Jerusalem, 25 January 2026 (TPS-IL) - Scientists have uncovered a rare, sharply defined neural circuit that behaves like an “on/off” switch, showing striking differences between males and females.
The discovery, made by researchers in Israel and Canada, could transform our understanding of how sex, experience, and hormones interact in the brain, and eventually inform approaches to social behavior, mental health, and parenting, the Hebrew University of Jerusalem announced.
The study, led by Dr. Tamar Licht and Dr. Dan Rokni from the Institute of Medical Research Israel-Canada (IMRIC) at the Hebrew University of Jerusalem, identified a previously unknown group of neurons in the medial amygdala, a brain region involved in social behavior, emotional processing, and reproduction.
What makes this cluster unusual is its binary activity pattern: it is consistently active in females but largely inactive in males, only turning on during major social or reproductive events.
“This is a discrete group of neurons that behaves almost like a biological switch, reflecting sex and social state in a very robust way,” Dr. Licht said. “Most sex differences in the brain are subtle and distributed. What surprised us here was the clarity of the signal.”
Neuron cluster activity is dynamic
The research, published in the peer-reviewed Proceedings of the National Academy of Sciences journal, also shows that the cluster’s activity is dynamic, not fixed. In males, it turns on only after sexual contact or reproductive experience, demonstrating that the brain can adapt neural circuits based on life events. Before sexual maturity, males and females show similar levels of activity, but after puberty, the cluster disappears in males until these social or reproductive triggers occur.
“This shows the brain can ‘flip’ neural states to match social and reproductive circumstances,” Dr. Rokni said. “It’s an example of how experience can shape behavior differently in males and females.”
The team found that the cluster is sensitive to prolactin, a hormone released after sexual contact that influences social and parental behaviors. The prolactin connection is significant because it shows that hormonal signals tied to social and reproductive experiences can dynamically regulate a specific, sex-specific neural circuit, rather than sex differences being fixed or solely determined by testosterone or estrogen.
Because most known sex differences in the brain are gradual and overlapping, the discovery of a sharply defined, functionally distinct neural switch is rare. By integrating sex, social experience, and hormonal responsiveness, this cluster provides a tangible target for studying how life-stage transitions and social interactions shape behavior, the scientists said.
The findings could help explain why males and females behave differently in social, sexual, or parenting contexts, and why certain neuropsychiatric conditions affect the sexes differently. “Our findings provide a framework for understanding how the brain organizes sex-related differences in behavior in a discrete, adaptive way,” Licht said.
The discovery may also have important implications for parenting, social bonding, and mental health. Because the cluster’s activity is influenced by social and reproductive experiences as well as by prolactin, it could help explain how males and females respond differently to caregiving and social interaction. Understanding this circuit may shed light on why certain neuropsychiatric conditions, such as depression, anxiety, or social disorders, affect the sexes differently, and it could eventually guide the development of hormone-based therapies.