Nature: Don't know how to comfort people, the amygdala is back?

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Social contact is a common and interactive way to express feelings, caring and intimacy
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From an evolutionary perspective, close social contact is necessary for social and cognitive development throughout the life stage
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Social contact helps in the establishment, maintenance and repair of social alliances, and contributes to the emotional stability of individuals and the cohesion of social groups
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Humans and other animals exhibit social behaviors such as comfort, mutual assistance, and resource sharing
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Pro-social social contact behaviors such as combing hair for companions promote the social connection of primates and rodents
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On October 13, 2021, the Weizhe Hong research team at the David Geffen School of Medicine at the University of California, University of California, discovered that mice performed comforting behaviors to mice that had been stressed, and further revealed inhibitory neurons that express tachykinin in the medial amygdala The neural circuit projecting to the medial preoptic zone mediates this comforting behavior
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Social grooming behavior of mice.
After two mice lived in the same litter for 5 weeks, one was randomly assigned as the subject, and the other as the partner, in a single cage.
During this process, the companion mice received 20 plantar electric shocks
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Then the two mice were put back to live together.
The test mice occasionally performed social grooming on the companion mice that did not receive the electric shocks, but they did not receive the electric shocks.
The electric-shocked companion mice have significantly increased grooming behavior, and can relieve the anxiety of the companion mice, which has a comforting effect
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In addition, this social grooming behavior exists in both male and female mice
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On the other hand, companion mice that received electric shocks did not perform this social grooming behavior on the test mice
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Researchers found that after being subjected to forced swimming or acute restraint stress, the social grooming behavior of the test mice to their companion mice increased significantly, which indicates that this social grooming behavior is widespread under stress situations
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Previous studies have shown that olfactory cues from stressed individuals can regulate the social transmission of animal stress
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When the unstressed mice were wiped with the urine of the stressed mice, the social grooming behavior of the tested mice to these unstressed mice also increased
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This indicates that odor cues can induce social grooming behavior
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Miniscope calcium imaging technology detects changes in calcium ion in the amygdala.
In vivo Miniscope calcium imaging technology found that when the test mice were in contact with unstressed companion mice and stressed companion mice, the activity of calcium ions in the MEA brain area increased, but it was compared with the latter.
The change in exposure is even more significant
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This indicates that the neurons in the MEA brain region are more sensitive in encoding information related to the social interaction of the stressed companion mice
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Allogroming behavior is a kind of pro-social behavior of grooming peers.
This article finds that this social grooming behavior has the characteristics of reducing anxiety, so this behavior is called comfort behavior in the following
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When the tested mice contacted their companion mice, they appeared comforting behaviors, sniffing behaviors, and self-grooming behaviors.
Neurons in the MeA brain region all responded to these behaviors
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Performing principal component analysis on these behavioral response neurons is the key to cause comfort behavior
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Weizhe Hong, who was still a postdoc in Professor David J.
Anderson’s laboratory in 2014, discovered that there are two different types of neurons in the amygdala brain area: inhibitory neurons that release the neurotransmitter GABA to promote social behaviors, such as mating and fighting.
Or social grooming; another type of excitatory neurons that release the neurotransmitter glutamate controls non-social behaviors, such as repeated self grooming
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In-body calcium imaging technology found that the calcium ion activity of GABAergic neurons in the MeA brain area was significantly increased during the comfort behavior
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Light inhibits this type of neuron and weakens the comforting behavior
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These inhibitory neurons express Tac1 (Tachykinin), Sst (Somatostatin) and Cck (Cholecystokinin)
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Specific activation of Tac1-positive GABAergic neurons in the MeA brain area can induce comfort behavior, while photo-inhibition of this type of neuron weakens social grooming behavior
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Virus tracing experiment MeA brain area Tac1 positive GABAergic neurons project to the medial preoptic area (MPOA), and light activates the neural circuit to induce comfort behavior
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In general, this article reveals that the medial amygdala brain area is the key hub for driving comfort behavior.
There is a key GABAergic neuron subtype-Tac1 positive neuron that controls comfort behavior; there is also a key ring that controls comfort behavior.
Road-MeA→MPOA
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[References] https://doi.
org/10.
1038/s41586-021-03962-w The pictures in the text are from the references