An opioid made in the brain is crucial for remembering other people
Without enkephalin, a neuropeptide, mice were unable to recognize other mice they'd already met
It would be inconvenient if we couldn’t remember the people we have or haven’t met before. Social recognition, the ability to differentiate familiar or novel individuals of the same species is part of a larger process of social memory that allows groups within a species to build and maintain stable networks or relationships, like what we know as friend groups or communities.
The hippocampus, known for its role in memory, is divided into subregions that contribute to different memory processes, and one called CA2 is particularly important for social memory. Scientists have found one particular neurochemical to be important in social recognition. Enkephalin, a neuropeptide that interacts with opioid receptors, is needed in CA2 to recognize new people.
Enkephalins belong to a class of opioids produced by the brain which are often associated with stress response and pain relief. The researchers found that in CA2, these compounds are released by specific type of neuron, boosting information transfer to the CA2, thus enabling our brains to form social memories.
Scientists studied the effects of enkephalin through a social memory test in mice. They introduced one mouse to a space with two others, and the subject mouse was allowed to interact with each mouse for fiver minutes. The subject mouse was removed, then returned half an hour later, this time with one of the mice from the last entry and one mouse it had not met before. The typical response for mice in this case is to pay attention to the new mouse for longer. The scientists observed that, while mice with regular enkephalin levels sniffed out the new mouse for a longer amount of time, mice without enkephalin spent the same amount of time between both mice, as if they had not previously encountered one of them.
A better understanding of social memory can help demystify related diseases. Schizophrenia, a condition in which social memory is impaired, is treated with drugs affecting opioid receptors, for example. The results of this study shed light on how these treatments work.