Nature vs Nurture update: Social mice subdue their violent urges

As someone currently working from home, you don’t have to tell me about the strange impact of isolation, especially when even the cats blank you. But a new study from Stanford University’s school of medicine has revealed the surprising side effects of socialisation on mice – and while I like to think I’m slightly more sophisticated than a rodent, it’s probably just as well I’ll be back in the office tomorrow.

Nature vs Nurture update: Social mice subdue their violent urges

In a study published today in Neuron, researchers reveal that when it comes to the age-old nature vs nurture debate, environmental factors may play a decisive role – at least when it comes to aggression. Socialised mice can overrule their baser instincts, even when every fibre of their being is telling them to lose their heads and attack.

We know that mice can have their aggression switch flicked on at will, and scientists used another method to trigger rage in a group of male rats: triggering the PR+ VMHvl nerve cells, which contain receptors for sex hormones. “Selectively activating just this tiny cluster – about 5,000 nerve cells in a brain with 80 million nerve cells – escalates the level and extent of male mice’s aggressiveness dramatically,” explained the study’s senior author Nirao Shah, professor of psychiatry and behavioural sciences at Stanford University medical centre.

When the PR+ VMHvl nerve cells were activated in mice kept in isolation for up to ten days, the rodents would fly into a rage, with fierce acts of territorial aggression. Not only would the maddened mice attack other any other male thrown into the cage, but they would also lay into female mice and other species – which they never do under normal conditions. They would also attack their own reflection and inflated surgical gloves, which must have been quite something to watch. Intriguingly, the mouse would show no signs of aggression until it spotted an intruder (real or imagined) – no matter how hyped up its PR+ VMHvl wiring became.nature_vs_nurture_update_social_mice_subdue_their_violent_urges_2

But here’s where things get really interesting: for male mice housed together in social accommodation, a mouse with its PR+ VMHvl centre ramped up will still not attack other mice on their turf. This seems to be down to the “home” mouse’s pheromones, which Shah describes as a “pretty offensive” odour. Previous studies show that mice with activated “rage centres” will attack the host mouse once the resident’s pheromones are undetectable.

What does this mean? There’s one clear take-home, according to Shah: “Nature versus nurture is a false dichotomy.

“We’ve showed, on the one hand, that genetically programmed circuitry massively influences mammalian behavior. And we’ve seen that, under certain circumstances, nurture wins: Your social conditions can override your natural impulse to fight.”

While there are plenty of differences between mouse and man, Shah believes there are enough similarities for this phenomenon to be considered in humans too. And if he’s right, there are two important parallels to draw: first, solitary confinement is probably a hugely counterintuitive punishment for prison offenders. If prisoners reflect rodents, then keeping them away from other inmates will do more harm than good from a rehabilitative point of view.

Second, 5% of adults are estimated to experience intermittent explosive disorder: a bout of rage and ferocity disproportionate to the trigger. Shah speculates that this could be humans’ own version of the PR+ VMHvl overdose – and if we can fix that in mice, we might be able to treat humans.

And for me personally, I’m suddenly looking forward to being in the office again tomorrow. Just as long as nobody leaves any inflated surgical gloves lying around, things should go swimmingly…

Images: Elena Gurzhly and Yu-Chan Chen used under Creative Commons

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