What are the differences between the brains of children who “don’t like taking naps” and those who “take naps every day”?

Review expert: Yin Tielun, deputy chief physician of the Department of Neurology, Peking University Third Hospital

Everyone must have had the experience of being forced to take a nap by their parents when they were young, right?

Children are always full of energy. Some children can sleep for several hours, while some children don’t want to take a nap at all and are full of energy all day long.

The difference in napping habits is likely to continue for many years, so why does this difference occur? A recent foreign study shows that children’s reluctance to take naps is not because they are “young”, but the problem is actually related to the structure of their brains.

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Sleep pattern transitions in infants and toddlers

From the moment we are born, the human sleep process has different sleep transition periods as the brain and memory develop.

Studies have shown that newborn babies can sleep up to 20 hours a day. Because they need to be fed frequently by their caregivers, newborns' sleep is distributed across multiple sleep periods, that is, they are in a polyphasic sleep stage.

Between 4 and 6 months of age, infants' nighttime sleep begins to diverge from their daytime naps, but polyphasic sleep remains , with three or more nap periods in addition to the nighttime sleep period.

At 9 months old, babies' sleep patterns change to a three-phase sleep pattern consisting of two daytime nap periods and one nighttime sleep period.

In the first two years of life, the baby's morning nap will gradually disappear and develop into two sleep segments: midday nap and night sleep.

Children aged 13-15 years generally show a shift toward the monophasic nocturnal sleep pattern of adults.

The researchers found that different children have significant differences in the transition age and transition time of their sleep periods. These sleep transition periods can reflect the maturation of the brain and the development of memory. The sleep differences between different individuals are closely related to the development of their respective brain structures.

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The causes of nap transition

To understand the reasons for the above-mentioned sleep transition phenomenon, we first need to know that the human body's sleep regulation is affected by the interaction of two different biological regulation processes, one is the circadian rhythm control process, and the other is the internal environment homeostasis regulation process.

The circadian rhythm regulation process is a 24-hour sleep behavior pattern formed by humans in the long process of evolution over billions of years in order to adapt to the earth's rotation cycle . It is mainly controlled and regulated by the central circadian pacemaker located in the hypothalamus, which will adjust the human body according to time signals. The most common time signals are light or darkness stimulation. After sensing the light signal stimulation, the central circadian pacemaker will send signals to other brain organs according to the 24-hour circadian rhythm, promoting the synthesis of related hormones to inhibit brain activity.

The process of regulating the homeostasis of the internal environment is driven by an internal balance mechanism that drives sleep. When awake, the internal balance sleep pressure in the human body will continue to accumulate as the wakefulness time continues. When it accumulates to a certain level, the human body will feel tired. This pressure can only be dissipated through sleep .

Nap transitions are affected by many factors such as environment and culture, and the two-process model of sleep can help us understand how these factors affect sleep. For example, parents can strengthen circadian-driven sleep by adjusting light and other means to encourage children to take naps at the same time, which actually takes advantage of the circadian rhythm's control over nap patterns.

However, in many cases, many children will take a nap even without any promotional measures, while some children will not take a nap even in an environment that promotes sleep. This needs to be explained from the perspective of the homeostatic regulation process.

The accumulation of homeostatic sleep pressure is variable , and experimental studies have shown that young children accumulate homeostatic sleep pressure faster than older children, and therefore need more frequent naps to release this sleep pressure. Researchers believe that brain development and memory development are the basis for this difference in sleep pressure, and have concluded that brain development is related to nap transitions from studies comparing the cognitive performance of habitual napping and non-habitual napping children of the same age. The more mature the early infant brain is (especially the more mature the memory network dominated by the hippocampus), the more effectively it stores memories, thereby reducing the accumulation of homeostatic sleep pressure and ultimately leading to a transition from naps to adult-style monophasic nighttime sleep.

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Children who don't like to nap have more mature brains and better cognitive performance

Our brain's ability to learn and remember mainly relies on a network of brain regions including the hippocampus and neocortex. The hippocampus plays a major role in early cognitive activities such as forming new memories and remembering the connections between different things. In short, this organ provides short-term storage, where memory traces generated by learning are temporarily stored, but they are easily disturbed and forgotten. As the brain develops over time, the connectivity between the distributed cortical areas in the brain increases, the role of the hippocampus gradually weakens, and the memory consolidated in the neocortex can be more stable and effectively resist external interference.

A large number of animal studies have shown that during naps, memories in the hippocampus related to learning events are activated, which means that sleep can help consolidate short-term memory . When a baby is just born, the different brain regions of the baby's brain are not yet fully developed, and the ability to learn and remember is not strong. Multiple sleeps are needed throughout the day to continuously consolidate memories. As the brain continues to mature, the connections between the neocortical areas of the brain continue to strengthen, and the short-term memories initially formed in the hippocampus will be consolidated in the neocortical area, which can more effectively fight forgetting, and our ability to learn and remember will gradually improve.

In a cognitive test of children of the same age, researchers found that children who took fewer naps remembered the number sequences they heard longer and had a larger vocabulary than children who took naps regularly. The results showed that children who did not take naps frequently had stronger cognitive abilities and better memory performance .

In order to make a reasonable explanation for the results of the above cognitive test experiments, the researchers used the size of the hippocampal subregion (an area of ​​the hippocampus that has significantly different volume changes at different stages of brain development) as an indicator to further explore the relationship between the hippocampus, which plays an important role in the early formation and consolidation of memory, and children's cognitive behavioral performance. The study found that among all the 4-8-year-old children studied, children with smaller hippocampal subregions had better memory performance. Based on this, the researchers inferred that children who do not like to take naps have better cognitive performance, which may be because their memory storage is more efficient, the hippocampal subregion is smaller, and they do not need to rely on frequent sleep to consolidate the short-term memory of the hippocampus.

Afterwards, the researchers compared the volume of hippocampal subregions in children aged 4 to 6 who habitually took naps and those who did not, and found that compared with children who habitually took naps, the hippocampal subregions of children who did not take naps were smaller and their corresponding cognitive performance was better .

Combining all the above experimental results, it can be concluded that napping habits are related to the degree of brain maturity. Children with more mature brains have stronger connections between distributed cortices, can store memories more effectively , and the function of the hippocampus is weakened, thereby reducing the accumulation of homeostatic sleep pressure in the body. Therefore, there is no need for frequent naps to consolidate memories and relieve homeostatic sleep pressure.

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A better understanding of the transition and conversion of nap patterns will help increase our understanding of children's health. Scientific evidence shows that nap transitions are a product of brain development and vary greatly among different children. Parents should realize that nap pattern conversion cannot be determined solely by age, but should be judged in combination with the child's daily behavior. For children who habitually take naps, the memory damage caused by not taking naps is far greater than that of children who do not like to take naps. Therefore, if you find that your child does not like to take naps, you don't need to worry too much; if your child has the habit of taking a nap every day, you should fully support him and provide him with the conditions for taking a nap .