Hi, "there are three main functions of the brainstem. The first is its role in conduit functions. That is, all information related from the body to the cerebrum and cerebellum and vice versa, must traverse the brain stem. Second, the cranial nerves 3-12 emerge from the brain stem. Third, the brain stem has integrative functions (it is involved in cardiovascular system control, respiratory control, pain sensitivity control, alertness, and consciousness). Thus, brain stem damage is a very serious and often life-threatening problem". Taken from http://en.wikipedia.org/wiki/Brain_stem
"Diseases of the brainstem can result to abnormalities in the function of cranial nerves which may lead to visual disturbances, pupil abnormalities, changes in sensation, muscle weakness, hearing problems, vertigo, swallowing and speech difficulty, voice change, and co-ordination problems". Taken from http://en.wikipedia.org/wiki/Brain_stem
I've had a stroke of the brainstem (and have lived to talk about it).
The brainstem is pretty important in that, among other things, controls a lot of the body's "automatic" functions (heartbeat, breathing, etc). He'll need a lot of therapy (occupational, physical and speech) after his coma, but everyone can help him now by keeping his joints and muscles limber and making-sure there is constant touch (for the firing of neurons) with his skin. Maybe, most important of all, he needs to be constantly reminded that he is needed and loved.
Best wishes!