session13-biological

• Biological models explain stable personality traits by underlying biological systems such as brain structure and function, neurotransmitters, hormones, and genetic factors.

• They assume personality has a biological basis that can be measured objectively.

• Top-down approaches start from traits and search for biological correlates (e.g., Big Five).

• Bottom-up approaches start from brain systems and examine resulting behavioral tendencies (e.g., Gray’s RST).

• Hippocrates proposed four temperament types based on bodily humors: phlegmatic, sanguine, choleric, and melancholic.

• There is no empirical or biological evidence supporting the idea that body humors determine personality traits.

• Phrenology claimed that specific personality traits are localized in brain areas and reflected by skull shape.

• Because skull shape does not reflect brain function and relationships between body type and personality are weak.

• He developed a biologically grounded trait model using factor analysis

• and criticized circular explanations in personality theory.

Extraversion–Introversion, Neuroticism, and Psychoticism.

• Individual differences in baseline cortical arousal in response to environmental stimulation

  • Introverts are more easily cortically aroused, experience stimulation as aversive, and therefore avoid highly stimulating situations.

  • Extraverts have lower baseline cortical arousal and seek strong social or sensory stimulation to reach optimal arousal.

    • EEG, heart rate, sweat gland activity, noise and pain sensitivity correlate with extraversion, although fMRI findings are inconclusive.

The limbic system and autonomic nervous system (ANS), especially stress reactivity.

• High Neuroticism: Fast, intense reactions to stress and slow recovery of autonomic arousal after threat.

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Higher testosterone levels and possible involvement of dopamine, especially related to aggression and antisocial behavior.

• A personality trait describing the tendency to seek novel, complex, intense sensory experiences, even when involving risk.

• They engage more often in risky behaviors (e.g., extreme sports, substance use) but may also choose high-risk professions.

• High sensation seekers need stronger dopamine release to experience reward, leading them to seek intense stimulation.

• Lower serotonin levels are associated with impulsivity, disinhibition, and aggression.

Reduced prefrontal cortex control, increased reward sensitivity in the striatum and nucleus accumbens, and reduced amygdala reactivity.

• A personality model including

  • Sociability,

  • Activity,

  • Sensation Seeking,

  • Aggression–Hostility,

  • and Neuroticism.

Plasticity and Stability.

• Adaptability,

• exploration, and engagement with novelty;

• shared variance of Extraversion and Openness;

• linked to dopamine.

• Emotional regulation,

• impulse control, and consistency;

• shared variance of Conscientiousness, Agreeableness, and low Neuroticism;

• linked to serotonin.

Extraversion → medial OFC (orbite frontal)

Conscientiousness → LPFC; (lateral prefrontal cortex)

Agreeableness → STS; (superior temporal Sulcus)

Neuroticism → reduced DMPFC (Dorso médial prefrontal cortex) and hippocampus.

A higher-order factor accounting for shared variance across all personality traits.

Approximately 30–50% of variance in personality measures.

It may reflect social desirability or response bias rather than a true biological trait.

Personality differences arise from individual sensitivity to reward, punishment, and conflict-processing systems.

• A system responding to appetitive stimuli,

• driving approach behavior,

• impulsivity, and positive affect;

• linked to dopamine and basal ganglia.

A system responding to aversive stimuli with fear and panic reactions via fight, flight, or freeze responses.

A system resolving conflicts between BAS and FFFS, regulating attention and arousal; associated with anxiety.

Neuroticism → negative emotions;

Extraversion → positive emotions;

Agreeableness → empathy and trust;

Openness → curiosity;

Conscientiousness → emotion regulation.

• High dopamine is linked to positive emotion, energy, impulsivity, and reward sensitivity;

• low dopamine to low energy and anxiety.

• High serotonin is linked to mood stability and self-control;

• low serotonin to depression, aggression, and impulsivity.

Cortisol is involved in stress and threat responses.

Dominance, competitiveness, aggression, and sexually dimorphic characteristics.

Individual differences in left versus right hemispheric activity related to emotional processing.

EEG-based comparison of left and right frontal cortex activity at rest to measure emotional tendencies.

Left → positive emotion and approach; Right → negative emotion and avoidance.

Although anger is negative in valence, it is linked to left frontal asymmetry due to its approach motivation.

The idea that biological systems and personality traits change as a result of environmental influences.

-> Winning increases testosterone; leadership increases serotonin; juggling or taxi training changes brain anatomy.

They allow causal testing, use objective measures, and provide insight into emotional and motivational processes.

Reductionism, weak mapping between biology and traits, and limited research on higher-order cognition.