Personality & Biology: Research Notes

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
- EEG Studies
  - Basal measures: EEG frequency bands
  - Phasic measures: Evoked Potentials (EPs)
- Functional Imaging Studies
Autonomic Nervous System (ANS) Functioning
- Skin Conductance Studies
  - Basal measures: SCL
  - Phasic measures: SCR/NS-SCR
- Heart Rate Studies
Concluding Comments

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

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

Hans Berger (1929) identified Beta and Alpha waves:
- Beta waves: 14-30 Hz, low amplitude, desynchronized. Found in excited states or high emotional arousal.
- Alpha waves: 8-13 Hz, moderate amplitude, synchronized. Occur primarily in the occipital region during relaxed wakefulness, reduced by stimulation.
Other brain waves identified:
- Theta waves: 4-7 Hz, high amplitude. Associated with lower arousal, drowsiness, more frequent in children.
- Delta waves: < 4 Hz, high amplitude. Mainly occur during sleep in normal individuals.
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).

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.

Positron emission tomography (PET) was the first functional imaging method.
- Radioactive-tagged deoxyglucose (DG) is injected. Active brain structures absorb more glucose.
- Decaying DG molecules emit positrons, detected by a scanner.
- A computer generates a