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This article comes from the official account of Wechat: SF Chinese (ID:kexuejiaodian), author: SF

We have all heard that dolphins can take turns to rest their left and right brains so that they can always be on guard against sharks. Relatively speaking, today's human beings are relatively lucky, do not have to face such a dangerous environment, can do nothing and get some sleep. So, how does the brain wake up? Why do some people sleep deeply and others sleep lightly?

Wen Jing | Wen Jing

An important brain node, "as soon as your eyes are closed and opened, the day goes by." this is what you go through every day when you are looking at your phone. Many times we can control when we fall asleep, such as staying up late watching football, watching dramas, singing high songs, waiting for the flag-raising ceremony, or brushing our cell phones late for nothing. But it seems difficult for us to control when we wake up.

If you don't get into a deep sleep, people can easily be woken up by the wind, thunder, rain at night, or the sound of people getting up and going to the toilet. And even if the person who sleeps well, others really have something to look for him, shake him hard, he will wake up. Also, even if we set the alarm, we may not necessarily wake up when the alarm rings. It will be a pity if we wake up early.

How does the brain wake us up and let us "turn it on"? Why is it that some noise is easy to wake people who are asleep? Why do some people wake up easily? Recently, the scientific research team of Tsinghua University published an article in Neuron, an authoritative journal in the field of neuroscience, announcing that there is an important node in the brain's thalamus that shares a general arousal neural network and a defensive arousal neural network-the medial part of the auditory thalamus (ATm).

Associated with multiple brain structures almost all mammals have a structure in the center of the brain-the thalamus. The thalamus is closely related to the cerebral cortex and subcortical brain area, which is considered to be the central brain area responsible for uploading and sending information, and plays an important role in many brain functions.

There is a structure responsible for primary hearing in the auditory thalamus-the ventral part of the medial geniculate body (MGBv), and a structure responsible for the primary hearing-the dorsal part of the medial geniculate body (MGBd). ATm is the multimodal joint area of the auditory thalamus, which is responsible for integrating multimodal auditory information (voice, sound, music, etc.).

In past studies, scientists have found that in addition to receiving multimodal information, ATm can also interact with multiple brain regions (including the brain structures responsible for arousal, emotion, decision-making and other inner feelings, such as the thalamus, the amygdala, and TeA, one of the cortical hubs).

Therefore, scientists speculate that ATm is likely to be an important node in the biological regulation of inner perception. In the new study, scientists focused on ATm and MGBv in the auditory thalamus.

The scientists observed mice during waking, slow-wave sleep (also known as normal sleep or non-REM sleep) and REM sleep, respectively, and recorded the activity of nerve cell populations in their ATm and MGBv. The results showed that only the nerve cell activity in ATm was significantly correlated with cortical activation, and the increase of nerve cell activity level was always slightly earlier than the time point of sleep-wake transition.

The scientists also found that the connections between ATm and multiple brain structures responsible for inner feelings all play a role in the awakening mechanism.

After the balance between arousal and excessive sleep determined that ATm played a role in the arousal mechanism, the scientists used sound and light to stimulate sleeping mice and measured their probability of awakening. The results showed that the population of nerve cells in both ATm and MGBv became active due to these stimuli, but only the response of nerve cells in ATm was significantly correlated with the probability of awakening in mice.

In addition, by artificially inhibiting the activity of nerve cells in ATm, the probability of awakening induced by sound and light stimulation in mice was significantly reduced.

By stimulating nerve cells in ATm, the scientists found that while these cells were active, the mice showed significant pupil dilation, increased anxiety levels and avoidance behavior. This suggests that the activity of nerve cells in ATm is related to defensive emotion.

In addition, artificially blocking the release of neurotransmitters from nerve cells in ATm will cause the defensive behavior of mice to return to the nest and escape behavior to disappear.

It is said that good rest can make you feel good. Light sleep is like a chronic disease, which will have a long-term impact on people's health. However, under special circumstances, we need to "wake up". For example, a loud sound often means danger; if a strong sense of hunger does not awaken a person, it can lead to problems such as hypoglycemia. Under certain circumstances, the brain can balance these conditions, but if it exceeds the brain's limit, it will cause problems such as sleep disorders and abnormal sensory sensitivity.

The new study found the thalamic nodes that play a role in both the general arousal neural network and the defensive arousal neural network, and explored the related mechanism, which provides a new idea for the cure of specific neuropsychiatric diseases.

References:

Https://doi.org/10.1016/j.neuron.2023.07.007

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