Hormones, Pheromones, Genes on behaviour

Endocrine system

System of hormones - released directly into bloodstream

• target specific organ to carry out func

Hormone examples

Oxytocin 

• produced by hypothalamus 

  • Secreted - pituitary gland 

• Control social interaction + sexual repro

• Act as neurotransmitter in brain, attach to receptor sites of neurons 

  • Lead to inhibitory/excitatory response

• Affects trust levels

Melatonin

• Secreted by pineal gland

• Control sleep/circadian rhythm 

Testosterone 

• secreted by testes

Adrenaline 

• Secreted by adrenal gland 

• control fight/flight response in humans

Cortisol

• secreted by adrenal glands

• control blood sugar level

• high level of cortisol → trigger fight/flight → higher glucose

• Increase bp → interfere w learning + memory

Baumgartner et al

Aim:

• Investigate role of oxytocin when trust is broken

Method:

• nearly 50P placed in fMRI

• 2 conditions

  • Oxytocin

  • Placebo

Progress:

Trust game - built upon dilemma of either trusting/not trusting 

• Trusting profitable but there is risk of trusting 

• Part 1:

  • Investor (P1) must decide whether they will keep a sum of money OR share with trustee (P2)

  • If sum shared → investment is tripled 

• Part 2:

  • Trustee now has to decide if they will repay trust

    • If trust, each get $15 

    • If trust is violated, trustee keeps all the money

P told to act as investors in several diff rounds of trust game q diff trustees

Condition 1: played against humans

Condition 2: played against computer

Both P’s in oxy + placebo → received feedback from R their decision to trust 

• result in poor investment → trust was broken

• Then asked to make next investment decision

Results:

• Placebo

  • more likely - decreate rate of trust after being briefed that trust was broken

• Oxytocin

  • No change in trusting behaviour, even when informed that ‘trustees’ did not honour trust

• fMRI scan

  • oxytocin → less amygdala activity → less fear rxn → lower activation of caudate nucleus → trust persists 

  • Amygdala → Involved in emotional processing + fear

  • Caudate nucleus → learning + memory + reward-related response + learning to trust

Conclusion

• Oxytocin → play role in lowering fear rxn (amygdala) → arise when betrayal occurs + reliance on +ve feedback → influence future decisions (Caudate nucleus)

• Increased levels of oxy → correlate increased levels of trust

Eval of Baumgartner et al

Strength

• High int validity (lab expt)

  • Int validity - ext which IV affect DV

• Lab expt

  • conducted in controlled envt

  • more EV controlled

  • High int valid

• Results reliable - results caused by presence of heightened oxytocin levels, not other reasons potentially affecting the results from the envt

Limitation

• Oxytocin artifically administrated through nasal spray → not accurately reflect how hormone func in body

• Real world situation

  • Oxy - influenced by multiple complex biological factors

  • Artificial administration → affect brain activity that differ from natural hormonal release

  • Observed changes in trust + amygdala activity may not be the same wn lab + ext envt

• Reduce eco validity + generalisation of findings 

  • Results don’t fully rep oxytocin influence IRL context

Newcomer et al

Aim:

• investigate high level of cortisol interfere w verbal declarative memory

Method:

• P - employees/students from uni

• p given clinical interview w physician

• Matched-pair design for gender + age

• Double-blind control

• 3 conditions

  • High cortisol (160mg)

    • 4 day expt

    • Dose → similar levels to those seen to indiv on major stress event

  • low cortisol (40mg)

    • similar to amt circulating blood stream - indiv gg minor surgical procedure (having stitches removed)

  • placebo

    • placebo - tablet look like other tablets → no active ingredient

Process:

• tested verbal declarative memory (VDM)

  • Affected during long-term stress + memory impairment from previous research

• First tested before taking corisol

  • No significant diff btwn grp

  • Establish baseline diff (not confounding var)

• After cortisol 4 day period

  • Tested again

Results:

• High cortisol → impaired performance in memory task

  • Worst performance in VDM

  • Effect isn’t permenant - performance of p went back to normal after pills were no longer adminstreated

• No statistical significant diff btwn low cortisol + placebo

  • increased over time - practiced effects + procedure learning

Conc:

• clear link btwn level of cortisol + rmb

• High level of cortisol

  • Reduce declarative memory capabilities + ability to form LTM

• Cortisol receptor sites in hippocampus → responsible for transferring info from STM to LTM

  • Low cortisol assist recall of passage

Eval of Newcomer et al

Strength

• Double blind study - lower proabibility of reseracher bias + demand char

  • Both r + p - unaware of which condition they are in

  • r could not unintentionally influence p behaviour / interpretation of results

  • p - less likely to change performance based on expectations of what they think the ideal result study is trying to achieve

• increase int validity - ensure diff in memory performance

  • more likely due to cortisol level rather than r infleunce/p expectations

Limitation:

• low eco valid

  • conducted in controlled lab expt - asked to do memory recall task

  • Memory - influenced by variety of factors, not just cortisol in RW

• Limit generalisation of findings + effect of cortisol on memory in RWS

  • Differ from results in artificial setting 

  • Reduce reliability + validity 

Pheromones (Definition + process)

Chemical messenger - comm info from one member of species to anothe

• signal to other animals readiness to mate 

Process:

• Bodies - naturally secrete fluids through glands in our body

  • Control natural pheromones

• Vomeronasal organ → detect pheromone → send signal to olfactory nerve → stimulate hypothalamus in cortex of brain → stimulate emotion

• Pheromones trigger illicit rxn in hypo

  • Ex. Attraction, desire, etc. 

Note:

• insufficient evidence → suggest pheromones exist

• Role of pheromone - lack of functional vomeronasal organ as accessory to olfactory bulb

• Without anatomical ability to detect pheromone → no evidence to suggest that pheromones exist + affect human behaviour

Wedekind et al

Aim:

• investigate if major histocompatibility complex wld affect one mate choice

Method:

• nearly 50M + F from uni

• M + F → diff course → decrease likelihood of knowing eo

  • Impt to ensure previous personal exp doesn’t influence p

Process:

• Men prep:

  • wore same shirt for 2 nights, air it out in the morning

  • Gave them scent free soaps

  • Were asked not to drink, smoke, eat spicy food, wear deodorant, no sex (ensure pheromones are not tampered w)

• Women on contraceptives noted

• 2 days later

  • Women asked to rank smell of 7 shirts, each in cardboard box w “smelling hole”

  • Shirts:

    • 3 shirts were of MHC similar to woman

    • 3 shirts MHC diff to woman

    • 1 control unworn

Results:

• More pleasant body odour → diff from own MHC

• odor of MHC-dissimilar men - more frequently reminded women of own present/former partner than odour of MHC-similar men

• Diff in odour assessment reversed when oral contraceptives were taken

Conclusion:

• Sexual selection in humans → partly based on selecting partners w dissimilar MHC

• Choosing varied MHC → increase genetic variation in offspring

• MHC → plays role in choice of mate

Eval of Wedekind et al

Strength:

• High int valid → Men not allowed to wear/do anything that might affect natural scent

• Control ext factors, ensure odour on shirt (Ex. Were not allowed to take spicy food, etc.)

  • Come only from pheromones released through male sweat

  • Not artificial/envt smell

• Increase int valid of study → result more accurately reflect effect of pheromones on female mate preference

Limitation:

• Low pop valid → Didn’t test male perception on female scent, reduce applicability of findings

• Only made men wear shirts, made women smell them

  • Reverse not tested 

• Not doing other way, reduce population valid

  • Limit generalisability to wider population - only females

Genes and behaviour

Genotype

• Chromosomes - found in nucleus, tightly coiled DNA around histones

• DNA: deoxyribonucleic acid

  • Store genetic info in combi of 4 nitrogenous bases

• Genes

  • Inheritable units

  • Pieces of DNA - code for protein → perform specific functions

  • Alleles

    • diff form of gene (recessive/dominant)

  • Genotype:

    • Set of traits coded in all genes in indiv body

  • Phenotype:

    • Observable char - develop from genotype

• Epigenetics changes

  • Change in genes + behaviour due to envt change

• Epigenetic info

  • Which genes are expressed

Role of genes in behaviour

• Family studies 

  • more closely related to family member, more similar genes will be

  • Determine if behaviour is inherited from gen to gen

• Twin studies

  • MZ twins develop from one ovum - share 100% of genes

  • DZ twins from 2 ova - share 50% of genes

  • Compare effect of envt in dvpt of behaviour - use concordance rates of MZ twins 

Weissman et al

Aim: investigate potential genetic nature of MDD

Method:

• Longitudinal family study - 20 years

• abt 160 families of 3 generations - study potential genetic nature of MDD 

• Look at fam w high + low risk for depression

• Research triangulation

  • Child eval by child psychiatrist + psychologist 

Process:

• Grandparents:

  • Depressed: selected from outpatient clinic w specialisation in treatment of mood disorders

  • Non-depressed: selected from same local comm → reduce generalisability

• og sample (parent + children)

  • Interviewed 4 times during 20 years

• Final interview 

  • Children became adults + had children of their own (3rd gen)

• Data collection done by clinicians blind to

  • previous depression diagnosis

  • prior interview data

Results

• Inter-rater reliability of diagnostic assessment high

  • Data is quantifiable and consistent 

• High rate of psychiatric disorder found among grandchildren w 2 gen of MDD 

  • Age 12 → nearly 60% of grandchildren showed signs of psychiatric disorder → common: anxiety disorder

• Children risk of mental disorder → increase when both parents + grandparents had history of depression

• BUT

  • If only parent depressed, gps no depression history

  • no significant effect on grandchildren 

Conclusion

• Association btwn parental MDD + child diagnosis → moderated by gps MDD status

• Genes play a significant role in passing down MDD

• (Link to main topic being discussed in the essay)

Eval - Weissman et al

Strength

• Longitudinal design → increase reliability

• Data - same families, 20 year period

  • R observe pattern of depression consistently over time X single observation

  • More data to observe outcomes across generations

• Data across multiple time points → consistent, repeated measurements

  • Results more reliable

  • Less influenced by short-term changes

Limitation

• small sample size → low pop valid

• 161 p

  • Does not rep wider pop

  • Findings cant be applied to diverse range of families

• Limit generalisation 

  • rs btwn depression across gen observed

  • not accurate rep of patterns in broader pop

Kendler et al

Aim: 

• investigate heritability of MDD in sample of MZ and DZ twins

Method:

• over 15,000 twins called from Swedish Registry 

Procedure:

• Asked abt childhood + adult home envt 

• Assessed for lifetime MDD using modified DSM-IV crit 

Results:

• 80% of twins → symptoms of MDD

• over 300 p came fwd abt previous use of antidepressants 

• Highest concordance rate for MDD → MZ female twin

  • if one twin dev depression, other twin high chance of dev

Conclusion

• heritability of MDD far higher in woman than man

  • some genetic risk factors → sex specific

Diathesis stress theory

indiv rxn to stressful situation depend on genetic makeup

indiv have specific genotype → more likely for genes to be expressed from situation

Caspi et al

Aim:

• investigate role of serotonin transporter gene (5-HHT) + role in dev of MDD

• hypothesise ppl w short allele of 5-HHT gene → more likely to develop depression

Method:

• Mutation of 5-HHT gene → shorter allele

• 3 expt grp

  • 2 short allele

  • 1 long 1 short

  • 2 long

• Longitudinal study in NZ (25 yrs)

  • Age 3-26 yr old

Procedure:

• Asked to fill in “stressful life event” questionnaire

  • Ex. Financial, health, rs stressor, etc.

• Interviewed for symptoms of depression

results:

• presence of at least 1 short allele → more symptoms of depression + suicidal ideation

• Effect → strongest w > 3 stressful events

Conclusion:

• 5-HHT responsible for modulating indiv/vulnerability to stress

• However, impt to note - genes alone not enough to lead to depression

  • Genes interaction w stressful life event → increase likelihood of developing depression