You can simulate "ADHD brain" with drugs and conditioning, similar to how PTSD alters people's brain chemistry.

The human brain is plastic/adaptive and can change, depending on the cost/benefit of action/reward conditioning. Just like how people with ADHD can see some improvement with training, a neurotypical brain can see some ADHD-like changes with the same sort of (anti?) training. That's what I'm suggesting is happening in this AI study: People were rewarded for using the AI initially (dopamine response) but then that reward (easy way out) was taken away, and they performed more poorly as a result.

It stands to reason that their reward center was trained to behave like an ADHD brain in that it could tell there was not going to be an easy way to gain a reward from the activity, so it didn't bother putting in the necessary resources to achieve the outcome it would have accomplished if they were never given AI in the first place.

The usual dopamine response was overridden, thus behaving like an ADHD brain.