Compulsive mechanical stimulation of nociceptor

Compulsive mechanical stimulation of nociceptors (CMSN) is the compulsive poking and prodding of one's nociceptors when they are in a peculiar long-lasting ambivalent state. Ambivalent nociceptors produce feelings of gratification when properly stimulated; for example, itchiness is caused by ambivalent nociceptors, and scratching them produces feelings of gratification. Normally, scratching quickly returns the nociceptors to their normal (pain-sensing) state, but in the case of CMSN, the ambivalent state (and the gratification) can last for hours.
Nociceptor Ambivalence
Ambivalent nociceptors feel itchy or tingly; indeed, nociceptor ambivalence is the direct cause of itchiness. When it occurs, mechanical stimulation causes feelings of gratification, briefly, until the affected nociceptors return to the normal state. It is a grooming mechanism designed to provoke the scratch reflex, and then the animal or person scratches something off his or her skin.
CMSN can occur when nociceptors:
* enter the ambivalent state without a physiological justification (i.e. without there being an objective need to scratch), and
* remain in that state for an extended period of time—minutes, tens of minutes, even hours.
In that situation, there can be a strong desire to pick, poke, and otherwise scratch the itch. CMSN is a chronic pattern of acting on that desire. For that purpose, afflicted individuals often keep a variety of implements handy, carefully chosen for having the correct point or edge. Different sharpnesses are sometimes required at different periods during the ambivalent state.
CMSN sufferers report that during an attack it can be very difficult to summon the willpower to stop stimulating the affected areas—akin to the difficulty of halting a scratch before the itch is satisfied. Nevertheless, because the compulsion is felt only when the nociceptors are in an ambivalent (itchy) state, CMSN does not qualify as an obsessive compulsive disorder.
CMSN on the Trigeminal Nerve
CMSN occurs on all three divisions of the trigeminal nerve: the maxillary and mandibular divisions as well as the opthalmic division.
Gingival CMSN
Known colloquially as "gum pushing", "gum picking", or "gum poking", the gums are the most common site for CMSN.
The upper gums are sensitized by the maxillary division of the trigeminal nerve, and the lower gums by the mandibular division. CMSN on these two nerve divisions is probably a vestige of the teething condition, in which toddlers seek gratification by chewing their new teeth out through their gums. The condition only qualifies as CMSN when it occurs absent any teething imperative, and so can strike at any age.
Gum pushers anecdotally report getting started as children or adolescents, usually continuing through adulthood, even in spite of consequent receding gums and tooth loss. Other than that risk, CMSN is apparently harmless unless and until it substantially interferes with normal life.
Gingival CMSN often leads the sufferer to experiment with a variety of implements for triggering his or her nociceptors: toothpicks, fingernails, paperclips, the edges of playing cards and knives, plastic fork tines, drinking straws, even Gameboy DS styluses.
Opthalmic CMSN
The opthalmic nerve is the third division of the trigeminal nerve, and is a less common site for CMSN. When it occurs on this nerve, nociceptors become ambivalent in the eyebrows, forehead, temples, and sometimes all around the crown of the head.
Any edged or sharp object capable of causing a normal (i.e. painful) nociceptor response can gratify the CMSN compulsion. As with gingival CMSN, the feeling of gratification is nearly identical to the "pleasurable pain" of having an itch scratched.
Trichotillomania (compulsive eyebrow plucking) may be related to opthalmic CMSN: trichotillomaniacs report similar feelings of gratification when they stimulate their opthalmic nerve by plucking their eyebrows.

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