Does A Curb Stimulate Endorphines?

[Wendy]

I am a big fan of the rubber pelham/elastic curb. My horse clearly much more relaxed than with a snaffle and works much better.

I'm sure I read somewhere that the action of a curb chain stimulates endorphines, same theory as a twitch.  Has anyone else heard that?  

[Cobstar]

I've read that somewhere as well.  I'd be interested to know if there is any scientifi evidence relating to this.