Though there are individual differences in brain chemistry within each type, I also think there are similarities. There's an article about this at the Enneagram Institute's website; basically it's been hypothesized that different types have different levels of neurotransmitters in their brains, specifically dopamine (drive, motivation, energy-level, ability to concentrate), norepinephrine (related to anxiety levels, mental focus), and serotonin (feelings of well-being or lack thereof). Here's the link:
"The Enneagram and Brain Chemistry"
How do you think this relates to Socionics types? I know that certain types, by their very description, likely have different levels of neurotransmitters than others (I, as an INFp and a 4w5, sometimes display symptoms of low serotonin and dopamine, but not always). Also, if a person is treated with a specific medication (i.e. an SSRI like Prozac, or a dopamine reuptake inhibitor such as Wellbutrin or L-Dopa), how do you think this would this affect his or her type?
I know this is just one variable and that there are a ton of variables that contribute to one's overall type, and also that the brain is an incredibly complex mechanism whose total actions can't be fully explained by these three neurotransmitters, but I find the topic interesting nonetheless. Thoughts?