Posts tagged aggression
Articles and news from the latest research reports.
Repeated aggressions trigger social aversion in mice
One of the mechanisms involved in the onset of stress-induced depression has been highlighted in mice by researchers from CNRS, Inserm and UPMC. They have determined the role of the corticosterone (stress hormone) receptor, in the long-term behavioral change triggered by chronic stress. In mice subject to repeated aggressions, this receptor participates in the development of social aversion by controlling the release of dopamine, a key chemical messenger. If this receptor is blocked, the animals become “resilient”: although anxious, they overcome the trauma and no longer avoid contact with their fellow creatures. This work is published in Science on 18 January 2013.
Human hands have ‘evolved for fighting’
Compared with apes, humans have shorter palms and fingers and longer, stronger flexible thumbs. Experts have long assumed these features evolved to help our ancestors make and use tools. But new evidence from the US suggests it was not just dexterity that shaped the human hand, but violence also.
Hands largely evolved through natural selection to form a punching fist, it is claimed. ”The role aggression has played in our evolution has not been adequately appreciated,” said Professor David Carrier, from the University of Utah.
”There are people who do not like this idea but it is clear that compared with other mammals, great apes are a relatively aggressive group with lots of fighting and violence, and that includes us. We’re the poster children for violence.”
The forces of natural selection that drove hands to become nimble-fingered also turned them into weapons, Prof Carrier believes.
”Individuals who could strike with a clenched fish could hit harder without injuring themselves, so they were better able to fight for mates and thus be more likely to reproduce,” he said.
”If a fist posture does provide a performance advantage for punching, the proportions of our hands also may have evolved in response to selection for fighting ability, in addition to selection for dexterity.”
A Blueprint for ‘Affective’ Aggression
A North Carolina State University researcher has created a roadmap to areas of the brain associated with affective aggression in mice. This roadmap may be the first step toward finding therapies for humans suffering from affective aggression disorders that lead to impulsive violent acts.
Affective aggression differs from defensive aggression or premeditated aggression used by predators, in that the role of affective aggression isn’t clear and could be considered maladaptive. NC State neurobiologist Dr. Troy Ghashghaei was interested in finding the areas of the brain engaged with this type of aggressive behavior. Using mice that had been specially bred for affective aggression by his research associate Dr. Derrick L Nehrenberg, Ghashghaei and former undergraduate student Atif Sheikh were able to locate the regions in the mouse brain that switched on and those that were off when the mice displayed affective aggression.
“The brain works by using clusters of neurons that cross communicate at extremely rapid rates, much like a computer,” Ghashghaei explains. “One region will process a stimulus, and then that region sends messages to other clusters within the brain, like circuits within a computer. We looked at how the switches flipped in the brains of aggressive mice, and compared that with the brains of completely nonaggressive mice in the same setting, to see how the two processed the situation differently.”
They found that affectively aggressive mice demonstrated a large difference in the way their “executive centers” operated when the mice encountered another mouse. “Sensory inputs come in and are sent to the executive center, the part of the brain that decides how to respond to the input,” Ghashghaei says. “In the meantime, the information about the response you made gets processed back with either a pleasant or unpleasant association.”
According to Ghashghaei, the affectively aggressive mice could react violently because their brains are hardwiredto respond to certain situations aggressively without assessing whether their response to the situation is appropriate or without regard to the behavior’s consequences. In addition, affectively aggressive mice may be forming pleasant associations with their violent displays, which would reinforce their aggressive tendencies.
“We cannot say which of the two possibilities underlie the persistent aggressive displays by our mice,” Ghashghaei says, “but we can see that the patterns of neuronal activity are very different in the executive centers of these mice. Additionally, there are differences in the neuronal clusters involved with creating pleasant or unpleasant associations to the stimulus or their response. That gives us a few starting spots to begin identifying the mechanisms that underlie these profound behavioral differences.”
The regions of the brain that were involved in affective aggression in the mice are similar across all mammalian species. Ghashghaei hopes that his findings in mice will be useful to researchers studying violent behavior in humans, as well as aggression in other animals.
“With the brain, just knowing where to start looking is huge,” Ghashghaei says. “Once you have a few targets, you can tease out the possibilities and get to the heart of the problem. We are confident that manipulation of some of the identified targets in our study will disrupt displays of affective aggression in our mouse model.”
(Source: news.ncsu.edu)
Smell the potassium: Surprising find in study of sex- and aggression-triggering vomeronasal organ
"We found two new ion channels—both of them potassium channels—through which VNO neurons are activated in mice," says Associate Investigator C. Ron Yu, Ph.D., senior author of the study. "This is quite unusual; potassium channels normally don’t play a direct role in the activation of sensory neurons."
Humans have shrunken, seemingly vestigial VNOs, but still exhibit instinctive, pre-programmed behaviors relating to reproduction and aggression. Scientists hope that an understanding of how the VNO works in mice and other lower mammals will provide clues to how these innate behaviors are triggered in humans.
The VNO works in much the same way as the main olfactory organ that provides the sense of smell. Its neurons and their input stalks, known as dendrites, are studded with specialized receptors that can be activated by contact with specific messenger-chemicals called pheromones, found mostly in body fluids. When activated, VNO receptors cause adjacent ion channels to open or close allowing ions to flood into or out of a neuron. These inflows and outflows of electric charge create voltage surges that can activate a VNO neuron, so that it signals to the brain to turn on a specific behavior.
Molecular Imaging Finds Link Between Low Dopamine Levels and Aggression
ScienceDaily (June 11, 2012) — Out of control competitive aggression could be a result of a lagging neurotransmitter called dopamine, say researchers presenting a study at the Society of Nuclear Medicine’s 2012 Annual Meeting. During a computer game against a putative cheating adversary, participants who had a lower capacity to synthesize this neurotransmitter in the brain were more distracted from their basic motivation to earn money and were more likely to act out with aggression.
Out of control competitive aggression could be a result of a lagging neurotransmitter called dopamine, say researchers. During a computer game against a putative cheating adversary, participants who had a lower capacity to synthesize this neurotransmitter in the brain were more distracted from their basic motivation to earn money and were more likely to act out with aggression. (Credit: © lassedesignen / Fotolia)
For many people, anger is an almost automatic response to life’s challenges. In clinical psychiatry, scientists look at not only the impact of aggressive behavior on the individual, their loved ones and the community but also the triggers in the brain that lead to aggressive response. The neurobiology of aggression is not well understood, but scientists are aware of a relationship between the neurotransmitter serotonin and certain aggressive behaviors. The objective of this study was to explore whether higher levels of another brain chemical called dopamine, involved in pleasure and reward, increased aggressive response in its subjects. To scientists’ surprise, it was not as they first theorized.
"The results of this study were astonishingly opposite of what was previously hypothesized," says Ingo Vernaleken, M.D., lead author of the study and research scientist for the department of psychiatry at RWTH Aachen University in Aachen, Germany. "Subjects with more functional dopaminergic reward-systems were not more aggressive in competitive situations and could concentrate even more on the game. Subjects with lower dopaminergic capacity were more likely to be distracted by the cheating behavior."
In this study, 18 healthy adults in their twenties were tested for aggression using the psychological behavioral task known as the point subtraction aggression paradigm (PSAP). Participants were asked to play a computer game that required them to press a bar multiple times with the incentive of winning money, but they were also told that an adversary in the next room who is able to cheat may steal some of their winnings. What the paranoid participants did not know was that there was no adversary. The computer program is designed to perform randomized deductions of the subjects’ monetary reward to simulate the cheating competitor.The participant had three choices to react: punish the cheater, shield against the adversary by repeatedly pressing a defense button, or continue playing the game in order to maximize their ability to win cash, which indicated resilience.
"The PSAP focuses on aggressive reaction within a competitive situation," says Vernaleken. "Aggression and its neurobiological mechanisms in humans have been only moderately investigated in the past. Furthermore, most of the previous studies mainly covered the more reactive part of aggression, which merely reflects impulsive behavior and appears to be associated merely with the serotonin system. This investigation focuses on the association with the dopaminergic reward-system, which reflects goal-directed aggression."
Subjects’ brains were imaged using positron emission tomography, which provides a range of information about physiological functions inside the body, depending on the imaging probe used. In this investigation, F-18 FDOPA, a biomarker that lights up enzymes’ ability to synthesize this transmitter, was used and the uptake of this drug in the brain was analyzed to gauge the correlation between the participants’ dopamine synthesis capacity and aggressive behavior.
Results of the study showed a significant impact on aggressive response in areas in the brain where dopamine synthesis was present, especially in the basal ganglia, which among other functions include the motivation center. Minimized aggression was associated with higher dopamine levels in both the midbrain and the striatum, which plays a role in planning and executive function. People with greater capacity for dopamine synthesis were more invested in the monetary reward aspect of the PSAP, instead of acting in defense or with aggression against their perceived adversary, whereas subjects with lower capacities had a higher vulnerability to act either aggressive, defensive or both.
"Thus, we think that a well-functioning reward system causes more resilience against provocation," says Vernaleken. "However, we cannot exclude that in a situation where the subject would directly profit from aggressive behavior, in absence of alternatives, the correlation might be the other way around."
Further research is required to explore the link between dopamine and a range of aggressive behavior. More insight into these relationships could potentially lead to new psychological therapies and drug treatments to moderate or prevent aggressive response.
Source: Science Daily