Presentation on theme: "PERSONALITY AND THE BRAIN Professor Glenn Wilson, Gresham College, London."— Presentation transcript:
PERSONALITY AND THE BRAIN Professor Glenn Wilson, Gresham College, London
WHAT IS PERSONALITY? Study of individual differences – what makes one person different from another. Given the same situation people react differently. Personality = consistent patterns of behaviour that differentiate people. Traits are stable and enduring (c.f., states).
LEVELS OF PERSONALITY Personality has antecedents (genes and biological structures) and consequences (laboratory and social behaviour). (Eysenck, 1997)
FACTOR ANALYSIS Statistical classification method used in modern test construction. Reduces matrix of intercorrelations to main factors underlying it. Tells how many factors needed to explain a field. Loadings on items give clues as to content (and appropriate name) for factor.
MAIN SYSTEMS H.J.Eysenck 3-factor solution (Extraversion, Neuroticism, Psychoticism). Big 5 E, N, Agreeableness, Conscientiousness, Openness. J.A.Gray E & N rotated to Anxiety & Impulsiveness = Behavioural inhibition system (BIS) vs Behavioural activation system (BAS).
EYSENCK’S DIMENSIONS Eysenck’s initial personality system comprised two independent dimensions, (E and N) Compared with the ancient Greek classification of the “four humours”. Later added a third (orthogonal dimension) called Psychoticism (P). This included bizarre, impulsive & anti-social tendencies.
EYSENCK’S THIRD DIMENSION (P) Psychoticism conceived as independent of E and N. Includes Impulsivity, Psychopathy, Tough-mindedness, Risk taking, Bizarre thinking.
EPQ SAMPLE ITEMS Extraversion Can you get a party going? Do you have many different hobbies? Neuroticism Do you suffer from your “nerves”? Are you often troubled by feelings of guilt? Psychoticism Would you take drugs which may have strange or dangerous effects? Would it upset you to see a child or animal suffer? (-ve) Lie Are all your habits good and desirable ones? As a child were you ever cheeky to your parents?
EPQ SUBFACTORS For some purposes, research or clinical, it is useful to subdivide the 3 major factors into more specific subtypes. e.g., N may be separated into self- esteem, depression, anxiety, guilt, obsessionality, etc.
REINFORCEMENT SENSITIVITY THEORY Gray’s theory rotates E & N diagonally to Anxiety (Behavioural Inhibition) and Impulsivity (Behavioural Activation)
GENETIC FACTORS Stable temperament observed from birth (e.g. activity, sociability, emotional reactivity). MZ twins more similar than DZ twins. MZ twins reared apart are still very alike. Roughly half of variance is genetic – rest mostly non-shared environment; family environment seems rather unimportant. Gene loci now being discovered - connect with neurotransmitters, e.g. dopamine (novelty-seeking) serotonin (neuroticism).
PERSONALITY GENETICS The contribution of genetics to personality is revealed in twin studies. Ids are much more similar than frats on Big 5 dimensions.
PHINEAS GAGE Daguerreotype of railway worker P. Gage holding the iron bar that, in 1848, blew upward through his brain. He was taken away still conscious and made a remarkable recovery, living 11 more years, though his personality was changed. He appeared as emotionally disinhibited (c.f. leucotomy patients).
DAMAGE TO GAGE’S BRAIN Van Horn et al (2012) estimated that 4% of Gage’s cortex was destroyed and 11% of white matter in the frontal lobe. This included tracts connecting the frontal cortex to limbic (emotional) areas. Gage’s behaviour was described at the time as “fitful, irreverent, impatient and unrestrained”.
E AND CORTICAL AROUSAL Eysenck proposed that introverts had a reticulo- cortical system that led to higher arousal levels in the cerebral cortex. Many experimental observations support this: Introverts more reactive to standard stimulus (e.g. lemon drop). Require more sedative/analgesia to produce same effect. Stimulants make people more introvert; sedatives make them extravert. Skin conductance higher in introverts across the day.
EXTRAVERSION IN THE BRAIN Extraverts show lower levels of resting fMRI activity than introverts in several brain regions predicted by Eysenck’s theory. Extraverts’ arousal shifts more during a memory task. Colour depicts strength of correlation of resting signal intensity with E. (Kumari et al, 2004)
EXTRAVERSION & BRAIN VOLUME Extraverts have less white matter in areas that include ascending projections to parts of the cortex concerned with behavioural control (colours show negative correlation of E with brain volume). Es also have less gray matter in various parts of the cortex, esp. right prefrontal and right temporo-parietal areas concerned with restraint, introspection & social intelligence. (Forsman et al, 2012)
BRAIN-DAMAGE IN PSYCHOPATHS Psychopaths often have structural and functional impairments to the connections between emotional areas (e.g., amygdala) and brain areas controlling decision-making and conscience (prefrontal cortex). Diagram from Motzkin et al, (2011) shows reduced connectivity in psychopaths as indexed by fMRI.
ANATOMY OF PERSONALITY DeYoung (2010) found MRI brain structure correlates of Big 5 personality traits. E = vol. in medial orbitofrontal cortex (reward processing). C = vol. in lateral prefrontal area (planning/control). N = vol. in various threat/punishment regions. A = vol. in “mind reading” areas.
N AND STARTLE RESPONSES The startle response (e.g., eyeblink amplitude) measures anxiety. When people watch frightening film-clips, high N individuals usually show greater SR. However, when material is disgusting and inescapable, high N individuals show defensive blunting (inhibited response). (Wilson et al, 2000)
BLUNTING IN THE BRAIN Although N goes with higher fear ratings, fMRI activity in many brain regions is actually reduced in high N individuals in “shock” vs “safe” trials. (Kumari et al, 2007)
Behavioural Inhibition is associated with high resting EEG in the right posterior dorsolateral prefrontal cortex (Shackman et al, 2009). ANXIETY IN THE PREFRONTAL CORTEX
INHIBITING BRAIN WAVES High levels of alpha oscillations, and low delta, are associated with inhibitory personality (neurotic- introversion) Knyazev (2010).
ADDICTIVE PERSONALITY Addictive behaviours are predicted by negative emotionality (anxiety, anger, inability to cope with stress) and lack of constraint (disregarding rules, risk-taking). (Slutske et al, 2005).
DOPAMINE & IMPULSIVITY Impulsivity is associated with greater amphetamine-induced DA release in the striatum and reduced DA receptor binding in the mid-brain. Apparently, impulsive people get more of a “high” because their brains do not bind DA so readily. This may help explain addictiveness. (PET-scans by Buckholtz et al, 2010)
COSTS AND BENEFITS Personality extremes have survival advantages and disadvantages. Neuroticism has psychiatric implications (e.g. anxiety, phobias, OCD) but helps to avoid danger. Extraversion promotes meeting and mating, while introversion makes for better parenting. Psychopathy thrives when reliability and trust are normative within the population (deceit less anticipated).
MIGRATION & NOVELTY-SEEKING Genes associated with novelty-seeking (DRD4) are more common with distance out of Africa (Matthews & Butler, 2011).
BIRTH ORDER EFFECTS Sibling position is one form of non-shared environment. 1 st born : serious, studious, responsible. Later born: more outgoing, relaxed, thrill-seeking. Middle-born: economically deprived & resentful. Effects small & not reliably detected but illustrate possibility of niche-dependent personality differences.
MACHIAVELLIANISM SCORES OF MEN & WOMEN (Online survey, N = 4814)
THE MARS-VENUS GAP Men are typically more competitive, cold & risk-taking, women more emotional, warm & sensitive. Data below from study of 10,262 US adults using 16PF Test (Giudice et al 2012). Multivariate effect size is substantial.
EMPATHY IN CHIMPS Chimps show consolation behaviour when another is upset, suggesting emotional empathy. This is more common in females than males and has been shown to reduce stress in the recipient.
DIGIT RATIO RESEARCH
EMPATHY vs SYSTEMATISING Baron-Cohen (2005) describes men as systematisers (relating to things/principles), women as empathisers (people/examples). Asperger’s & autistic people are hypermale in both respects – and show evidence of high exposure to pre-natal testosterone.
SOCIAL PERCEPTION AND THE SG Using MRI, Wood et al (2008) found that part of the frontal cortex, the straight gyrus (SG) (in purple) was 10% larger in women than men. Its volume also correlated with feminine personality traits like social awareness.
EPIGENETICS The genes/environment distinction is now known to be oversimplified. Sex differences and personality are impacted by epigenetics – factors determining whether genes will be expressed (switched on or off). These are believed to include maternal stressors, diet and toxins, and may be carried over from previous generations. This is why MZ twins are not always identical. They may even be opposite (e.g., in handedness or sex orientation).