Do people with pba have history of head injuries or major psychological trauma? And does pba associate with other neurological disorders such as als?

Pseudobulbar affect. (pba) has several causes including ALS and tbi as you mention. It has also been described in hypertensive encephalopathy, multiple sclerosis, parkinson's disease, or pseudobulbar palsy to name a few. The term refers to involuntary or uncontrollable crying/laughter which is frequently mood incongruent. Neudextra has been shown to be useful in reducing these emotional displays.
Yes and yes. Pseudobulbar Affect Disorder can be associated with head injuries, ALS, strokes, and multiple sclerosis. Major psychological trauma may cause PTSD, but NOT PBA.