mulling it over, while there is something definitely logical with associating introversion with parasympathetic dominance and extroversion with sympathetic dominance, there is something that doesn't ring true to me. mostly because of my own experiences as an introvert. to me, for some reason, it seems the fundamental differences seem to be at a higher level of neurological functioning. the autonomic nervous system is just too low level for me to believe it entirely. sure, Laney mentions the differences in the cholinergic tracts in the CNS between introverts and extroverts, and the real determinant must be somewhere in the CNS. and, certainly, there is a link to the dopaminergic reward circuit (the mesolimbic dopaminergic tracts). i want to find more scientific papers regarding this topic and hopefully figure out some sort of conclusion.