If this strikes your fancy, it has an eternal voting slotA fact about the current wound system:
1- Having your brain destroyed instantly kills you (almost certain).
" Damage to the brain is fatal at a certain point, [...]" --Toady One, two years ago.
This is almost assuredly due to a property of the brain which is an invisible [THOUGHT] or [CAN_THINK] tag or something, and a hardcoded 'if brain = heavily damaged, kill brain's owner'
In the newest wound system, this probably will be apparant, assuming lungs have the [CAN_BREATHE] tag and heart has the [PUMPS_BLOOD] tag and so forth designating their function, allowing custom organs. Further, damaging lungs should damage one's ability to breathe, but having your lungs destroyed doesn't necessarily instantly kill you- you just suffocate later. Further, damaged lungs don't heal, meaning dwarves with damaged lungs are going to be alive but disadvantaged and somewhat disabled due to low stamina or propensity to start suffocating.
What if the Brain operated like that? Damage to the brain directly or damaged skulls could cause major damage (damaging the skull is more common and rather dangerous in itself since sharp fragments of bone might be loose in there). Assuming the brain doesn't start bleeding (which itself could cause a stroke, but that's another issue for another day) too badly, you could get... brain damaged dwarves.
" [...] but I've left minor brain damage alone so that I can do some personality disorders later." --Toady One, 2 years ago
Thus you could have this happen:
A dwarf is smashed in the head, fracturing his skull and damaging the brain, but not ruining it completely.
As far as brain injuries, you could divide the brain up into lobes (very simplified model:
Frontal Lobe- does conscious thought, conversation skills, etc.
Parietal Lobe- gives dwarves some sensory info and handles handles coordination and 3d handling of objects
Occipital Lobe- handles sight
Temporal Lobe- handles smell, sound, and complex images like faces
Cerebellum- handles motion
Brain Stem- handles autonomous functions, damage = death
Notice- only one of those technically will kill you to be damaged if it isn't severe. Dwarves with damaged frontal lobes could have changed or vanished personality readings, happy thought/unhappy thoughts, moods, etc. Parietal Lobe damage could wipe skill levels. Cerebellum damage could make a dwarf constantly fall over, go unconscious, etc. Temporal Lobe damage could potentially wipe out some of a dwarf's relationships, causing major anguish among former friends and family. Some of them like cerebellum also are very easily placed into 'death' compared to 'disability' categories, but still, it could be interesting.
The Body Part Size system of the new wounds system is perfect for animals- animals can have much, much smaller frontal cortices. Further modeling of the brain such as specific areas would rapidly grow complicated and it's far less certain than anatomy in terms of being able to easily model 'hit this, break this piece, cause this', so a simple lobed model would probably be ideal.
Now, granted, 90% of strikes hitting the brain via cutting and half the bludgeoning ones will kill a dwarf outright. So why would a complex model of the brain be good?
Well, it's fun. I think it'd be awesome:
Brain Damage simulation!
Dwarven Lobotomies, with varying 'success' rates!
Trepanning (not technically brain related, but still)!
Urist McPhineasGage (a man who had a railroad spike driven through his brain completely, somehow not killing him, but irrevocably altering his personality due to destroying part of the frontal lobe)!
and, above all else, more ways for your dwarves to die/be horribly permanently maimed!
* Purposefully destroying the frontal lobe in order to destroy capacity for strong emotion at the cost of thinking ability dates only from the late 19th century for our world, but there's nothing preventing it having been invented beforehand- it just requires knowledge that damaging the brain does that, and a pair of metal ice picks, and a really strong stomached 'doctor'. And a way to knock a dwarf out, so that he doesn't move accidentally or struggle.