Reduced C-afferent fibre density affects perceived pleasantness and empathy for touch.

@article{Morrison2011ReducedCF,
  title={Reduced C-afferent fibre density affects perceived pleasantness and empathy for touch.},
  author={India Morrison and Line S. L{\"o}ken and Jan Minde and Johan Wessberg and Irene Perini and Inger Nennesmo and H{\aa}kan Olausson},
  journal={Brain : a journal of neurology},
  year={2011},
  volume={134 Pt 4},
  pages={
          1116-26
        }
}
We examined patients with a heritable disorder associated with a mutation affecting the nerve growth factor beta gene. Their condition has been classified as hereditary sensory and autonomic neuropathy type V. Carriers of the mutation show a reduction in density of thin and unmyelinated nerve fibres, including C afferents. A distinct type of unmyelinated, low-threshold mechanoreceptive C fibre, the C-tactile afferent, is present in hairy but not glabrous skin of humans and other mammals. They… 

Figures from this paper

Disturbances in affective touch in hereditary sensory & autonomic neuropathy type III
SMALL DIAMETER CUTANEOUS AFFERENT STIMULATION AND ITS EFFECT ON BEHAVIOR IN HUMANS
TLDR
An understanding of the cerebral and behavioral mechanisms underlying the experience of painful and pleasant somatosensory stimuli in healthy individuals and following thin fiber neuropathy is provided.
The role of the human C-tactile system in affective somatosensation and pain
TLDR
The contribution of CTs to experimental tactile allodynia seems to be a reduced CT mediated hedonic processing and possibly also a loss of their pain inhibitory role, suggesting that restoring normal CT function could be considered when investigating novel therapeutic strategies for neuropathic pain.
Tactile C fibers and their contributions to pleasant sensations and to tactile allodynia
TLDR
It is proposed that the contribution of CT afferents to tactile allodynia is mainly through a loss of their normally pain inhibiting role, suggesting loss of the normally analgesic effect of CT signaling.
Vicarious Responses to Social Touch in Posterior Insular Cortex Are Tuned to Pleasant Caressing Speeds
TLDR
These findings provide direct evidence for a functional relationship between CT signaling and processing in posterior insular cortex, and selective tuning for CT-optimal signals in insula may allow recognition of the hedonic relevance of a merely observed caress.
Hedonic, neural, and autonomic responses to prolonged gentle touch
TLDR
The results demonstrate that long-lasting Stroking is processed in similar areas to shorter-lasting stroking, and that the recruitment of the reward-related orbitofrontal network likely reflects updating of the rewarding network.
Gentle touch perception across the lifespan.
TLDR
It is concluded that the affective, but not the discriminative, aspects of touch are enhanced with increasing age, and the increase of pleasantness of all touch stimuli in late adulthood is discussed in relation to cognitive modulations.
Affective Touch: The Enigmatic Spinal Pathway of the C-Tactile Afferent
TLDR
These novel findings appear to indicate that perceptual judgments about the affective nature of touch pleasantness do not depend on the integrity of the lamina I-spinothalamic tract, and suggest that signaling of emotionally relevant C-tactile mediated touch occurs in an alternative ascending pathway.
C-tactile touch perception in migraineurs – a case-control study
TLDR
The C-tactile function of migraineurs is subclinically altered and repeated C-Tactile stimulation leads to altered habituation but differs from previous work by the direction of the changes.
...
...

References

SHOWING 1-10 OF 54 REFERENCES
Feeling good: on the role of C fiber mediated touch in interoception
TLDR
It is concluded that from the skin through the brain, C touch shares more characteristics with interoceptive modalities than exteroceptive Aβ touch, vision or hearing, and is an integral part of a thin-fiber afferent homeostatic network for the maintenance of physical and social well-being.
Functional role of unmyelinated tactile afferents in human hairy skin: sympathetic response and perceptual localization
TLDR
It is demonstrated that CT stimulation can elicit a sympathetic skin response and the findings support the interpretation that the CT system is well suited to underpin affective rather than discriminative functions of tactile sensations.
Discriminative touch and emotional touch.
TLDR
It seems reasonable to conclude that CT afferents have not been found in the glabrous skin of the hand in spite of numerous electrophysiological explorations of this area, and a fuller understanding of their function awaits.
Empathy for pain and touch in the human somatosensory cortex.
TLDR
Results indicate that the S1 is not only involved in the actual perception of pain and touch but also plays an important role in extracting somatic features from social interactions.
Not 'indifference to pain' but varieties of hereditary sensory and autonomic neuropathy.
Three children, from different kinships, with generalized insensitivity to pain, showed unusual manifestations of congenital, presumably inherited, sensory and autonomic neuropathy. The first child
Transcranial magnetic stimulation highlights the sensorimotor side of empathy for pain
TLDR
This work used transcranial magnetic stimulation to record changes in corticospinal motor representations of hand muscles of individuals observing needles penetrating hands or feet of a human model or noncorporeal objects and found a reduction in amplitude of motor-evoked potentials that was specific to the muscle that subjects observed being pricked.
Somatotopic Organization of Gentle Touch Processing in the Posterior Insular Cortex
TLDR
Substantial similarities of the presently observed insular activation with that described for noxious and cooling stimuli solidify the hypothesized sensory-affective role of the CT system in the maintenance of physical well-being as part of a thin-afferent homeostatic network.
Somatosensory activations during the observation of touch and a case of vision-touch synaesthesia.
TLDR
The results suggest that, in C, the mirror system for touch is overactive, above the threshold for conscious tactile perception.
A mutation in the nerve growth factor beta gene (NGFB) causes loss of pain perception.
TLDR
A mutation in the coding region of the nerve growth-factor beta (NGFB) gene specific for the disease haplotype seems to separate the effects of NGF involved in development of central nervous system functions such as mental abilities, from those involved in peripheral pain pathways.
Unmyelinated afferents constitute a second system coding tactile stimuli of the human hairy skin.
TLDR
It was concluded that human hairy skin is innervated by a system of highly sensitive mechanoreceptive units with unmyelinated afferents akin to the system previously described in other mammals.
...
...