neural and hormonal influences

• What is the limbic system?


  includesthe amygdala,hypothalamus, andhippocampusthat are implicated in reactive aggression.plays a key role in how an organismresponds toenvironmental threatsand challengeskey factor in whether we respond aggressively or not to an external stimulus.
• What is the Amygdala


  •thecentre for emotions, emotional behaviour and motivation.•Involved in giving us thatinstinctive feelings and reactions to the environment,which includes aggression.Studies have revealed that the removal of the amygdala results in a reduction of aggression,whereasdamage to the amygdala leads to increased testosterone levels and heightened aggressive behavior.
• What didPapez and Maclean propose?

  •the heightened responsiveness of the amygdala to perceived environmental threats is associated with increased aggression in both humans and other mammals. The greater the reactivity of the amygdala, the more aggressive the behavior.
• What isGospic et als ultimatum game study?


  Lab study- The Ultimatum game.1) The proposer offers to split money in a certain way with the responder.2) If the responder accepts, the money is split as proposed but if the responder rejects the offer, both players receive nothing.3)Participants in this study played as responders while having their brain scanned byfMRI- which highlights activity in different areas of the brain4)The researchers found thatwhen responders rejected unfair offers - an aggressive reaction to social provocation, scans revealed aheightened response by the amygdala.
• What did they find the affect of the benzodiazepine drug?


  Researchers also found that a benzodiazepine drug which reduces arousal of the autonomic nervous system (ANS), when taken before the game had two effects on responses to unfair offers:

  1)It halved the number of rejections (i.e. reduced aggression).

  2)Decreased the activity of the amygdala. This is strong evidence of an association between reactive aggression and amygdala activity
• summarise gospic et al

  •Gospic et al. carried outbrain scans(fMRI) on participants in alab-based game that provoked aggression.•Scan showed aggressive reactions produced afast and heightened response from the amygdala.•Also,benzodiazepine(reduces arousal of the ANS) taken before the game halved the number of aggressive reactions and also decreased amygdala activity.
• What are key research into serotonin and aggression?

  1.Denson et al.(2012)found that when serotonin was present at normal concentrations in the orbitofrontal cortex (OFC)it was associated with a reduced firing of neurons which is linked to a greater degree of behavioural self-control.

  2.Virkkunen (1994)compared levels of serotonin breakdown in the cerebrospinal fluid of violent impulsive and violent non-impulsive offenders. They found levels were significantly lower in the impulsive offenders. They also found they suffered more sleep irregularities (which serotonin regulates).
• What are hormones?


  Hormonesare chemical messengers in the body which can change behaviour and cause physical changes in the body.
• What is testosterone?


  Testosterone is a hormone primarily produced by males but also found in females and is associated with the promotion of male characteristics and increased aggression
• What is the effect of testosterone?

  Decreased amounts of the enzyme aromatase, responsible for processing testosterone, may result in decreased emotional response and heightened aggression.
• What is key research for testosterone and aggression?

  1.Giammanco et al.’s (2015)animal studies have shown experimental increases in testosterone have produced aggressive behaviour in several species and vice versa when testosterone levels are experimentally decreased.

  2.Dolan et al. (2001)found a positive correlation between testosterone levels and aggressive behaviour in a sample of 60 male offenders in UK maximum security hospitals. These men mostly suffered from personality disorders (e.g. psychopathy) and had histories of impulsively violent behaviour)
• Outline the differences between the role of testosterone and serotonin in aggression (4)

  Testosterone is a mainly found in males and influences aggression. Reduced levels of aromatase (which processes testosterone) leads to higher levels of testosterone thus a higher level of aggression.

  Whereas serotonin is a neurotransmitter involved in stabilizing the mood, it inhibits activity in the amygdala, therefore having a calming effect on mood. Reduced levels of serotonin have been found to increase aggression.
• What did Berman et al show- strength?


  Role of Serotonin in Regulating Aggression•The serotonin explanation is strengthened by research into drugs likeparoxetine,which raise serotonin levels and decrease aggression.participants were given either a placebo or paroxetine.•Participants then took part in a lab study in which they could give shocks of varying intensity as a response to provocation.•Participants in theparoxetine groupgave fewer and less shocks than those in the placebo group.•However, this was only true if they had a prior history of aggression.•Providing evidence of a connection between serotonin and aggression.
• what is support for animal research?

  •Giammanco et al. (2005) carried out a review of studies and found for example, male rhesus macaque monkeys exhibit increased testosterone levels and aggressive behavior during mating season. Castration of male rats reduces testosterone levels and mouse-killing behavior, and testosterone injections in female rats increase mouse-killing.•These findings demonstrate the impact of testosterone on aggression across various animal species.
• what is a limitation of the limbic system

  •The amygdala, a limbic structure, works in conjunction with the orbitofrontal cortex (OFC) to regulate aggressive behavior, with the OFC playing a role in controlling impulsive behavior and reducing aggression, even though the OFC is not part of the limbic system.•Coccaro et al.(2007) found thatreduced activity in the OFC contributes to aggressive behavior in psychiatric disorders.•Emphasising that the brain’s regulation of aggression is more intricate than theories that only concentrate on the amygdala.
• what is the dual hormone hypothesis?

  •Carré and Mehta (2011) proposed a dual-hormone hypothesis, which suggested that high testosterone levels can increase aggression only when cortisol levels are low.

  •Cortisol can inhibit the effect of testosterone on aggression when cortisol levels are high, making the interaction of both hormones a better predictor of aggressive behavior than each hormone individually.
• what is the issues with cause and effect


  Most research into both neural and hormonal influences on aggression iscorrelational. Although there are goodethical reasonsfor this - when two variables are correlated, it is impossible to establish which one is the cause of the other, or if a third variable is involved.LIMITATION–If cause and effect can be established in this case, it is impossible to fully understand the link between testosterone and aggression. Furthermore, correlational research is susceptible to the third variable problem which could be why the OFC is not considered in some research.
• Describe neural mechanisms in aggression. 6marks

  •Limbic system, particularly the hypothalamus and amygdala, is responsible for aggressive behaviour

  •fMRI scans show heightened amygdala activity during aggressive response

  •Stimulation of the amygdala can increase/decrease aggression response

  •Frontal cortex moderates the expression of aggression - reduced serotonin activity in the prefrontal cortex is related to reduced self-control/disinhibition

  •Lower levels of 5-HIAA (by-product of serotonin breakdown) are found in impulsive/poorly controlled offenders

  •Testosterone may mediate the activity of the amygdala and/or the orbitofrontal cortex.