Aggression
Neural and hormonal mechanisms in
aggression
Hot-blooded/reactive aggression: impulsive, angry, physiological arousal
Cold-blooded/proactive aggression: premeditated
Economic implications of aggression: prisoners, lawyers + courts, police, NHs,
property damage, therapy, lost worker productivity.
Neural mechanisms in aggression
Papez and Maclean: limbic system linked to emotional behaviour including aggression.
Limbic system = hypothalamus, amygdala and parts of hippocampus (+ others).
Reactivity of amygdala in humans and other mammals is an important predictor of
aggressive behaviour (more responsive = more aggressive).
- Role in assessing and responding to environmental threats
Gospic et al.:
o Participants played the ‘ultimatum game’ – ‘Proposer’ given money, has to offer
some to ‘Responder’ – if B accepts they both keep, if B accepts they both lose
o B subjected to mild provocation (offered unfair amounts)
o When they rejected the offer (aggression) fMRI scans showed fast and
heightened response by amygdala.
o Benzodiazepine drug (reduces arousal of autonomic nervous system) taken
before provocation = decreased activity of amygdala, halved number of
rejections
o Association amygdala-reactive aggression
Serotonin has widespread inhibitory effects in the brain.
- Normal levels of serotonin in the orbitofrontal cortex (OFC) are linked with
reduced firing of neurons --> greater behavioural self-control
- Serotonin deficiency = reduced self-control, increase in impulsive behaviour inc.
aggression (Denson et al.)
Virkkunen et al.: compared levels of serotonin breakdown product (metabolite 5-HIAA)
in the cerebrospinal fluid of violent impulsive and violent non-impulsive offenders.
- Levels lower in the impulsive offenders
Evaluation
Other brain structures
, o Research shows that non-limbic brain structures are also involved in
aggression
o Limbic structures e.g. amygdala function with the OFC (not part of limbic
system)
o OFC involved in impulse regulation + inhibition of aggressive behaviour
o Coccaro et al. – OFC activity reduced in psychiatric disorders that feature
aggression
o Reduced activity disrupts impulse-control function --> aggression
o More complex
Drugs and serotonin
o Drugs (e.g. paroxetine) that increase serotonin have been found to also
reduce levels of aggressive behaviour
o Berman et al.: gave ppts placebo/paroxetine, then lab-based game
involving giving and receiving electric shocks in response to provocation
(e.g. insults)
o Paroxetine group: fewer and less intense shocks
o Causal evidence
Supporting research for relationship the amygdala and aggression
o Kluver and Bucy: destruction of amygdala in monkey dominant in social
group – lost dominance
o Mark and Ervin: women with painless stimulation to amygdala became
enraged, smashed guitar against wall
Direct or indirect?
o Neural factors directly linked – Gospic et al. + serotonin reduces
aggression by inhibiting neuronal activity
o Indirect: Denson et al. – link between serotonin and aggression indirect as
other factors e.g. social, psychological may influence it
Correlational research
o Ethics – provoking aggression not protecting from harm
o Brain scans
o Changes to OFC/amygdala not necessarily cause of aggression or vv
o Could be intervening variable
Hormonal mechanisms in aggression
Testosterone is an androgen responsible for the development of masculine features.
Linked to aggressive behaviour because:
- Males more aggressive than females
- Males become more aggressive to other males when testosterone levels are
highest in development (after 20 years of age) (Daly and Wilson)
Role in regulating social behaviour.
Castration studies: removing testes reduces aggression in males of many species,
giving injections of testosterone to same animals restores aggressive behaviour (e.g.
Giammanco et al.)
, Prison studies: Dolan et al. – positive correlation between testosterone levels and
aggressive behaviours in sample of 60 male offenders in UK maximum security
hospitals
- Men mostly had personality disorders (e.g. psychopathy) + histories of
impulsively violent behaviour
Progesterone (female ovarian hormone) has role in female aggression.
- Levels vary during the ovulation cycle, lowest during and just after menstruation
Ziomkiewicz et al.: negative correlation between progesterone levels and self-
reported aggression
- Low levels = aggression
Evaluation
Animal research
o Giammanco et al. – review of studies, confirms role of testosterone
o Male rhesus macaque monkeys – increase in testosterone levels and
aggressive behaviour during mating season
o Rats – castration of males reduces testosterone and mouse-killing
behaviour, injecting female rats w testosterone increases mouse-killing
COUNTERPOINT
o Animal research validity
o Low construct validity – aggression for dominance in social group
o Mazur – must distinguish aggression from dominance
o Aggression – individuals want to injure, dominance – to keep status
o Animals artificially enhanced with testosterone – dominance not injury
o Testosterone can make females nicer to obtain status
Empirical evidence
o Mehta and Josephs – changes in testosterone levels before and after
losing a competitive game + then could challenge again or do an
unrelated activity
o Rising testosterone – 73% re-challenged vs 22% falling
o Loss of status --> increased testosterone and aggression
o Correlational link, validity
Dual hormone hypothesis
o Carre and Mehta: high levels of testosterone cause aggression but only
when cortisol is low
o When cortisol high, testosterone’s influence on aggression is blocked
o Cortisol plays role in body’s response to chronic stress
o Combined activity really the predictor of aggression over either alone
o Reductionist
Animal research
o Hormones in humans and animals likely to be very similar
o But aggressive behaviour in humans more complex
o E.g. cortisol findings applied to only human aggression
o Cognitive factors in humans esp. in ‘cold-blooded’ proactive aggression
Neural and hormonal mechanisms in
aggression
Hot-blooded/reactive aggression: impulsive, angry, physiological arousal
Cold-blooded/proactive aggression: premeditated
Economic implications of aggression: prisoners, lawyers + courts, police, NHs,
property damage, therapy, lost worker productivity.
Neural mechanisms in aggression
Papez and Maclean: limbic system linked to emotional behaviour including aggression.
Limbic system = hypothalamus, amygdala and parts of hippocampus (+ others).
Reactivity of amygdala in humans and other mammals is an important predictor of
aggressive behaviour (more responsive = more aggressive).
- Role in assessing and responding to environmental threats
Gospic et al.:
o Participants played the ‘ultimatum game’ – ‘Proposer’ given money, has to offer
some to ‘Responder’ – if B accepts they both keep, if B accepts they both lose
o B subjected to mild provocation (offered unfair amounts)
o When they rejected the offer (aggression) fMRI scans showed fast and
heightened response by amygdala.
o Benzodiazepine drug (reduces arousal of autonomic nervous system) taken
before provocation = decreased activity of amygdala, halved number of
rejections
o Association amygdala-reactive aggression
Serotonin has widespread inhibitory effects in the brain.
- Normal levels of serotonin in the orbitofrontal cortex (OFC) are linked with
reduced firing of neurons --> greater behavioural self-control
- Serotonin deficiency = reduced self-control, increase in impulsive behaviour inc.
aggression (Denson et al.)
Virkkunen et al.: compared levels of serotonin breakdown product (metabolite 5-HIAA)
in the cerebrospinal fluid of violent impulsive and violent non-impulsive offenders.
- Levels lower in the impulsive offenders
Evaluation
Other brain structures
, o Research shows that non-limbic brain structures are also involved in
aggression
o Limbic structures e.g. amygdala function with the OFC (not part of limbic
system)
o OFC involved in impulse regulation + inhibition of aggressive behaviour
o Coccaro et al. – OFC activity reduced in psychiatric disorders that feature
aggression
o Reduced activity disrupts impulse-control function --> aggression
o More complex
Drugs and serotonin
o Drugs (e.g. paroxetine) that increase serotonin have been found to also
reduce levels of aggressive behaviour
o Berman et al.: gave ppts placebo/paroxetine, then lab-based game
involving giving and receiving electric shocks in response to provocation
(e.g. insults)
o Paroxetine group: fewer and less intense shocks
o Causal evidence
Supporting research for relationship the amygdala and aggression
o Kluver and Bucy: destruction of amygdala in monkey dominant in social
group – lost dominance
o Mark and Ervin: women with painless stimulation to amygdala became
enraged, smashed guitar against wall
Direct or indirect?
o Neural factors directly linked – Gospic et al. + serotonin reduces
aggression by inhibiting neuronal activity
o Indirect: Denson et al. – link between serotonin and aggression indirect as
other factors e.g. social, psychological may influence it
Correlational research
o Ethics – provoking aggression not protecting from harm
o Brain scans
o Changes to OFC/amygdala not necessarily cause of aggression or vv
o Could be intervening variable
Hormonal mechanisms in aggression
Testosterone is an androgen responsible for the development of masculine features.
Linked to aggressive behaviour because:
- Males more aggressive than females
- Males become more aggressive to other males when testosterone levels are
highest in development (after 20 years of age) (Daly and Wilson)
Role in regulating social behaviour.
Castration studies: removing testes reduces aggression in males of many species,
giving injections of testosterone to same animals restores aggressive behaviour (e.g.
Giammanco et al.)
, Prison studies: Dolan et al. – positive correlation between testosterone levels and
aggressive behaviours in sample of 60 male offenders in UK maximum security
hospitals
- Men mostly had personality disorders (e.g. psychopathy) + histories of
impulsively violent behaviour
Progesterone (female ovarian hormone) has role in female aggression.
- Levels vary during the ovulation cycle, lowest during and just after menstruation
Ziomkiewicz et al.: negative correlation between progesterone levels and self-
reported aggression
- Low levels = aggression
Evaluation
Animal research
o Giammanco et al. – review of studies, confirms role of testosterone
o Male rhesus macaque monkeys – increase in testosterone levels and
aggressive behaviour during mating season
o Rats – castration of males reduces testosterone and mouse-killing
behaviour, injecting female rats w testosterone increases mouse-killing
COUNTERPOINT
o Animal research validity
o Low construct validity – aggression for dominance in social group
o Mazur – must distinguish aggression from dominance
o Aggression – individuals want to injure, dominance – to keep status
o Animals artificially enhanced with testosterone – dominance not injury
o Testosterone can make females nicer to obtain status
Empirical evidence
o Mehta and Josephs – changes in testosterone levels before and after
losing a competitive game + then could challenge again or do an
unrelated activity
o Rising testosterone – 73% re-challenged vs 22% falling
o Loss of status --> increased testosterone and aggression
o Correlational link, validity
Dual hormone hypothesis
o Carre and Mehta: high levels of testosterone cause aggression but only
when cortisol is low
o When cortisol high, testosterone’s influence on aggression is blocked
o Cortisol plays role in body’s response to chronic stress
o Combined activity really the predictor of aggression over either alone
o Reductionist
Animal research
o Hormones in humans and animals likely to be very similar
o But aggressive behaviour in humans more complex
o E.g. cortisol findings applied to only human aggression
o Cognitive factors in humans esp. in ‘cold-blooded’ proactive aggression
