Drooling can be a symptom of TBI:
"Drooling in anoxic brain injury is due to impaired neuromuscular control where the voluntary oral (mouth/throat) motor activity stops functioning leading to an overflow of saliva from the mouth. The affected person will have inefficient and infrequent swallowing. Other problems that worsen drooling are positioning due to poor head control and decreased neck strength..."

It can go the other way, too. In my case, the whiplash/tbi damaged my saliva glands and I suffer from dry mouth and swallowing problems.