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Korea Brain Research Institute Reveals How Social Isolation Alters Social Value Judgments

A South Korean research team has discovered that even a single day of social isolation can significantly increase serotonin receptors in the brain, and this change can alter the way individuals perceive social relationships. The team also proposed new therapeutic targets for depression and anxiety disorders caused by social isolation.

The Korea Brain Research Institute (KBRI) announced on July 6 that a joint research team led by Dr. Jeong-yeon Kim of the Affective and Cognitive Disorders Research Group at KBRI and Professor Se-hyun Chae of Kangwon National University has identified the mechanism by which social isolation changes serotonin signaling in the brain, thereby altering value judgments toward social targets. The results of the study were published in the international journal "Cell Reports."

Control of familiarity bias in mice experiencing social isolation mediated by the action of lateral habenula serotonin receptor type 4. Provided by the research team

The research team isolated mice for 24 hours and then allowed them to encounter both a familiar and a novel individual at the same time. While typical mice showed greater interest in the novel individual, socially isolated mice instead preferred the familiar one. The researchers interpreted this as social isolation not simply diminishing sociability, but rather changing the very criteria by which social targets are evaluated.

The cause was found in the lateral habenula (LHb) of the thalamus. In isolated mice, expression of the 5-HT4 receptor—a type of serotonin receptor—was more than 2.5 times higher than normal, while serotonin signaling to the lateral habenula was reduced. The team explained that the increased receptor expression is an adaptive response by the brain to compensate for the decreased serotonin signal.

Research team photo. (From left) Mi-sun Kang (first author, KBRI), Se-hyun Chae (corresponding author, Kangwon National University), Jeong-yeon Kim (co-corresponding author, KBRI). Courtesy of KBRI

Next, when a drug that activates the 5-HT4 receptor was administered, the function regulating connections between nerve cells was restored, and excessive neural excitation was normalized. The 'preference for familiar individuals' behavior observed after isolation also returned to a normal pattern of social preference.

Dr. Jeong-yeon Kim said, "Anyone can experience changes in how they view social relationships after just a short period of isolation. We hope that this study will offer new insights for understanding and treating mental health issues stemming from loneliness and social isolation."

This content was produced with the assistance of AI translation services.