I've gotten them from taking SNRIs, so I wonder if norepinephrine is involved somehow, or maybe SNRIs are not actually that selective.
The only time I got them was getting off a high dose of Strattera (atomoxetine), the rare non-stimulant ADHD medication, cold turkey.
got them after weaning of SNRIs, for about 1-2 years I had random brain zaps. Not that big of a deal per se, but definitely annoying.
If you're talking about Effexor - famous for wicked brain zaps after only one missed dose - this could have more to do with its very short half life.