For as long as I can recall most therapists talk about tactile defensiveness as being an oversensitivity to touch - and that it includes a sympathetic nervous system response that is allegedly 'out of proportion' to the incoming stimulus. The result of this characterization is that most people start looking AT the sense of touch as the primary culprit of the problem. This is why you then see therapists struggling to describe what textures a child tolerates and does not tolerate. This structural understanding of the problem is reinforced by sensory integration theory which posits that children are not able to process incoming sensory information accurately.
In the real world this model is poorly described and subsequently notoriously unreliable - and again you will hear therapists explain the inconsistency in sensitivity as a "sensory modulation" problem because sometimes certain kinds of touch will be tolerated and other times it will not be tolerated. Still, the focus often remains on describing the problem in terms of the sensory channel and not as much on the central nervous system mechanism that governs the response.
I would like to see all this evolve to a point where people understand that there is not a problem WITH the sense of touch. The problem can be observed THROUGH the sense of touch.
This is a pretty important distinction because when we continually describe something as 'tactile defensiveness' it leads people down a natural thinking path that the tactile input is the critical issue that requires study or intervention. That causes us to wring our hands over trying to find a way to accurately and reliably measure tactile localization or how we can provide an alternate form of tactile stimulation that will help to 'modulate' the system. We would probably be better served by also looking at central control mechanisms as opposed to only considering these peripheral tactile-based mechanisms.
This reminds me of some rather large fights I had with a neurologist who HATED splinting when I told him we were trying to see if we could achieve an inhibitory effect on spasticity by effectively lengthening the muscle and 're-biasing' the muscle spindle. He understood spasticity as something that was centrally driven by a lesion and not a function of a whole system - so he used to take my splints and toss them in the trash can. Anyway, not to get off topic, but I am saying that I am aware that we might have some impact on a central problem by intervening at the periphery but that doesn't mean we ignore the central problem either. So I am hat tipping to that crotchety old neurologist.
Still, therapists bristle at any threat to their longstanding description and understanding of the 'tactile' problem. Several notable studies have been completed that talk about 'anxiety' constructs but as close as these studies come to hitting what I think will eventually be considered as the pay-dirt of this problem, they tend to veer off and talk about how this 'anxiety' is co-morbid to the sensory processing problem. This is a classic example of several people feeling different parts of the elephant and describing the elephant in absolutely disparate terms.
I've been thinking about all this again lately because I had a young fellow come into my office recently who stated, "I can't write because I can't touch paper. The only way I can write is when I put my papers into these plastic protectors and I use a marker to write on the plastic."
"What do you mean - you can't touch paper?" I said. This was new for me to have a child be THAT aversive to paper - and then I was doubly surprised to see another clinician describe the same level of sensitivity on an online forum - and TRIPLY surprised to see that for the child discussed on the online forum the school came up with the same solution of writing on plastic overlays. So either we are all talking about the same child or people around the country come up with the same 'solutions' to this 'problem.'
"Touching paper gives me goosebumps. See!!!" Then he dragged his index finger across the VMI test booklet and pointed to the piloerection on his forearms. Indeed, he had goosebumps. "Its not just goosebumps. Touching paper also makes my teeth hurt."
The problem with my young friend's story is that as far as I know there are no tactile receptors for paper. Over the course of the evaluation I observed him touching other objects of equivalent texture quality and with equivalent amplitude or force. I also brushed papers against him when he wasn't paying attention and couldn't elicit the same physiological response. I also focused his attention on his hands while I was checking range of motion, and while doing so brushed and rubbed his forearms against the VMI test booklet that was resting on the table. No aversive response. Still, the piloerection that he could automatically elicit by dragging his fingers across paper was very real.
I qualitatively checked his stereognosis using the SIPT Manual Forms Perception subtest and he was functionally unable to discriminate the forms, but he did not have any defensiveness to the plastic pieces of the test. I also checked for defensive responses by trying the Localization of Tactile Stimulation Test and the Graphesthesia test and he was not defensive to that stimulation either. He had no other apparent or reported defensiveness to sound or movement or visual stimulation. He was a very picky eater. Still, none of this helps to explain his defensiveness to paper.
I get a lot of referrals like this, actually. Kids are 'defensive' to their clothing, or they are 'defensive' to their shoes/socks, or they are 'defensive' to having their hair washed. These all tend to be very focal kinds of defensiveness and in fact they cause severe functional difficulties with ADL completion or school. But how can we understand this in 'sensory' terms when there is no physiological explanation or consistency based on what we KNOW to be true about tactile perception?
The answer to this is that we need to understand that sometimes the explanation is best found in behavioral terms and conditioned responses. Although there may have initially been some developmental sensitivity or even a negative sensory experience, the operant cause of the piloerection and tooth pain can sometimes be conditioned fear.
If we consider this as a possibility, our interventions change dramatically. You still might try some 'brushing' technique IN CASE there is some local physiological dampening effect on the overall amplitude of incoming sensory messages to the CNS. You might get equal impact off of the placebo effect of giving the child attention and suggesting that the intervention actually works. You might also try progressive desensitization and relaxation training.
The particular child I saw had many other problems in addition to his 'paper sensitivity.' There were perceptual deficits, hyperkinesis, mood instability, and many other problems that all can cycle around a chicken or egg argument of what was causing what. I can state rather emphatically that he does not have tactile defensiveness (if that even exists). However, we can understand his central emotional regulation problem that is triggered by a conditioned fear to very specific forms of tactile input.
This distinction matters because accuracy in understanding the problem can lead us to correct interventions that respect the scientific evidence and our understanding of how sensory processing actually works.
Quick thoughts for background reading:
Masuda, Y., Suzuki, M., et.al. (1999) Developmental and pharmacological features of mouse emotional piloerection. Experimental Animals, 48(3), 209-211.
Reynolds, S., & Lane, S. J. (2009). Sensory overresponsivity and anxiety in children with ADHD. American Journal of Occupational Therapy, 63, 433–440.