Biological explanations: Neural serotonin

Question 1

Serotonin background/ function

Answer 1

Neurotransmitters are chemicals that allow signal transmission and this communication among nerve bells
20% of serotonin in the body is located in the central nervous system and regulates mood, appetite, sleep and some cognitive functions like memory and learning

Question 2

Serotonin background: role of serotonin

Answer 2

• Serotonergic neurons are located in the raphe nucleus in the brain. The raphe nuclei interact with every region of the brain and thus plays a role in control of emotion + motivation.
• It helps counterbalance the tendency of dopamine and noradrenaline, which encourage fear, anger, aggression etc.

Question 3

Lenard (2008)

Answer 3

“Low serotonin levels in the brain can result in impulsive behaviour, aggression, overeating, depression, alcohol abuse and violent suicide”

Question 4

Brown (1982)

Answer 4

• Showed that major waste product of serotonin tends to be low in cerebrospinal fluid of those who display agg behv.
• Method: Amount of cerebrospinal fluid (non-experimental)
• Eval: causality issues; no direct cause

Question 5

Mann (1990)

Answer 5

• Manipulated levels of serotonin. Administered dexfenfluramine (known to deplete sero levels) to 35 healthy adults. Assessed agg by using a questionnaire. They found males (not females) agg + hostility increased after drug treatment.
• Method: Manipulated serotonin levels (experimental) +questionnaires
• Eval: Strength over brown, (causality) low serotonin = agg. However, social desirability bias (questionnaires) explain why no females said they were aggressive.

Question 6

Ferrari (2003)

Answer 6

• Allowed a rat to fight for 10 days, on the 11th day it was prevented from fighting. Measured levels of sero and dopa. Found anticipation of the fight increased dopa and decreased sero.
• Method: lab experiment
• Eval: Good causality, poss not generalisable as animals

Question 7

Causal role of dopamine: Lavine (1997)

Answer 7

Evidence to suggest increases in dopamine activity (e.g. via the use of amphetamines) are associated with increases in aggressive behaviour)

Question 8

Causal role of dopamine: Buitelaar (2003)

Answer 8

-Similarly the use of dopamine antagonists (drugs that prevent normal activity of dopamine) have been used as a way of reducing aggressive behaviour in violent delinquents.

Question 9

Causal role of dopamine: Ferrari et al (2003)

Answer 9

-Provides support for the influence of dopamine in aggressive behaviour. They allowed a rat to fight everyday for 10 days and on the 11th day they were prevented from fighting. They measured the levels of dopamine and serotonin and found in anticipation of the fight dopamine increased, serotonin decreased.

Question 10

Motivational role of dopamine: Couppis et al (2008)

Answer 10

They found that dopamine plays an important reinforcing role in aggression. Their research suggests that some individuals intentionally seek out aggressive encounters because of the rewarding sensation caused by the increase in dopamine which these encounters provide.

Question 11

Difficulty with demonstrating role of dopamine experimentally - Couppis et al (2008)

Answer 11

Preventing dopamine activity in an animal’s brains also makes it difficult for the animal to move because of dopamine’s role in coordination. So it’s difficult to explain a drop in aggressive behaviour as it would be due to a lack of motivation or the fact the mice find it difficult to move.

Question 12

A01: Neural mechanisms - brain structure

Answer 12

• The brain structure can be used as an alternative explanation to neurotransmitters.
• The brain consists of many anatomical ‘regions’ and structures, all have been shown that have distinct functions.
• When there are irregularities in brain structure, either through injury of inherited; these causes consequences for functioning.

Question 13

Neurotransmitters on their own…

Answer 13

Neurotransmitters on their own, out of the context of the wider physiology of the brain, ignore the influence that brain structure has on demonstrating aggressive behaviour. You can therefore use this material as AO2 – discussing ‘neural mechanisms’ in a wider context than just neurotransmitter activity.

Question 14

Brain structure + aggression

Answer 14

It would be too simplistic to assume that aggressive behaviour is simply the result of abnormal levels of brain neurotransmitters. The structures of the brain are finely tuned to work together and research in this area seems to show that the hypothalamus and amygdala are associated with aggressive responses.

Question 15

Evidence of the hypothalamus having an effect of the stimulation of aggressive behaviour (Flynn)

Answer 15

(Flynn 2006) found that stimulating the lateral hypothalamus in cats made them more likely to show ‘predatorial aggression’, but when the medial hypothalamus was stimulated ‘vicious attack behaviour’ was more likely.

Question 16

Evidence of the amygdala having an effect of the stimulation of aggressive behaviour (Potegal)

Answer 16

Potegal et al. found the corticomedial amygdala was identified as an area for meditating and regulating aggressive reaction. They found that hamsters have more active neurons around the medial nucleus in acts of aggression.

Question 17

Evidence of the amygdala having an effect of the lesioning of aggressive behaviour

Answer 17

Research has suggested when the careful lesioning of the amygdala of aggressive animals was shown to have a taming effect.

Question 18

Evidence of the frontal lobe having an effect of the stimulation of aggressive behaviour (Phineas Gage)

Answer 18

-A railway worker Phineas Gage was involved in a railway incident that cause a pole to be lodged in his frontal lobe and damage the skull. This lead to him having an very aggressive personality, which he did not have prior to the accident. Suggesting this area controls for aggressive behaviour.

Question 19

Problems with the evidence that injury to the brain causes aggressive behaviour

Answer 19

-Gage’s case is very convincing, but this is the case of only one individual and so generalisability is very limited. Furthermore, we are relying on the accuracy of the medial notes made by Harlow (Gage’s physician)

Question 20

Why is Delgado’s research on bulls significant in a discussion of the role of brain structure on aggressive behaviour?

Answer 20

The research may suggest that activity in one brain region (caudate nucleus) inhibits aggression as Delgado stimulated it via a radio operated electrode. However the caudate nucleus also affects voluntary movement, so it is questionable whether this really related to aggression.

Question 21

Blair et al (2001)

Answer 21

-Blair et al studied aggression in humans that had been institutionalised due to psychopathic tendencies. He proposed that psychopathy involves damage to the amygdala and this is further supported by various findings in non-human animals.

Question 22

Blair’s findings lend some reliability and validity to the results of research performed on animals (such as Potegal, Ferris & Delville, 1994, & Delgado). Why, according to Potegal et al (1994) should we trust the generalisation from animals to humans in neural research?

Answer 22

Potegal et al argues that generalisation between animals and humans should be more viable, the differences between them are quantitative (i.e the basics are the same but the details are different) The underlying circuitry neural systems relating emotional expression seems more similar, allowing for more avenues of generalisation.

Question 23

What qualitative ‘details’ differ between animals and humans that might undermine the relevance of animal neural research for understanding human aggression?

Answer 23

• Conscious thought (consequences for actions)
• Morals
• Social norms + values

Question 24

Problems with the biological explanation

Answer 24

-The biological explanation is too simplistic and ignores the influences of aggressive behaviours as a result of social influence and cultural influence.

Question 25

Social learning aggression (Anderson & Dill 2000)

Answer 25

-For instance sanderson et al argue that aggression might be learnt through observing various situations or forms of media available to people.

Question 26

Situational factors (alcohol) Bushman (1993, 1997)

Answer 26

Biological views also ignore situational factors for instance bushman et al show how alcohol disrupts information processing - so an accidental comment or behaviour is interpreted as meaningful therefore contributing to an aggressive response.

Question 27

Adrian Raine (1997) (video)

Answer 27

• Damage to the prefrontal cortex can lead to ASB.
• They scanned the brains of the people with anti-social personality disorder.
• The scans revealed that have a 11% reduction in neurons, compared to those who don’t, have aggression.
• Scanned the brains of 41 impulsive murders and found they have a distinct lack of activation in the prefrontal cortex. They are more likely to lash out and kill someone.

Question 28

Adrian Raine & Yang (2010)

Answer 28

-Meta analysis on 43 structural functioning, results showed significantly reduced prefrontal structure and functioning in antisocial individuals.

Question 29

What should we note about Raines findings?

Answer 29

Raine et al. are cautious about the implications of their findings. There is evidence to suggest that murderers pleading NGRI have significantly different levels of activity in the brain and that these differences may predispose such individuals towards violence. However the researchers note that these findings should not be taken to indicate that violence is determined by biology alone.

Question 30

The role of testosterone in aggression:

Answer 30

Testosterone is a steroid hormone (affects development and growth of sex organs). It is the principle male sex hormone.
-On average an adult human male produces about ten times more testosterone than an adult female.

Question 31

Issues with testosterone

Answer 31

• As with neurotransmitters, it is impossible to measure what precise role testosterone play in aggression.
• It is clear that testosterone is present in aggression, however there is no clear causal relationship.

Question 32

Basal model (testosterone)

Answer 32

• The basal model claims that testosterone determines the level of aggression.
• Testerone causes aggression.

Question 33

Reciprocal model (testosterone)

Answer 33

• Testosterone levels vary with levels of social dominance/ aggression.
• Testosterone is a consequence of dominance & aggression.

Question 34

The challenge hypothesis

Answer 34

-According to the challenge hypothesis in monogamous species, testosterone levels should only rise above the baseline level in response to social challenges.

Question 35

Nelson (1995)

Answer 35

-Reviewed how hormones influence aggressive behaviour. Generally a positive correlation between levels of androgens and aggressive behaviour.

Question 36

What are androgens?

Answer 36

-Androgens are male sex hormones, and testosterone is a androgen.

Question 37

Methodological issues with Nelson

Answer 37

-However such assertions weaken, since levels of androgens were not measured at the precise point when the aggressive act was being performed. Therefore we can not be 100% that this was the only variable affecting behaviour.

Question 38

Wagner, Beuving & Hutchinson. (1979)

Answer 38

• Animal research also supports testosterone
• They castrated a male mouse and showed how levels of aggression vary
• the levels of aggression in the mice were significantly less post-castration
• the levels of aggression then began to rise after receiving testosterone.

Question 39

Methodological eval of Wagner et al.

Answer 39

-Wagner et al. shows support for testosterone increasing aggression as the mice that received testosterone became more aggressive with quantity of testosterone.

Question 40

The basal model of testosterone

Answer 40

-The model suggests that testosterone causes a change in a person’s dominance. The more testosterone that a person has, the more competitive and dominant they become. It follows then that a man with high levels of testosterone with take part in ASB.

Question 41

Mazur & Booth (1998):

Answer 41

-After reviewing a number of studies in this field, they concluded that men with higher levels of T are more likely to divorce or remain single.

Question 42

The reciprocal model of aggression

Answer 42

-This model suggests that testosterone levels vary with the persons dominance. The level of testosterone is the effect of and not the cause of the dominance.

Question 43

Mazur & Booth #2 (1998)

Answer 43

• 2100 air force veterans were studied.
• Over a ten year period the veterans were given four medical examinations
• Their testosterone levels varied -they reduced when married and increased upon divorce.