New Study Examines Impact of Violent Media on the Brain

With the longstanding debate over whether violent movies cause real world violence as a backstop, a study published today in PLOS One found that each person’s reaction to violent images depends on that individual’s brain circuitry, and on how aggressive they were to begin with.

The study, which was led by researchers at the Icahn School of Medicine at Mount Sinai and the NIH Intramural Program, featured brain scans which revealed that both watching and not watching violent images caused different brain activity in people with different aggression levels. The findings may have implications for intervention programs that seek to reduce aggressive behavior starting in childhood.

“Our aim was to investigate what is going on in the brains of people when they watch violent movies,” said lead investigator Nelly Alia-Klein, PhD, Associate Professor of Neuroscience and Psychiatry at the Friedman Brain Institute and Icahn School of Medicine at Mount Sinai. “We hypothesized that if people have aggressive traits to begin with, they will process violent media in a very different way as compared to non-aggressive people, a theory supported by these findings.”

After answering a questionnaire, a group of 54 men were split by the research team into two groups—one with individuals possessing aggressive traits, including a history of physical assault, and a second group without these tendencies. The participants’ brains were then scanned as they watched a succession of violent scenes (shootings and street fights) on day one, emotional, but non-violent scenes (people interacting during a natural disaster) on day two, and nothing on day three.

The scans measured the subjects’ brain metabolic activity, a marker of brain function. Participants also had their blood pressure taken every 5 minutes, and were asked how they were feeling at 15 minute intervals.

Investigators discovered that during mind wandering, when no movies were presented, the participants with aggressive traits had unusually high brain activity in a network of regions that are known to be active when not doing anything in particular. This suggests that participants with aggressive traits have a different brain function map than non-aggressive participants, researchers said.

Interestingly, while watching scenes from violent movies, the aggressive group had less brain activity than the non-aggressive group in the orbitofrontal cortex, a brain region associated by past studies with emotion-related decision making and self-control. The aggressive subjects described feeling more inspired and determined and less upset or nervous than non-aggressive participants when watching violent (day 1) versus just emotional (day 2) media. In line with these responses, while watching the violent media, aggressive participants’ blood pressure went down progressively with time while the non-aggressive participants experienced a rise in blood pressure.

“How an individual responds to their environment depends on the brain of the beholder,” said Dr. Alia-Klein. “Aggression is a trait that develops together with the nervous system over time starting from childhood; patterns of behavior become solidified and the nervous system prepares to continue the behavior patterns into adulthood when they become increasingly coached in personality. This could be at the root of the differences in people who are aggressive and not aggressive, and how media motivates them to do certain things. Hopefully these results will give educators an opportunity to identify children with aggressive traits and teach them to be more aware of how aggressive material activates them specifically.”

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Researchers boost insect aggression by altering brain metabolism

Scientists report they can crank up insect aggression simply by interfering with a basic metabolic pathway in the insect brain. Their study, of fruit flies and honey bees, shows a direct, causal link between brain metabolism (how the brain generates the energy it needs to function) and aggression.

The team reports its findings in the Proceedings of the National Academy of Sciences.

The new research follows up on previous work from the laboratory of University of Illinois entomology professor and Institute for Genomic Biology director Gene Robinson, who also led the new analysis. When he and his colleagues looked at brain gene activity in honey bees after they had faced down an intruder, the team found that some metabolic genes were suppressed. These genes play a key role in the most efficient type of energy generation in cells, a process called oxidative phosphorylation.

“It was a counterintuitive finding because these genes were down-regulated,” Robinson said. “You tend to think of aggression as requiring more energy, not less.”

In the new study, postdoctoral researcher Clare Rittschof used drugs to suppress key steps in oxidative phosphorylation in the bee brains. She saw that aggression increased in the drugged bees in a dose-responsive manner, Robinson said. But the drugs had no effect on chronically stressed bees – they were not able to increase their aggression in response to an intruder.

“Something about chronic stress changed their response to the drug, which is a fascinating finding in and of itself,” Robinson said. “We want to know just how this experience gets under their skin to affect their brain.”

In separate experiments, postdoctoral researcher Hongmei Li-Byarlay and undergraduate student Jonathan Massey found that reduced oxidative phosphorylation in fruit flies also increased aggression. Using advanced fly genetics, the team found this effect only when oxidative phosphorylation was reduced in neurons, but not in neighboring cells known as glia. This finding, too, was surprising, since “glia are metabolically very active, and are the energy storehouses of the brain,” Robinson said.

The findings offer insight into the immediate and longer-term changes that occur in response to threats, Robinson said.

“When an animal faces a threat, it has an immediate aggressive response, within seconds,” Robinson said. But changes in brain metabolism take much longer and cannot account for this immediate response, he said. Such changes likely make individuals more vigilant to subsequent threats.

“This makes good sense in an ecological sense,” Robinson said, “because threats often come in bunches.”

The fact that the researchers observed these effects in two species that diverged 300 million years ago makes the findings even more compelling, Robinson said.

“Because fruit flies and honey bees are separated by 300 million years of evolution, this is a very robust and well-conserved mechanism.”

Temper trap: the genetics of aggression and self-control

Everyone knows someone with a quick temper – it might even be you. And while scientists have known for decades that aggression is hereditary, there is another biological layer to those angry flare-ups: self-control.

In a paper published earlier this year in the Journal of Cognitive Neuroscience, my colleagues and I found that people who are genetically predisposed toward aggression try hard to control their anger, but have inefficient functioning in brain regions that control emotions.

In other words, self-control is, in part, biological.

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Researchers Discover the Seat of Sex and Violence in the Brain

As reported in a paper published online today in the journal Nature, Caltech biologist David J. Anderson and his colleagues have genetically identified neurons that control aggressive behavior in the mouse hypothalamus, a structure that lies deep in the brain (orange circle in the image). Researchers have long known that innate social behaviors like mating and aggression are closely related, but the specific neurons in the brain that control these behaviors had not been identified until now.

The interdisciplinary team of graduate students and postdocs, led by Caltech senior research fellow Hyosang Lee, found that if these neurons are strongly activated by pulses of light, using a method called optogenetics, a male mouse will attack another male or even a female. However, weaker activation of the same neurons will trigger sniffing and mounting: mating behaviors. In fact, the researchers could switch the behavior of a single animal from mounting to attack by gradually increasing the strength of neuronal stimulation during a social encounter (inhibiting the neurons, in contrast, stops these behaviors dead in their tracks).

These results suggest that the level of activity within the population of neurons may control the decision between mating and fighting.  

The neurons initially were identified because they express a protein receptor for the hormone estrogen, reinforcing the view that estrogen plays an important role in the control of male aggression, contrary to popular opinion. Because the human brain contains a hypothalamus that is structurally similar to that in the mouse, these results may be relevant to human behavior as well.

Feelings of Failure, Not Violent Content, Foster Aggression in Video Gamers

The disturbing imagery or violent storylines of videos games like World of Warcraft or Grand Theft Auto are often accused of fostering feelings of aggression in players. But a new study shows hostile behavior is linked to gamers’ experiences of failure and frustration during play—not to a game’s violent content.

The study is the first to look at the player’s psychological experience with video games instead of focusing solely on its content. Researchers found that failure to master a game and its controls led to frustration and aggression, regardless of whether the game was violent or not. The findings of the study were published online in the March edition of the Journal of Personality and Social Psychology.

“Any player who has thrown down a remote control after losing an electronic game can relate to the intense feelings or anger failure can cause,” explains lead author Andrew Przybylski, a researcher at the Oxford Internet Institute at Oxford University, who said such frustration is commonly known among gamers as “rage-quitting.”

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Fighting Flies

When one encounters a group of fruit flies invading their kitchen, it probably appears as if the whole group is vying for a sweet treat. But a closer look would likely reveal the male flies in the group are putting up more of a fight, particularly if ripe fruit or female flies are present. According to the latest studies from the fly laboratory of California Institute of Technology (Caltech) biologist David Anderson, male Drosophilae, commonly known as fruit flies, fight more than their female counterparts because they have special cells in their brains that promote fighting. These cells appear to be absent in the brains of female fruit flies.  

"The sex-specific cells that we identified exert their effects on fighting by releasing a particular type of neuropeptide, or hormone, that has also been implicated in aggression in mammals including mouse and rat," says Anderson, the Seymour Benzer Professor of Biology at Caltech, and corresponding author of the study. "In addition, there are some recent papers implicating increased levels of this hormone in people with personality disorders that lead to higher levels of aggression."

The team’s findings are outlined in the January 16 version of the journal Cell.

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Fight Control: Researchers link individual neurons to regulation of aggressive behavior in flies

Scientists have long pondered the roots of aggression—and ways to temper it. Now, new research is beginning to illuminate the cellular-level circuitry responsible for modulating aggression in fruit flies, with the hope of someday translating the findings to humans.

Researchers at Harvard Medical School have identified two pairs of dopamine-producing neurons, also called dopaminergic neurons, and traced their aggression-modulating action to a common structure in the fly brain called the central complex, suggesting that important components of aggression-related behaviors may be processed there.

“This is the first research to identify single dopaminergic neurons that modulate a complex behavior—aggression—in fruit flies,” said Edward Kravitz, George Packer Berry Professor of Neurobiology at HMS and lead author of the study.

“We don’t know how complex this modulatory circuit is, but we now have a key element of it. If we eliminate or increase the function of that dopaminergic neuron, it affects the circuit of the brain responsible for controlling aggression,” Kravitz said.

The findings were published last week in PNAS.

Flies are an ideal animal model for neurological research because genetic methods allow scientists to manipulate neurons and simultaneously observe the resulting behaviors. Many fundamental nervous system mechanisms in flies are similar to those in humans. In fact, both flies and humans share the same neurohormones.

Dopamine is one such neurohormone, and across species it affects a range of behaviors, from learning and memory to motivation and movement. In humans, neurohormones are associated with conditions such as Parkinson’s disease and psychiatric disorders.

Dopaminergic neurons are found in small numbers in particular parts of nervous systems. In humans, there are about 200,000 to 400,000 of these neurons; in fruit flies there are about 100. While their numbers are few, these neurons influence a vast array of behaviors.

Kravitz, along with Olga Alekseyenko, a postdoctoral fellow in the Kravitz lab and first author on the paper, set out to discover how these few dopaminergic neurons can influence such a wide range of behaviors.

To do this, study co-first author, Yick-Bun Chan, HMS research associate in neurobiology, genetically engineered 200 lines of fruit flies. He then used them to target select dopaminergic neurons that could be activated or silenced while the flies engaged in various behaviors.

The team detected two pairs of dopaminergic neurons that affected aggressive behavior in the flies. Interestingly, aggression was increased in the flies either by augmenting the function of these cells or by deactivating them.

In fruit flies, males fight for territory and form stable hierarchical relationships. Using previous observations and analysis of more than 20,000 interactions in fly fights, the team established quantitative measures of aggressive behavior, such as lunging, that allowed them to compare aggression levels in different fly attacks.

“When we turned off the pairs of dopaminergic neurons, the flies fought with more lunging; when we turned them on, they also fought at higher intensity levels. Apparently normal levels of aggression require a precise amount of dopamine released at a specific time and place in the nervous system. These results suggest that these neurons ordinarily hold aggression in check,” said Alekseyenko.

Also significant was the finding that while the two sets of dopaminergic neurons modulated aggression, they did not influence other behaviors.

The first pair of neurons are found in the PPM3 cluster of neurons in the fly brain and the second are within the T1 cluster. Both pairs innervate different parts of the central complex, an important structure in the fly brain.

“We already knew that dopamine receptors are present in the central complex, but we didn’t know which dopamine neurons connected to the receptors or what behaviors those neurons affected,” said Alekseyenko.

“Now we know that two pairs of aggression-mediating dopaminergic neurons terminate in different regions of the central complex, and we know that those regions have different types of dopamine receptors. Our study shows that aggression is one of the behaviors coordinated in these regions of the brain, but we still don’t fully understand the process,” he said.

In a third group of flies, a neuron pair that projected into a different part of the brain was identified. These neurons affected locomotion and sleep, but did not influence aggression.

Kravitz said the next phase of the research will be to use genetic tools to allow his team to identify the subsequent steps in the brain circuitry—which neurons are pre- and post-synaptic to the T1 and PPM3 neurons and how that affects neuronal network function.

The goal will be to establish fundamental principles for how dopaminergic neurons work in the fruit fly system, with the hope that the research will one day translate to how these neurons work in higher species. This may ultimately aid in the development of new dopamine-targeted medications for humans.

“We can now relate these two pairs of neurons specifically to one behavior, and that is aggression,” Kravitz said. “That means we have one piece of the puzzle.”

Real Angry Birds Flip ‘the Bird’ Before a Fight

Male sparrows are capable of fighting to the death. But a new study shows that they often wave their wings wildly first in an attempt to avoid a dangerous brawl.

"For birds, wing waves are like flipping the bird or saying ‘put up your dukes. I’m ready to fight,’" said Duke biologist Rindy Anderson.

Male swamp sparrows use wing waves as an aggressive signal to defend their territories and mates from intruding males, Anderson said. The findings also are a first step toward understanding how the birds use a combination of visual displays and songs to communicate with other males.

Anderson and her colleagues published the results online Jan. 28 in the journal Behavioral Ecology and Sociobiology.

Scientists had assumed the sparrows’ wing-waving behavior was a signal intended for other males, but testing the observations was difficult, Anderson said. So she and her co-author, former Duke engineering undergraduate student David Piech (‘12), built a miniature computer and some robotics, which the team then stuffed into the body cavity of a deceased bird. The result was a ‘robosparrow’ that looked just like a male swamp sparrow, which could flip its wings just like a live male.

Anderson took the wing-waving robosparrow to a swamp sparrow breeding ground in Pennsylvania and placed it in the territories of live males. The robotic bird “sang” swamp sparrow songs using a nearby sound system to let the birds know he was intruding, while Anderson and her colleagues crouched in the swampy grasses and watched the live birds’ responses. She also performed the tests with a stuffed sparrow that stayed stationary and one that twisted from side to side. These tests showed that wing waves combined with song are more potent than song on its own, and that wing waves in particular, not just any movement, evoked aggression from live birds.

The live birds responded most aggressively to the invading, wing-waving robotic sparrow, which Anderson said she expected. “What I didn’€™t expect to see was that the birds would give strikingly similar aggressive wing-wave signals to the three types of invaders,” she said. That means that if a bird wing-waved five times to the stationary stuffed bird, he would also wing-wave five times to the wing-waving robot.

Anderson had hypothesized that the defending birds would match the signals of the intruding robots, but her team’s results suggest that the males are more individualistic and consistent in the level of aggressiveness that they want to signal, she said.

"That response makes sense, in retrospect, since attacks can be devastating," Anderson said. Because of the risk, the real males may only want to signal a certain level of aggression to see if they could scare off an intruder without the conflict coming to a fight and possible death.