Aggression Flashcards
What are the neural mechanisms in aggression?
The limbic system
Serotonin
What are the hormonal mechanisms in aggression?
Testosterone
What is the limbic system?
The limbic system is a subcortical structure in the brain (including the hypothalamus and amygdala) thought to be closely involved in regulating emotional behaviour including aggression.
Describe how the limbic system is a neural mechanism for aggression.
The first attempt to link limbic structures to emotional behaviours such as aggression was by James Papez, and later revised by Paul Maclean. They identified the limbic system as comprising the cingulate gyrus, septal area, hypothalamus, fornix, amygdala and parts of the hippocampus and the thalamus.
The amygdala has a key role in humans and nonhuman animals in how an organism assesses and responds to environmental threats and challenges. The reactivity of the amygdala in humans has proven to be important predictor of aggressive behaviour.
Describe Katarina Gospic’s Ultimatum Game.
What does it show?
Katarina Gospic et al used a well-established lab method of assessing aggressive behaviour, the Ultimatum Game. This features two players, the proposer offers to split money in a certain way with the responder. If the responder accepts, the money is split as proposed. If the responder rejects the offer, both receive nothing.
Participants in this study played as responders while having their brains scanned by fMRI, which highlights activity in different areas of the brain. The researchers found that when responders rejected unfair offers (an aggressive reaction to a social provocation), scans revealed a fast and heightened response by the amygdala).
They also found that a benzodiazepine drug (which reduces arousal of the autonomic nervous system) taken before the game had two effects on responses to unfair offers. It halved the number of rejections (reduced aggression) and decreased the activity of the amygdala. This is strong evidence of an association between reactive aggression and amygdala activity.
Describe how serotonin is a neural mechanism for aggression.
Serotonin is a neurotransmitter involved in communication of impulses between neurons. It has widespread inhibitory effects on the brain; it slows down and dampens neuronal activity. Normal levels of serotonin in the orbitofrontal cortex are linked with reduced firing of neurons, and this is associated with a greater degree of behavioural self-control.
Decreased serotonin may well disturb this mechanism, reducing self-control and leading to an increase in impulsive behaviour, including aggression.
Virkkunen compared levels of a serotonin breakdown product (a metabolite called 5-HIAA) in the cerebrospinal fluid of a violent impulsive and violent non-impulsive offenders. The levels were significantly lower in the impulsive offenders, and they also suffered from more sleep irregularities. Disturbance of this pattern strongly implies some disruption of serotonin functioning, further supporting the role of serotonin in reactive aggression.
Describe how testosterone is a hormonal mechanism for aggression.
Testosterone is an androgen responsible for the development of masculine features. It also has a role in regulating social behaviour via its influence on certain areas of the brain implicated in aggression. Animal studies have demonstrated experimental increases in testosterone are related to greater aggressive behaviour in several species. Some evidence for a similar association in humans comes from studies of prison populations, Dolan et al found a positive correlation between testosterone levels and aggressive behaviours in a sample of 60 offenders in UK maximum security hospitals. These men mostly suffered from personality disorders and had histories of impulsively violent behaviour.
Evaluate neural mechanisms in aggression.
- Role of other brain structures, recent studies indicate that the amygdala does not operate in isolation in determining aggression. It appears to function in tandem with the orbitofrontal cortex, which is not part of the limbic system. The OFC is thought to be involved in self-control, impulse regulation and inhibition of aggressive behaviour. Coccaro found that patients with psychiatric disorders that prominently feature aggression, activity in the OFC is reduced, disrupting its impulsive-control function and thus leading to increased aggression.
- Effects of drugs of serotonin, drugs that increase serotonin activity also reduce levels of aggressive behaviour. Berman et al gave participants either a placebo or a dose of paroxetine (a drug that enhances serotonin activity). Participants then took part in a lab based game where electric shocks of varying intensity were given and received in response to provocation. The paroxetine participants gave fewer and less intense shocks than those in the placebo group. However, this was only true for participants who had a prior history of aggressive behaviour.
- Cause and effect, research is correlational, this is good and ethical because opportunities to experimentally manipulate brain structures and hormones are very limited. But when two variables are correlated, it is impossible to establish which one is the cause of the other, or if a third variable is involved.
Evaluate hormonal mechanisms in aggression.
- Explaining the role of testosterone, Mazur explains that a change in testosterone levels following a loss of status should affect post-competition aggression. Mehta and Josephs measured changes in their male participants’ testosterone levels before and after a competitive game which they all lost. Once the second sample was taken the pp’s could either challenge the opponent to another competition (aggressive) or complete an unrelated task (non-aggressive). Of the pp’s whose testosterone levels rose after their loss, 73% rechallenged, those whose testosterone levels dropped, only 22% rechallenged. Therefore, after a loss of status, people behaved aggressively only after an increase in testosterone levels. This confirms Mazur’s findings, increasing its validity as an explanation of how testosterone may exert its effects on aggression.
- Other hormones, Carre and Mehta’s dual-hormone hypothesis claims that high levels of testosterone lead to aggressive behaviour when levels of cortisol are low. When cortisol is high, testosterone’s influence on aggression is blocked. Cortisol is a glucocorticoid hormone that plays a central role in the stress response. Popma et al supports this explanation with a study of adolescent males about direct physical aggression. The combined activity of testosterone and cortisol may be a better predictor of human aggression than other hormone alone.
- Cause and effect, research is correlational, this is good and ethical because opportunities to experimentally manipulate brain structures and hormones are very limited. But when two variables are correlated, it is impossible to establish which one is the cause of the other, or if a third variable is involved.
What are the genetic factors in aggression?
Twin studies
Adoption studies
The MAOA gene
Gene-environment interactions
How do twin studies support genetic factors in aggression?
Several twin studies have suggested that heritability accounts for about 50% of the variance in aggressive behaviour. Coccaro et al studies adult male monozygotic and dizygotic twins. We would expect to find greater similarities in aggressive behaviour between MZ twins if aggression is mostly influenced by genetic factors. This is because both MZ and DZ twins are raised together in the same environment, but MZ twins have a greater degree of genetic similarity that DZ.
