Neural/Genetic/hormonal mechanisms in aggression

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Neural/Genetic/hormonal mechanisms in aggression

• Exam tips too

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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.
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Neural mechanismsSerotonin
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.
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Neural mechanismsSerotonin supporting evidence

• Metabolite levels- Waste product of serotonin
  tends to be low in the cerebrospinal fluid in
  people who are aggressive (Brown et al,1982)
• 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.

• 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 non-aggressive dogs, the Serotonin
  levels of aggressive dogs 278 units vs. 387 for
  non aggressive dogs.

Marks for AO1 are awarded for accuracy, detail,
support depth breadth)
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Neural mechanismsDopamine
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.
BE AWARE
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!!!!!!
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Neural mechanismsDopamine 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.

Marks for AO1 are awarded for accuracy, detail,
support depth breadth)
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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.

So get used to paraphrasing material Create a
200 word précis (9/8 marks) 100 word précis
(4/5 marks)
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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
compensate 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.
BUT...No difference in adulthood even with levels
still low!!
Alcohol, Serotonin aggression Badawy (2006)
alcohol caused major disturbances in metabolism
of brain serotonin. In susceptible individuals
can lead to aggression.
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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
  relevant..
• Dont just describe it, but explain how it fits
  in with what you are suggesting...sometimes it is
  as simple as pointing out differences.

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Hormonal mechanisms in aggression

• Testosterone is a androgen hormone- because it
  produces male characteristics
• 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 bodys reaction to
  stress.

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Hormonal mechanisms- testosterone.
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.
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Hormonal mechanisms- testosterone.
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.
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Genetic Factors Aggression.
Summarise what Sapolsky means.
What implications are there for politicians who
wish to reduce aggression in our society?
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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.

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Huh???

• 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?????
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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
  messenger......Hormones.

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Where did genetic factors begin?

• 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)

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How would you investigate Genes?

• 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.

• A way of studying aggression is heritability
  studies. This has been investigated by scientists
  using non human participants.

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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

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Other animals used for heritability..Mice......

• Scientists have cloned genetic DNA and
  investigated the role of neurotransmitters by
  mimicking the effects using reverse genetics.

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)
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MAOAmonoamine 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
  dominant-submissive relationships..resulting in
  more injuries when confined with other mice
  (Mattson, 2003).

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Kennel club
Why concentrate on genetics targeted dog
breeds, not dog owners?

• Genetics and BehaviourGenetics (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 dogs keeper on
  its behaviour is likely to be ineffective.

Why would scientists not be impressed with this
statement?
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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.... Mesomorphic Ec
tomorphic Endomorphic Cesare Lombroso
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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 research?
• 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?

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What about adoption studies??

• Adoption studies have corroborated the genetic
  weak common family effect on anti social
  behaviour.
• Mednick et al (1984) 14000 adoptees

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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 20. 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.
however.....
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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.
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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. .