Neurons that are responsible for recognition

Researchers from the Centre for Cognition and Sociality (CCS) at the Institute for Basic Science (IBS), South Korea, have made a discovery in understanding how our brains recognise and remember others. The team has identified specific neurons located in the CA1 region of the hippocampus that are responsible for processing information associated with different individuals.

Establishing social relationships and recognising the identity of others are crucial aspects of human interaction. However, there has been limited research on the neural processes underlying these abilities. Previous studies on the neural mechanisms of individual recognition in mice have primarily focused on the CA2 region of the hippocampus. However, these studies used behavioural experiments that only involved distinguishing unfamiliar mice from familiar ones, making it challenging to interpret the results accurately.

To address this gap in knowledge, the IBS-CCS research team developed a new behavioural paradigm using mice to investigate their ability to recognise other individuals more comprehensively. The experimental method, published in Nature Communications, involved associating specific mice with rewards and observing the subject mouse’s behaviour when encountering reward-associated mice versus non-associated ones.

The mice were immobilised on a spinning disk and randomly presented to the subject mouse, which relied on scent to recognise its neighbour. The subject mouse received water as a reward when licking in response to the reward-associated mouse but not to another mouse. The researchers analysed the subject mouse’s ability to discriminate between different individuals and examined the activity of brain cells during the experiment.

Using this new behavioural paradigm demonstrated that the dorsal CA1 region of the hippocampus plays a vital role in individual recognition. When the CA1 region was suppressed using a neuro-inhibitor, the subject mouse was unable to distinguish its neighbour. Using a two-photon imaging technique, the research team even identified the specific neuronal cells responsible for recognising individual mice within the hippocampal CA1 region.

These findings challenged previous beliefs that the dorsal CA2 region of the hippocampus was the crucial brain area for social memory, while the dorsal CA1 region played a lesser role. Additionally, the researchers discovered that mice can form long-term memories about individual subjects, contrary to the belief that social memories in rodents are short-lived.

Dr LEE Doyun, the lead researcher, emphasised the significance of this research: “We have revealed for the first time how value information about others obtained through positive or negative interactions with them is represented and stored in our brains. Furthermore, this provides significant insights into understanding the role of our brains in building and developing human relationships through various social interactions.”

The researchers also identified specific neurons in the hippocampal CA1 region of the subject mice that process positive information associated with different individual mice. Assigning positive or negative value to social encounters and updating that value is a crucial aspect of forming social relationships. The CA1 neurons were found to respond when encountering reward-associated individuals, but not to unrelated odours.

This discovery opens up new possibilities for understanding and treating brain disorders that affect social relationship formation. Doyun suggests that these findings could be utilised to develop treatment methods for conditions such as autism, which involve abnormalities in brain functions related to processing memories and information about others.

He concluded that the findings provide valuable insights into the neural mechanisms underlying individual recognition and the formation of social memories. By uncovering the specific role of the hippocampal CA1 region and its associated neurons, this study enhances our understanding of human social interactions and offers potential avenues for the development of treatments for brain disorders affecting social relationships.