The University of Tokyo finds that memories of familiar individuals function through combinations of neurons

The memory of "others", such as family and friends, functions through a mechanism where different neurons that respond to information about attributes like gender and lineage and information about specific individuals work in combination. This was elucidated through animal experiments with mice by a research group at the University of Tokyo.

It was also found that these neurons are located in the "hippocampus," the brain region that retains memory. The long-standing mystery of how the brain remembers others is gradually being revealed. The research group aims to apply these findings to new treatment strategies for autism spectrum disorder (ASD) and other conditions that involve symptoms of declined ability to remember others such as friends.

Recognizing familiar individuals, such as friends, is called "social memory" and plays an important role in daily life for humans. Professor Teruhiro Okuyama and his colleagues at the Institute for Quantitative Biosciences, the University of Tokyo, had previously identified that memory of familiar individuals is retained in a part called the "ventral CA1 region" within the hippocampus, which is the memory center.

However, the detailed mechanisms of how neurons in the ventral CA1 region organize and process information about others as individual memories based on various attributes (including gender) were not understood.

Okuyama and his colleagues conducted detailed studies of neurons when mice remembered other mice, using mice of different genders and types (strains). Specifically, they had one male mouse (test mouse) encounter a total of four mice (stimulus mice)—males and females from two different strains with different appearances—to form social memory. They then had the test mouse meet the stimulus mice again and recorded the electrical activity of neurons in the ventral CA1 region to examine neural activity.

As a result, it was revealed that this region contains "property cells" that respond to attributes such as gender and strain, and "identity cells" that respond to specific individuals. When predicting which individual the test mouse encountered based solely on analysis of neural cell activity patterns in this region, they could correctly identify the actual contact with 70% accuracy.

According to Okuyama, a survey published by the U.S. Centers for Disease Control and Prevention (CDC) in 2023 showed that 1 in 36 Americans are diagnosed with ASD, with an increasing trend. It is reported that in addition to having limited interests and difficulties with communication and empathy, some aspects of social memory ability, such as remembering individual friends, also decline.

Okuyama and colleagues have previously revealed that mice with deficiencies in a gene (Shank3) associated with ASD show decreased social memory. The professor stated, "Unraveling the series of neural mechanisms that recognize and remember others will lead to the development of ASD treatments in the future."

The research was conducted with support from the Japan Science and Technology Agency (JST) Fusion Oriented REsearch for disruptive Science and Technology (FOREST) program, the Japan Society for the Promotion of Science Grants-in-Aid for Scientific Research program, and others, and was published in the American journal Science on July 4.