Two Key Studies of Neurotransmitters: Fisher et al. (2003) & Brunner et al. (1993) (SL IB Psychology)

Aim: To investigate a possible link between dopaminergic brain regions/systems and the early stages of romantic love

Participants: A self-selected sample of 10 female and 7 male students from New York State University, aged 18-26 years old (mean age = 20 years). All participants reported that they were ‘in love’ (time spent together from a range of 1-17 months with a mean of 7 months)

Procedure: Participants were placed in an fMRI scanner and shown a photograph of their romantic partner followed by a distraction task and then a ‘neutral’ photograph of an acquaintance with whom they had no emotional connection

Results: The fMRI showed that the areas of the brain most active when the photograph of the romantic partner was viewed were the right ventral tegmental areas in the midbrain and the right caudate nucleus also in the midbrain. These regions of the brain have been associated with dopamine production which in turn has been associated with motivation and reward i.e. someone has the desire to perform a behaviour because of the positive consequences of that behaviour

Conclusion: People who are in the early stages of romantic love may access brain regions associated with dopamine release when in the presence (physical or virtual) of their romantic partner. Therefore, it could be said that people become ‘addicted to love’

Evaluation of Fisher et al. (2005)

   Strengths

• • The findings support previous research into the role of dopamine in substance addiction so it is interesting to see how romantic love may fall under the same framework of craving and withdrawal
  • The use of fMRI clearly shows a link between dopaminergic areas of the brain only when the photograph of the romantic partner was shown which increases the internal validity of the study i.e. Fisher really was measuring the effect of romantic love on the brain 

   Limitations

• • It could be argued that a sample with a mean age of 20 years are more likely to be socially active and involved in pleasure-focused activities than an older sample which would mean that the ‘pleasure centre’ of their brains would be more receptive to dopamine
  • There could be other explanations for the activation of the dopamine-rich areas of the brain being active during the fMRI e.g. excitement at taking part in a study; curiosity as to the outcome of the study, so Fisher cannot claim cause-and-effect from her findings

Key terms:

• Dopamine  
• Ventral tegmental area  
• Caudate nucleus

Aim: To investigate the violent, anti-social behaviour of specific male members of a large family in the Netherlands. The behaviour exhibited by the males in the family was borderline mental retardation (their average IQ was around 85), and violent behaviour. 

Participants: 5 males from a family in the Netherlands, all of whom had the same genetic condition, transmitted via the X chromosome on the MAOA gene. The family lived in a remote rural region of the Netherlands. Two carrier females and one non-carrier female were used as a control and compared with 3 clinically affected males. (Carrier means that some of the females carried the faulty gene in their genotype but it was not expressed in the phenotype i.e. their behaviour).

All of the affected males acted aggressively when angry, fearful, or frustrated. Examples of their violent, anti-social behaviour included attempted rape of one of the female members of the family, arson, attacking a mental institute warden with a pitchfork, voyeurism (spying on the females in the family at night), exhibitionism (appearing naked in public). Only one of the males in the family with the faulty gene finished primary education.

Procedure: A case study (close study of a small group of individuals from one family) and quasi experiment. A quasi experiment is one in which the IV is naturally occurring i.e. it can’t be manipulated by the researcher – in this case the individuals involved either had the faulty gene or they didn’t have the faulty gene. Brunner conducted DNA analysis, obtained via urine samples. Observations of the males and interviews with the family provided qualitative data.

Results: None of the affected males had dysmorphic signs of the genetic mutation i.e. they didn’t ‘look abnormal’ or different physically to the unaffected males. Unaffected males in this family attended normal schools, and most had steady jobs. All the females (including several carriers) also functioned normally.

A base change in the DNA structure was identified in all 5 affected males. This in turn resulted in flawed monoamine metabolism, which is linked with a deficit of the enzyme monoamine oxidase A (MAOA) – an enzyme which (among other functions) regulates the supply of serotonin levels to the brain. The reason only males are affected is because it is specifically the single X chromosome which is responsible for the production of MAOA.

Conclusion: The dysfunctional MAOA gene may be linked to irregular serotonin metabolism which could in turn be responsible for the mental retardation and aggressive behaviour of the affected males. MAOA deficiency may account for an individual’s inability to regulate their aggression. This MAOA deficiency is now known as ‘Brunner syndrome’.

Evaluation of Brunner et al. (1993)

   Strengths

• • Serotonin deficiency has been linked to unbalanced mood in previous research so there may be some validity to 'Brunner Syndrome'
  • By using one extended family the researchers were able to directly test their theory by using family members as control samples rather than an unrelated general population, thus validating the idea that the males’ behaviour was genetic rather than as a result of their environment

   Limitations

• • Brunner’s research cannot conclusively support the idea that the affected males’ anti-social behaviour was as a result of serotonin deficiency which means that the findings may lack validity
  • The affected males may have encountered more adverse reactions from others e.g. hostility, aggression, confrontations due to their reduced IQ and lack of impulse-control which could have exacerbated their anti-social tendencies i.e. nurture may have influenced their behaviour as well as nature

Key terms:

• X Chromosome  
• MAOA gene  
• Serotonin