Neural + Hormonal Influences Flashcards
what do biological explanations of aggression assume?
1
biological explanations of aggression assume that aggression is located within the biological make-up of the individual rather than in the environment around them
features of the biological explanation of aggression
2
NEURAL INFLUENCES
• the limbic system; amygdala + hippocampus
• serotonin
HORMONAL INFLUENCES
• testosterone
neural influences
4
the limbic system is an area of the brain that helps to coordinate behaviours that satisfy motivational and emotional urges such as aggression and fear
a subcortiol system of structures lying beneath the cortex (includes the amygdala, hippocampus and hypothalamus)
associated with emotional behaviour
2 key structures in the limbic system that are associated with aggression; the amygdala and the hippocampus
amygdala
4
responsible for quickly evaluating the emotional importance of sensory information and prompting an appropriate response
if certain areas of the amygdala are stimulated electrically, an animal responds with aggression — e.g. by snarling and adopting an aggressive posture
if the same areas are surgically removed, the animal no longer responds to stimuli that would have previously led to rage and aggression
Kluver and Bucy (1937) discovered that the destruction of the amygdala in a monkey who was dominant in a social group caused it to lose its dominant place in the group
hippocampus
5
involved with the formation of long-term memories and so allows an animal to compare the conditions of a current threat with similar past experiences
for example, if an animal had previously been attacked by another animal, the next time they encounter that animal they are likely to respond either with aggression or fear, whichever is more appropriate
impaired hippocampal function prevents the nervous system from putting things into a relevant and meaningful context
this may cause the amygdala to respond inappropriately to sensory stimuli, resulting in aggressive behaviour
Boccardi et al (2010) found that habitually violent offenders exhibited abnormalities of hippocampal functioning
research into seratonin
4
low levels of serotonin in the brain have been associated with an increased susceptibility to impulsive behaviour, aggression and even violent suicide
some drugs are thought to alter serotonin levels and thus increase aggressive behaviour
Mann et al (1990) gave 35 healthy participants dexfenfluramine, which is known to deplete serotonin
using a questionnaire to assess hostility and aggression levels, they found that dexfenfluramine treatment in males (but not females) was associated with an increase in hostility and aggression scores
seratonin
6
a neurotransmitter implicated in many different behaviours and physiological processes including aggression, eating behaviour, sleep and depression
in normal levels, serotonin exerts a calming, inhibitory effect on neuronal firing in the brain
it typically inhibits the firing of the amygdala which is the part of the brain that controls fear, anger and other emotional responses
low levels of serotonin remove this inhibitory effect, with the consequence being that individuals are less able to control impulsive and aggressive behaviour (the serotonin deficiency hypothesis)
as a result, when the amygdala stimulated by external events, it becomes more active and causes the person to act on their impulses, thus making aggression more likely
serotonin is also thought to reduce aggression by inhibiting responses to emotional stimuli that might otherwise lead to an aggressive response
hormonal influences
7
testosterone is a hormone produced mainly by the testes in males, but also occurs in females
it is associated with the development of secondary sexual characteristics in males such as body hair BUT it has also been implicated in aggression and dominance behaviours
produces male characteristics, one of which is thought to be aggressive behaviour
levels of testosterone reach a peak in young males and then decline
it is thought to influence aggression from young adulthood onwards due to its action on brain areas involved in controlling aggression
Sapolsky (1998) summarised research evidence in this area by describing how removing the source of testosterone in different species typically resulted in much lower levels of aggression
subsequently, reinstating normal testosterone levels with injections of the synthetic testosterone led to a return of aggressive behaviour
research into testosterone
5
many research studies in the last 30 years have shown that violent criminals were high in the hormone testosterone, suggesting that testosterone is related to human aggression
Archer (2009) found that men are generally more aggressive than women and Dabbs (1990) found that they have much higher concentrations of testosterone than women
in addition, when testosterone concentrations are at their highest (ages 21 to 35), there is an increase in male on male aggressive behaviour
Dabbs et al (1987) measured salivary testosterone in violent and non-violent criminals, finding that those with the highest testosterone levels had a history of primarily violent crimes, whereas those with the lowest levels had committed only non-violent crimes
changes in testosterone levels appear to influence aggressive behaviour by increasing amygdala reactivity during the processing of social threats such as angry facial expressions
x4 evaluation points for neural influences
evidence for the role of the amygdala in aggression
evidence for the role of the hippocampus in aggression
research support for the serotonin deficiency hypothesis
evidence from animal studies
EVALUATION
evidence for the role of the amygdala in aggression
6
Pardini et al (2014) found that reduced amygdala volume can predict the development of severe and persistent aggression
they carried out a longitudinal study of male participants from childhood to adulthood
56 of the participants with varying histories of violence were subjected to a brain MRI scan at age 26
the results showed that participants with lower amygdala volumes exhibited higher levels of aggression and violence
the relationship between amygdala volume and aggressive behaviour remained even after other confounding variables were controlled
this suggests that the amygdala plays an important role in evaluating the emotional importance of sensory information and that lower amygdala volume compromises this ability to evaluate sensory information, making a violent response more likely
EVALUATION
evidence for the role of the hippocampus in aggression
7
Raine et al (2004) provided support for the role of the hippocampus in aggressive behaviour in their study of violent offenders
they studied two groups of violent criminals — some who had faced conviction (unsuccessful psychopaths) and some who had evaded the law (successful psychopaths)
the group of successful psychopaths were considered to be “cold, calculating criminals” whereas the group of unsuccessful psychopaths had acted more impulsively, which is why they were caught
MRI scans revealed asymmetries in the hippocampus, which is part of the limbic system, in the unsuccessful psychopath group
the hippocampus in either hemisphere of the brain in these individuals differed in size, an imbalance presumed to have arisen early in brain development
the researchers suggested that this asymmetry might impair the ability of the hippocampus and the amygdala to work together, so that emotional information is not processed correctly, which leads to inappropriate verbal and physical responses as a result
this supports the idea that the hippocampus and the limbic system as a whole plays an important role in aggression
EVALUATION
research support for the serotonin deficiency hypothesis
6
Duke et al (2013) provided some support for the serotonin deficiency hypothesis as an explanation for aggressive behaviour in human beings
they carried out a meta analysis of 175 studies involving 6500 participants
this analysis found a small inverse relationship between serotonin levels and aggression, anger and hostility
they also found that the magnitude of the relationship varied with the methods used to assess serotonin functioning, with the year of publication (effect sizes tended to diminish with time) and with self-reported versus other reported aggression
only other reported aggression was positively correlated to serotonin functioning
this suggests that the relationship between serotonin and aggression is more complex than originally thought
EVALUATION
evidence from animal studies
4
Raleigh et al (1991) found that vervet monkeys fed on experimental diets high in tryptophan, which increases serotonin levels in the brain, exhibited decreased levels of aggression
but monkeys fed on diets that were low in tryptophan exhibited increased aggressive behaviour, suggesting that the difference in aggression between the two groups could be attributed to their serotonin levels
low serotonin levels led to increased aggression in the monkeys, suggesting that serotonin plays a role in aggression
this study supports the idea that serotonin plays a role in aggression, in particular, low levels of serotonin can lead to aggressive behaviour
x2 evaluation points for hormonal influences
inconsistent evidence
testosterone may simply promote status seeking behaviour, rather than directly increasing aggression
