Now that the biologists had identified one site—out of many—housing neurons that activated selectively for social encounters, they listened in on the goings-on by placing very fine electrodes in proximity. Silent when the mouse is solitary, these cells’ activity level progressively increased as a male intruder entered the cage and the resident mouse attacked. More puzzling was the observation that some neurons were also active, albeit only transiently, in the initial exploratory phases of mating with a female. Conversely, many of the cells signaling during fighting were actively suppressed during mating, indicating an inherent opposition between aggression and sex. To paraphrase the 1960s slogan: you either make love or war, but not both.
So far these experiments have revealed interesting correlations between neuronal activity and behavior (fighting). But what role does VMHvl play in aggression? Are its neurons the cause of fighting?
Marrying Light and Genes
Anderson and his team are masters at exploiting a remarkable technique known as optogenetics [see “Playing the Body Electric,” Consciousness Redux; March/April 2010] to stimulate hundreds to perhaps thousands of cells in the VMHvl, out of the 40 million cells of the mouse brain. Scientists injected into the VMHvl on one side of the animal stunted viruses carrying a modified piece of DNA engineered to encode a photosensitive ion channel selective to blue light. Because it is dark in the catacombs of the brain, enlightenment comes from a tiny optical fiber snaking its way through the tissue. Expressed in the membrane separating the cell from the outside, the neuron responded to blue light with excitation. Every pulse of light reliably triggered one or more electrical pulses in the infected neuron. Once the animals recovered, little difference was apparent in their behavior alone or when interacting with another.
Stimulating the VMHvl when the mouse was by itself did not do anything. Yet in the presence of another animal, the mouse initiated a concerted attack, often by biting the back of the intruder. Unusually for this species, the illuminated male indiscriminately attacked female, castrated male or anesthetized mice—and sometimes even a blown-up latex glove. Aggression ceased once the light stopped. The infection and light delivery had to be targeted to the VMHvl nucleus; stimulating nearby regions did not produce such an effect. It is a striking and immediate demonstration of the link between neurons and behavior. Exciting VMHvl neurons causes aggression.
Finally, Anderson and his team turned to the question of whether the VMHvl cells are necessary for aggression to occur. Using a different technique, they genetically “silenced” VMHvl cells, turning them effectively off for days at a time. This silencing significantly reduced the chances of an aggressive encounter and lengthened the time it took to initiate an attack.
Of course, we do not know what the infected rodent experiences in its murine mind when light beams illuminate its hypothalamic attack center. But its behavior is fully compatible with the idea that its sudden violence is accompanied by a bout of petulant anger directed at anything nearby, including helpless victims that pose no threat. Some readers may not be strangers to such “irrational” impulsive feelings welling up. But fortunately, most of us can control our anger, not lashing out at our screaming boss, possibly by inhibiting our hypothalamus via descending fibers from the prefrontal cortex. It is not unreasonable to hope that researchers can investigate the neuronal basis of such anger management in the mouse in the near future.
This article was originally published with the title Sex and Violence.
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9 Comments
Add Commentinteresting article
Reply | Report Abuse | Link to thisNow Ii know why those cats out there do all that screeching.
Reply | Report Abuse | Link to thisNot sure this passes the sniff test.Where does one see sexual activity without some aspect of aggression? Look at life and human sexuality studies.
Reply | Report Abuse | Link to thisI think the conclusions based upon the data might be a stretch.My guess is there is both overlap and differences.I dont it is one or the other ie disagree with love not war.Oversimplified.
Yes, such kind of an off switch for sex and violence must exist. Otherwise people will stay 24 hours a day playing sex or fighting. Now we know that the switch exists, and will be learning how to operate it. Now that we found the switch what are we gonna do with it ?
Reply | Report Abuse | Link to thisWhat would have been going on in Russiam brains when they entered Berlin at the end of World War Two?
Reply | Report Abuse | Link to thisSex and aggression would seem to have become rather confused.
So the neurons governing both sex and aggression are housed in the same brain organ, the ventromedial hypothalamus (VMH). But on the one hand, it says the populations of neurons for sex and aggression are intermingled, with only a small degree (about 20 percent) of overlap, but on the other hand the article focus on neurons in a specific region, the nucleus of the ventrolateral region of the VMH (VMHvl), and only in association with aggression. So is aggression controlled specifically by the VMHvl or does the VMHvl control both sex and aggression, with intermingled populations of neurons? The technique of modifying the ion channels to be selective to blue light can't be done with intermingled populations of neurons -- or can it? It can only be targeted at all neurons in a specific region, such as the nucleus of the VHMvl?
Reply | Report Abuse | Link to thisStimulating VMHvl leads to Zombie Apocalypse...
Reply | Report Abuse | Link to thisNeuroscientists found neurons in the VMH involved in sex or violence, one or the other...girls or guns..., although initially “albeit only transiently” girls and guns, right...then girls actively suppressed the guns, ok (good plan).
What pattern of activation in the VMH would we see if the inexperienced male mouse had the option to choose - fight or f? Which urge would be stronger?
It'd be interesting to know what other areas regulate those that the researcher's stimulated in the VHMvl. If the VMH “mating neurons” that actively suppressed the “aggressive neurons” (mentioned above) were stimulated, would they silence the VMHvl neurons specifically? What other neurons and associated behaviours suppress VMHvl or aggression? Pizza neurons? What behaviours do the female VMHvls trigger when specifically stimulated? Are male VMHvls equivalent to female VMHvls? Are there developmental differences? What role do hormones play?
Let’s hope there are so many more brain areas dedicated to peace and love, or at least that we evolve some more soon. =o) There's a fair few people on this planet - mating neurons definitely working AND people spend a great deal of time trying to kill each other...seems we are not so different from a bunch of angry mice with overactive VMHs!
PS I'd be pretty angry if they infected a blue strobe light into my brain...no matter where they put it. Poor lil dudes!
My essay, 'The chip in the brain', which you can access at the FQXi web site, outlines an alternative to the 'neural network' model. Background at www.scienceuncoiled.co.uk.
Reply | Report Abuse | Link to thisMichael T Deans, MA MSc
A bit behind on this boat, but I think you have large amount of questions that need to be added and applied to this article. I guess that is what commentary is for. Nice job, article would have been incomplete without it.
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