addictive nature (and keeps Walter White in business).
In Parkinson’s disease, the dopamine-producing cells of
a specific part of the brain called the substantia nigra
become damaged, so patients can take dopamine-boosting
drugs that alleviate symptoms for a time. Eventually, these
medications lose effectiveness in part because the artificial
flood of neurotransmitters causes the downregulation (or
lessening) of dopamine receptors throughout the brain.^25
This is actually a self-regulating mechanism that all neurons
have to reduce or increase the cell’s sensitivity to
neurotransmitters, but it is especially risky with dopamine.
One peculiar side effect of dopamine-enhancing therapies in
Parkinson’s disease is a potential increase in “risky
behavior,” including pathological gambling, compulsive
sexual behavior, and excessive shopping.
Dopaminergic activity is also reduced in ADHD, where
there are fewer dopamine receptors in the postsynaptic cell.
This means that more dopamine is required to sustain
attention and focus. But is this a disorder, or simply a brain
that is hardwired for novelty seeking?
ARE YOU A WORRIER OR WARRIOR?
Certain genes modulate neurotransmitter function and thus
play a role in key aspects of personality. The COMT gene is
one of the more well-studied genes of the bunch. It is
responsible for producing catechol-O-methyltransferase
(COMT), an enzyme that breaks down dopamine in the