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									                                                                                                    Psych 301, 10/3/3
                           What is the biological basis of personality?
Nearly all personality traits have a genetic component
   Twin studies
      show approximately half the variance in personality is explained by genetic similarity
      Identical twins become more alike as they grow older. This is not true for siblings and dizygotic twins
Family environment
   Shared home environment has limited impact on personality
      Adopted children have no significant personality relationship to adoptive parents
      Larger, but still small, relationship between adoptive children and biological parents
   Birth order is related to personality
   Particular parenting style may not have a major impact on personality
Temperaments are evident in infancy
   Temperament: Biologically based tendencies to feel or act in certain ways
   Three temperament dimensions (A. Buss & Plomin)
      Activity level
   Two temperament dimensions (Rothbart)
Types based on temperaments
   Three temperament styles (Chess & Thomas)
      Easy children (well-adjusted)
      Difficult children (undercontrolled)
      Slow-to-warm-up children (inhibited)
   About 60% of children fall into these types. Other 40% are combinations.
   New Zealand study
      Classification at age 3 predicted later personality and behavior
Neurophysiological mechanisms
   Eysenck’s theory
      Cortical arousal is regulated by the ascending reticular activating system (ARAS)
      We seek an optimum level of arousal
           Chronically underaroused
           Seek stimulation
           Chronically overaroused
           Seek calm
   More recent work
      Gray’s Approach-inhibition model of learning
      Extraverts have stronger BAS
      Introverts have stronger BIS
      BIS is associated with frontal lobe activity
      Extraverts have more active dopamine circuits (involved in BAS)
Functional approaches to personality
   Big 5 each provide important info for mate selection (D. Buss)
   Problem: natural/sexual selection should have eliminated variation
      Traits not evolutionarily relevant?
      Social equilibrium
          some traits more valuable when rare
          no univeral optimum; depends on peers
          selection creates balance among types
                                          Can personality change?
Traits remain stable over time
   Most research shows traits to be very stable over time
      Big Five study shows stability, but consistency increases as individuals get older
      Stability is in terms of ranking of individuals, not absolute scores
      People tend to become more agreeable and more conscientious as they get older
          This pattern holds across cultures
Characteristic adaptations change
   McCrae & Costa model
      Basic tendencies
         Dispositional traits determined by biological processes
      Characteristic adaptations
         Adjustments people make to situational demands
   Different aspects of personality (stable and fluid) interact to produce behavior
   Three levels of personality
      Stability of personality dependent on level at which you view it
   Quantum change
      Transformation of personality that is sudden, profound, enduring, and affects a wide range of behavior
      Appears to happen without effort
      Plays central role in life narratives
Brain injury and personality change
   Damage to specific brain regions can lead to personality changes
      Frontal lobe damage can cause people to become more extraverted, impulsive, socially inappropriate, and moody
      Temporal lobe damage can cause a person to become humorless, obsessive, paranoid, and rule-bound
      Alzheimer’s disease can cause a variety of surprising personality changes
Drugs and personality change
   Serotonin enhancing drugs can cause significant personality changes
      Decrease in neuroticism
      Increase in extraversion
      Independent of effects on depression
   SSRI study
      Non-depressed participants
      Reduction in hostility
      Increase in cooperative behaviors

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