sharp wave discharges that, in some way and at a higher speed, reproduce and integrate the same activity that generated the learning during wakefulness, which is like reviewing it quickly so that it is better recorded and protected from interference in the neurons that record it.
Thus, when a rat moves to a particular location in a maze, some neurons in its hippocampus fire electrical discharges in unison, thus creating a neuronal representation of that location. Later, during sleep or even during inactive wakefulness, the same neurons generate rapid and repetitive bursts of activity as a reproduction of that experience, activity that, in turn, seems closely related to the transfer of information from the hippocampus to the cerebral cortex, which is the ultimate storehouse of long-term memory, that is, the place where, so to speak, long-term memory resides. All of which explains why the memory of what we learn can improve even when we have not practiced for a while, since sleep is, in a certain way, a special way of practicing while we sleep.
Now we just met new and interesting details The authors of the study, published in the journal Nature, have found that the brain activity of rats exploring mazes is affected by the lack of sleep, or by the lack of quality sleep. They are part of the team led by Kamran Diva, a computational neuroscientist at the University of Michigan School of Medicine (Ann Arbor, USA). The first thing the researchers did was to find out that altering the aforementioned repetitive discharges, considered a mnesic biomarker, impairs the memory of rats in a subsequent test, while prolonging their memory improves. Then, over the course of several weeks, they recorded the electrical activity of the brains of rats as they explored mazes. They woke up one group regularly during sleep, while they let the others sleep peacefully.
To the researchers’ surprise, the rats whose sleep was disturbed by being awakened had similar or even higher levels of sharp-wave firing in the hippocampus than the rats that slept normally. But their firing was weaker and less organized, with a marked decrease in the repetition of previous firing patterns compared with the rats that slept normally. After rest, the sleep-deprived animals recovered in about two days, recreating previous patterns of activity but never matching those of the rats that slept without being awakened.
All of which suggests that the content or quality of the electrical discharges of neuronal activity in the hippocampus during sleep is more important than their quantity, that is, that the quality of sleep is more important than its quantity in promoting memory formation. Among the practical consequences of these findings, the researchers mention the possibility of interrupting sleep as a possible therapy to prevent traumatic and undesirable memories, such as those of a rape or a traffic accident, from being consolidated. The question remains as to how to do this without at the same time preventing the formation of memories that should be retained.
Gray matter is a space that tries to explain, in an accessible way, how the brain creates the mind and controls behavior. The senses, motivations and feelings, sleep, learning and memory, language and consciousness, as well as their main disorders, will be analyzed in the conviction that knowing how they work is equivalent to knowing ourselves better and increasing our well-being and relationships with other people.
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