This is why I am an occupational therapist and tend to keep myself in application/behavioral analysis - because as soon as I dunk my head into the literature of molecular pain I start to get a little lost. I find some solace in the knowledge that even the molecular pain people are still figuring it out though.
Itch and pain are oddly connected. Histaminergic systems seem to be square mediators between these two sensations. In conversations with OTs I have heard people talk about local histamine release associated with brushing - but this always seemed (to me) like it was an overly simplistic way to explain the complexity of itch/pain sensation. The complex fact is that histaminergic systems operate both peripherally and centrally - and that always adds a layer of complexity to the problem that I haven't seen addressed until recently.
Anyway, I just got this email which reminded me of this whole issue:
Hello, I am an Occupational Therapist and I am doing research on vasoactive effects/histamine release related to sensory integration and your blog came up.... could you point me in the right direction in terms of studies or literature to review...
Now it just so happens that there is a new study that documents a CENTRAL effect of how scratching ameliorates itch sensations.
Basically, the idea is that scratching suppresses the emotional components associated with itching sensations by reducing brain activity in the anterior cingulate cortex, which when activated normally drives aversion to unpleasant sensory experiences. These changes were noted on fMRI.
I personally like this study because it provides a functional explanation behind some of the molecular pain conversations in the literature. This should be an interesting read when it is fully published and hopefully will add to our understanding of the complexities of itch/scratch processing and how it impacts "pain."
Wake Forest University Baptist Medical Center (2008, February 1). Why Scratching Relieves An Itch. ScienceDaily. Retrieved February 25, 2009, from http://www.sciencedaily.com /releases/2008/01/080131121804.htm