Eysenck believes that the difference between two personality traits can be found in our #Ascending Reticular Activating System (ARAS), part of our brainstem that has ascending pathways to the cortex# and connections to other parts of the brain which contribute to our wakefulness and behavioral arousal. Eysenck speculated that ARAS maintains the balance between over- and under-arousal by controlling the amount of stimulation that goes into our brain: introverts have wide open channels where excessive stimulations can flow, causing them to feel overwhelmed, while extroverts have narrower channels making them prone to under-arousal. “Over-arousal doesn’t produce anxiety so much as the sense that you can’t think straight–that you’ve had enough and would like to go home now. Under-arousal is something like cabin fever. Not enough is happening: you feel itchy, restless, and sluggish, like you need to get out of the house already,” wrote Susan Cain.
