David Graber,
http://www.chiromt.com/content/20/1/26 www.chiromt.com
http://www.chiromt.com/content/20/1/26 www.chiromt.com
These results indicate that SMT has a direct local/regional hypoalgesic effect on experimental pain for some types of stimuli.
Interesting summary on an important topic...open access too!