lets say that the answers provided prove the huge lack of critical knowledge in this area.
there is but one off switch. it isnt the brain stem. medulla oblongata is the switch. a shot thru this about 2 inch round area will shut down a person. by shut down i mean everything shuts off the body goes limp and falls likes dead weight.
any other head shot will not have this effect. you might get this effect or you might get a spasm or tightening of muscles and if this happens then you get fists squeezing guns going off etc.
unless you hit the off switch you might not get any effect other than the physical movement from impact. the person may well die but ther could live and be fully functioning for seconds to hours.
this subject is often undiscussable because people preconceptions that head shot = dead causes them to argue or make stands that have no basis in fact but are fully based in movie magic.
the bottom line in all situations is there is only one shot that will shut a person down. it isnt a heart shot headshot or brain stem shot. while all these may very well kill there can be second to days where the one who is dieing can still kill others.
dont believe me what about the girl who just lived thru the separation of her brain stem to her cord. this kills 99.999999999999999999% instantly but she lived thru it and regained all feeling in her body.
99.99999999999% are outstanding odds but what if a cocked 1911 is pressed into your skull with a finger on the trigger. the sniper takes a shot and shoots a bit high and you dont get the instant kill or shut down. the guy tightens all his muscles from the trauma and bang goes the 1911. he dies within a minute or so and so do you.
head shots have the highest probability of one shot stops but only trained snipers or shooters who know anatomy and consistently shoot under moa can hit this almost automatically. there is still variables like the dead man hiccups or something and the sniper misses. or he is with some idiotic department using 556 as a sniper round or etc etc etc.
definitely a difficult shot. lots of us may be able to shoot under moa at 100 yards on paper all day but do it looking thru a scope at someone when you have 2 or more lives on the line.
trying this with a hand gun is lunacy. there are recorded instances where a hand gun made instant stop on hostage takers. usually these are short range where the shooter was able to get perfect position unknown to the hostage taker.
one instant i remember was a guy has a gun to a woman's head backing down a street. he had just killed someone else so time is a ticking. an officer snuck up behind a van. the guy backing down the street with a gun to the woman's head walked right to where the officer placed his 357 in the right ear and fired. the hostage taker never even knew what happened he is just instantly dead. the officer is a hero, a murderer and hostage taker is dead and the lady will never be the same but she is alive and thankful..
you can see how the hostage taker could have flinched and the lady would be injured or dead also and then everything is different.
i hope none of us have to be in a position to make this decision.