According to the researchers, a group of neurons in the ventral premammillary nucleus (PMv) of the hypothalamus -- an evolutionarily well-preserved part of the brain that controls many of our fundamental drives -- plays a key role in initiating and organising aggressive behaviour.
"Aggressive behaviour and violence cause injury and lasting mental trauma for many people, with costly structural and economic consequences for society. Our study adds fundamental biological knowledge about its origins," said the study leader Christian Broberger from the Karolinska Institutet in Sweden.
Using a mouse model, the reseachers studied the ventral premammillary nucleus neurons. They could control the aggressive feeling in male mice by stimulating or inhibiting these cells.
The results, published in the journal Nature Neuroscience, showed that the neurons were more activated among the mice when they showed agressive behaviour as a new male was placed in their home cage.
By activating these neurons through optogenetics -- whereby neurons were controlled using light -- they were able to initiate aggressive behaviour in situations where animals do not normally attack, and by inhibiting the PMv, interrupt an ongoing attack.
The neurons could also activate other brain regions like reward centres.
"We also found that the brief activation of the PMv cells could trigger a protracted outburst, which may explain something we all recognise -- how after a quarrel has ended, the feeling of antagonism can persist for a long time," said Stefanos Stagkourakis from the Karolinska Institutet.
In a an experiment, the researchers also found that by inhibiting the PMv cells in a dominant male and stimulating the same cells in a submissive male, they were able to invert their mutual hierarchical status.
"One of the most surprising findings in our study was that the role-switch we achieved by manipulating PMv activity during an encounter lasted up to two weeks," Broberger added.
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