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1. AGreater amygdala reactivity to threat cues, producing heightened anxiety in unfamiliar social situations
2. BLower resting cortical arousal, leading introverts to actively seek out additional external stimulation
3. CReduced serotonergic transmission in the prefrontal cortex, producing impulsive and disinhibited behaviour
4. DHigher resting cortical arousal, leading introverts to avoid excessive external stimulation
5. EIncreased dopaminergic reward sensitivity, producing a stronger drive toward novel and exciting activities