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Aggression increases cell growth in the brain
Last reviewed: 02.07.2025
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An international group of neurobiologists, which also included specialists from the Moscow Institute of Physics and Technology, have established that aggression leads to the growth of new neurons in the brain.
After a series of experiments with rodents, scientists discovered that aggressive mice, i.e. those that started fights with their fellow mice, became more aggressive after winning, but in addition, new cells formed in their hippocampus.
The experiment consisted of the following: two males were placed in a cage divided into two parts by a net, which did not prevent the rodents from seeing, hearing, smelling each other, but thanks to the net, the animals could not engage in a fight. Every day, specialists (at about the same time) removed the net from the cage and observed the behavior of the males. A fight between them usually occurred almost immediately. The scientists determined the winner themselves, on average, after 3 minutes, the experts had to partition the cage again.
Three days later, the rodents were moved to other cages, i.e. their "neighbors" were changed, and each time the defeated males were moved to other winners. In one group of test subjects, the winners were removed from the fights, while in the other, the clashes continued.
The researchers also conducted a test that showed the impact of aggression on the animals' behavior. The rodents were placed in a plus-shaped maze with one closed corridor, the second part of the maze was open. The behavior of the mice was assessed by which of the two corridors the male would choose - those that chose the dark and closed part of the maze, the scientists characterized as "risk-avoiding."
The scientists also placed mice in cages with transparent partitions and assessed the level of aggression of the test subjects. The males that approached the partition more often and spent more time there were potentially more aggressive, compared to their cage "neighbors" who preferred to stay away from the partition.
After all the tests and trials, scientists found that the rodents that won several battles were more brazen and more likely to start a fight.
In addition, the males who were not allowed to fight before the experiments were more aggressive, they attacked the enemy faster and the fight itself lasted longer. But along with aggression, the animals showed increased anxiety - the males who won the fights preferred to sit in the dark and closed parts of the maze, i.e. they avoided risk.
It was previously suggested that the brains of aggressive animals function differently, and this study confirmed this.
In the brain of aggressors, the number of neurons in the hippocampus increases, which causes an increase in the level of aggressiveness of the rodents. In addition, the animals showed changes in the structure of the amygdalas (the area responsible for emotions). In humans, changes in the amygdalas are associated with the development of autism, and some signs of this disease were found in the experimental animals - an increased sense of anxiety, repetitive movements, and impaired communication with other rodents.
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