neural and hormonal mechanisms in aggression

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  • Neural and hormonal mechanisms in aggression
    • Neurotransmitters
      • NTs are chemicals enabling impulses within brain to be transmitted from one area to another
        • Low levels of serotonin and high levels of dopamine have been associated with aggression in animals and humans.
      • Serotonin
        • Thought to reduce aggression by inhibiting responses to emotional stimuli
          • Low levels associated with increased susceptibility to impulsive behaviour
            • Mann et al – 35 healthy subjects given a dexfenfluramine which depletes serotonin
              • Using questionnaire to assess hostility levels and aggression scores they found in males that treatment increased hostility and aggression scores
        • Serotonin
          • Evidence from non-human studies – Raleigh et al found that Vervet monkeys who were fed on diets high in tryptophan which increases serotonin exhibited decreased levels of aggression but monkeys fed on diets low in tryptophan showed increased aggression.
            • Popova et al – animals bred for domestication and docile temps have increased concentration of serotonin
              • Evidence from anti-depressants – Bond – clinical study of antidepressant drugs that inhibited aggressive behaviour
                • Elevated serotonin levels tend to reduce irritability and impulsive aggression
      • Dopamine
        • Lavin – increases in dopamine activity by use of amphetamines have also been associated with increased aggressive behaviour
          • Buitella – anti psychotics which reduce dopamine activity in brain shown to reduce aggressive behaviour in violent delinquents
        • Couppis and Kennedy – found that in mice a reward pathway in the brain becomes engaged in response to an aggressive event and that dopamine evolved as a positive reinforcer suggesting that people seek out aggressive encounters to feel rewarding sensation after.
          • Dopamine might be consequence not cause
      • Reductionism and biological mechanisms
        • Links between serotonin and testosterone (T) are established in animal studies but isn’t as clear a link in humans
          • Complexity of human social behaviour makes biological explanations for human aggression is insignificant on its own to explain all the many different types/aspects of aggressive or violent behaviour
    • Hormonal Mechanisms - Testosterone
      • Testosterone thought to influence aggression from young adulthood onwards due to its effect on hormonal areas controlling aggression
      • Research studies
        • Highest testosterone levels in violent criminals
          • Low levels committed non violent crime
            • Non prison populations have found similar results
              • Lindman et al found that young males who behaved aggressively when drunk had higher levels of testosterone
      • The challenge hypothesis
        • Wingfield et al - in monogamous species testosterone levels should only rise above baseline breeding level in response to social challenges (male to male aggression or a threat to status).
          • Human species are monogamous, male testosterone levels would sharply rise in response to such a challenge
            • The surge is to be expected and the consequence is increased aggression if the threat is deemed relevant
      • Gender bias
        • The association between testosterone and aggression is height per for females than males. Archer et al
          • Women with night testosterone had higher occupational status as a result of being more assertive. Baucom et al.
            • Studies indicate women respond to challenging situations with increased testosterone, displaying assertiveness and dominance
              • Eisenegger et al - testosterone can make women nicer rather than more aggressive in certain situations
                • Testosterone promotes status-seeking behaviour of which one is aggression, rather than it directly increasing aggression.
      • Inconsistent evidence
        • Albert et al. - some studies show positive correlation between testosterone and aggression other studies show no such relationship, particularly ones the distinguish between aggressive and non aggressive individuals
          • Studies showing positive correlation use self report techniques or judgement based on severity of crime using a small population of men in prisons
    • hormonal mechanisms - cortisol
      • Appears to have mediating effect on aggression related hormones
        • Possibly because it increases anxiety and likelihood of social withdrawal - Dabbs
          • High levels of cortisol inhibits testosterone levels and so inhibit aggression
            • Virkkunen - low levels of cortisol in habitual violent offenders and in violent schoolchildren - Tennes and Kreye
              • This suggests that although relatively higher testosterone is the primary biochemical influence on aggression, low cortisol also plays an important role by increasing the likelihood of aggressive behavior
      • Cortisol
        • Supported by McBurnett et all, 4yr study of boys with behavioural problems
          • Boys that had consistently low levels of cortisol began antisocial acts at a younger age + 3x the no. of aggressive symptoms
            • Cortisol levels strongly related to aggressive conduct disorder
  • The challenge hypothesis
    • Wingfield et al - in monogamous species testosterone levels should only rise above baseline breeding level in response to social challenges (male to male aggression or a threat to status).
      • Human species are monogamous, male testosterone levels would sharply rise in response to such a challenge
        • The surge is to be expected and the consequence is increased aggression if the threat is deemed relevant

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