"Dynamic touch reduces physiological arousal in preterm infants : a role for C-Tactile afferents ?"
Francesco Cerritelli DO (RAISE Lab, Clinical-Based Human Research Department, Foundation COME Collaboration, Pescara, Italy) and his colleagues presented this research in January 2019 and it was recently published by Elsevier in August 2019. I know Francesco Cerritelli a little bit: I sent him my final thesis in osteopathy in 2009, asking him for his comments (as I had sent it also to many osteopaths and doctors). He did much more than comment, he guided me in a new direction, neuroscience, to add substance to my research, and I will always be grateful to him. He was the one who first told me about Arthur D. Craig, an event that totally changed my vision of manual therapy.
Their recent research is original in two main ways. First, it was done with premature babies. Several other similar studies on C-Tactile afferent fibres have already been conducted by different groups of researchers. Among others, there are "Physiological and behavioural responses revealed 9-month-old infants' sensitivity to pleasant touch" Fairhurst et al. 2014, "Massage for promoting growth and development of preterm and/or low birth-weight infants" Vickers et al. 2004, and several others. Some with animals, others with humans, even babies. But this particular subject (the influence of the C-Tactile afferent fibres and physiological arousal), I believe it is the first time it has been developed with subjects so young (33.4 weeks of life) and fragile. Its second originality, I will tell you about it at the end of the article, because you have to read until the end!
How did they proceed?
Participants were premature babies with an average of 33.4 (± 4) weeks of gestational life and an average weight at birth of 2100 g (± 874). So the younger ones were around 29-week-old and the lighter ones weighed around 1300 g. Very, very small subjects.
They identified 2 groups: those with dynamic stimuli, those with static stimuli.
Oxygenation and heart rate were monitored.
All tests were done on the babies using a protocol that lasted 15 minutes, both for the group that received the dynamic stimuli and the group that received the static stimuli.
Each test session was composed of: a) 5 min Pre-Touch Baseline recording, b) 5 min Touch Procedure, c) 5 min Post-Touch recording.
Dynamic stimulation was performed on the child's back, from the first thoracic vertebra to the fifth lumbar vertebra, an area that covers about 10 cm in these babies. The contact was made with bare hands on the child's bare skin.
The strength and speed of the dynamic stimuli were chosen according to the optimal response of the C-Tactile afferent fibres (Sensual Touch: A Slow Touch System Revealed with Microneurography, Vallbo et al, ; © Springer Science+Business Media New York 2016 1 H. Olausson et al (eds.), Affective Touch and the Neurophysiology
of CT Afferents, DOI 10.1007/978-1-4939-6418-5_1, p. 24)
For babies who received static stimuli, the researchers placed their hands on the child's back, taking care to cover the same area from the first thoracic vertebrae to the fifth lumbar vertebrae. The contact was made with bare hands on the child's bare skin and lasted for 5 minutes, without moving.
«The results of the present study show that a short period of dynamic stroking touch, delivered at a force and velocity to optimally activate CTs, produces a reduction in the heart-rate of preterm infants that was sustained into a 5-min post-touch period. In contrast, static touch, which would not activate CTs as strongly, produced no significant change in the heart-rate of preterm infants matched for weight and gestational age. Dynamic touch was also associated with an increase in levels of oxygen saturation, which was not seen in those infants receiving static touch. » (Dynamic touch reduces physiological arousal in preterm infants : a role for C-Tactile afferents ? Cerritelli et al. p. 4)
I'll let you read it again, and think about it.
C -Tactile afferent fibres
When we talk about C fibres, we immediately think of nociception, or C-nociceptive fibres. It is interesting to read this passage from A.D. Craig's book (How do you feel, An Interoceptive Moment with your Neurobiological Self), p. 173 :
« Affective touch is conveyed by small-diameter, unmyelinated C-Tactile ("slow brush") sensory fibres with peripheral endings in the epidermis and central terminals in the superficial dorsal horn. Microneurographic recordings in human participants indicate that they conduct spikes very slowly (∼ 1 m/s), and they fire at very low rates (which saves energy). They innervate hairy skin all over the body; they are not found in glabrous skin (e.g., the palms), where high acuity mechanoreception is needed. They are reported to be at least as numerous as C-nociceptors or myelinated mechanoreceptors. The C-Tactile sensory fibres are activated only by light brushing within a limited range of slow velocities that are not fast enough to activate large-diameter cutaneous mechanoreceptors. More recent evidence indicates that C-Tactile sensory fibres in mice are genetically characterized by a particular receptor molecule that differentiates them from both C-nociceptors and hair follicle C-mechanoreceptors; that article reporter also that they are activated by "massage-like stroking of hairy skin", are anxiolytic, and generate a positive affective behavioral motivation in mice. »
Thus, we have as many C-Tactile fibres sensitive to pleasant touch as we have C-nociceptive fibres sensitive to "danger" and as many, if not more, receptors sensitive to pleasant touch as we have mechanoreceptors in the skin. They have to be important to be so many.
But like the myelinated receptors that are sensitive to discriminative touch, for example in the hand, these C-Tactile fibres are not evenly distributed over the body. Some parts of our body have more than others.
For the most clever amongst us, you will have understood that these are the receptors that are sensitive to the « soft line drawings » as I proposed to apply them during my presentation at the Niromathé annual meeting in December 2015.
If you are interested in C-Tactile afferent fibres, I suggest you get Håkan Olausson's excellent book "Affective Touch and the Neurophysiology of CT Afferents" which is no more than a compilation of 24 published scientific studies, which have requested contributions from 45 researchers from many countries. All this research has the same theme: the C-Tactile afferent fibres. Attention: you must be able to decipher the scientific language.
The oxytocin hypothesis
So if we go back to the research of Mr. Cerritelli and his colleagues, one of the conclusions is this:
« Further support for our hypothesis that CTs are the cutaneous nerves underpinning these effects comes from comparison of the physiological and behavioural effects of CT targeted skin stimulation with those of oxytocin, release of which can be induced by low intensity cutaneous stimulation. (Uvnäs-Moberg et al., 2014 ; Walker et al., 2017). »
It's very interesting, and there's a lot of research going on concerning this particular topic: the stimulation of C-Tactile afferent fibres and the release of oxytocin, the first and most important researcher in this field would be Kerstin Uvnäs-Moberg.
But be careful: don't fall into the trap and say that the stimulation of the C-Tactile afferent fibres will necessarily lead to the release of oxytocin: for example, if I don't like the person who performs this kind of stimulation, or if I feel worried in the environment where I receive them, there is a much greater chance that cortisol will be released into my body and not oxytocin. Hence the importance that must be given to the whole bio-psycho-social aspect for the patient.
Then, the C-Tactile afferent fibres do not have "direct" access to the paraventricular and supraoptic neurons of the hypothalamus where this peptide is produced. It is probably through the insula and its "dialogue" with the centres of homoeostasis in the brainstem that oxytocin release is achieved.
But this is not over. I have a few more ideas and that will probably be the subject of the next article. I need to check 3-4 points before.
The major difference from other research?
Yes, they measured the Therapeutic Pause and even found that the positive effects of a cutaneous stimulation lasted for at least 5 minutes. They did not measure beyond these 5 minutes nor did they measure the effect of any other skin stimulation that would interrupt these 5 minutes. But: THEY HAVE DONE IT.
« The present study compared the effect of 5 min of CT optimal velocity stroking touch to 5 min of static touch on the heart-rate and oxygen saturation levels of preterm infants between 28- & 37-weeks gestational age. CT touch produced a significant decrease in infants’ heart-rates and increase in their blood oxygenation levels, which sustained throughout a 5-min post-touch period. In contrast, there was no significant change in heart-rate or blood oxygenation levels of infants receiving static touch»
It's beautiful! « We already knew that,» some therapists would say. But there is nothing like a good scientific measure to give value to our hypotheses.
They are the first to do so systematically. There are other studies where pauses between stimuli are observed « to reset the counters » or to return to baseline data. But here, it is voluntarily; it is to see if a stimulation was going to be prolonged in time. And YES, it extends over time!
I would like to believe that Mr. Cerritelli was « influenced » by my thesis that he read in 2009 and that has since become a book: « The Therapeutic Pause in Osteopathy and Manual Therapy, the Somatosensory Integration Time » published by Handsping Publishing. To be totally honest with you, I should say « I sincerely believe » that he remembers it and has found a wonderful way to introduce it into the scientific community.
Montréal, le 20 septembre 2019
This document carries this number: ISBN 978-2-924352-16-8 and was sent to the Archives Nationales du Canada on Septembre 20, 2019 by Les Éditions Louise Tremblay
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