Personality and Personality Disorders

Personality

• Personality traits: relatively stable (across time and situation) individual differences in behaviour

• Genes make major contributions (~40%)

• Unique environment also important (~60%)

• Shared environment has little effect (but…)

Quantifying Personality

• Huge number of specific tests, models, designs• Typically self-report questionnaires

– E.g., Myers-Briggs uses 93 forced choice questions, assuming that the individuals are the best judges of their own traits

• Traditional theories of personality have put great value on the shared family environment– E.g., Freudian analysis, Behaviorism, any nurturist

perspective

Five-Factor Model

• Openness to experience (culture)

• Conscientiousness (conformity)

• Extraversion (sociability, impulsiveness)

• Agreeableness (likeability)

• Neuroticism (emotional instability)

• Extraversion and neuroticism have received most behavioural genetics research

Self- vs. Peer Report

• Most use self-reports

• Tends to discount shared environment

• Peer reports generally similar on genes and unique, but do suggest greater role for shared environment

Plomin & Caspi (1999)

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Extraversion Neuroticism Agreeableness Conscien-tiousness

Openness to experience

Unique environment Shared environment Genetic

Contrast Effects

• Psychometric methodological issue

• Correlational studies with twins

• Parental assessment

• MZ twins typically high

• DZ low or sometimes negative

• Parents contrast fraternal twins, not identical

However…

• Lots of personality traits

• Intersection between personality and social psychology

• Relationships, self-esteem, attitudes

• In some cases, shared environment does play larger role

Attachment

• Parent-offspring relationship

• Strange Situation test

• Modest heritability

• Substantial shared environment influence

Romantic Relationships

• Waller & Shaver (1994)– No heritable component to styles/type/aspects of

romantic love (companionship, passion, etc.)– 0.26 for MZ twins and 0.25 for DZ twins– Shared environment and unique environment are

determinants

• Text indicates that initial attraction in mate selection also has no heritable component, but there are a lot of evolved genetic predispositions and preferences….

Self-Esteem

• Linked back to depression (low self-esteem is a core feature of depression)

• Like basic personality traits, moderate heritability but limited shared environment effects

Attitudes and Interests

• Specific attitudes and interests are learned• Hence, will come from shared or unique

environment in the specifics• However, heritable traits can influence what sorts

of attitudes/interests are acquired• Consider specific cognitive abilities

– E.g., individual with high mathematical abilities may be better at chess or poker; reinforced, so plays more

Nature via Nurture

• Traditionalism (conservative vs. liberal views on wide range of issues)

• Twin and family analysis puts heritability at about 50% and shared environment at 15%

• Traditionalism could influence religious, political, sexual, etc. attitudes

Personality Disorders

• Similarities to psychopathology• Personality traits causing impairment• Generally viewed by individuals as part of their

“nature” and not a condition to be treated• Multivariate analysis finds genetic link between

personality disorders and major dimensions of personality (especially neuroticism)

Personality Disorders

• Schizotypal• Obsessive-compulsive personality• Antisocial• Avoidant• Borderline• Dependent• Histrionic• Narcissistic• Paranoid• Schizoid

Schizotypal Personality Disorder

• Less intense schizophrenia-like symptoms• Runs in families

– Concordance MZ 33%, DZ 4%

– Higher proportion of 1st degree relative schizotypals of schizophrenic probands (11%) than controls (2%)

• Danish adoptees:1st degree biol. rel Adoptees & controls

Schizophrenia 5% 0%Schizotypal 24% 3%

Obsessive-Compulsive Personality Disorder

• OCD compulsion is single sequence of bizarre behaviours

• OCPD involves general preoccupations of trivial details; interferes with decisions

• No really good twin, adoption, or family studies with DSM-IV diagnosis

• Twin studies of obsessive symptoms in unselected population show evidence of moderate heritability

• Substantial overlap with neuroticism

• Obsessive symptoms more common in 1st deg. rel. of OCD probands (15%) than controls (5%)

Antisocial Personalilty Disorder

• Lying, cheating, stealing; highly variable– Irresponsibility, irritability, aggressiveness, recklessness, disregard

for truth

• Antisocial personality (ASP)– Chronic indifference to and violation of rights of others– Previously often called psychopathy and sociopathy

• DSM-IV: history of illegal or socially disapproved behaviour, starting before 15 years and continuing into adulthood, 1% of females, 4% of males (13-40 years)

• Vast majority of juvenile delinquents and children with conduct disorders do not develop ASP disorder

ASP

• Runs in families• Adoption studies show genetic, not shared

environment factors• 1st deg. rel. of male and female probands at

5x and 10x risk, respectively, whether adopted or not– Disproportionately male disorder; females need

greater genetic loading

Antisocial Behaviour

• Meta-analysis of 46 twin and adoption studies: shared environment 24%, genetics 40%

• Genetic effects increase with age and shared environmental factors decrease

• Family members of ASP probands: males at increased risk of ASP & drug abuse; females for somatization disorders

Crime

• Criminal records are good data sets to work with• 40% of males & 8% of females with records diagnosed ASP• Two studies find parents with criminal records have

increased rates of ASP in their adopted away offspring• Meta-analysis of concordances: MZ 52%, DZ 21%• 3000 Vietnam War veteran US twins (self-reports) shows

genetics has negligible effect on arrests prior to 15 years; shared environment has no effect after 15 years

• Adoption studies show less heritability than twin studies• Some studies find genetic effects on property crime but not

violent crime• Remember XYY discussion re: general cognition…

Genotype-Environment Interaction

• Alcohol abuse increases probability of violent crime

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Identifying Genes for Personality• Early days• Novelty seeking and DRD4 (dopamine D4 receptor) alleleic

association• 7 DRD4 alleles, 2 to 8 repeats of 48 bp sequence

(chromosome 11) codes for dopamine receptor, expressed in limbic system

• Fewer repeats make protein more effective at binding (in vitro)

• Within families, long DRD4 --> higher novelty seeking behaviour

• As if longer repeats make dopamine less effective, so individual seeks more stimulation to release more dopamine

DRD4• Variation in DRD4 explains about 4% of variation in

novelty seeking• Longer DRD4 repeats also show more hyperactivity and

heroin addiction• Studies on allelic variation and aggression, shyness, and

neuroticism beginning to turn up significant amounts of non-additive genetic variance

Neuroticism

• 5-HTTLPR (serotonin transporter gene)– Linked to neuroticism– Also linked to schizophrenia, depression

• COMT valine mutation– Linked to sensation seeking, related to

neuroticism

• Wide ranging neurotransmitter effects• Conflicting study results re: neuroticism