personality summary

The Jim Twins

• Jim Springer and Jim Lewis, identical twins separated shortly after birth and reunited at age 39.
  • Shared many similarities, including:
    • Both named "Jim" by adoptive parents.
    • Similar physical characteristics (weight, height).
    • Shared interests (mechanical drawing, carpentry).
    • Police training and part-time work in law enforcement.
    • Marital similarities (divorced Linda, remarried Betty).
    • Similar names for firstborn sons (James Alan/Allan).
    • Shared habits (chain-smoking Salem cigarettes, nail-biting, liking Miller Lite beer).
    • Similar health issues (high blood pressure, heart attacks, vasectomies, tension headaches, weight gain).
    • Vacationed on the same beach in Florida and drove the same model light blue Chevrolet.
• Psychometric tests showed similar personality and intelligence scores.
• The first participants in the Minnesota Study of Twins Reared Apart (MISTRA).

Limitations of the Jim Twins Case Study

• Confirmatory bias: Similarities can be found even in randomly selected individuals if one looks hard enough.
• However, the coincidences in the Jim twins' lives were remarkable compared to other MISTRA twins.
• Genes do not code for specific preferences.
• The case highlights the question of genetics' role in shaping personality.

Basic Concepts in Behavioral Genetics

• Genes are small parts of DNA (Deoxyribonucleic Acid).
• DNA's double helix consists of:
  • Deoxyribose (a sugar).
  • A phosphate group.
  • A base (Adenine, Thymine, Cytosine, Guanine).
• Specific base pairing allows DNA to replicate and direct protein synthesis.
  • DNA replication occurs during cell division, creating two identical DNA double helices.
  • Humans begin as a single cell replicating DNA into trillions of cells (approximately 50 trillion).
• DNA directs protein synthesis, with base sequences coding for amino acid sequences.
  • A gene is a base sequence coding for one protein chain.
  • Examples of Amino Acid & DNA Code: Alanine (CGA, CGG, CGT, CGC), Glutamine (GTT, GTC), Phenylalanine (AAA, AAG).
  • Gene regulators control protein synthesis by turning genes on or off in different cells.
• DNA is organized into chromosomes.
  • Humans usually have 46 chromosomes (two sets of 23).
  • A genome is an entire set of chromosomes; the human genome has about 3.3 billion base pairs.
  • These base pairs contain about 25,000 protein-coding genes, ranging in size from about 1000 bases to 2 million bases.
• New DNA differences arise from mutations during DNA copying.
  • Single-base mutations: a base pair is left out, added, or substituted.
  • Alternative forms of a gene are called alleles, differing by one or more bases but occupying the same locus on the chromosome.
  • Mutations in gametes can be passed to the next generation, leading to different characteristics.
• Genotype: an individual's unique combination of alleles.
• Phenotype: an observed characteristic resulting from the interaction between genotype and environment.
  • Phenotypes include Huntington's disease, height, weight, or personality traits.

Quantitative Genetics Goals

• Estimating the heritability of quantitative traits.
• Estimating the influence of shared and non-shared environment on quantitative traits.

Goal 1: Heritability

• Heritability can be defined as the proportion of the total variance in the phenotype which is due to variance in the genotype.
• Heritability is a population statistic:
  • Heritability estimates are not constant or immutable.
  • Heritability estimates cannot be applied to a single individual.

Goal 2: Environmental Influence

• Shared factors: environmental factors experienced the same by siblings in the same family.
  • Examples: number of books in the home, some parenting practices, SES, religion.
• Non-shared factors: environmental factors experienced differently by siblings in the same family.
  • Examples: differential treatment from parents, different teachers, friends, hobbies, life events.

Estimating Heritability

• Twin studies.
• Adoption studies.

Twin Studies

• If genetic factors affect a quantitative trait, phenotypic resemblance of identical twins should be greater than fraternal twins.
  • Identical twins (monozygotic or MZ) share 100% of their genes.
  • Fraternal twins (dizygotic or DZ) share approximately 50% of their genes.
• A rough estimate of heritability can be obtained in the following manner:
  • MZ twins share 100% of variable genes, DZ twins roughly 50% of variable genes – the difference in their correlations then reflects half of the genetic effect and is doubled to estimate heritability:
  • Heritability = 2 * (r{MZ} - r{DZ})
• The variance not explained by genetics is attributed to the environment and measurement error.
• Less reliable scales produce lower heritability estimates.
• Results for adolescent or adult twins tested using questionnaire or other self-report methods (Zuckerman, 2005):
  • Extraversion
  • Neuroticism

Limitations of Twin Studies

• Twin studies compare identical (MZ) and same-sex fraternal (DZ) twins to control for environmental factors.
• The twin method assumes that environments experienced by identical twins are no more similar than those of fraternal twins (equal environments assumption).
• If MZ twins are more alike than DZ twins, the higher concordance is attributed to their higher genetic overlap.
• The equal environments assumption may be violated in two ways:
  • Equal prenatal environments?
    • Roughly three-quarters of MZ twins share a common placenta and chorionic sac (monochorionic), while DZ twins are always dichorionic
    • Maternal effects may contribute to greater personality concordance in MZ twins.
  • Equal postnatal environments?
    • Parents may treat identical twins more similarly because they look more alike.
    • The postnatal equal environments assumption appears reasonable for most traits.
    • MZ twins don't seem to resemble each other more in personality if treated alike.
    • MZ twins believed to be DZ are as concordant as correctly classified MZ twins for personality traits.

Adoption Studies

• Adoption studies disentangle genetic and environmental sources of family resemblance.
• Adoption creates pairs of genetically related individuals who do not share a common family environment.
• Types of adoption studies:
  • Non-twin adoption studies (biological parents and adopted-away offspring; siblings adopted apart).
  • Separated twin studies (MZ or DZ twins adopted apart).
  • Studies of identical twins raised apart (MZ-A) without contact during formative years are most powerful.
• The correlation on a trait between separated identical twins directly estimates heritability (i.e., h^2 = r_{MZ-A}).
• Results of adult monozygotic twins raised apart (MZ-A) (Zuckerman, 2005):
  • Extraversion
  • Neuroticism

Limitations of Adoption Studies

• Selective placement: foster homes vetted by social service agencies may be more similar than families at large.
• If foster families are more homogenous, heritability estimates may underestimate the effect of family environment.

Concluding Comments

• Genetic research on personality has focused on extraversion and neuroticism.
• Estimates of heritability differ due to age, tests, reliability, countries, and so on.
• Advanced model-fitting analyses across twin and adoption designs produce heritability estimates of about 50% for extraversion and about 40% for neuroticism (Loehlin, 1992).
• These genetic effect sizes are amongst the largest effect sizes found anywhere in the behavioural sciences!
• Other dimensions in the FFM:
  • Openness to experience: 45%
  • Conscientiousness: 38%
  • Agreeableness: 35%

Importance of Environment

• Despite its name, behavioral genetics is as useful in the study of environment as it is in the study of genetics.
• Indeed genetic research provides the best available evidence yet for the importance of the environment.
• Heritability estimates rarely exceed 50% and thus the environmental influence is rarely less than 50%.

Molecular Quantitative Genetics

• Estimating Heritability:
  • Behavioral geneticists aim to determine the relative influence of genetic and environmental factors on behavior.
• Estimating Environmental Influences:
  • Shared factors: environmental factors experienced similarly by siblings in the same family (vary between families but not within).
  • Non-shared factors: environmental factors experienced differently by siblings in the same family (vary within families).

Shared Environment

• Contribution to phenotypic resemblance inferred from:
  • MZ Twin Adoption Studies
  • Non-Twin Adoption Studies

MZ Twin Adoption Studies

• Adoption creates genetically related individuals without a common family environment (e.g., MZ twins raised apart).
• Compare the correlation of MZ twins raised apart with those raised together.
• If the shared environment contributes to phenotypic resemblance, MZ twins raised together will have a higher correlation.
• Data from the MISTRA study:
  • Various traits were measured and correlations calculated for MZ twins reared apart.
  • Traits include non-religious social attitudes, vocational interests, personality, IQ, blood pressure, and EEG alpha %.

Non-Twin Adoption Studies

• Adoption creates family members who share the environment but are not genetically related (e.g., adopted children and their adoptive parents).
• Their similarities estimate the contribution of the shared environment.
• Results for children & their adoptive parents and adoptive siblings:
  • Correlations on extraversion and neuroticism between children and adoptive parents/siblings are examined across multiple studies (Loehlin et al., Scarr et al., Eaves et al.).
  • Generally, these correlations are low, suggesting a limited role of shared environment in these traits.

Non-Shared Environment

• Traditional views assume offspring resemble parents due to the shared family environment.
• Adoption research suggests family resemblance is mainly due to shared heredity.
• Research focuses on identifying non-shared environmental factors:
  • Sibling interactions: Siblings develop different roles and interaction styles.
  • Differential parental treatment: Parents treat siblings differently (Dunn & Plomin, 1990).
    • Maternal affection may be a non-shared environmental influence.
    • Differential treatment may be the effect of sibling differences (Pike et al. 1996; Reiss, et al., 2000).
  • Family structure variables: Birth order and sibling age spacing.
  • Extra-familial experiences: Experiences with peers, friends, teachers, sports, and other activities (Harris, 1995).
  • Major life events: Accidents, prenatal effects, illness, trauma.
• MZ Differences Method:
  • Focuses on MZ twins raised together but are notably different.
  • Identifies reasons for differences (Asbury et al., 2006).
  • Example: Negative school experiences, peer rejection, illness, accidents, perinatal events like birth weight.
• Implications:
  • Non-shared environment has far-reaching implications for understanding how the environment works in behavioral development.
  • Environmental influences are specific to each child, not general to an entire family.

Genes and Environments

• Need to consider genes and the environment together to understand their effects on a case-by-case basis.
• Two ways genes and environment interact:
  • Genotype-environment interactions
  • Genotype-environment correlations
    • passive
    • evocative
    • active

Genotype-Environment Interactions

• Occurs when people with different genotypes respond differently to the same environment.
• Example (Haeffel et al., 2008):
  • Studied 176 male adolescent inmates in Russia.
  • Examined the dopamine transporter gene DAT1 and maternal rejection.
  • DAT1 gene variants: “allele 1”, “allele 2”, and “allele 3”.
  • Environmental feature: Maternal rejection (self-report).
  • Depression assessed by clinical psychologists.
  • DAT1 genotype and maternal rejection contributed to depression only in combination.

Genotype-Environment Correlations

• Occurs when people with different genotypes are exposed to different environments based on their genotype.
  • Passive genotype-environment correlation: Parents passively provide both genes and correlated environments.
    • Musical ability example: Musically gifted children likely have musically gifted parents who provide both genes and a conducive environment.
  • Evocative genotype-environment correlation: Individuals evoke reactions from others based on their genetic propensities.
    • Musically talented children might be picked out at school and given special opportunities.
  • Active genotype-environment correlation: Individuals select, modify, or construct experiences correlated with their genetic propensities.
    • Gifted children might seek out musical environments by selecting musical friends or creating musical experiences.
• Consequences:
  • Environmental measures show a genetic influence because there is some genetic control over the exposure to environmental influences (Plomin et al., 2002).
  • Review of 55 genetic studies found an average heritability of 0.27 across 35 environmental measures (Kendler & Baker, 2006).
    • Measures included social support, childhood accidents, propensity to marry, marital quality, divorce, exposure to drugs, and trauma.
  • Supports a shift from passive models to models recognizing the active role we play in selecting, modifying, and creating our environments.

Molecular Genetics

• When heredity is important, molecular genetics can identify specific genes involved.
• Difficulties:
  • Subtle DNA variations can produce marked phenotypic differences.
  • Humans share 98.5 % of genes with chimpanzees and 99.5 % with one another.
  • Broad traits are likely polygenic (influenced by many genes).
  • Each gene contributes a relatively small effect.
    • Height example: Each single gene likely contributes less than 1% to trait variance (Visscher, 2008).
• Allelic association method:
  • Compares allelic frequencies for groups of low-scoring and high-scoring individuals on a quantitative trait.

Selected Findings

• Earliest application: Association between the D4DR gene and novelty seeking.
• Novelty seeking:
  • One of the 3 traits in Cloninger’s theory of temperament.
  • Similar to Zuckerman’s ImpSS dimension.
  • Characterized by impulsivity, exploratory behavior, fickleness, excitability, quick- temperedness, and extravagance.
  • Linked to individual differences in dopamine transmission (Cloninger, et al., 1993).
• D4DR gene:
  • Located on chromosome 11 and codes for the D4 receptor of dopamine.
  • Expressed primarily in the limbic system.
  • Has seven alleles involving 2, 3, 4, 5, 6, 7, or 8 repeats of a 48 base pair sequence.
  • Number of repeats changes the receptor’s structure, affecting its efficiency in vitro.
  • Shorter alleles (2, 3, 4, or 5 repeats) code for more efficient receptors than longer alleles (6, 7, or 8 repeats).
  • Theory: Individuals with long-repeat D4DR alleles are less efficient at processing dopamine and seek novelty to increase dopamine release.
• First two studies (Benjamin et al., 1996; Epstein et al., 1996):
  • Individuals with longer D4DR alleles had significantly higher novelty-seeking scores.
  • Effect was small, accounting for about 4% of the variance.
  • Many studies have since failed to replicate the association (Munafo, et al., 2003).
  • Effect size is probably much smaller than 4% (Jang, 2005).
• Other research supports the association:
  • D4DR associated with novelty seeking in vervet monkeys (Bailey, et. al., 2007).
  • Longer D4DR repeat alleles associated with greater risk for ADHD (Li et al., 2006).
  • Impulsivity is a defining feature of both novelty seeking and ADHD.
  • Association between D4DR long repeat alleles and heroin addiction (Ebstein & Belmaker, 1997; Kotler et al., 1997; Li et al., 1997).
  • Extensive literature relates sensation seeking to drug abuse (Zuckerman, 1994).
• Other researchers investigate aggression, shyness, and neuroticism.
• Neuroticism:
  • Linked to a gene (5-HTTLPR) involved in the serotonin system (Jang et al., 2001).
  • Meta-analysis of 22 studies found some evidence for an association between 5-HTTLPR and neuroticism (Munafo et al., 2003; Munafo et al., 2005), although a subsequent study of >100,000 individuals found no association (Willis-Owen et al., 2005).

Concluding Comments

• Quantitative genetics' message that both nature and nurture are important is being integrated into mainstream thought.
• Survey: Over 90% of parents and teachers indicated genetics is at least as important as environment for mental illness, learning difficulties, intelligence, and personality (Walker & Plomin, 2005).
• Behavioral genetics is at the dawn of a new era where molecular genetics will revolutionize genetic research by identifying specific genes responsible for the heritability of behavioral traits.

The Classical Temperaments

• Attributed to Hippocrates (370 BC) and popularized by Galen (200 AD).
• Result of imbalances in the four humors (bodily fluids):
  • Sanguine (blood): Sociable, active, optimistic, playful.
  • Phlegmatic (phlegm): Careful, controlled, anxious, rigid.
  • Choleric (yellow bile): Changeable, restless, lively, touchy.
  • Melancholic (black bile): Pessimistic, reserved, calm, persistent.

Eysenck’s Arousal Theory of Extraversion

• Influenced by Pavlov’s work on the strength of the nervous system.
• Neurological basis founded on Moruzzi and Magoun’s (1949) discovery of the Ascending Reticular Activating System (ARAS).

Pavlov’s Influence

• Eysenck's arousal theory origins traced to Pavlov's work on the strength of conditioned reflex, where strength indexed the working capacity of cortical cells.
• Neutral stimulus paired with unconditioned stimulus acquires capacity to elicit salivary response.
  • UCS (food/acid) leads to UCR (drops of saliva).
  • Neutral stimulus (e.g., tone) becomes CS leading to CR (drops of saliva).
  • Strength of conditioned response (CR) measured by saliva drops in a surgically attached fistula.
• Law of Strength: Strength of conditioned response is directly proportional to intensity of conditioned stimulus (CS).
• Transmarginal Inhibition (TI): Law of strength is self-limiting, ultra-strong stimuli reduce response magnitude.
• Onset of transmarginal inhibition is related to classical temperaments:
  • Melancholic dogs: Early onset of TI, believed to have a weak nervous system, highly reactive cortical cells become functionally exhausted at lower stimulus intensities.
  • Sanguine dogs: Delayed onset of TI, believed to have a strong nervous system, low reactive cortical cells require more intense stimulation before exhaustion.

Ascending Reticular Activating System (ARAS)

• Eysenck (1967) arousal theory of extraversion influenced by Pavlov’s work.
• Neurological substrates underpinned by Moruzzi and Magoun’s (1949) discovery of the reticular activating system.
• Moruzzi and Magoun (1949) experiments on chloralsane-anaesthetised cats.
• Electrical stimulation of brainstem ARAS produced shift in EEG from sleep to alert wakefulness.
• ARAS mediates cortical arousal reaction to environmental stimuli.
• Classical ascending afferent pathways send neural messages via specific thalamic nuclei to relevant projection regions in cortex.
• Classical pathways also send collaterals to ARAS, which relays non-specific excitation to cortex.
• ARAS arouses cortex when activated by stimulation from any of the senses, including proprioceptive ones.
• Provides background cortical activity necessary for attention and learning.
• Cortex can inhibit stimulation from ARAS via descending pathways, preventing over-responsiveness of the brain (Jasper et al., 1952).
• Eysenck (1967) linked extraversion differences to the sensitivity of the ARAS; Neural messages (“sensations”) going along the classical ascending afferent pathways relay to the particular projection areas involved in the cortex; they also send collaterals into the reticular formation, which in turn sends “arousal” messages to the cortex to keep it in a state of functional tonus. Depending on the nature of the information transmitted, the cortex in turn instructs the reticular formation to continue sending “arousal” messages or else to switch to “inhibition”. This loop then is concerned with information processing, with cortical arousal and inhibition, and in its application to personality differences with introversion and extraversion. (p. 231).
• Cortical arousability or reactivity (trait?) rather than cortical arousal (state?).
• Introverts with a more reactive ARAS will typically have greater cortical arousal.

Performance and Motivation

• Drawing on Hebb’s (1955) work, Eysenck argued that cortical arousal differences between introverts and extraverts have far reaching implications in terms of both performance and motivation.
• Hebb (1955) characterised the relationship between ARAS induced non-specific cortical arousal & performance in terms of an inverted-U-function.
• If introverts have a highly reactive ARAS which amplifies the value of stimuli → Introverts will reach the optimal level of arousal for performance at lower levels of stimulation.
• If extraverts have a less reactive ARAS which dampens the value of stimuli → Extraverts will reach the optimal level of arousal for performance at higher levels of stimulation.
• Hebb (1955) also linked non-specific cortical arousal levels to affect or mood.
• Low and high levels of arousal produce negative affect. We are motivated to find some inter - mediate level of arousal that is not only optimal for performance but also pleasant.
• If introverts have a highly reactive ARAS which amplifies the value of incoming stimuli they regularly risk unpleasantly high levels of cortical arousal → introverts will have a drive to lower the levels of stimulation in their lives in order to reach a pleasant level of arousal.
  • Stimulus Aversion: introverts are motivated to seek out low arousing situations and avoid active social interactions which may easily cause them to become over-stimulated.
• If extraverts have a low reactive ARAS which dampens the value of incoming stimuli they regularly risk unpleasantly low levels of cortical arousal → extraverts will have a drive to seek out higher levels of stimulation in their lives in order to reach a pleasant level of arousal.
  • Stimulus Hunger: extraverts are motivated to seek out stimulating activities, and engage in more unrestrained behaviours.

Eysenck’s Theory of N & P

• Neuroticism: Linked to the sensitivity of the limbic system (i.e., the hippocampus, amygdala, cingulum, septum and hypothalamus).
  • Neurotics have a more reactive limbic system than Stable individuals. This greater sensitivity makes neurotic individuals more susceptible to mood fluctuations, fear and anxiety.
    • High N → greater autonomic activation.
  • Individuals high on neuroticism find situations involving high ego threat more anxiety- provoking than individuals low on neuroticism. (Competitive situations, complex situations, evaluative situations.)
• Psychoticism: Eysenck had little to say about the biological basis of psychoticism.
  • Differences in testosterone might be implicated. Males tend to score higher on the psychoticism scale than females.

Gray’s Reinforcement Sensitivity Theory (RST)

• Focuses on differences in the sensitivity to reward and punishment.
• Attempts to account for personality differences at the neurotransmitter level.
• Jeffrey Gray’s Reinforcement Sensitivity Theory (RST).

Pavlov’s Influence

• Gray’s theory was founded on Pavlov’s work on canine temperament.
• Conditionability (i.e., the number of trials required to establish a conditioned response).
• Two temperamental extremes on this conditioning index were the sanguine and melancholic types
• Pavlov made no distinction between appetitive conditioning (reward) and aversive conditioning (punishment).
• Gray argued that the speed of conditionability will depend on whether the UCS is a reward (e.g., food powder) or a punishment (e.g., acid).

BIS & BAS

• Model of personality based on two hypothetical biological systems that respond to different subclasses of reinforcing events:
  • The Behavioural Activation System (BAS): which is activated by conditioned stimuli associated with reward (i.e., signals of reward)
    • CS (tone) signals reward (food) → BAS → approach behaviour.
  • Behavioural Inhibition System (BIS): which is activated by conditioned aversive stimuli (i.e., signals of punishment, frustrative non-reward and novelty).
    • CS (tone) signals punishment (acid) → BIS → avoidance behaviour.
• Differences in the sensitivity of the BAS are thought to underlie differences in IMPULSIVITY.
  • Individuals with a very active BAS – who are sensitive to signals of reward – will be less able to inhibit approach behaviour, especially in the presence of desirable goals or rewards.
• Differences in the sensitivity of the BIS are thought to underlie differences in ANXIETY.
  • Individuals with a very active BIS – who are sensitive to signals of punishment and frustration – will tend to be inhibited and anxious. Moreover, they will find uncertainty and novelty more distressing.
• Gray locates his impulsivity and anxiety dimensions within the two dimensional space defined by E and N.
• Biological substrates of the BAS (impulsivity/extraversion) focuses on the dopaminergic pathways, particularly the mesolimbic dopamine subsystem.
  • The nigrostriatal dopamine subsystem has also been suggested as a possible BAS substrate.
• Dopamine appears to function like a reward system and has been called the feeling good chemical (Hamer, 1997).
  • Animals will work to obtain doses of dopamine, much as they would work to obtain food.
  • Drugs of abuse, such as cocaine, mimic dopamine in the nervous system, which accounts for the pleasure associated with taking them → such drugs deplete a person’s natural levels of dopamine, leading to unpleasant feelings after the drug leaves the system.
• The dopaminergic pathways have also been proposed as the biological substrates of personality traits that have been related to impulsivity/extraversion: Sensation seeking (Zuckerman, 1994), Novelty seeking (Cloninger, 1987).
• The bis
  • The BIS (anxiety/neuroticism) is associated with the septo- hippocampal system which in innervated by ascending noradrenergic and serotonergic systems.
    • The ascending noradrenergic system that Gray emphasises as being of most importance.
• The link between the BIS and the noradrenergic system is based primarily on neurophysiological evidence from rats: Destruction of the ascending noradrenergic system impairs passive-avoidance learning in rats. Additionally, the effects of anti- anxiety drugs such as benzodiazepines, barbiturates, and alcohol are thought to be mediated by the septo-hippocampal system.

Concluding Comments

• Eysenck claimed that extraverted individuals engage in approach behaviour because they have a low reactive reticular system that needs stimulation.
• Gray argued that impulsive/extraverted individuals engage in approach behaviour because they are sensitive to rewards.
• Eysenck argued that neurotic individuals are more sensitive to situations involving threat to ego because they have a more reactive limbic system.
• Gray argued that anxious/neurotic individuals are sensitive to situations involving threat to ego because they are sensitive to signals of punishment.
• Eysenck focused his theory and research primarily on the ARAS and extraversion.
• Gray focused his theory and research primarily on the BIS and anxiety.
• Gray’s attempts to link the BAS to impulsivity are far more speculative in nature.

Introduction

• Eysenck suggested physiological measures are the most direct way to test biologically based personality theories.
• Physiological variables often reflect arousal or arousability levels, making them relevant to Eysenck's theory.
• Gray's Reinforcement Sensitivity Theory heavily relied on rat brain studies, not just human psychophysiological data.
• Eysenck (1967) proposed a general concept of arousal where cortical and autonomic activity are unitary.
  • Fluctuations in the ARAS (Ascending Reticular Activating System) cause changes in electrocortical activity, skin properties, heart rate, respiration, pupillary response, and other physiological responses.
• However, unitary theories were challenged because physiological indicators of arousal are often uncorrelated or minimally correlated (Lacey, 1967; Duffy, 1972).
• Lacey (1967) argued against a unified arousal process, suggesting multiple physiological processes are activated simultaneously by separate but related pathways.
• Distinction between basal and phasic measures:
  • Basal measures: assess physiological activity at rest with minimal stimulation.
  • Phasic measures: assess the immediate physiological response to a specific event or stimulus.

Central Nervous System (CNS) Functioning

• The CNS includes the brain and spinal cord, integrating and coordinating bodily activities.

EEG Studies

• EEG measures electrical fields generated by synaptic currents within neurons' dendrites when activated.

Basal Measures: EEG Frequency Bands

• Hans Berger (1929) identified Beta and Alpha waves:
• Other brain waves identified in later investigations: theta and delta

• Based on Eysenck's theory, it was expected that extraverts would show more activity in low-arousal bands (alpha, theta, delta).
• Some weak support exists:
  • Mathews & Amelang (1993) found a positive correlation (r=.16) between extraversion and delta wave activity, supporting Eysenck’s view that extraverts have lower cortical arousal levels than introverts.
• Overall, EEG frequency band studies do not strongly support extraversion-related differences in basal cortical arousal levels (e.g., Stelmack & Rammsayer, 2008; Zuckerman, 2005).

Phasic Measures: EPs

• Cortical evoked potential (EP) is a change in EEG activity in response to stimuli.
• Phasic reactivity is operationalized via peak-to-peak amplitudes (e.g., P1-N1 or N1-P2).
• Eysenck’s theory suggests introverts will show larger peak-to-peak amplitudes than extraverts.
• Larger EP amplitudes are frequently reported for introverts in response to moderate intensity (70-80dB) auditory stimuli (Zuckerman, 2005).
• No consistent extraversion-related differences have been found for visual EPs (Buckingham, 2002).
• Studies testing Gray's theory using auditory and visual EPs show inconsistent results (Zuckerman, 2005).
• Bartussek et al. (1993) found extraverts had larger P2 EP amplitudes to tones associated with winning, while introverts had larger P2 amplitudes to tones associated with losing, supporting Gray's theory.

Functional Imaging Studies

Positron Emission Tomography (PET)

• The first functional imaging method developed.
• Involves injecting a subject with radioactive-tagged deoxyglucose (DG).
• Active brain structures absorb more glucose.
• Radioactive DG molecules decay, emitting positrons.
• Positrons are detected by a scanner.
• A computer generates a "slice" picture, illustrating activity levels across brain structures.
• Disadvantages:
  • Poor spatial resolution (blurry images).
  • Poor temporal resolution (requires long sampling periods).
  • Cannot measure phasic reactivity to specific stimuli but captures total experience over an extended period.

Functional Magnetic Resonance Imaging (fMRI)

• Imaging technique with the best spatial and temporal resolution.
• The formal name of the imaging is BOLD: blood oxygen level-dependent signal.
• Measures brain activity indirectly by detecting oxygen levels in blood vessels.
• Increased brain region activity stimulates blood flow, raising local blood oxygen levels.
• Inconsistencies with Personality Theories: