Neural/Genetic/hormonal mechanisms in

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Transcript Neural/Genetic/hormonal mechanisms in

mechanisms in aggression
Exam tips too…
Neural mechanisms
• The two neurotransmitters that are
believed to be most associated with
aggression are
• Low levels of Serotonin.
• High levels of Dopamine.
These chemicals allow
impulses to be
transmitted to another
area. Therefore all
behaviours are influenced
by neurotransmitters.
Neural mechanisms…Serotonin
Q: How does serotonin influence aggression?
A: In normal levels it exerts a calming, inhibitory effect.
Low levels (esp: in the prefrontal cortex) remove the above effect,
leaving the individual less able to control their impulsive/aggressive behaviour.
Serotonin usually inhibits the firing of the amygdala
(controls emotional responses).
If there is less Serotonin, there is less inhibition
Thus when stimulated by external events it becomes more active,
causing the person to become more angry.
Neural mechanisms…Serotonin
supporting evidence…
• Metabolite levels-
product of serotonin tends to be low
in the cerebrospinal fluid in people
who are aggressive (Brown et
• Dexfenfluramine- levels of
serotonin manipulated to see if
there are any changes in aggression.
Mann et al (1990) administered the
above drug to 35 healty males &
gave questionnaire to PPs-Hostility &
anger rose in males but not females.
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• Anti-social studies- Scerbo &
Raine (1993) carried out meta
analysis of serotonin levels of anti
social children & adults (esp. suicide
attempts!) suggesting less serotonin
leads to impulsive behaviour making
aggression more likely.
• Non-human studies- Rosado et
al (2010) took blood samples
form 80 dogs referred to vet
hospital for aggressive
behaviour toward human. Blood
was compared with nonaggressive dogs, the Serotonin
levels of aggressive dogs = 278
units vs. 387 for non aggressive
Neural mechanisms…Dopamine
How does dopamine influence aggression?
The brain appears to see aggression as a reward (Couppis et al, 2008)
Whenever we perform an activity we find rewarding, (sex, eating etc)
the brain releases higher levels of dopamine,
it attaches itself to our receptors & creates a pleasure circuit
…we therefore find this rewarding.
We therefore repeat this cycle
and this can lead to aggression becoming more frequent.
Unlike serotonin where the link is casual, the link with dopamine is less clear,
the link suggests raised levels
of dopamine are a consequence rather than a cause!!!!!!
Neural mechanisms…Dopamine
supporting evidence…
• Schizophrenia & anti
psychotics- Increased rates of
violence in schizophrenia sufferers
where there is delusions and history
of violence. Dopamine is a
dysfunction is implicated in
schizophrenia so anti psychotics
that reduce dopamine have been
suggested as a intervention (Glazer
& Dickinson, 1998)
• Amphetamines
Use of
amphetamines has been associated
with increase in dopamine
activity,however much is anecdotal!!!
Cherek et al (1986) administered
caffeine or amphetamines to PPs &
found amphetamines raised hostility
whereas caffeine reduced it.
• Non-human studies- Van Erp &
Miczek (2000) measured
dopamine in prefrontal cortex of
male rats before during & after
confrontation with other rat.
They found increase in dopamine
levels over baseline levels after
the confrontation suggesting
increased dopamine levels are
the result not cause of
aggressive behaviour.
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Things to know & activity #1
• A question entirely on neural
mechanisms could be answered using the
material on the previous slides.
• However the question is more likely to
be on both neural & hormonal….
Evaluation of Neural mechanisms.
Could the cause of aggression
be post-synaptic receptors??
If there is low levels
of serotonin there will be low of
receptors to
EVIDENCE: Mann et al 1996)
suicide completers
had increased serotonin
more violent deaths!!
Other factors as not all low
serotonin suffers are violent
EVIDENCE Booij et al (2010)
longitudinal study. They measured aggression
from parental
& self reports & PET scans .
Higher levels of aggression in children
with low levels of Serotonin.
Alcohol, Serotonin & aggression
Badawy (2006) alcohol caused major
disturbances in metabolism of brain serotonin.
In susceptible individuals can lead to aggression.
even with
levels still
Exam help..
• If you are going to introduce alternative
explanations you must make good use of it
• If you are gong to use non human studies, use
t for validity reasons, ethics would not be
• Don’t just describe it, but explain how it fits
in with what you are suggesting...sometimes it
is as simple as pointing out differences.
Hormonal mechanisms in
• Testosterone is a androgen
hormone- because it produces male
• Levels of testosterone tend to peak
in young adult males and then
typically decline in age.
• Cortisol- produced by the adrenal
glands & plays an important part of
the body’s reaction to stress.
Hormonal mechanismstestosterone.
Q: How does Testosterone influence aggression.
Not a simple cause and effect: The action of testosterone brain areas involve
Controlling aggression makes it more likely a specific
behaviour will be displayed.
Archer (1991) meta analysis on 5 studies and found positive correlation between
Testosterone and aggression.
Olweus et al (1988) comparison of delinquent boys
& non delinquent male students. Higher levels of testosterone in
delinquent sample, although not statistically significant!!
Book et al (2001) Meta analysis of 45 studies found average
correlation of +0.14 between testosterone & aggression.
Hormonal mechanismstestosterone.
Q: How does Testosterone influence aggression.
The challenge hypothesis (Wingfield et al 1990)
In monogamous species
testosterone should only rise above baseline level in response to social challenges,
such as male-male aggression or threat to status.
Genetic Factors & Aggression.
Summarise what Sapolsky
What implications are there for
politicians who wish to reduce
aggression in our society?
Genetic Factors & Aggression.
• Be really certain before you ever
pronounce something to be the norm,
because at that instant, you have made
it supremely difficult to ever again look
at an exception to that supposed norm
and to see it objectively.”
• Genetic factors work alongside
environmental influences.
• Genes act like the puppet master...they
control the level of testosterone or
oestrogen and how quickly it circulates
around the body
• Genes are responsible for the sensitivity
of synthesis receptors
So what does this really mean?????
Genes= Puppet master because...
• Testosterone may be responsible &
affect brain function & contribute to
aggression but is Genes that control our
behaviour via the medium of our
Where did genetic factors
• Early studies attempted to identify
chromosomal abnormalities, e.g. XYY
genotype, as being correlated with
aggression (Court Brown, 1967)
• This has not proven to be the case
(Milunsky, 2004)
How would you investigate Genes?
• A way of studying
aggression is
heritability studies.
This has been
investigated by
scientists using non
human participants.
• They selectively breed
animals to see if
aggression levels are
inherited from parent
to off spring
• Turner (2007) reported
that aggression in pigs is
moderately heritable
trait & that aggressive
characteristics in pigs
can therefore be seen
as passed on from
parent to off spring.
Turner 2007
• Commercial farmers might want to
selectively breed non aggressive pigs
and hypothesise that if selection
pressure is placed on aggressiveness,
the average aggressiveness of the herd
would fall by 5%
Other animals used for
• Scientists have cloned genetic DNA and
investigated the role of neurotransmitters
by mimicking the effects using reverse
Mutant mice that lack the gene for serotonin are
produced ...they exhibit normal behaviour, but seem
x2 as aggressive normal mice if in their territory.
Male mice reared alone also attack...suggesting
aggression is a natural biological tendency, since the
aggression could not have been learned. Those
reared with their parents illustrated aggression
when and if it was necessary.
(Bock & Goode, 1996)
MAOA=monoamine oxidase A
• Discovered by chance by scientists in mice that had
anger issues?!!!
• The role of the enzyme is to mop up excess, so mice
lacking the gene would have unusually high levels of
serotonin, noradrenaline & dopamine.
• MOAO-A deficient male mice quickly attacked
intruders and failed to establish the usual dominantsubmissive relationships..resulting in more injuries
when confined with other mice (Mattson, 2003).
Why concentrate on genetics &
targeted dog breeds, not dog owners?
Kennel club
• Genetics and Behaviour
Genetics (breed) plays only a part in the temperament of an
individual dog and scientific studies from around the world show
that environment probably has a far greater effect. A large
percentage of dog biting incidents are due to the irresponsible
actions of owners, who have either not taken the time and
trouble to train their dog correctly, or have indeed trained them
to behave aggressively. Consequently any legislation based on
genetics that ignores the influence of the dog’s keeper on its
behaviour is likely to be ineffective.
Why would scientists not be
impressed with this statement?
Caspi et al (2002)
• See worksheet for details........
In conjunction with all the information we
have gone through, now would be a good time
to consider your synoptic content....
Cesare Lombroso
Stretch & challenge...
Read the article on Heredity-Versus-Environment and try to
answer the following questions.....
• What methodological problems occur with twin and
adoption studies?
• What problems would you face as a researcher if you
concluded aggression was almost entirely genetic?
• What might policy makers and Joe public make of the
• What if you concluded it was entirely environmental, what
would the media, Joe public and policy makers make of
your research?
• Would it be possible to identify individuals at risk prior to
committing violent acts? Would this information be
beneficial for society?
What about adoption studies??
• Adoption studies have corroborated the
genetic & weak common family effect on
anti social behaviour.
• Mednick et al (1984) 14000 adoptees
Mednick et al (1984)
What: 14,000 adoptees & found boys with no criminal parents (either
adopt/biological) had baseline criminal conviction of 14%.
RESULTS: If adoptive parents but not biological parents were criminals,
boys still had conviction rate of 15%.
If biological & not adoptive parents were criminals rate increased to
If both sets were criminals rates increased to 25%
CONCLUSIONS: The results seem to suggest biological characteristics
increase the likelihood of anti social behaviour ad aggression is in part
genetically transmitted from parent to offspring. And the effect is
greater than environmental effect.
Miles & Carey (1997)
What: Conducted a meta-analysis on data from 24 genetically
informative studies using personality as a measure of aggression.
RESULTS: Strong overall genetic effect that may account for upto 50%
of the variance in aggression.
CONCLUSIONS: Affect was not attributed to methodological
inadequacies in twin or adoption designs and that the influence of genes
increased but that of family environment decreased in later ages.
Observational ratings
of lab behaviour found
no evidence for
heritability but strong
family effect.
Evaluation of Genetic basis
Animal research: fewer ethical concerns, quicker breeding cycles
allow for inter-generational effects to be seen
Methodological issues with twin/adoption studies.
Multi gene studies. .