To the best of my knowledge, there have been no conclusive Western scientific studies of "pressure points" from a combative perspective. There have hardly been any from a health perspective, and those have mostly been inconclusive or have shown that any health benefits seem to be due to the placebo effect.
Now, that said, "pressure points" (I'm not personally fond of that term) do work. Not all of them work as advertised, and not all of them work on all people, but they certainly exist. I prefer to think of them as "vulnerable points," and that includes all kinds of biological structures that are particularly vulnerable to negative stimuli. This means that I include obvious targets like the eyes, throat, groin, temple, floating ribs, joints, etc., along with more esoteric ones like nerve plexuses and the carotid sinus. A friend of mine has put together this article on his view of vulnerable points from a Western perspective, and while he is not a professional researcher or medical expert, he does have extensive training in classical Okinawan arts--be sure to check the comments, too, where he addresses a common complaint regarding combat sports:
Ryukyu Martial Arts A Neurophysiological Approach to Kyusho
In the end, at least to me, vulnerable points are extra credit. A punch to the head is a punch to the head, certainly, but a punch to the temple works a bit better than a punch that lands on the forehead. The key is to never put yourself in a vulnerable position trying to access a vulnerable point, in the hope that it will end the fight. Follow sound principles, and the appropriate targets will be evident. If you attack a vulnerable point and it doesn't have an enhanced effect, it should still have been better than doing nothing. Kyusho-jutsu is a component of martial arts, not an art in and of itself, like some snake-oil salesmen like to claim. It is present, but it isn't its own fighting system--people who treat it as such tend to lose sight of reality.
