How many times a week do you want to meet up with people? And has that number changed since the increased social isolation caused by the COVID-19 pandemic? It has been shown that long-term social isolation can cause loneliness, depression, anxiety, and general mental decline. This means that our brain knows when we are alone for an extended period and can change our behavior in response, but how exactly this happens is currently unclear. To address questions like these, Lukas Anneser of the Max Planck Institute for Brain Research led a study on how changes in the social environment affect the response of genes in the brain neurons of zebrafish.

Zebrafish are fish that form social groups to better survive: the more there are of them, the less likely an individual zebrafish is to be eaten by predators. This is even reflected in the activity of neuronal genes regulating their behavior, which changes when the fish is alone compared to when it is with others. To see exactly how the activity of these genes changes, the authors of this study put a zebrafish in a tank either by itself or with varying numbers of other zebrafish. They found that one neuronal gene called pth2, which is known to regulate maternal behavior, emotional bonding, and pain in rodents, had lower activity when the fish was alone and increasing activity with the number of the fish present. In addition, the researchers were able to use this gene activity to determine that zebrafish do not sense other fish through sight or chemicals, but rather through touch and motion. When the researchers used a machine that vibrates in a way mimicking a zebrafish swimming, the activity of pth2 increased, which indicates the fish thought it was with other zebrafish.

With this recent study, we now know that zebrafish sense other zebrafish through motion/touch and that pth2 is how the brain responds to the presence of others. While we are still a long way away from understanding how a social environment exactly affects the brain and animal behavior, in the future, researchers can study: 1) how pth2 changes fish behavior, 2) whether the effect seen in fish is the same or different in other animals like rodents or primates, and 3) what additional pathways connect social environment to the brain and behavior. With continued research, maybe we can really start understanding the complex organ that determines who we are: the brain.

Lukas Anneser is currently a graduate student in the Department of Synaptic Plasticity at the Max Planck Institute for Brain Research. For his paper, he worked with Professor Erin Schuman.

Managing Correspondent: Jenny Zheng

Press Release:

Original Article: Nature

Image Credits: Pixabay

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