University of Tokyo Study Maps Neural Circuit for Aversion to Specific Individuals

University of Tokyo researchers identified a neural mechanism that allows the brain to develop an aversion to a specific individual. Japan Times reported the findings on July 10, 2026. The team, including professor Teruhiro Okuyama, first introduced test mice to two other mice so the animals could form distinct social memories.

Researchers then used genetic techniques to increase aggression in one of the familiar mice, causing it to attack the test animals repeatedly. After the encounters, the test mice avoided only the attacker while continuing normal interactions with the second familiar mouse.

Analysis showed strengthened connections between social memory cells in the ventral CA1 region of the hippocampus and fear-responsive cells in the amygdala.

The researchers used optogenetics to weaken those connections, after which the mice stopped avoiding their attackers and resumed approaching them. In a separate experiment, simultaneously activating memory cells for one mouse and fear-linked cells caused the test animals to avoid a mouse they had previously tolerated.

The study also found that signals traveling from the amygdala to the nucleus accumbens helped produce avoidance behavior.

Changes in the nucleus accumbens were linked to broader social avoidance, indicating the circuit can tie a negative experience to one individual or spread into generalized reluctance to interact. The experiments were conducted in mice and do not demonstrate identical mechanisms in humans.