Aggression
Aggression
Neural and hormonal mechanisms in aggression
Neural mechanisms
The limbic system
‣ Papez (1937) and Maclean (1952) identi ed the limbic system as the cingulate gyrus,
hypothalamus, fornix and amygdala
‣ Speed and sensitivity of limbic system responses to stimulus are important predictors
of aggressive behaviour in humans
‣ Gospic et al (2011) carried out brain scans on participants in a lab-based game that
provoked aggression and found participants with an aggressive reaction had a fast and
heightened response in the amygdala
‣ Benzodiazepine is a drug that reduces the arousal of the autonomic nervous system
‣ This was taken before the game in a separate condition and it halved the number
of aggressive reactions as well as decreasing amygdala activity
Cingulate gyrus: Helps regulate emotion and pain.
Hypothalamus: Links the nervous system to the endocrine system via the pituitary gland.
Fornix: Unclear function but when damaged, a ects memory recall.
Amygdala: Emotion, survival instincts and memory.
The role of serotonin
‣ Low levels result in reduced self-control and increased aggression
‣ Normal levels of serotonin seen in the orbitofrontal cortex are inhibitory and linked with
reducing ring neurones - associated with a greater behavioural self control
‣ Denson et al (2012) found decreased serotonin disturbs the neural mechanism
involved in emotional regulation, reduces self control and increases impulsive
behaviours
‣ Virkkunen et al (1994) compared levels of the serotonin metabolite (breakdown
product of 5-HIAA) in the cerebrospinal uid of violent impulsive and non-impulsive
o enders
‣ Found impulsive o enders had signi cantly lower levels of 5-HIAA indicating lower
levels of serotonin
Evaluation of Theory
Strengths Limitations
Supporting evidence for the role of the The limbic system explanation is
amygdala oversimpli ed
Supporting evidence for the role of The serotonin explanation is oversimpli ed
serotonin
Real life applications Neural explanations of aggression are
reductionist
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, Aggression
STRENGTH
P: There is research support for the role of the limbic system.
E: Raine et al (1997) scanned the brains of 41 murderers and 41 controls. They found,
using PET scans, that some had abnormalities in the way that their limbic systems
functioned.
E: This is a strength because it demonstrates that the limbic system could be implicated
in aggressive behaviour, because if there wasn’t a link then there’d be no di erence
between the PET scan results of the murderers and controls.
L: Due to real-life examples, there is high external validity.
STRENGTH
P: There is supporting evidence for the role of the amygdala.
E: Pardini (2014) found reduced amygdala volume can predict the development of
severe and persistent aggression using a longitudinal study of male participants from
childhood to adulthood.
E: Participants with amygdala volumes exhibited higher levels of aggression and the
relationship was maintained even after confounding variables were controlled for.
L: Longitudinal, reduced amygdala volume came before aggression and confounding
variables were controlled for so has high validity as an explanation.
STRENGTH
P: Supporting evidence for the link between low serotonin levels and aggression.
E: Raleigh et al (1991) found vervet monkeys on a diet high in tryptophan (which
increases serotonin levels in brain) had decreased levels of aggression and vice versa.
E: Shows low levels of serotonin are related to aggression, since calmer monkeys had
more of it, and the aggressive monkeys had less.
L: This therefore suggests that aggressive behaviour is biologically determined.
CP: Vervet monkeys and humans are biologically and physiological different, the
biological changes in a monkey’s body that lead to aggression may not lead to
aggression in humans. Therefore, ndings cannot easily be generalised or extrapolated.
WEAKNESS
P: The research that links the limbic system to aggressive behaviour is correlational.
E: For example, research suggests that abnormalities in the limbic system causes
aggressive behaviour however, it could be that an increase in aggressive behaviour
causes abnormalities in the limbic system.
E: This means a cause and e ect relationship cannot be established between
abnormalities in the limbic system and aggressive behaviour.
L: Due to bidirectional ambiguity, we cannot draw rm conclusions.
Hormonal mechanisms
‣ Testosterone is a hormone responsible for the development of masculine features
‣ It helps regulate social behaviour via in uence on the brain areas involved in aggression
‣ Male sex hormone
‣ Androgen produced by the Leydig cells in the male testes and the adrenal cortex
‣ Action on the brain areas linked to controlling aggression
‣ Two in uence life periods:
‣ At birth “critical time period: during which the sensitisation of neural circuits occurs
‣ Adulthood where testosterone modulates neurotransmitter pathways
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, Aggression
‣ Peak of testosterone is around puberty and this corresponds with peak in aggression
levels among boys - suggests that testosterone and aggression linked
‣ Testosterone acts on a serotonergic synapse, lowering the amount of neurotransmitter
serotonin
‣ Research has identi ed low levels of serotonin as being involved in heightened levels of
aggressiveness
‣ Dolan et Al (2001) found a positive correlation between testosterone levels and
aggressive behaviours in male o enders in a UK maximum security prison
‣ Most su ered from personality disorders and had histories of impulsively and violent
behaviour
PROBLEM WITH CORRELATION —> cannot determine cause and e ect so
bidirectional ambiguity can be prevalent, we cannot determine whether
personality disorders cause high levels of testosterone or vice versa, other factors
such as abuse in childhood, not a strictly controlled lab experiment
Animal studies
‣ Giammanco et Al (2005) found experimental increases in testosterone are related to
aggressive behaviour in several species
‣ The opposite is also true castration (loss of the testicles) studies have show reduction
in aggression
‣ As the testicles proceed testosterone this would suggest it is the lowering levels of
testosterone production causing the reduction in aggressive behaviour.
PROBLEM WITH ANIMAL STUDIES —> limited insights into aggression win
humans as the ndings may not be generalisable. Humans brains are much more
complex than animals, therefore the way hormones act on them may be di erent.
Human societies, cultures and relationships are all very di erent to animals and
may also in uence aggression in humans.
STRENGTH
P: There is research support for the link between low serotonin levels and aggression.
E: Connor & Levine (1969) found rats who had been castrated when they were young
had lower levels of testosterone and displayed lower levels of aggression.
E: Supports a link between testosterone and aggression, the higher the level of
testosterone, the more aggressive behaviour is demonstrated.
L: There is high external validity.
CP: Rats and humans are biologically and physiological different, the biological changes
in a rats body that lead to aggression may not lead to aggression in humans. Therefore,
the ndings cannot easily be generalised or extrapolated.
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