Unlocking the Science Behind Positive Social Interactions: The Surprising Key Player You Never Knew About!

Social animals, including humans, constantly interact with others. In this process, the ability to recognize the identity of the social counterpart, retrieve relevant information about them from memory, and update it from the current interaction is essential to establish social relationships. However, there has been limited research into how these processes occur in the brain.

To answer this question, previous efforts have focused primarily on studies of the mouse brain, particularly the hippocampus. The hippocampus was thought to be the answer, as it is a brain structure that is well known to be responsible for memory formation. Within the hippocampus, the Cornu Ammonis (CA) fields, which are numbered CA1 to CA3, are involved in various functions related to memory and spatial processing and were therefore key research interests.

Until now, studies in mice on the neural mechanisms of individual recognition have focused primarily on the CA2 region of the hippocampus. However, previous studies have used behavioral experiments that only involve distinguishing unknown mice from familiar mice, making it difficult to interpret whether the results reflect the animal’s ability to truly perceive or recognize individual characteristics.

In this study, the IBS-CCS research team developed a new behavioral paradigm using mice to better investigate their ability to recognize other people. Their new method involved having the subject’s mouse associate specific individual mice with rewards and study their behavior after finding reward-associated and non-associated individuals.

Specifically, two mice were immobilized on a spinning disk and randomly presented to a subject mouse, which would recognize the neighbor through scent. Water is then delivered from the device to the subject mouse as a reward when it licks itself in response to the mouse associated with the reward, but not another. The researchers tried to determine if the subject mouse could discriminate between different individuals and analyzed brain cell activity during the experiment.

The challenge mice on the spinning disk were male littermates and the subject mice were already familiar with the challenge mice. This means that the subject mice distinguished between the challenge mice solely based on the unique characteristics of the challenge mice, suggesting the high reliability of the experimental results.

Using this behavioral paradigm, the researchers clearly demonstrated that the CA1 region of the dorsal hippocampus plays an essential role in individual recognition. For example, when the CA1 region of the hippocampus is suppressed using a neuroinhibitor, the subject mouse was unable to distinguish its neighbor. Furthermore, by using a two-photon imaging technique that allows real-time observation of neural cell activity in deep brain regions, the IBS-CCS team even identified specific neural cells in the CA1 region. of the hippocampus that is responsible for the recognition of individual mice.

This was an interesting addition to previous findings, which proposed that the dorsal CA2 region of the hippocampus is the brain area important for social memory, while reporting that the dorsal CA1 region does not play an important role.

Also, in the past, researchers believed that social memories in rodents only last for a short period of time and that they do not form long-term memories about individual subjects. However, the latest IBS-CCS study has shown that long-term memories about people can be formed in mice.

Dr. LEE Doyun, who led this research, said: “We have revealed for the first time how valuable information about others obtained through positive or negative interactions with them is represented and stored in our brains. In addition, this provides information important for understanding the role of our brains in building and developing human relationships through various social interactions.”

Beyond that, the researchers have also revealed the presence of specific neurons in the CA1 region of the subject mouse’s hippocampus that process positive information associated with different individual mice. An important part of forming a social relationship is assigning a positive or negative value to a social encounter with another individual and actualizing that value. For example, just as it is essential to develop a friendship with a particular individual, it is essential to evaluate how enjoyable and rewarding it was to interact with them.

These specific CA1 neurons were found to respond when encountered with reward-associated individuals. However, such reward expectancy responses were not observed when the subject was exposed to odors unrelated to social activity, such as citral or butanol. These findings indicate that the CA1 region of the hippocampus plays a selectively important role in the formation of associative social memories.

It is hoped that this new discovery could lead to a potential solution for the treatment of various brain disorders that cause difficulty in forming social relationships.

“Our results could be used to understand and propose treatment methods for mental disorders such as autism, which present abnormalities in brain functions involved in processing memories and information related to others,” explains Dr. Lee.