Originally posted by PeterR
One of the tanto dori kata I am practicing at the moment basically involves an irimi-like taisabaki to uke's rear followed up by a sharp strike to the back of the head.
In the kata you are supposed to get close enough to tickle the hairs at the back of the head but once I misjudged and hit and once someone else misjudged and hit me. In the latter case I went down fast but was not knocked unconcious. Same with the reversed role. These were both not full force blows and I have never had the guts to ask Shihan how dangerous the technique really is (this would have to be done in Japanese).
It's been a while since I've posted here and I've also done this particular exercise a few times in the past.
Peter, the area we strike in that kata is on the Occipital Bone, right where the trapezius muscles are attached to the skull.
The area of the brain that this bone covers is responsible for muscle coordination and posture, so I guess that has something to do with the desire to hit the deck when the strike is applied properly (has happened to me too
My guess is that the brain in general (esp. the cerebellum) doesn't react too well to being banged around on a regular basis (hence the reason for keeping chin tucked for ushiro ukemi), so I think it would have extremely undesirable effects over time. Probably conditions linked to muscle coordination and even urinary tract issues since it is very close to the Bladder meridian in shiatsu as well.
I guess tickling the back of their head isn't a bad idea after all