The neuro-chemistry of intrusive feelings

Intrusive feelings of arousal seem to be a common symptom for people with OCD. But it’s not something talked about in detail very often.

Could someone explain what’s really happening in the brain when this occurs, and what the factors are that cause it? It would help me transcend the OCD narrative, if I could understand what’s happening neuro-psychologically and neuro-chemically. The problem with intrusive feelings is that they are very different from thoughts alone, and thus more convincing, which makes them harder to discredit.

Is your brain reacting to a specific trigger, and sending the emotional signal automatically?

Is it something you unintentionally condition your brain to do, by compulsively ruminating on the intrusive feeling over and over?

Are intrusive feelings limited to merely unwanted, inappropriate feelings of arousal? Or is there also such a thing as an intrusive feeling of anger, intrusive feeling of excitement, intrusive feeling of sadness, etc.? There are lots of feeling and emotions that could be ego-dystonic.