The way I understand it, it's pretty much every person's brain all the time. We all, always, emotionally decide then rationalize. We can build systems that protect us from this inherent flaw, but that's different than not experiencing it.

Smart people are more susceptible to high impact biases though, which is maybe what you meant? Lower IQ people are experience this less?

It's not general intelligence per se. Self-awareness and objective decision making are skills: a result of environment as well as individual capability.

I know lots of very intelligent people who seemingly can't apply that intelligence any time they have strong emotions about an outcome. We also know that children can be inculcated with difficulties distinguishing fiction from fact (1).

IMHO, as you mention, it's a spectrum, perhaps the equivalent of the Autistic spectrum for Emotional Reactivity Disorder. Though unlike autism or borderline personality disorder, I believe that it's a skill deficit rather than an inherent disorder of personality.

I also believe that more than half this country is suffering much more profoundly from it than we are aware.

(1) https://onlinelibrary.wiley.com/doi/full/10.1111/cogs.12138

I hope you're not thinking about that weird study trying to prove the "decide subconsciously, then backfill rationalizations" hypothesis by "demonstrating" it with fMRI; AFAIR that made about as much sense as saying that a CPU isn't actually working, but measuring potential on output pins and backfilling "computation" because you can measure voltage on the pins faster than you can measure temperature increase in the CPU...

No, I don't put much stock into fMRI results.