AGGRESSION
BIOLOGICAL EXPLANATIONS OF AGGRESSION
Proactive aggression: Behaviour in which the primary aim is to inflict
physical or psychological pain or harm on others- ‘cold blooded’, planned
method of getting what you want
Reactive aggression: ‘hot blooded’ reaction to emotional arousal- angry
+ impulsive behaviour
Biological explanations assume that aggression is located withing
biological make-up rather than environment
Neural mechanisms in aggression
Aggression is due to our genes, hormones + neural influences
The limbic system is an area of the brain that coordinates
behaviours that satisfy motivational + emotional urges
The amygdala
Responsible for quickly evaluating emotional importance of sensory
info + prompting an appropriate response
If certain areas are stimulated electrically, animal responds with
aggression
If same areas are removed, animal no longer responds to stimuli
with rage
Kluver + Bucy (1937): destruction of amygdala in a monkey who
was dominant in group cased it to lose dominance
The hippocampus
Involved w formation of long-term memories, allows animals to
compare conditions of current threat w similar past experiences
E.g. if animal had been attacked by another animal, next time they
encounter them they’re more likely to respond w aggression or fear
Impaired hippocampal function prevents NS from putting things into
relevant context, may cause amygdala to respond inappropriately,
resulting in aggressive behaviour
Boccardi et al. (2010): found habitually violent offenders
exhibited abnormalities of hippocampal functioning
Gospic et al. (2011)
, Carried out fMRI scans on ppts in lab-based game that provoked
aggression
The Ultimatum Game
Two players- the proposer offers to split money in certain way w the
responder
If responder accepts, money is split as proposed
If responder rejects, both receive nothing
When responders rejected unfair offers (aggressive reaction to
social provocation), scans showed aggressive reactions associated
w fast + heightened response by amygdala
Benzodiazepine (reduced arousal of autonomic NS) taken before
game halved number of aggressive reactions + decreased
amygdala activity
Orbitofrontal cortex + serotonin
Serotonin= neurotransmitter that exerts calming effect on neuronal
firing in brain
Low/decreased levels remove inhibitory effect- individuals less able
to control impulsive + aggressive behaviours: serotonin deficiency
hypothesis
As a result, when amygdala is stimulated, it becomes more active,
causing person to act on impulses, aggression is more likely
Some drugs thought to alter serotonin levels + increase aggressive
behaviour
Mann et al. (1990): gave 35 healthy ppts dexfenfluramine- using
a questionnaire to assess aggression levels, found treatment in
males associated with increase in aggression scores
Virkkunen et al. (1994): compared levels of serotonin breakdown
product in cerebrospinal fluid of violent impulsive + violent non-
impulsive offenders- levels significantly lower in impulsive offenders
Hormonal influences on aggression
Testosterone thought to bring out aggressive behaviour
Sapolsky (1998): summarised research evidence in area by
describing how removing source of testosterone in species resulted
in lower levels of aggression
Retaining normal testosterone levels w injections of synthetic
testosterone led to return of aggression
Testosterone
Idea that testosterone is related to human aggression comes from
various sources
Men generally more aggressive than women (Archer, 2009), and
have higher concentration of testosterone than women
Dabbs et al. (1987): measured salivary testosterone in violent +
non-violent criminals- those w highest testosterone levels had
history of violent crimes
Carre + Olmstead (2015): claim testosterone concentrations not
static, but fluctuate rapidly in context of environment
, Changes in testosterone levels appear to influence aggressive
behaviour by increasing amygdala activity during processing of
social threat
Progesterone
Some evidence that female hormone may play a role in women’s
aggression
Levels vary during ovulation cycle + lowest just after menstruation
Ziomkiewicz et al. (2012): found negative correlation between
progesterone level + self-reported aggression
Suggests low levels of progesterone are linked to aggression in
women
Duel-hormone hypothesis
Cortisol is a hormone that plays role in stress response
Carre + Mehta (2011): duel-hormone hypothesis
o High levels of testosterone -> aggressive behaviour only when
cortisol levels are low
o When cortisol levels are high testosterone’s influence is
blocked
Pompa et al. (2007): adolescent males confirmed this hypothesis
in relation to physical aggression- combined activity of testosterone
+ cortisol may be better predictor of human aggression than single
hormone
Evaluation
LIMITATION
Other brain structures
More recent research showing non-limbic brain structures also
involved in aggression
Limbic structures function together with OFC- not part of limbic
system
OFC involved in impulse regulation + inhibition of aggression
behaviours
Coccaro et al. (2007): OFC activity is reduced in disorders that
cause aggressive behaviour
Shows that the neural explanation is more complex
STRENGTH
Research into effects of drugs
Paroxetine that increases serotonin been found to reduce
aggressive behaviour
Berman (2009): gave either Paroxetine or a placebo to ppts who
went to play a lab-based game that involved giving + receiving
shocks in response to provocation
Paroxetine group gave fewer + less intense shocks than placebo
group
, Suggests causal link between serotonin + aggression
STRENGTH
Support from research with animals
Giammanco et al (2005): review of studies confirms role of
testosterone
In male rhesus monkeys there’s an increase in testosterone levels +
aggression during mating season
In rats castration of males reduces testosterone + also mouse killing
behaviour
Injecting female rats with testosterone increases mouse killing
Findings show the role of testosterone plays in aggression in a range
of species
LIMITATION
Mixed evidence of link between testosterone + aggression in humans
Carre + Mehta (2011): dual-hormone hypothesis claims high
levels of testosterone lead to aggression only when cortisol is low
When cortisol is high testosterone influence on aggression is
blocked
Cortisol plays role in stress response
May be argued that combined activity of testosterone + cortisol
may be better predictor of aggression than either hormone alone
GENETIC FACTORS IN AGGRESSION
Possible that high levels of testosterone or fluctuating levels of
serotonin could be genetically determined
Certain individuals/families could display higher levels of aggression
due to their predisposition to biochemical differences
Genes can determine levels of testosterone + speed which it’s
metabolised
Can also determine physiology of brain in terms of receptors + how
sensitive they are
Different brain physiology determined by genetics may mean
pathway between limbic system + prefrontal cortex is weak
Aggression + genes
No single gene identified as responsible for aggression
Research evidence supporting that all behaviour influence by
genetic factors
Genes don’t directly cause aggression but influence elements that
contribute to aggressive behaviour:
o Structural characteristics
o Functional characteristics
Genetic influence investigated through twin + adoption studies
Sometimes psychologists prefer to manipulate situation by using
studies on animals bred for purpose of research
BIOLOGICAL EXPLANATIONS OF AGGRESSION
Proactive aggression: Behaviour in which the primary aim is to inflict
physical or psychological pain or harm on others- ‘cold blooded’, planned
method of getting what you want
Reactive aggression: ‘hot blooded’ reaction to emotional arousal- angry
+ impulsive behaviour
Biological explanations assume that aggression is located withing
biological make-up rather than environment
Neural mechanisms in aggression
Aggression is due to our genes, hormones + neural influences
The limbic system is an area of the brain that coordinates
behaviours that satisfy motivational + emotional urges
The amygdala
Responsible for quickly evaluating emotional importance of sensory
info + prompting an appropriate response
If certain areas are stimulated electrically, animal responds with
aggression
If same areas are removed, animal no longer responds to stimuli
with rage
Kluver + Bucy (1937): destruction of amygdala in a monkey who
was dominant in group cased it to lose dominance
The hippocampus
Involved w formation of long-term memories, allows animals to
compare conditions of current threat w similar past experiences
E.g. if animal had been attacked by another animal, next time they
encounter them they’re more likely to respond w aggression or fear
Impaired hippocampal function prevents NS from putting things into
relevant context, may cause amygdala to respond inappropriately,
resulting in aggressive behaviour
Boccardi et al. (2010): found habitually violent offenders
exhibited abnormalities of hippocampal functioning
Gospic et al. (2011)
, Carried out fMRI scans on ppts in lab-based game that provoked
aggression
The Ultimatum Game
Two players- the proposer offers to split money in certain way w the
responder
If responder accepts, money is split as proposed
If responder rejects, both receive nothing
When responders rejected unfair offers (aggressive reaction to
social provocation), scans showed aggressive reactions associated
w fast + heightened response by amygdala
Benzodiazepine (reduced arousal of autonomic NS) taken before
game halved number of aggressive reactions + decreased
amygdala activity
Orbitofrontal cortex + serotonin
Serotonin= neurotransmitter that exerts calming effect on neuronal
firing in brain
Low/decreased levels remove inhibitory effect- individuals less able
to control impulsive + aggressive behaviours: serotonin deficiency
hypothesis
As a result, when amygdala is stimulated, it becomes more active,
causing person to act on impulses, aggression is more likely
Some drugs thought to alter serotonin levels + increase aggressive
behaviour
Mann et al. (1990): gave 35 healthy ppts dexfenfluramine- using
a questionnaire to assess aggression levels, found treatment in
males associated with increase in aggression scores
Virkkunen et al. (1994): compared levels of serotonin breakdown
product in cerebrospinal fluid of violent impulsive + violent non-
impulsive offenders- levels significantly lower in impulsive offenders
Hormonal influences on aggression
Testosterone thought to bring out aggressive behaviour
Sapolsky (1998): summarised research evidence in area by
describing how removing source of testosterone in species resulted
in lower levels of aggression
Retaining normal testosterone levels w injections of synthetic
testosterone led to return of aggression
Testosterone
Idea that testosterone is related to human aggression comes from
various sources
Men generally more aggressive than women (Archer, 2009), and
have higher concentration of testosterone than women
Dabbs et al. (1987): measured salivary testosterone in violent +
non-violent criminals- those w highest testosterone levels had
history of violent crimes
Carre + Olmstead (2015): claim testosterone concentrations not
static, but fluctuate rapidly in context of environment
, Changes in testosterone levels appear to influence aggressive
behaviour by increasing amygdala activity during processing of
social threat
Progesterone
Some evidence that female hormone may play a role in women’s
aggression
Levels vary during ovulation cycle + lowest just after menstruation
Ziomkiewicz et al. (2012): found negative correlation between
progesterone level + self-reported aggression
Suggests low levels of progesterone are linked to aggression in
women
Duel-hormone hypothesis
Cortisol is a hormone that plays role in stress response
Carre + Mehta (2011): duel-hormone hypothesis
o High levels of testosterone -> aggressive behaviour only when
cortisol levels are low
o When cortisol levels are high testosterone’s influence is
blocked
Pompa et al. (2007): adolescent males confirmed this hypothesis
in relation to physical aggression- combined activity of testosterone
+ cortisol may be better predictor of human aggression than single
hormone
Evaluation
LIMITATION
Other brain structures
More recent research showing non-limbic brain structures also
involved in aggression
Limbic structures function together with OFC- not part of limbic
system
OFC involved in impulse regulation + inhibition of aggression
behaviours
Coccaro et al. (2007): OFC activity is reduced in disorders that
cause aggressive behaviour
Shows that the neural explanation is more complex
STRENGTH
Research into effects of drugs
Paroxetine that increases serotonin been found to reduce
aggressive behaviour
Berman (2009): gave either Paroxetine or a placebo to ppts who
went to play a lab-based game that involved giving + receiving
shocks in response to provocation
Paroxetine group gave fewer + less intense shocks than placebo
group
, Suggests causal link between serotonin + aggression
STRENGTH
Support from research with animals
Giammanco et al (2005): review of studies confirms role of
testosterone
In male rhesus monkeys there’s an increase in testosterone levels +
aggression during mating season
In rats castration of males reduces testosterone + also mouse killing
behaviour
Injecting female rats with testosterone increases mouse killing
Findings show the role of testosterone plays in aggression in a range
of species
LIMITATION
Mixed evidence of link between testosterone + aggression in humans
Carre + Mehta (2011): dual-hormone hypothesis claims high
levels of testosterone lead to aggression only when cortisol is low
When cortisol is high testosterone influence on aggression is
blocked
Cortisol plays role in stress response
May be argued that combined activity of testosterone + cortisol
may be better predictor of aggression than either hormone alone
GENETIC FACTORS IN AGGRESSION
Possible that high levels of testosterone or fluctuating levels of
serotonin could be genetically determined
Certain individuals/families could display higher levels of aggression
due to their predisposition to biochemical differences
Genes can determine levels of testosterone + speed which it’s
metabolised
Can also determine physiology of brain in terms of receptors + how
sensitive they are
Different brain physiology determined by genetics may mean
pathway between limbic system + prefrontal cortex is weak
Aggression + genes
No single gene identified as responsible for aggression
Research evidence supporting that all behaviour influence by
genetic factors
Genes don’t directly cause aggression but influence elements that
contribute to aggressive behaviour:
o Structural characteristics
o Functional characteristics
Genetic influence investigated through twin + adoption studies
Sometimes psychologists prefer to manipulate situation by using
studies on animals bred for purpose of research
