what is the limbic system?
structures such as the: amygdala, hypothalamus and hippocampus are implicated and reactive in aggression. plays a key role in how an organism responds to environmental threats and challenges.
hypothalamus role in aggression
regulation of autonomous nervous system, which regulates response in emotional circumstances
amygdala role in aggression
responsible for attaching emotional significance to sensory info.
who linked the limbic system to aggression
papez-mclean
Gospic (2011)
put participants in an fMRI scanner and provoked them. this caused the amygdala to light up (become active)
participants on benzodiazapine drug (which lowers activity of the nervous system) had reduced amydala activity and were less aggressive.
how do neural transmitters affect aggression?
serotonin has a calming influence on the brain. low levels mean people cannot control there impulses. also regulates prefrontal cortex thereffore low levels mean we cannot control our responses in a ‘normal’ way.
OFC and seretonin
serotonin has an inhibitory effect in the brain, reduces firing of neurons associated with greater self-control. decreased serotonin disrupts this mechanism reducing self control leading to impulsive behaviour
Virkunen (1994)
compared levels of seretonin break down fluid 5-IAA in criminals and ‘normal’ people. levels were significantly lower in the impulse offenders
hormonal explanation of aggression.
male hormone, testosterone, peaks in adolescent males before declining with age.
evidence for hormonal role of aggression
castration studies- animals whose testes are removed have reduced aggression. when these animals are injected with testosterone they become more aggressive again thus establishing a cause and effect relationship. (giammanco)
prison studies- positive correlation between testosterone and aggression. (Dolan et al.) often had personality disorders and histories of impulsive violence.
describe the supporting evidence of the limbic systems role in aggression according to kluver and bucy.
rhesus monkeys, removed the main areas of the limbic system including the amygdala, hippocampus and surrounding areas. displayed an absence of emotional, motor and vocal reactions. no fear. monkeys tried to fight more dominant members of the group, shows the importance of the limbic system in regulating aggresive response. can it be extrapolated?
contradictory evidence from ferrari
- male adult rats fight at same time every day for 10 days. on 11th day the rats didn’t fight but dopamine had increased by 65% and serotonin decreased by 35%. therefore the aggression changed the brain chemistry of the rats showing serotonins role in aggression, raises question of caue or effect.
how is biological explanation of aggression biologically determinist.
implies individuals with low seretonin, high testosterone, or an overactive amygdala are destined to behave aggressively. this creates tension with the criminal justice system, which suggests free will is what people are convicted for. however it does provide concrete scientific evidence for aggression.
genetic factors of aggression
-tendencies for aggressive behaviour lie in the persons genetic make-up
- genetically related individuals are more similar in their aggressive tendencies than non-related individuals
-agression is studied genetically based on its heritability through generations
twin studies
mz- 100% genes shared dz-50% genes shared
coccaro- mz show 50% concordance rate of aggression
dz- 19% concordance rate
Rhee and Waldman carried out meta-analysis of…
adoption studies
Genetic influence accounted for 41% of variance in aggression
In line with twin studies
gene responsible for aggression
MAOA regulates metabolism of serotonin in the brain.
found on x chromosome so move common in men.
supporting evidence for MAOA
Brunner et al. dutch family 28 men from dutch family who were all agressive. all carried maoa-l
limitation- case study
gene and environment interaction
capsi, longitudinal study age 3-26. studied 3 variables, variants of maoa, maltreatment and abuse 3-11, reports of aggressive behaviour
findings:
low maoa alone- no effect alone
low maoa and maltreatment- effect (85% liklihood of aggressive behaviours)
why is genetic explanation of aggression socially sensitive.
If people are predisposed to aggressive
behaviour then questions about their
treatment arise. Some people advocate
chemical castration as a way of addressing the
problem. There are however extreme ethical
consequences of labelling an individual as a
threat to society on the basis of their genetic
inheritance so must be aware of the
limitations of these studies.
Evolutionary explanations of aggression- ethological
Aggression is adaptive and promotes survival. Dominance and aggression gives status - the aggressive males climb the social hierarchy and more access to mates
Lorenz and ritualistic aggression
Most aggressive encounters are ritualistic and end with appeasement displays. This indicates acceptance of defeat and prevents further damage or death. This ensures survival of species is not threatened
What is an IRM
A built in switch in the brain that gets turned on when animal sees as cue
4 features of FAP
stereotyped behaviour
Universal
Unaffected by learning
Ballistic
