| 1. |
- Björnsdotter, Malin, et al.
(author)
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Somatotopic organization of gentle touch processing in the posterior insular cortex.
- 2009
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In: The Journal of neuroscience : the official journal of the Society for Neuroscience. - Washington, DC, United States : Society for Neuroscience. - 1529-2401 .- 0270-6474. ; 29:29, s. 9314-20
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Journal article (peer-reviewed)abstract
- A network of thin (C and A delta) afferents relays various signals related to the physiological condition of the body, including sensations of gentle touch, pain, and temperature changes. Such afferents project to the insular cortex, where a somatotopic organization of responses to noxious and cooling stimuli was recently observed. To explore the possibility of a corresponding body-map topography in relation to gentle touch mediated through C tactile (CT) fibers, we applied soft brush stimuli to the right forearm and thigh of a patient (GL) lacking A beta afferents, and six healthy subjects during functional magnetic resonance imaging (fMRI). For improved fMRI analysis, we used a highly sensitive multivariate voxel clustering approach. A somatotopic organization of the left (contralateral) posterior insular cortex was consistently demonstrated in all subjects, including GL, with forearm projecting anterior to thigh stimulation. Also, despite denying any sense of touch in daily life, GL correctly localized 97% of the stimuli to the forearm or thigh in a forced-choice paradigm. The consistency in activation patterns across GL and the healthy subjects suggests that the identified organization reflects the central projection of CT fibers. Moreover, 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.
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| 2. |
- Löken, Line Sofie, 1977
(author)
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A pathway for pleasant touch: linking peripheral receptors to central processing and hedonic experience
- 2009
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Doctoral thesis (other academic/artistic)abstract
- This thesis investigates the mechanisms underpinning pleasant touch, describes a pathway from peripheral nerve endings in the skin to the insular cortex, and relates these findings to the subjective hedonic experience of touch. In Paper I, the relationship between primary afferent encoding and perception of pleasantness was investigated by combining microneurography recordings from human mechanoreceptors with psychophysical measurements during soft brush stroking at 6 different velocities between 0.1–30 cm/s. Results showed that low-threshold unmyelinated fibers (C tactile, CT), but not myelinated afferents, responded most vigorously to intermediate brushing velocities (1–10 cm/s), which were perceived by subjects as being the most pleasant. In Paper II, a group of patients with reduced C fiber density due to a rare inheritable disorder (hereditary sensory and autonomic neuropathy type V, HSAN-V), provided the opportunity to address how pleasantness is perceived when the number of CT afferents is reduced. In comparison with healthy control subjects the C fiber denervated patients displayed atypical pleasantness ratings for soft brush stroking across different brushing velocities. These results suggest that conventional pleasant touch is dependent on CT fiber density. CT afferents are lacking in glabrous skin which suggests that pleasant touch is perceived differently in the palm compared to the forearm. In Paper III, three different experiments were performed on three different groups of experimentally naive, healthy subjects. In experiment 1, a series of brush strokes was first applied to the palm followed by a series of brush strokes on the arm; in experiment 2, this order was reversed. In experiment 3, brush strokes were applied to the palm and arm in an alternating fashion. In experiment 1 subjects rated gentle stroking as less pleasant on the palm compared to the arm. In experiments 2 and 3, similar ratings were seen for the palm and arm. These results suggest that the perception of pleasantness on the palm is affected by previous stimulation of the arm, but not vice versa. It was speculated that assessment of pleasant touch may be influenced by affective reactions elicited through activation of the CT afferent pathway. Paper IV investigated whether CT afferents project to the cortex in a somatotopic fashion. In order to distinguish between cortical activations evoked by myelinated (Aβ) fibers and those specifically related to CT afferents six healthy subjects were compared to a unique patient (GL), who lacks Aβ afferents. Soft brush stimulation was applied to the participants’ arm and thigh during functional magnetic resonance imaging (fMRI). CT afferents were shown to project somatotopically to the posterior insular cortex in a similar fashion to those previously identified for signalling temperature and pain. In conclusion, this thesis provides an improvement to the understanding of the neural substrates governing pleasant touch. Further knowledge on the mechanisms behind affective touch may be useful for understanding certain psychiatric disorders, such as autism, where gentle touch is perceived as unpleasant.
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| 3. |
- Löken, Line Sofie, 1977, et al.
(author)
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A topographical and physiological exploration of C-tactile afferents and their response to menthol and histamine
- 2022
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In: Journal of Neurophysiology. - : AMER PHYSIOLOGICAL SOC. - 0022-3077 .- 1522-1598. ; 127:2, s. 463-473
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Journal article (peer-reviewed)abstract
- Unmyelinated tactile (C-tactile or CT) afferents are abundant in arm hairy skin and have been suggested to signal features of soda) affective touch. Here, we recorded from unmyelinated low-threshold mechanosensitive afferents in the peroneal and radial nerves. The most distal receptive fields were located on the proximal phalanx of the third finger for the superficial branch of the radial nerve and near the lateral malleolus for the peroneal nerve. We found that the physiological properties with regard to conduction velocity and mechanical threshold, as well as their tuning to brush velocity, were similar in CT units across the antebrachial (n = 27), radial (n = 8), and peroneal (n = 4) nerves. Moreover, we found that although CT afferents are readily found during microneurography of the arm nerves, they appear to be much more sparse in the lower leg compared with C-nociceptors. We continued to explore CT afferents with regard to their chemical sensitivity and found that they could not be activated by topical application to their receptive field of either the cooling agent menthol or the pruritogen histamine. In light of previous studies showing the combined effects that temperature and mechanical stimuli have on these neurons, these findings add to the growing body of research suggesting that CT afferents constitute a unique class of sensory afferents with highly specialized mechanisms for transducing gentle touch. NEW & NOTEWORHY Unmyelinated tactile (CT) afferents are abundant in arm hairy skin and are thought to signal features of social affective touch. We show that CTs are also present but are relatively sparse in the lower leg compared with C-nociceptors. CTs display similar physiological properties across the arm and leg nerves. Furthermore, CT afferents do not respond to the cooling agent menthol or the pruritogen histamine, and their mechanical response properties are not altered by these chemicals.
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| 4. |
- Löken, Line Sofie, 1977, et al.
(author)
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Coding of pleasant touch by unmyelinated afferents in humans.
- 2009
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In: Nature neuroscience. - : Springer Science and Business Media LLC. - 1546-1726 .- 1097-6256. ; 12:5, s. 547-8
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Journal article (peer-reviewed)abstract
- Pleasant touch sensations may begin with neural coding in the periphery by specific afferents. We found that during soft brush stroking, low-threshold unmyelinated mechanoreceptors (C-tactile), but not myelinated afferents, responded most vigorously at intermediate brushing velocities (1-10 cm s(-1)), which were perceived by subjects as being the most pleasant. Our results indicate that C-tactile afferents constitute a privileged peripheral pathway for pleasant tactile stimulation that is likely to signal affiliative social body contact.
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| 5. |
- Löken, Line Sofie, 1977, et al.
(author)
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Contribution of dorsal horn CGRP-expressing interneurons to mechanical sensitivity
- 2021
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In: Elife. - 2050-084X. ; 10
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Journal article (peer-reviewed)abstract
- Primary sensory neurons are generally considered the only source of dorsal horn calcitonin gene-related peptide (CGRP), a neuropeptide critical to the transmission of pain messages. Using a tamoxifen-inducible CalcaCreER transgenic mouse, here we identified a distinct population of CGRP-expressing excitatory interneurons in lamina III of the spinal cord dorsal horn and trigeminal nucleus caudalis. These interneurons have spine-laden, dorsally directed, dendrites, and ventrally directed axons. As under resting conditions, CGRP interneurons are under tonic inhibitory control, neither innocuous nor noxious stimulation provoked significant Fos expression in these neurons. However, synchronous, electrical non-nociceptive Ab primary afferent stimulation of dorsal roots depolarized the CGRP interneurons, consistent with their receipt of a VGLUT1 innervation. On the other hand, chemogenetic activation of the neurons produced a mechanical hypersensitivity in response to von Frey stimulation, whereas their caspase-mediated ablation led to mechanical hyposensitivity. Finally, after partial peripheral nerve injury, innocuous stimulation (brush) induced significant Fos expression in the CGRP interneurons. These findings suggest that CGRP interneurons become hyperexcitable and contribute either to ascending circuits originating in deep dorsal horn or to the reflex circuits in baseline conditions, but not in the setting of nerve injury.
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| 6. |
- Löken, Line Sofie, 1977, et al.
(author)
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Pleasantness of touch in human glabrous and hairy skin: Order effects on affective ratings
- 2011
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In: Brain Research. - : Elsevier BV. - 0006-8993. ; 1417, s. 9-15
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Journal article (peer-reviewed)abstract
- The tactile sense comprises pathways for both discriminative and affective touch. Low threshold unmyelinated mechanoafferents (C tactile, CT) in the human hairy skin have recently been linked to pleasant touch sensation. Here, we investigated how perception of the hedonic aspect of tactile stimulation differs between the hairy skin of the arm, and the glabrous skin of the palm, which is not innervated by CT afferents. Three groups of naïve, healthy subjects (total n = 28) rated pleasantness on a visual analogue scale (VAS) when we stroked with a soft brush with speeds from 0.1 to 30 cm/s on the palm or forearm. We used two different experimental approaches: in experiments 1 and 2, stimuli were delivered successively on the palm and arm (or arm and palm) in temporally separate sequential blocks. In experiment 3, stimuli were delivered alternately on arm and palm. We found that the order of stimulus presentation, palm/arm or arm/palm, has an effect on pleasantness ratings of gentle brush stroking with varying velocity. Notably, the perception of pleasantness for palm stimulation was affected by previous stimulation of the arm, but not vice versa. Thus, assessment of valence of touch may be influenced by affective reactions elicited by activation of the CT afferent pathway.
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| 7. |
- Löken, Line Sofie, 1977, et al.
(author)
-
Tactile direction discrimination and vibration detection in diabetic neuropathy.
- 2009
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In: Acta neurologica Scandinavica. - : Hindawi Limited. - 1600-0404 .- 0001-6314. ; 121:5, s. 302-308
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Journal article (peer-reviewed)abstract
- Löken LS, Lundblad LC, Elam M, Olausson HW. Tactile direction discrimination and vibration detection in diabetic neuropathy. Acta Neurol Scand: DOI: 10.1111/j.1600-0404.2009.01282.x. (c) 2009 The Authors Journal compilation (c) 2009 Blackwell Munksgaard.Objective - To evaluate the clinical usefulness of quantitative testing of tactile direction discrimination (TDD) in patients with diabetic neuropathy. Materials and methods - TDD and vibration detection were examined on the dorsum of the feet in 43 patients with type 1 diabetes mellitus and clinical signs and symptoms indicating mild neuropathy, and abnormal results for neurography, temperature detection, or heart rate variability. Test-retest examination of TDD was performed in nine of the patients. Results - Twenty-six of the patients had abnormal TDD (sensitivity 0.60) and 20 had abnormal vibration detection (sensitivity 0.46). Ten of the patients had abnormal TDD and normal vibration detection. Four of the patients had abnormal vibration detection and normal TDD. Test-retest examination of TDD showed a high degree of reproducibility (r = 0.87). Conclusion - TDD seems more useful than vibration detection in examination of diabetic neuropathy.
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| 8. |
- McGlone, Francis, et al.
(author)
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Discriminative touch and emotional touch.
- 2007
-
In: Canadian journal of experimental psychology = Revue canadienne de psychologie expérimentale. - : American Psychological Association (APA). - 1196-1961 .- 1878-7290. ; 61:3, s. 173-83
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Research review (peer-reviewed)abstract
- Somatic sensation comprises four main modalities, each relaying tactile, thermal, painful, or pruritic (itch) information to the central nervous system. These input channels can be further classified as subserving a sensory function of spatial and temporal localization, discrimination, and provision of essential information for controlling and guiding exploratory tactile behaviours, and an affective function that is widely recognized as providing the afferent neural input driving the subjective experience of pain, but not so widely recognized as also providing the subjective experience of affiliative or emotional somatic pleasure of touch. The discriminative properties of tactile sensation are mediated by a class of fast-conducting myelinated peripheral nerve fibres--A-beta fibres--whereas the rewarding, emotional properties of touch are hypothesized to be mediated by a class of unmyelinated peripheral nerve fibres--CT afferents (C tactile)--that have biophysical, electrophysiological, neurobiological, and anatomical properties that drive the temporally delayed emotional somatic system. CT afferents have not been found in the glabrous skin of the hand in spite of numerous electrophysiological explorations of this area. Hence, it seems reasonable to conclude that they are lacking in the glabrous skin. A full understanding of the behavioural and affective consequences of the differential innervation of CT afferents awaits a fuller understanding of their function.
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| 9. |
- Middleton, Steven J, et al.
(author)
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Nav1.7 is required for normal C-low threshold mechanoreceptor function in humans and mice.
- 2022
-
In: Brain : a journal of neurology. - : Oxford University Press (OUP). - 1460-2156 .- 0006-8950. ; 145:10, s. 3637-3653
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Journal article (peer-reviewed)abstract
- Patients with bi-allelic loss of function mutations in the voltage-gated sodium channel Nav1.7 present with congenital insensitivity to pain (CIP), whilst low threshold mechanosensation is reportedly normal. Using psychophysics (n = 6 CIP participants and n = 86 healthy controls) and facial EMG (n = 3 CIP participants and n = 8 healthy controls) we have found that these patients also have abnormalities in the encoding of affective touch which is mediated by the specialised afferents; C-low threshold mechanoreceptors (C-LTMRs). In the mouse we found that C-LTMRs express high levels of Nav1.7. Genetic loss or selective pharmacological inhibition of Nav1.7 in C-LTMRs resulted in a significant reduction in the total sodium current density, an increased mechanical threshold and reduced sensitivity to non-noxious cooling. The behavioural consequence of loss of Nav1.7 in C-LTMRs in mice was an elevation in the von Frey mechanical threshold and less sensitivity to cooling on a thermal gradient. Nav1.7 is therefore not only essential for normal pain perception but also for normal C-LTMR function, cool sensitivity and affective touch.
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| 10. |
- Morrison, India, 1972, et al.
(author)
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Reduced C-afferent fibre density affects perceived pleasantness and empathy for touch.
- 2011
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In: Brain : a journal of neurology. - : Oxford University Press (OUP). - 1460-2156. ; 134:Pt 4, s. 1116-26
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Journal article (peer-reviewed)abstract
- 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 have been implicated in the coding of pleasant, hedonic touch of the kind that occurs in affiliative social interactions. We addressed the relationship between C fibre function and pleasant touch perception in 10 individuals from a unique population of mutation carriers in Sweden. We also investigated the effect of reduced C-fibre density on patients' evaluation of observed interpersonal touch (empathy). Results showed that patients perceived gentle, slow arm stroking, optimal for eliciting C-tactile afferent responses (1-10 cm/s), as less pleasant than did matched controls and also differed in their rating patterns across stimulation velocities. Further, patients' blood-oxygen-level-dependent responses in posterior insular cortex--a target for C afferents--were not modulated by stimulation optimal for activating C-tactile afferents. Hence, perception of the hedonic aspect of dynamic touch likely depends on C-tactile afferent density. Closely similar patterns between individuals' ratings of felt and seen touch suggest that appraisal of others' touch is anchored in one's own perceptual experience, whether typical or atypical.
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| 11. |
- Morrison, India, 1972, et al.
(author)
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The skin as a social organ.
- 2010
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In: Experimental brain research. Experimentelle Hirnforschung. Experimentation cerebrale. - : Springer Science and Business Media LLC. - 1432-1106. ; 204:3, s. 305-14
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Research review (peer-reviewed)abstract
- In general, social neuroscience research tends to focus on visual and auditory channels as routes for social information. However, because the skin is the site of events and processes crucial to the way we think about, feel about, and interact with one another, touch can mediate social perceptions in various ways. This review situates cutaneous perception within a social neuroscience framework by discussing evidence for considering touch (and to some extent pain) as a channel for social information. Social information conveys features of individuals or their interactions that have potential bearing on future interactions, and attendant mental and emotional states. Here, we discuss evidence for an affective dimension of touch and explore its wider implications for the exchange of social information. We consider three important roles for this affective dimension of the cutaneous senses in the transmission and processing of social information: first, through affiliative behavior and communication; second, via affective processing in skin-brain pathways; and third, as a basis for intersubjective representation.
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| 12. |
- Vallbo, Åke, 1933, et al.
(author)
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Sensual touch: A slow touch system revealed with microneurography
- 2016
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In: Affective touch and the neurophysiology of CT afferents. Olausson, H., Wessberg, J., Morrison, I., McGlone, F. (Eds.). - New York : Springer. - 9781493964161 ; , s. 1-30
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Book chapter (peer-reviewed)
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| 13. |
- Wasling, Helena Backlund, 1972, et al.
(author)
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Cortical processing of lateral skin stretch stimulation in humans.
- 2008
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In: Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale. - : Springer Science and Business Media LLC. - 1432-1106. ; 190:2, s. 117-24
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Journal article (peer-reviewed)abstract
- Direction discrimination of a moving tactile stimulus requires intact dorsal columns and provides a sensitive clinical test of somatosensory dysfunction. Cortical mechanisms are poorly understood. We have applied tangential skin pulls to the right lower leg during functional magnetic resonance imaging. Healthy subjects judged the direction of the skin pulls (task experiment, n = 7) or received skin pulls passively (no task experiment, n = 8). Second somatosensory cortex (S2) was activated in the task as well as no task experiment, and there was no significant difference in cortical activation between the two experiments. Within S2 nearly all subjects had prominent activations in the caudal and superficial part, i.e., in the opercular parietal (OP) area 1. S1 was activated in only one of the subjects. Thus, S2 and especially OP 1 seems to be important for processing of lateral skin stretch stimulation. The finding suggests that a lesion of this area might cause a disturbance in tactile direction discrimination which should be relevant for clinical testing.
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| 14. |
- Watkins, Roger H., 1988, et al.
(author)
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Evidence for sparse C-tactile afferent innervation of glabrous human hand skin
- 2021
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In: Journal of neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 125:1, s. 232-237
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Journal article (peer-reviewed)abstract
- C-tactile (CT) afferents were long-believed to be lacking in humans, but these were subsequently shown to densely innervate the face and arm skin, and to a lesser extent the leg. Their firing frequency to stroking touch at different velocities has been correlated with ratings of tactile pleasantness. CT afferents were thought to be absent in human glabrous skin; however, tactile pleasantness can be perceived across the whole body, including glabrous hand skin. We used microneurography to investigate mechanoreceptive afferents in the glabrous skin of the human hand, during median and radial nerve recordings. We describe CTs found in the glabrous skin, with characteristics comparable with those in hairy arm skin, and detail recordings from three such afferents. CTs were infrequently encountered in the glabrous skin and we estimate that the ratio of recorded CTs relative to myelinated mechanoreceptors (1:80) corresponds to an absolute innervation density of around seven times lower than in hairy skin. This sparse innervation sheds light on discrepancies between psychophysical findings of touch perception on glabrous skin and hairy skin, although the role of these CT afferents in the glabrous skin remains subject to future work. NEW & NOTEWORTHY Human touch is encoded by low-threshold mechanoreceptors, including myelinated A beta afferents and unmyelinated C-tactile (CT) afferents. CTs are abundant in hairy skin and are thought to code gentle, stroking touch that signals positive affective interactions. CTs have never been described in human glabrous skin, yet we show evidence of their existence on the hand, albeit at a relatively low density. Glabrous skin CTs may provide modulatory reinforcement of gentle tactile interactions during touch using the hands.
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| 15. |
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