PSYC10004 Lecture Notes - Lecture 22: Pessimism, Personality Development, Death Drive
29 Jun 2018
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PSYC10004 Mind, Brain & Behaviour 2
LECTURE 22 (8.1) – Biological Approaches
Biological approaches
Efforts to explain biological bases of personality differences
Several levels
oGenetics
oBrain functioning: neural systems, neural structures, neurochemicals
oHormonal factors
Genetics of personality
DNA as a source of human similarities & differences
o~20k protein-coding genes
o~3 billion DNA base pairs
o~99.9% of base pairs shared between individuals
o0.1% of base pairs differ between individuals due to genetic polymorphisms
Research designs
Family studies
oExamine resemblance between family members as function of genetic
relatedness
50% child, parent, sibling (1st degree relatives)
25% grandparent, uncle, niece etc. (2nd degree relatives)
oGreater resemblance for closer relations implies genetic contribution
Genetic contributions confounded with shared environments
Twin studies
oCompare resemblance between monozygotic (MZ) & dizygotic (DZ) twins
MZ twins 100% related, DZ twins 50%
oGreater resemblance for MZ twins implies genetic contribution
oEnvironments same for both, so environmental factors not confounded
oBUT: possibly more similar environments for MZ twins, perhaps twins
unrepresentative
Adoption studies
oCompare resemblance of adopted children to adoptive (APs) & biological
parents (BPs)
APs 0% related but supply environment, BPs 50% related
oDegree of resemblance to APs & BPs show environmental & genetic
contributions
oBut: adoption must occur early; problem of selective placement; biological
mother provides prenatal environment + genes
Heritability
Behavioural genetic studies estimate heritability = proportion of variance in
traits, accounted for by genes
oMost personality attributes show heritability from .3 - .5
oTrue for even apparently purely learned attributes
Important caveats regarding this:
oEven if personality substantially heritable
Doesn’t entail strong resemblance between parent & child personality traits
1
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PSYC10004 Mind, Brain & Behaviour 2
H relates to variation within a population; nothing about genetic contribution
to any individual’s personality
H doesn’t imply personality is fixed
H consistent with environmental contributions to personality
Role of the environment
Awareness of this role = an outcome of behavioural genetic research
Most environmental influences not shared
Most non-shared environment
Environmental factors can be genetically influenced
Specific personality-related genes
H says nothing about specific genes or genetic mechanisms
Assumption that most traits represent sum of many small genetic influences
Several specific genes identified
oNovelty-seeking & dopamine sensitivity
oNeuroticism/shyness & serotonergic functioning
Increases risk of depression to life stress
Study by Caspi et al. (2003)
847 NZ kids followed from age 3 - 26
Examined which form of the 5-HTT gene they had
oShort allele (s) associated with reduced serotonergic function & greater stress
response than long version (l)
o3 versions of the gene: ss ; sl ; ll
Assessed:
o# of stressful life events in past 5 years at age 26; current depression
Results
oStress associated with depression only in ss & sl genes
oChildhood maltreatment only predicted depression in people with ss or sl gene
versions; indicates gene causes susceptibility to environment
Brain functioning: Systems
Eysenck’s theory
oExtraversion & low brain arousal
Leads to desire for stimulation
oNeuroticism & limbic system reactivity
Leads to greater autonomic NS arousal to threat & stress
Gray’s theory
oImpulsivity & “behavioural activation system” (BAS)
Linked to sensitivity to reward & pleasure
oAnxiety and “behavioural inhibition system” (BIS)
Linked to sensitivity to punishment & pain
Brain functioning: Structures
Some links between Big 5 & brain structure volumes
oExtraversion with region evolved in processing reward info
2
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PSYC10004 Mind, Brain & Behaviour 2
oNeuroticism with regions associated with threat, punishment & negative
emotion
oAgreeableness with regions processing info about other people’s intentions &
mental states
oConscientiousness with region involved in planning & voluntary control of
behaviour
Implies that personality has neuronal basis
oNo brain volume correlates Openness
Brain functioning: Chemicals
Personality factors may be associated with neurotransmitter (NT)
concentration in brain
Extraversion & dopamine levels
oLinked to: exploration, approach and incentive motivation
Neuroticism & norepinephrine levels
oLinked to: negative emotion; vigilance to threat; cautiousness;
neurobehavioural warning system
Constrain & serotonin levels
oLinked to: inhibition of emotional response & low impulsiveness
oLow serotonin linked to aggression & emotional instability
Hormonal factors
Evidence personality influenced by prenatal exposure to sex hormones
Ratio of index to ring finger (2D:4D) associated with testosterone exposure
oLower ratio in men than women, especially right hand
oLower ratio in men correlates with:
Physical aggression; more ‘masculine’ career interests (realistic, enterprising);
less feminine gender role
Lower ratio in women correlates with:
oMore indirect aggression (spreading rumours, malicious humour, excluding
people); more ‘masculine’ interests (enterprising, less social)
e.g. study Benderlioglu & Nelson (2004)
oExamined reactive aggression in women
oParticipants asked to raise money for fictitious charity by making calls
Calls went to kind but non-donating or hostile confederates
Hostility assessed by how hard phone put down & tone of follow-up letter
oWomen with lower 2D:4D more hostile
Risks of bio explanation
Reductionism; determinism; immutability; complexity of nature/nurture
relations
LECTURE 23 (8.2) – Psychoanalytic Approaches
Psychoanalysis
3
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Document Summary
Efforts to explain biological bases of personality differences. Dna as a source of human similarities & differences. 0. 1% of base pairs differ between individuals due to genetic polymorphisms. Examine resemblance between family members as function of genetic relatedness o o o o o. 25% grandparent, uncle, niece etc. (2nd degree relatives) Greater resemblance for closer relations implies genetic contribution. Compare resemblance between monozygotic (mz) & dizygotic (dz) twins. Greater resemblance for mz twins implies genetic contribution. Environments same for both, so environmental factors not confounded. But: possibly more similar environments for mz twins, perhaps twins unrepresentative o. Compare resemblance of adopted children to adoptive (aps) & biological parents (bps) o. Aps 0% related but supply environment, bps 50% related. Degree of resemblance to aps & bps show environmental & genetic contributions o. But: adoption must occur early; problem of selective placement; biological mother provides prenatal environment + genes.
