Serotonin and Sexuality

Serotonin and Sexual Orientation (Liu et al., 2011)

• Aim: Is serotonin related to sexual preference in rats?
• Method: Male mice were genetically manipulated to have a gene that produced normal amounts of serotonin or low amounts of serotonin
• The independent variable was whether the mice got manipulated to have a low or normal serotoning producing gene
• They placed the manipulated mice in cages with other male mice and/or female mice
• The dependent variable was which sexes the male mice chose to mount
• Results: Normal serotonin males mounted females 60-80% of the time and mounted males 20% of the time
• Low serotonin males lost their sexual preference for females and mounted both males and females equally 80% of the time
• Conclusion: Serotonin affects sexual preference in rats such that low serotonin mice become more bisexual than normal serotonin rats
• Evaluation: Cannot generalize these findings to humans and it would be unethical to genetically manipulate humans to test for the chemical roots of sexual preference
• What about female rats? Only male rats were used in this study

Here are some videos of the rats in Liu's study

Normal serotonin male chooses a female over a male - hetero rat

Low serotonin male mounts a male - homo rat?

Low serotonin male mounts both male and female - bisexual rat?

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?

Hippocampus and Spatial Navigation

Hippocampus and Spatial Navigation (Maguire et al., 2000)

• Aim: Does the hippocampus play a role in spatial navigation?
• Method: The independent variable was the group of people and how much they had been navigating - they compared London taxi drivers to a control group
• The dependent variable was the hippocampus size
• Results: They found that taxi drivers have a larger posterior hippocampus than the control group
• The size of the posterior hippocampus positively correlated with how long the taxi drivers had been working as taxi drivers
• Conclusion: This suggests that the posterior hippocampus has the localized function of spatial navigation
• The longer you spend taxi driving the more it affects the posterior size of the hippocampus
• This suggests that practicing navigation (a form of cognition) affects hippocampus size (physiology)
• You can also use this study for the syllabus point of an interaction of cognition and physiology

Broca's Area

• Aim: Broca noticed some patients had problems with speech production and he wanted to find out if their impediment was related to the brain
• Method: Dissected the brains of the patients to look for lesions
• Results: He found that there was an overlapping damaged area in the left frontal lobe of the patients
• Evaluation: MRI results of Broca's patients showed more damage than just Broca's area (Dronkers et al., 2007)
  
  • Dronkers results suggests that the speech production difficulty of Broca's patients may be due to more extensive brain damage than just Broca's area
  • Plaza et al., (2009) found that patients other brain areas took over the function of Broca's area if their Broca's area was damaged
• Conclusion: Broca's area is localized for some aspects of speech production but Broca's aphasia can be a combination of various lesions to brain areas beyond Broca's area
• Here is a video of Broca's patients demonstrating a lack of speech fluency

Biological Research Methods

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• Lab Experiments
  
  • Vontrolled studies that attempt to find cause and effect relationships between independent and dependent variables
• Neuroimaging allow you to find brain regions (biological correlates) of behavior
• PET
• fMRI
• Correlational studies allow you to test the role of genetics vs. environment on behavior
• Twin studies - twins reared apart to test the effect of genetic vs. environment on their behavior
• Any differences found between twins reared apart are considered environmental
• Family studies
• Lesion studies allow you to find biological correlates of behavior, we assume the missing behavior and damaged brain area are related
• Phineas Gage's personality changed because of damage to his frontal lobe area
• HM
• Clive Wearing

Biological Principles

• Behavior is biologically determined by physiological processes such as the nervous system neurotransmitters (e.g. serotonin) and the endocrine system (hormones e.g. adrenalin increases heart rate and fight or flight response)
• "All that is psychological is first physiological" (Sperry)
• Patterns of behavior can be inherited through genetics
• Some patterns of behavior may be a result of natural selection
• The study of animals can inform our understanding of human behavior
• Psychologists use rats and monkeys for a lot of research but the results cannot always be generalized to humans

Updates This Summer

I will be adding bullet pointed summaries of studies for each syllabus question. This should make it more straightforward and informative. The links to original papers will still be provided where possible for anyone who wants more information.