According to foreign media reports, human beings have a variety of emotions, which can be perfectly expressed through facial muscles and organ movements. In fact, this kind of emotional expression ability is not unique to human beings. American researchers have found that mice also have emotions. Researchers at California Institute of Technology have successfully deciphered the seemingly incomprehensible facial expressions of mice by using machine learning algorithms in the laboratory. This work may have a great impact on accurately locating neurons encoding specific expressions in the human brain.
Rats express their emotions by moving their ears, cheeks and eyes.
David andersen, a neuroscientist at the California Institute of Technology, said that their research "took a very important first step" and helped to uncover the mystery of emotions and how they are reflected in the brain.
About 150 years ago, Charles Darwin, a famous biologist, suggested that the facial expressions of animals may be like human beings, and these expressions provide a window to understand their emotions. But only in recent years have researchers acquired tools, such as powerful microscopes, cameras and genetic technology, to accurately capture and analyze facial movements and to study how emotions are generated in the brain.
Nadine Gogula, a neuroscientist at the Max Planck Institute for Neurobiology in Germany, led the three-year study. She said, "We humans have rich emotional states, which fascinates me. I want to see if we can understand how these States appear in the brain from animal research. "
It is found that mice also have emotions similar to human beings, including joy and anger, which can be expressed through their faces.
Gogula was inspired by a cell paper written by Anderson and Ralph adolphs, a professor at California Institute of Technology. In this study, they think that "brain states" such as emotions may show special characteristics. For example, they should last for a long time, and they should last for a period of time after the stimulus that caused them disappears. In addition, with the increase of stimulation, emotions may be more intense.
Gegula's team first fixed the heads of mice to keep them still, and then provided different sensory stimuli to trigger specific emotions and photographed their faces. For example, researchers put a sweet or bitter liquid on the lips of mice to arouse feelings of pleasure or disgust. They also give appropriate electric shocks to the tail of mice, or inject lithium chloride into mice to induce discomfort.
Scientists know that mice can change their expressions by moving their ears, cheeks, nose and upper eyes, but they can't reliably match these expressions with specific emotions. Therefore, when mice responded to different stimuli, the researchers decomposed the video of facial muscle movement of mice into ultra-short snapshots.
AI algorithm recognizes different expressions produced by the movement of specific facial muscle groups. These expressions are related to the aroused emotional state, such as pleasure, disgust or fear. For example, a happy mouse will pull its nose to its mouth, ears and chin forward. In contrast, when it feels pain, it pulls its ears back, bulges its cheeks and sometimes narrows its eyes.
These facial expressions of mice have the characteristics proposed by Anderson and adolphs. For example, they can last for a long time, and the intensity is closely related to the intensity of stimulation. Camilla Veron, who studies neuropsychiatric disorders at the University of Geneva in Switzerland, said: "This way of recognizing facial expressions has great advantages because it can avoid any prejudice imposed by researchers."
After that, scientists looked for brain cells that might encode these emotions in the brain. Using a technique called optogenetics, they targeted single neuronal circuits in mice, which have been shown to trigger specific emotions in humans and other animals. When researchers directly stimulate these circuits, mice will show corresponding facial expressions.
Finally, the researchers also used a technique called two-photon calcium imaging to identify individual neurons in the mouse brain, which only activate when specific emotions and specific facial expressions are aroused. "They may represent part of the emotional code in the brain," Gogula speculated. We think that emotional coding may be evolutionarily conservative, so human and mouse coding may have many common characteristics. "
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