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.
