Actually introversion/extroversion is the only personality trait for which we have hard, physiological evidence. Introverts and extroverts use different chemical pathways in the brain.
Introverts have longer dopamine pathways and high cortical arousal, lending to getting too stimulated.
Even the way blood flows in the brain during tasks is different. In introverts, it tends more toward the frontal cortex while in extroverts it flows more toward sensory pathways (sight, sound, touch).
Actually introversion/extroversion is the only personality trait for which we have hard, physiological evidence. Introverts and extroverts use different chemical pathways in the brain.
Introverts have longer dopamine pathways and high cortical arousal, lending to getting too stimulated.
Even the way blood flows in the brain during tasks is different. In introverts, it tends more toward the frontal cortex while in extroverts it flows more toward sensory pathways (sight, sound, touch).