Neural genetic hormonal mechanisms in aggression
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Neural/Genetic/hormonal 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.

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Neural mechanisms
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
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-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.

Neural mechanisms…Serotonin supporting evidence…

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

Neural mechanisms dopamine
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)

AmphetaminesUse 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.

Neural mechanisms…Dopamine supporting evidence…

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

Things to know activity 1
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)

Evaluation of neural mechanisms
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.

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.

Exam help
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..

  • 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 aggression
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 body’s reaction to stress.

Hormonal mechanisms testosterone
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.

Hormonal mechanisms testosterone1
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.

Genetic factors aggression
Genetic Factors & Aggression.

Summarise what Sapolsky means.

What implications are there for politicians who wish to reduce aggression in our society?

Genetic factors aggression1
Genetic Factors & Aggression.

  • Be reallycertain 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
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.

Where did genetic factors begin
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)

How would you investigate genes
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.

Turner 2007
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 heritability mice
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)

Maoa monoamine oxidase a
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 dominant-submissive relationships..resulting in more injuries when confined with other mice (Mattson, 2003).

Kennel club
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 dog’s keeper on its behaviour is likely to be ineffective.

Why would scientists not be impressed with this statement?

Caspi et al 2002
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
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?

What about adoption studies
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
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.


Miles carey 1997
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
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. .