The Charlie Brown and Snoopy Show / CBS, 1983–1985
–
American scientists have found that a lack or lack of sleep can prevent the brain from forming an adequate response to a frightening stimulus. To do this, they conducted a study in which participants were shown colored cards, one of which was followed by an electric shock. In the brains of people who slept enough the night before the experiment, the prefrontal cortex, which is responsible for cognitive functions, was more active than in those who slept little or did not sleep at all. Those who slept a little, in turn, had the most active motor cortex, which indicates increased fear and readiness to quickly get rid of a possible threat. The reactions formed during the training also further influenced how the participants met the stimulus again, write scientists in the journal Biological Psychiatry: Cognitive Neuroscience and Neuroimaging.
Consolidation of memory, that is, the transition of memories from short-term memory to long-term memory, actively occurs during sleep – and that is why night rest is very important (according to researchers, an adult enough six to eight hours of sleep daily). Lack of sleep or sleepless nights in general, in turn, can disrupt this process, and in many respects this also applies to the effectiveness of learning, including evolutionarily significant, for example, the formation of a conditioned reaction to fear.
Researchers have already showedthat in mice, during sleep, the same neurons in the amygdala and hippocampus are active, which are active during a meeting with a frightening stimulus in reality. Now Anne Germain of the University of Pittsburgh and her colleagues set out to study the effects of sleep and lack of sleep on the formation of fear memories in people. To do this, they conducted an experiment that took place in three stages. The first stage began at eight in the evening in the laboratory: all participants (154 people aged 18 to 30) were connected to a somnograph (electroencephalograph, electrooculograph and electromyograph) and left to sleep. In the morning, the participants were released and asked to return at six o’clock in the evening – to the beginning of the second stage: the participants were not allowed to doze, drink coffee or alcohol all day.
The second stage took place at night: for it the participants were divided into three groups. The first group was allowed to sleep as much as they usually sleep, the second group needed to cut the number of hours of sleep in half, and the third was not allowed to sleep at all. The third stage took place the next morning at about ten o’clock: participants were shown cards with three different colors on a computer screen, one of which was followed by a light electric shock – this way the participants were taught which color to fear. After that, on the evening of the same day, the participants were told that the dangerous stimulus was no longer followed by a blow and was shown to them. The entire first stage of the experiment took place during fMRI: the researchers monitored which parts of the brain are active during the formation of experience, recall and the formation of new experiences.
Next, the scientists compared the activities of different parts of the brain between the groups. After undergoing training for the formation of a conditioned reflex in the first group, whose participants slept all night, the medial part of the prephrotal cortex, the areas responsible for cognitive processes, was most active. The participants in the second group, who slept only half of the prescribed time, had the most active motor cortex. At the same time, scientists from the third group, who did not sleep at all at night, did not find any significant activity (in comparison with the participants in other groups) (p> 0.05).
Analysis of the data obtained after the participants were taught that the dangerous stimulus was no longer dangerous indicated the activity of parts of the limbic system of the brain – but only in the group whose participants slept all night. The same was observed in the activity received during recalling the dangerous stimulus – that is, when the cards were shown again. In the other two groups, no significant differences in activity were observed (p> 0.05).
The researchers concluded that sleep deprivation and lack of sleep actually negatively affect the formation of fearful stimulus memories, but this effect is different. For example, during the formation of the conditioned reflex, the motor cortex was more active in sleepy people: this indicates a greater fear and a readiness to quickly initiate the “fight or flight” reaction. People who did not sleep at all did not show any particular activity – which means that they hardly distinguish between frightening and safe stimuli. The initially formed responses, in turn, influenced how the participants – depending on how much they slept at night – evaluated the already familiar stimuli.
Of course, memory is not the only cognitive process for which adequate sleep is important: a few years ago, scientists showedthat sleep deprivation and working the night shift can increase people’s inattention fivefold. In addition, sleep has a beneficial effect on the learning process – at least for a person who slept more effectively works positive reinforcement.
Elizaveta Ivtushok
–
