How does the brain judge danger signs? There is a "simple strategy" for the defense response
Our reporter Liu Chuanshu, correspondent Diao Wenhui
In the complex and changeable natural environment, how the brain "quickly", "concisely" and "precisely" judge the signals of natural enemies and produce a fast and appropriate defense response is an important prerequisite for the survival and reproduction of species.
On August 12, the reporter learned from the Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences, that Wang Liping's team discovered a "simple" strategy for animal brains to quickly defend against natural enemy reactions. The relevant results were published in the BMC Biology journal. The study revealed that the mouse brain has a "warning range" for detecting natural enemies when processing visual cues. In this way, danger signals can be quickly identified and defensive responses can be induced. Assistant researchers Yang Xing, Liu Qingqing and doctoral student Zhong Jinling are the co-first authors of the paper, and researcher Wang Liping is the corresponding author.
The natural environment is full of complex sensory cues, and animals need to make judgments based on these cues. On the one hand, they need to quickly detect approaching natural enemies and take appropriate defensive behaviors to ensure their own safety; on the other hand, they cannot overreact to non-hazardous clues, such as flying insects, so as not to waste in vain Physical strength and missed opportunities to get food and a spouse. This is the instinct gradually formed in the long evolutionary process of animals, which is vital to the survival and reproduction of animals.
"Visual cues are an important basis for animals to quickly detect danger. Previous studies often used a gradually expanding shadow disk to simulate the attack of predators, and successfully induced the instinctive defense response of mice. This shows that the visual system may be able to judge danger signals. Some details will be ignored and judgments will be made based only on certain key visual clues.” Yang Xing said.
So what visual cues do animals use to judge risk, and what cues do not require too much attention? During the research process, the research team developed an automatic monitoring system for small animal behavior based on infrared touch screens. By setting visual stimuli to mice, record the reaction parameters of mice when they encounter visual stimuli.
"Our automatic detection system can record the behavioral data of the mouse in the device, such as the size, location, and corresponding time of the mouse. Based on these data, we can calculate the speed at which the mouse escapes, the time it takes to freeze, the number of times it stands, etc. Data collection and subsequent calculations and statistics can be completed by programs. It can be said that our system has basically realized the automation of mouse behavior data collection and analysis." Yang Xing said.
The researchers used the monitoring system to present a series of disc shadows with different sizes and expansions at different speeds to the mice, and recorded and quantitatively analyzed the behavioral responses of the mice triggered by these visual stimuli, including running away, freezing, and standing. The team found that there is a “warning range” in the detection of the size change and expansion speed of the disc shadow in mice, that is, a circle with a size of 10° to 40° and an expansion speed of 57°/s to 320°/s. Disc shadows are more likely to trigger a strong flight response.
Based on the "warning range" discovered in the research, in further verification, the research team simulated the visual stimulation of barn owls, dragonflies, flies and other animals on mice based on the size and attack speed of the animals.
The team found that raptors that prey on rodents, such as black-winged kites, barn owls, etc., their images during the predation basically conform to the "warning range" of mice, while low-risk visual cues such as flies, dragonflies and other insects approaching The image does not overlap with the "warning range" or only slightly overlaps. It is inferred from this that the "warning range" represents the common visual characteristics of the attacking predator.
After a series of experiments, the team came up with a strategy for mice to detect predators: mice respond based on whether visual cues are in the alert range, instead of "customizing" specific detection mechanisms for different natural enemies. This simple strategy helps It can quickly and accurately identify real dangers in mice. The research will help to understand the neural mechanism of the brain to process danger signals and its evolutionary significance.