# Japanese scientists identify neural mechanism that may explain why we dislike people > Source: > Published: 2026-07-10 08:58:00+00:00 University of Tokyo researchers revealed Friday that they have identified a neural mechanism that allows the brain to develop an aversion to a specific individual. The study found that mice began avoiding a previously familiar animal after it suddenly became aggressive toward them. The behavioral shift was accompanied by stronger connections between brain cells responsible for social memory and those associated with fear and negative emotions. The researchers were also able to artificially weaken or create the aversion by manipulating the animals’ neural circuits. The team, including professor Teruhiro Okuyama, first introduced test mice to two other mice, allowing them to form memories of each animal. Researchers then used genetic techniques to increase aggression in one of the familiar mice, causing it to repeatedly attack the test animals. After the encounters, the test mice specifically avoided the animal that had attacked them while continuing to interact normally with the other familiar mouse. Analysis showed that connections had strengthened between social memory cells in the ventral CA1 region of the hippocampus and fear-responsive cells in the amygdala. The hippocampus plays a central role in memory, while the amygdala processes emotions including fear. The researchers used optogenetics, a technique that controls selected brain cells with light, to weaken those connections. The mice then stopped avoiding their attackers and resumed approaching them. In a separate experiment, simultaneously activating cells associated with the memory of a particular mouse and cells linked to fear caused the test animals to avoid a mouse they had not previously disliked. The study also identified a role for the nucleus accumbens, a region involved in motivation and behavioral choices. While the hippocampus-amygdala circuit appeared to connect a negative emotion to the memory of a specific individual, signals traveling from the amygdala to the nucleus accumbens helped produce avoidance behavior. Changes in the nucleus accumbens were also associated with broader social avoidance, suggesting the circuit may influence whether a negative experience remains linked to one individual or develops into a more generalized reluctance to interact socially. The findings were based on animal experiments and don’t demonstrate that human feelings operate in precisely the same way. Still, the researchers said the work could advance understanding of disorders in which social memory and emotional processing become disrupted, including anxiety and depression.