| 1. |
- Ackerley, Rochelle, 1980, et al.
(författare)
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Human C-tactile afferents are tuned to the temperature of a skin-stroking caress
- 2014
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Ingår i: Journal of Neuroscience. - 0270-6474. ; 34:8, s. 2879-2883
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Tidskriftsartikel (refereegranskat)abstract
- Human C-tactile (CT) afferents respond vigorously to gentle skin stroking and have gained attention for their importance in social touch. Pharmacogenetic activation of the mouse CT equivalent has positively reinforcing, anxiolytic effects, suggesting a role in grooming and affiliative behavior. We recorded from single CT axons in human participants, using the technique of microneurography, and stimulated a unit's receptive field using a novel, computer-controlled moving probe, which stroked the skin of the forearm over five velocities (0.3, 1, 3, 10, and 30 cm s-1) at three temperatures (cool, 18°C; neutral, 32°C; warm, 42°C). We show that CTs are unique among mechanoreceptive afferents: they discharged preferentially to slowly moving stimuli at a neutral (typical skin) temperature, rather than at the cooler or warmer stimulus temperatures. In contrast, myelinated hair mechanoreceptive afferents proportionally increased their firing frequency with stroking velocity and showed no temperature modulation. Furthermore, the CT firing frequency correlated with hedonic ratings to the same mechano-thermal stimulus only at the neutral stimulus temperature, where the stimuli were felt as pleasant at higher firing rates. We conclude that CT afferents are tuned to respond to tactile stimuli with the specific characteristics of a gentle caress delivered at typical skin temperature. This provides a peripheral mechanism for signaling pleasant skin-to-skin contact in humans, which promotes interpersonal touch and affiliative behavior. © 2014 the authors.
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| 2. |
- Ackerley, Rochelle, 1980, et al.
(författare)
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Touch perceptions across skin sites: Differences between sensitivity, direction discrimination and pleasantness
- 2014
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Ingår i: Frontiers in Behavioral Neuroscience. - : Frontiers Media SA. - 1662-5153. ; 8:54
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Tidskriftsartikel (refereegranskat)abstract
- Human skin is innervated with different tactile afferents, which are found at varying densities over the body. We investigate how the relationships between tactile pleasantness, sensitivity and discrimination differ across the skin. Tactile pleasantness was assessed by stroking a soft brush over the skin, using five velocities (0.3, 1, 3, 10, 30 cm s-1), known to differentiate hedonic touch, and pleasantness ratings were gained. The ratings velocity-profile is known to correlate with firing in unmyelinated C-tactile (CT) afferents. Tactile sensitivity thresholds were determined using monofilament force detection and the tactile discrimination level was obtained in the direction discrimination of a moving probe; both tasks readily activate myelinated touch receptors. Perceptions were measured over five skin sites: forehead, arm, palm, thigh and shin. The assessment of tactile pleasantness over the skin resulted in a preference for the middle velocities (1-10 cm s-1), where higher ratings were gained compared to the slowest and fastest velocities. This preference in tactile pleasantness was found across all the skin sites, apart from at the palm, where no decrease in pleasantness for the faster stroking velocities was seen. We find that tactile sensitivity and discrimination vary across the skin, where the forehead and palm show increased acuity. Tactile sensitivity and discrimination levels also correlated significantly, although the tactile acuity did not relate to the perceived pleasantness of touch. Tactile pleasantness varied in a subtle way across skin sites, where the middle velocities were always rated as the most pleasant, but the ratings at hairy skin sites were more receptive to changes in stroking velocity. We postulate that although the mechanoreceptive afferent physiology may be different over the skin, the perception of pleasant touch can be interpreted using all of the available incoming somatosensory information in combination with central processing. © 2014 Ackerley, Carlsson, Wester, Olausson and Backlund Wasling.
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| 3. |
- Björnsdotter, Malin, et al.
(författare)
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Development of brain mechanisms for processing affective touch
- 2014
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Ingår i: Frontiers in Behavioral Neuroscience. - Lausanne, Switzerland : Frontiers Media SA. - 1662-5153. ; 8:FEB
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Tidskriftsartikel (refereegranskat)abstract
- Affective tactile stimulation plays a key role in the maturation of neural circuits, but the development of brain mechanisms processing touch is poorly understood. We therefore used functional magnetic resonance imaging (fMRI) to study brain responses to soft brush stroking of both glabrous (palm) and hairy (forearm) skin in healthy children (5-13 years), adolescents (14-17 years), and adults (25-35 years). Adult-defined regions-of-interests in the primary somatosensory cortex (SI), secondary somatosensory cortex (SII), insular cortex and right posterior superior temporal sulcus (pSTS) were significantly and similarly activated in all age groups. Whole-brain analyses revealed that responses in the ipsilateral SII were positively correlated with age in both genders, and that responses in bilateral regions near the pSTS correlated significantly and strongly with age in females but not in males. These results suggest that brain mechanisms associated with both sensory-discriminative and affective-motivational aspects of touch are largely established in school-aged children, and that there is a general continuing maturation of SII and a female-specific increase in pSTS sensitivity with age. Our work establishes a groundwork for future comparative studies of tactile processing in developmental disorders characterized by disrupted social perception such as autism. © 2014 Björnsdotter, Gordon, Pelphrey, Olausson and Kaiser.
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| 4. |
- Condon, M., et al.
(författare)
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Differential sensitivity to surface compliance by tactile afferents in the human finger pad
- 2014
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Ingår i: Journal of Neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 111:6, s. 1308-1317
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Tidskriftsartikel (refereegranskat)abstract
- We undertook a neurophysiological investigation of the responses of low-threshold mechanoreceptors in the human finger pad to surfaces of differing softness. Unitary recordings were made from 26 slowly adapting type I (SAI), 17 fast-adapting type I (FAI), and 9 slowly adapting type II (SAII) afferents via tungsten microelectrodes inserted into the median nerve at the wrist. A servo-controlled stimulator applied ramp-and-hold forces (1, 2, 4 N) at a constant loading and unloading rate (2 N/s) via a flat silicone disc over the center of the finger pad. Nine discs were used, which linearly increased in stiffness across the range. Population responses of the SAI afferents showed the greatest sensitivity to compliance, with a steep monotonic increase in mean firing rate with increasing stiffness (decreasing compliance) of the surface during the loading and plateau (but not unloading) phases. FAI afferents also showed a linear increase in firing during the loading but not unloading phase, although the slope was significantly lower than that of the SAI afferents at all amplitudes. Conversely, SAII afferents were influenced by object compliance only in certain conditions. Given their high density in the finger pads and their linear relationship between firing rate and object compliance during the loading and plateau phases, SAI afferents (together with FAI afferents during the loading phase) are ideally suited to contributing information on surface compliance to the overall estimation of softness, but the SAII afferents appear to play only a minor role.
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| 5. |
- Croy, Ilona, et al.
(författare)
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Reduced Pleasant Touch Appraisal in the Presence of a Disgusting Odor
- 2014
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Ingår i: Plos One. - : Public Library of Science (PLoS). - 1932-6203. ; 9:3
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Tidskriftsartikel (refereegranskat)abstract
- Objectives: Odors are powerful emotional stimuli influencing mood, attention and behavior. Here we examined if odors change the perception of pleasant touch. In line with the warning function of the olfactory system, we proposed that especially unpleasant odors will reduce touch pleasantness, presumably through a disgust-related mechanism. Methods: Forty-five healthy participants (mean age 23.3 +/- 3years SD, 24 females) were presented to slow (3 cm/s) and fast (30 cm/s) brush stroking delivered by a robot to the forearm. Touch pleasantness under the influence of an unpleasant odor (Civette, smelling like feces) and an intensity matched pleasant odor (Rose) was compared to an odorless control condition. In a pilot study with 30 participants (mean age 25.9 +/-6 years, 21 females), the odors were matched according to their intensity, and we studied the influence of disgust sensitivity on the perception of 4 different odor qualities. Results: The unpleasant odor decreased touch pleasantness for both stroking velocities compared to the odorless control (p<0.005) whereas the rose odor did not change touch pleasantness significantly. Disgust sensitivity was correlated with the modulation of touch pleasantness. The pilot study revealed a significant correlation between disgust sensitivity and the perception of the unpleasant odor qualities (r = -0.56; p = 0.007), but not with any of the other odors. Conclusion: Unpleasant odors are powerful in modulating touch pleasantness, and disgust might be a moderating variable.
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| 6. |
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| 7. |
- Ellingsen, Dan-Mikael, 1985, et al.
(författare)
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In touch with your emotions: Oxytocin and touch change social impressions while others' facial expressions can alter touch
- 2014
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Ingår i: Psychoneuroendocrinology. - : Elsevier BV. - 0306-4530. ; 39, s. 11-20
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Tidskriftsartikel (refereegranskat)abstract
- Interpersonal touch is frequently used for communicating emotions, strengthen social bonds and to give others pleasure. The neuropeptide oxytocin increases social interest, improves recognition of others' emotions, and it is released during touch. Here, we investigated how oxytocin and gentle human touch affect social impressions of others, and vice versa, how others' facial expressions and oxytocin affect touch experience. In a placebo-controlled crossover study using intranasal oxytocin, 40 healthy volunteers viewed faces with different facial expressions along with concomitant gentle human touch or control machine touch, while pupil diameter was monitored. After each stimulus pair, participants rated the perceived friendliness and attractiveness of the faces, perceived facial expression, or pleasantness and intensity of the touch. After intranasal oxytocin treatment, gentle human touch had a sharpening effect on social evaluations of others relative to machine touch, such that frowning faces were rated as less friendly and attractive, whereas smiling faces were rated as more friendly and attractive. Conversely, smiling faces increased, whereas frowning faces reduced, pleasantness of concomitant touch the latter effect being stronger for human touch. Oxytocin did not alter touch pleasantness. Pupillary responses, a measure of attentional allocation, were larger to human touch than to equally intense machine touch, especially when paired with a smiling face. Overall, our results point to mechanisms important for human affiliation and social bond formation. (C) 2013 Elsevier Ltd. All rights reserved.
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| 8. |
- Liljencrantz, Jaquette, et al.
(författare)
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Discriminative and affective touch in human experimental tactile allodynia
- 2014
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Ingår i: Neuroscience Letters. - : Elsevier BV. - 0304-3940. ; 563, s. 75-79
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Tidskriftsartikel (refereegranskat)abstract
- Recently, several studies have suggested a role for unmyelinated (C-tactile, CT) low-threshold mechanoreceptive afferents in the allodynic condition. In this psychophysical study we explored the integrity of both Aβ and CT afferent processing following application of the heat capsaicin model of tactile allodynia on the left forearm in healthy subjects (n= 40). We measured tactile direction discrimination (TDD) to target the integrity of Aβ processing (n= 20). The TDD accuracy was significantly lower in the allodynic compared to a control zone. In addition, we measured the perceived pleasantness and pain of brush stroking at CT targeted (slow) and CT sub-optimal (fast) stroking velocities to investigate the integrity of CT processing (n= 20). When comparing touch pleasantness in the allodynic and control zone, there was a significantly larger difference in ratings for CT targeted compared to CT suboptimal stimulation. The results suggest a disturbance in both Aβ-mediated discriminative and CT-mediated affective touch processing in human experimental tactile allodynia. Our findings support the canonical view that tactile allodynia is signaled by Aβ afferents but that CTs seem to contribute by the loss of a pain inhibiting role. © 2014 Elsevier Ireland Ltd.
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| 9. |
- Liljencrantz, Jaquette, et al.
(författare)
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Tactile C fibers and their contributions to pleasant sensations and to tactile allodynia
- 2014
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Ingår i: Frontiers in Behavioral Neuroscience. - : Frontiers Media SA. - 1662-5153. ; 8
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Forskningsöversikt (refereegranskat)abstract
- In humans converging evidence indicates that affective aspects of touch are signaled by low threshold mechanoreceptive C tactile (CT) afferents. Analyses of electrophysiological recordings, psychophysical studies in denervated subjects, and functional brain imaging, all indicate that CT primary afferents contribute to pleasant touch and provide an important sensory underpinning of social behavior. Considering both these pleasant and social aspects of gentle skin-to-skin contact, we have put forward a framework within which to consider CT afferent coding properties and pathways-the CT affective touch hypothesis. Recent evidence from studies in mice suggest that CTs, when activated, may have analgesic or anxiolytic effects. However, in neuropathic pain conditions, light touch can elicit unpleasant sensations, so called tactile allodynia. In humans, tactile allodynia is associated with reduced CT mediated hedonic touch processing suggesting loss of the normally analgesic effect of CT signaling. We thus propose that the contribution of CT afferents to tactile allodynia is mainly through a loss of their normally pain inhibiting role.
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| 10. |
- McGlone, Francis, et al.
(författare)
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Discriminative and Affective Touch: Sensing and Feeling.
- 2014
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Ingår i: Neuron. - : Elsevier BV. - 1097-4199 .- 0896-6273. ; 82:4, s. 737-755
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Forskningsöversikt (refereegranskat)abstract
- The multimodal properties of the human somatosensory system continue to be unravelled. There is mounting evidence that one of these submodalities-touch-has another dimension, providing not only its well-recognized discriminative input to the brain, but also an affective input. It has long been recognized that touch plays an important role in many forms of social communication and a number of theories have been proposed to explain observations and beliefs about the "power of touch." Here, we propose that a class of low-threshold mechanosensitive C fibers that innervate the hairy skin represent the neurobiological substrate for the affective and rewarding properties of touch.
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