This might sound rather strange but I had a habit of suppressing my "bright emotions" whenever it came up.

You know, the "bright emotions" that you have in your head when you have an idea, understand a math problem, think of a great plan, or have a revelation.
"AHHH" type of feeling. It usually feels like an emotional flow.

I am guessing it might be dopamine release feeling because I used to have it whenever I accomplished something.

I think I suppressed it because I didn't want to get prideful but stay humble - but this "habit" became almost automatic so it has progressed to suppression of all kinds of positive emotions. For example, I don't feel any flowing of emotions with all these Christmas lights, songs, and spirit.

This happened about 10 years after the brain injury.

Do you think problem is due to brain injury or a bad cognitive habit?

This could be a common PCS symptom called flat affect. It makes it difficult to express active and true emotions. We often end up with a 'so what' feeling to events that should cause an emotional response.

There can be other factors involved.

How old are you ? Are you male or female ?

It can be made worse by hormonal issues.

Please tell us anything about your injury and history you feel free to share.

My best to you.

i believe mark in correct that its common in us with pcs.

Myself for example, I dont show any emotion unless its towards my daughter. Although there are times where I become way over emotional about certain things, which has never happened to me before.

Hormones can change from a brain injury. Also could be part of depression as well. Have you seen a dr? on any medication?

If you can rule out the effect of any prescription drug you may be on it sounds similar to PTSD symptoms - anhedonia. Personally I think it's a learnt behaviour which can be changed, so yes a bad cognitive habit, it's easy to fall into these habits during PCS.