Serotonin and Risky Behavior

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Serotonin and Risky Male Behavior in Monkeys (Higley et al., 1996)

• Aim: Is serotonin related to taking risks?
• Method: A field study where they followed male monkeys who were migrating to new social groups
• Measured the serotonin by extracting cerebrospinal flluid by placing needles in their spines
• The independent variable was dividing the monkeys into high, mid-high, mid-low and low serotonin groups
• The dependent variables were how aggressive the monkeys were observed to be, number of scars they had and death
• Results: 11/49 of the monkeys who died had low serotonin levels
• Conclusion: Monkeys with low levels of serotonin are more likely to take risks like fighting with other monkeys
• Evaluation: This field study has high ecological validity but lacks the control of lab experiments
  
  • Sex difference - What about female monkeys?
  • External validity - Do these results generalize to human males?

Serotonin and Risky Female Behavior in Monkeys (Westergaard et al., 1999)

• Aim: Is serotonin related to taking risks for females?
• Method: Observational study of captive monkeys
• The independent variable was the species of monkey: rhesus monkeys or pigtailed macaques
• Rhesus monkeys are known to be aggressive
• Pigtailed macaques are known to be friendly
• The dependent variable was the level of serotonin they measured in the cerebrospinal fluid like Higley et al., 1996
• Another dependent variable was how aggressive the monkeys behaved and how many wounds they had
• They placed each monkey in same sex groups to see how they behaved
• Results: Rhesus monkeys were more aggressive and had more wounds
• Rhesus monkeys had less serotoninthan pigtailed macaques
• Conclusion: Serotonin inhibits risky behavior in females as well
• Evaluation: This field study has high ecological validity but lacks the control of lab experiments
  
  • External validity - Do these results generalize to human females?

Serotonin and Gambling Monkeys (Long et al., 2009)

• Aim: Test if serotonin levels are related to gambling risks in a controlled environment
• Method: They manipulated the amount of serotonin the monkeys could produce by forcing a certain type of diet
• Tryptophan is the raw material required to produce serotonin and is found in certain foods
• The independent variable was the tryptophan level of the diet which was high or low in tryptophan
• High tryptophan meant more serotonin should be produced than the low tryptophan diet
• The dependent variable was the choice the monkey made in the gambling task
• In the gambling task the monkey could choose a safe option which would guarantee they would get a normal amount of juice
• There was a riskier option where they could get a low or high amount of juice
• Results: The low tryptophan group chose the risky option whereas the high tryptophan group chose the safe option
• Conclusion: Levels of tryptophan as determined by diet can affect serotonin levels and risky behavior
• Evaluation: Lab experiment had a high amount of control but a small sample size (only 3 monkeys) and low ecological validity
• Do these results generalize to humans?