Try: Inhale and talk at the same time.
Chatting, humming, yelling (?), we perform these vocalization behaviors almost every day. It is natural that we take speaking up as normal, "thinking" that we can speak up at all times. But a simple little experiment tells us: at least when we inhale, we can't speak.
Sometimes, you'll find some people talking about the rise and can't help but gush on and on, and no one seems to be able to interrupt them. Given that inhalation and vocalization cannot coexist, if they really can't stop talking, a tragedy like "talking to death" probably will happen.
Fortunately, we have never heard of such a witty and terrifying incident. After all, the human body will always prioritize one of the most basic needs - survival. If you notice that you are about to run out of oxygen, your brain forces you to stop making sounds and breathe quickly. After all, staying alive is the number one priority.
Vocalizations are tightly tied to breathing. We always seem to speak when we exhale and stop talking when we inhale. Because vocalization requires the release of air from the lungs, which flows through the larynx, forcing the vocal cords to vibrate in order to produce sound. The key to this is the airflow and vocal cord vibrations.
But if you think about it, it is clear that inhaling also allows air to flow through the throat, so why can't the reverse process trigger vocal cord vibrations? Why can't we speak while inhaling and have the ability to babble all the time? Why don't we "talk to death"?
Delicate and complex
To understand the first two questions, we also need to understand the process of vocalization in more detail. Although the complexity of vocalization systems varies from species to species, there are similarities in the basic processes that produce sound. As mentioned earlier, vocalization requires airflow and vibration of the vocal cords, which are closely related to the larynx.
Image source: Wikipedia
The larynx is an ancient organ. When fish climb from the ocean to land and evolve into a variety of animals, an important problem in this process is the need to separate the air they breathe from the food they eat. The larynx functions like the "anterior hall" of the trachea, with a layer of cartilage called the epiglottis that prevents food or liquid from falling into the trachea and causing asphyxia. Underneath the epiglottis, mammals have evolved additional folds of tissue that are essential for our vocal cords.
To vibrate the vocal cords, the larynx is usually contracted to adduct the vocal cords so that the air can pass through to provoke the vibrations of the folds. If you consciously feel it, you may find that when you squeeze your throat, the tone is usually high, and when you try to widen it, you can produce a low sound. This process is precisely to tighten or relax the vocal cords, thereby adjusting the frequency of the vocal cord vibrations.
However, when we try to inhale, in order to ensure efficient inhalation, the larynx needs to be opened, that is, the vocal cords are abducted, which naturally cannot cause the vocal cords to vibrate and make sounds. Of course, this is under the premise of natural relaxation, and we will not feel any sluggishness when we inhale. But if you consciously tighten your throat and inhale at the same time, you can actually make some exclamations similar to "stun me", but you will feel difficult to inhale.
Image source: Wikipedia
The complex and delicate coordinated movements of the vocal cords and breathing allow animals to make sounds and communicate with each other. But scientists are still curious about why vocalizations must give way to inhalation when it comes to life-threatening situations, and how to ensure that breathing takes precedence over vocalizations.
The "manipulator" who dominates the behavior
Either behavior, it is regulated by neural circuits. For example, vocal cord closure or external extractions are controlled by laryngeal motor neurons, while respiratory movements are controlled by complex breathing circuits. There is also a clear neural circuit between laryngeal movement and breathing, which seamlessly and silkily regulates the flexible switching between the two and ensures the prioritization of the respiratory circuit.
To explore the "manipulators" behind this dominant behavior, a team of researchers at the Massachusetts Institute of Technology (MIT) began using mouse models to try to identify the neurons that control vocal cord adduction and how these neurons interact with respiratory circuits.
The vocalization of mice also requires exhalation to allow the gas to flow through the nearly closed vocal cords. Adduction of the vocal cords leaves a very small hole in the middle, and when the gas passes through the hole, it is like whistling, allowing the mice to emit ultrasound waves to communicate with each other, a process also known as ultrasonic vocalization (USV).
Knowing that vocal cord adduction is controlled by laryngeal motor neurons, the researchers used a nerve tracer to map synaptic connections between neurons and began tracking backwards to find the neurons that innervated them. After observation, the researchers found that a group of motor neurons located in the retroambiguus nucleus (RAm) in the retroambiguus nucleus (RAm, which has been identified by previous studies as being associated with vocalization) was strongly activated during USV in mice. Eventually, the researchers targeted a subset of vocalization-specific neurons in RAm, known as RAmVOCs.
Image source: Original paper
When the researchers blocked RAmVOC neurons, mice were no longer able to produce USV or any other type of sound, their vocal cords did not close, and their abdominal muscles did not contract. Conversely, when RAmVOC neurons are activated, the vocal cords of the mice can close again, producing USV and exhaling at the same time. And, the longer the activation, the longer it takes to exhale and vocalize.
However, if the RAmVOC neuron is continuously stimulated for two seconds or more, the USV is interrupted by the inspiratory process. During prolonged RAmVOC activation, mice periodically interrupt vocalizations to inhale. The need to breathe significantly "overshadowed" the stimuli exerted by the researchers on RAmVOC neurons.
To find out what was behind the scenes, the research team mapped the neurons that provide inhibitory signals to RAmVOC neurons. As a result, they found that most of the inhibitory signals come from the part of the brainstem that controls respiratory rhythms, known as the preBötC complex.
Image source: Original paper
When the researchers blocked the connection of preBötC to RAmVOC, it was difficult for mice to interrupt vocalizations for breathing. Mice will breathe much shallower than normal. And when inhaling, the mice also make hoarse, asthma-like sounds.
Studies have shown that RAmVOC neurons control vocal cord adduction to produce sounds, but are periodically inhibited by preBötC, allowing for smooth breathing. The study, which reveals the neural circuitry behind the coordinated movement of breathing and vocalization, was published in Science in March.
Looking back at the evolution of humans, the shape of the vocal organs changed after we diverged from our early ape ancestors. The human mouth begins to become smaller, less prominent, and the tongue moves downward, pulling the larynx lower, giving us a longer neck. All of these changes have allowed humans to control tiny muscles with incredible precision, producing complex sounds that no other animal can achieve.
But with opportunities comes risk. Due to the lower larynx, all the food we eat must pass through the larynx, stagger the trachea, and then enter the esophagus. The thrill of this is that choking can happen if the food is in the wrong place. It seems that these structures, which enhance our ability to speak, allow us to suffocate "more effectively".
To avoid this "efficiency", please also note that avoiding eagerness to eat and drink while speaking can greatly increase the risk of choking, or if you continue to speak for too long, it may also cause your throat to tire and cause choking.
bibliography
[1]https://www.science.org/doi/10.1126/science.adi8081
[2]https://news.mit.edu/2024/how-brain-coordinates-speaking-and-breathing-0307
[3]https://www.nih.gov/news-events/nih-research-matters/coordinating-speech-breathing-brain
[4]https://www.smithsonianmag.com/smart-news/scientists-discover-how-some-whales-can-sing-while-holding-their-breath-underwater-180983836/
[5]https://www.npr.org/2010/08/11/129083762/from-grunting-to-gabbing-why-humans-can-talk
[6]https://www.nature.com/articles/s41586-024-07080-1
来源:环球科(id:huanqiukexue)