Serotonin

Q: Valzelli and Bernasconi (1979)

**Valzelli and Bernasconi (1979)** investigated the role of serotonin in aggression.

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Serotonin

Human aggression can be explained in terms of biological structures, for example, the role of brain mechanisms and hormones. The limbic system and neurochemicals, such as testosterone and serotonin, are also thought to be important.

Serotonin

Serotonin is a neurotransmitter involved in communication of impulses between neurons.
It has a widespread inhibitory effects on the brain.
It slows down and dampens neuronal activity, so is likely to be indicated in aggression.

Normal serotonin levels

Normal levels of serotonin in the orbitofrontal cortex are linked with reduced firing of neurons.
This is associated with a greater degree of behavioural self-control.

Decreased serotonin levels

Decreased serotonin may well disrupt the brain mechanism, reducing self-control and leading to an increase in impulsive behaviour, including aggression (Denson et al. 2012).

Virkkunen et al. (1994)

Virkkunen et al. (1994) compared levels of a serotonin breakdown product (a metabolite called 5-HIAA) in the cerebrospinal fluid of violent impulsive and violent non-impulsive offenders.
They found that levels were significantly lower in the impulsive offenders.
They also suffered more sleep irregularities (serotonin also helps to regulate sleep pattern).

Virkkunen et al. (1994) conclusions

This study by Virkkunen implies that there is some disruption of serotonin functions related to reactive aggressive behaviour.

Serotonin: Berman et al. (2009)

Serotonin is a neurotransmitter involved in communication of impulses between neurons and has a widespread inhibitory effects on the brain. It slows down and dampens neuronal activity, so is likely to be indicated in aggression.

Serotonin increasing drugs

Drugs that increase serotonin activity also reduce levels of aggressive behaviour.
Berman et al. (2009) gave patients either a placebo or paroxetine - a drug which enhances serotonin activity.
Participants then took part in a laboratory-based game in which electric shocks of varying intensity were given and received in response to provocation.

Berman et al. (2009) findings

The paroxetine participants consistently gave fewer and less intense shocks than those in the placebo group.
But this was only true of the participants who had a prior history of aggressive behaviour.
The study provides useful evidence of a link between serotonin function and aggression that goes far beyond the usual correlational findings.

Valzelli and Bernasconi (1979)

Valzelli and Bernasconi (1979) investigated the role of serotonin in aggression.

Procedure

Laboratory experiment.
7 different strains of mice were placed in prolonged isolation and their levels of serotonin and aggression measured.

Results & conclusions

Results
- Mice with low serotonin turnover in the brain showed more aggressive responses to isolation than those with high serotonin turnover.
Conclusion
- This research suggests a link between serotonin turnover in the brain and aggression.

Evaluation

Strengths
- Controlled and reliable.
Limitations
- Cause or effect?
- Ethics.
- Cannot generalise from animals to humans.

Studies linking serotonin & aggression

Strengths
- Support from animal studies.
Limitations
- Ignores environmental triggers (nurture).
- Cause or effect?
- Deterministic.
- Individual differences.
- More likely to be one of many factors (multifactor approach).