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Tactile perception encompasses several submodalities that are realized with distinct sensory subsystems. The processing of those submodalities and their interactions remains understudied. We developed a paradigm consisting of three types of touch tuned in terms of their force and velocity for different submodalities: discriminative touch (haptics), affective touch (C-tactile touch), and knismesis (alerting tickle). Touch was delivered with a high-precision robotic rotary touch stimulation device. A total of 39 healthy individuals participated in the study. EEG cluster analysis revealed a decrease in alpha and beta range (mu-rhythm) as well as theta and delta increase most pronounced to the most salient and fastest type of stimulation. The participants confirmed that slower stimuli targeted to affective touch low-threshold receptors were the most pleasant ones, and less intense stimuli aimed at knismesis were indeed the most ticklish ones, but those sensations did not form an EEG cluster, probably implying their processing involves deeper brain structures that are less accessible with EEG.

Studies over the last 25 years have convincingly demonstrated that humans have several independent cutaneous mechanoreception systems. Best studied is the discriminative touch system, which combines cutaneous mechanoreceptors innervated by fast myelinated afferent type Aβ fibers and provides detailed information on the site of contact and nature of the stimulus. The affective C-tactile system was discovered relatively recently and provides unconditioned positive emotions in response to slow, gentle touching. The dynamics of the electrical response of the cortex to afferents from the C-tactile system have received almost no study, while existing data are insufficient to distinguish the components of the brain response associated with the activity of the Aβ- and C-tactile systems. This pilot study analyzed EEG event-related potentials in response to fast (30 cm/sec) and slow (5 cm/sec) stroking, applied using a robot device. A total of 13 adult subjects took part in the study. The first ERP components in the response to stroking were seen during the time interval 400–1800 msec in the lateral frontal and central leads; their amplitude was greater for fast stroking, indicating their association with activity in the Aβ system. A P2100–N2300 complex was seen only for slow stroking and was probably linked with the reaction of the Aβ system to termination of stimulation; it was accompanied by an ultra-late positive potential presumptively associated with the response of the C-tactile system. The results confirm the existent of the ultra-late positive potential identified in previous studies for slow stroking and allow this potential to be differentiated from other late components of the response. [ABSTRACT FROM AUTHOR]

Small fiber neuropathy (SFN) is a common and debilitating disease in which the terminals of small diameter sensory axons degenerate, producing sensory loss, and in many patients neuropathic pain. While a substantial number of cases are attributable to diabetes, almost 50% are idiopathic. An underappreciated aspect of the disease is its late onset in most patients. Animal models of human genetic mutations that produce SFN also display age-dependent phenotypes suggesting that aging is an important contributor to the risk of development of the disease. In this review we define how particular sensory neurons are affected in SFN and discuss how aging may drive the disease. We also evaluate how animal models of SFN can define disease mechanisms that will provide insight into early risk detection and suggest novel therapeutic interventions. [Display omitted] [ABSTRACT FROM AUTHOR]

• The effect of affective habituation to touch was stable in two separate sessions on group level. • On individual level, only 43% of the participants presented a decrease of pleasantness ratings. • A discrepancy between group and individual level analysis of hedonic touch is shown. • Individual courses of pleasantness were not stable across sessions. • The individual pleasantness ratings could not be explained by physiological or behavioural data. Slow stroking touch activates C-tactile (CT) fibres in the human skin and is typically described as pleasant. Over a longer duration of stroking, affective habituation sets in, indicated by a reduction in rated pleasantness. However, it is not clear whether the group level effect is represented on an individual level. We analyse the stability of individual ratings of slow stroking touch and their relationship to behavioural and physiological measures. Forty-eight participants (23 women) were repeatedly stroked with a velocity maximally activating CT fibres. The perceived pleasantness was rated on a visual analogue scale. In order to examine the stability of pleasantness ratings, the experiment was repeated after a couple of days. During the experiment, electrocardiogram (ECG) and facial-electromyography (EMG) data were recorded. On the group-level, previous results of affective habituation to touch were replicated and stable across sessions. On the individual level, however, less than half of the participants showed a significant reduction of pleasantness in the course of the experiment. Moreover, the remaining participants showed either no change, random rating behaviour or even an increase in pleasantness ratings during the course of the experiment. The individual response patterns were variable across sessions but stable above the chance level. Furthermore, the response patterns could not be explicitly associated with any of the behavioural or physiological measures. Our findings indicate a lack of group-to-individual generalizability for affective habituation to touch. The variability of rating patterns over time indicates that they are not conclusively determined by stable individual characteristics. Future research investigating touch should favour a more individual approach to the more commonly applied group analysis. [ABSTRACT FROM AUTHOR]

Affective touch plays an important role in human social bonding, affiliative behavior, and in general emotional well-being. A system of unmyelinated low-threshold mechanosensitive C-type afferents innervating hairy skin (C-tactile or CT system) is postulated to provide the neurophysiological background of affective touch perception. C-tactile afferents respond optimally to soft and slow strokes, and this response correlates positively with pleasure ratings of tactile stimuli. As gentle touch is consistently associated with oxytocin release further promoting prosocial behavior, it has been suggested that this effect is mediated by the response of C-tactile afferents. This study assesses a possible link between CT-optimal touch, its subjective pleasantness, EEG indices of cortical arousal, and peripheral oxytocin response. EEG was recorded in 28 healthy volunteers during resting state and tactile stimulation[gentle slow brush strokes on forearm (CT-targeted touch) and palm (non-CT-targeted touch)]. Saliva samples were collected before and after the touch stimulation. Oxytocin concentration increase was significantly associated with greater subjective ratings of CT-targeted touch but not of non-CT-targeted touch, and with lower peak alpha frequency values indicating decreased cortical arousal. The findings suggest that CT-targeted stimulation triggers oxytocin release but only when the touch is perceived at an individual level as having clearly positive affective salience. This corresponds to previous studies reporting that oxytocin response to touch can be related to different personality factors, and bears important implications for planning touch-based interventions in social and medical care. [ABSTRACT FROM AUTHOR]

• The presence of a sex asymmetry in the tactile domain has been previously supported. • A meta-analysis is used to quantify sex differences in affective touch perception. • The size of the association does not vary as a function of the examined moderators. • Results are not influenced by publication bias. • Results show that women perceive affective touch as more pleasant than men. The unmyelinated C-tactile afferents system holds a hedonic function in touch experiences, shaping social functioning in the so-called affective touch hypothesis. Despite the fact that females are recognized as more sensitive to discriminative aspects of touch and respond more positively to touch than men, sex differences in the perception of affective touch have not been extensively investigated. We aimed to fill this gap by meta-analyzing existing studies on this topic. Thirteen studies were eligible and pooled effect sizes (Hedges' g) were compared. Random effect models were used. Results, which are not influenced by publication bias, show that there is a sex asymmetry in the pleasantness perceived during an affective tactile stimulation, with females showing higher pleasantness ratings than males. The size of the association does not vary as a function of sex distribution, age and methodological quality. Hormonal as well as evolutionary differences related to the caregiving and nurturing function of females may explain sex differences in affective touch. Results are limited by the small number of studies included in the meta-analysis. [ABSTRACT FROM AUTHOR]

Tactile perception encompasses several submodalities that are realized with distinct sensory subsystems. The processing of those submodalities and their interactions remains understudied. We developed a paradigm consisting of three types of touch tuned in terms of their force and velocity for different submodalities: discriminative touch (haptics), affective touch (C-tactile touch), and knismesis (alerting tickle). Touch was delivered with a high-precision robotic rotary touch stimulation device. A total of 39 healthy individuals participated in the study. EEG cluster analysis revealed a decrease in alpha and beta range (mu-rhythm) as well as theta and delta increase most pronounced to the most salient and fastest type of stimulation. The participants confirmed that slower stimuli targeted to affective touch low-threshold receptors were the most pleasant ones, and less intense stimuli aimed at knismesis were indeed the most ticklish ones, but those sensations did not form an EEG cluster, probably implying their processing involves deeper brain structures that are less accessible with EEG. [ABSTRACT FROM AUTHOR]

The building of physiological self-regulation during bonding is a crucial developmental process based on early cardio-respiratory maturation. The mother’s role as a facilitator of this physiological maturation has been evidenced and recognized in many respects. Research in fathers, however, remains sparse which may be due to the belief that bonding is a physiological behavior reserved for a mother’s maternal instinct. In the current study we compared the impact of paternal and maternal nurturing stroking touch on infants’ physiological self-regulation in terms of respiratory sinus arrhythmia (RSA). We compared the impact of a 3-min stroking period (STROKING) with a pre-baseline (PRE-STROKING) and post-baseline (POST-STROKING) of 25 mothers and 25 fathers (unrelated to one another) on their infants, aged 4–16 weeks. We registered infant electrocardiogram (ECG) and respiration to calculate infant RR-interval (RRI), respiration rate (fR) and (respiratory corrected) RSA (RSAcorr). Based on video-recordings, we analyzed the stroking speed. Infants’ RSAcorr significantly increased during and after stroking, no matter whether touch was delivered by fathers or mothers. This effect was mediated by both heart rate (HR) and respiration. However, respiratory mediation occurred later when delivered by fathers than by mothers. Both mothers’ and fathers’ stroking speed occurred within the optimal stimulation range of c-tactile (CT) afferents, a particular class of cutaneous unmyelinated, low-threshold mechano-sensitive nerves hypothesized to be involved in inter-personal bonding. The discussion builds on the idea to mitigate fathers’ doubts about their paternal capabilities and proposes a research agenda regarding the further examination of the role of nurturing touch and its underlying mechanisms within the development of infants’ physiological self-regulation. Finally, the importance of respiratory measurements in infant physiological research is emphasized.

Conflicting evidence points to the contribution of several key nodes of the 'social brain' to the processing of both discriminatory and affective qualities of interpersonal touch. Whether the primary somatosensory cortex (S1) and the medial prefrontal cortex (mPFC), two brain areas vital for tactile mirroring and affective mentalizing, play a functional role in shared representations of C-tactile (CT) targeted affective touch is still a matter of debate. Here, we used offline continuous theta-burst transcranial magnetic stimulation (cTBS) to mPFC, S1 and vertex (control) prior to participants providing ratings of vicarious touch pleasantness for self and others delivered across several body sites at CT-targeted velocities. We found that S1-cTBS led to a significant increase in touch ratings to the self, with this effect being positively associated to levels of interoceptive awareness. Conversely, mPFC-cTBS reduced pleasantness ratings for touch to another person. These effects were not specific for CT-optimal (slow) stroking velocities, but rather they applied to all types of social touch. Overall, our findings challenge the causal role of the S1 and mPFC in vicarious affective touch and suggest that self- vs other-directed vicarious touch responses might crucially depend on the specific involvement of key social networks in gentle tactile interactions., (© The Author(s) 2023. Published by Oxford University Press.)

The building of physiological self-regulation during bonding is a crucial developmental process based on early cardio-respiratory maturation. The mother's role as a facilitator of this physiological maturation has been evidenced and recognized in many respects. Research in fathers, however, remains sparse which may be due to the belief that bonding is a physiological behavior reserved for a mother's maternal instinct. In the current study we compared the impact of paternal and maternal nurturing stroking touch on infants' physiological self-regulation in terms of respiratory sinus arrhythmia (RSA). We compared the impact of a 3-min stroking period (STROKING) with a pre-baseline (PRE-STROKING) and post-baseline (POST-STROKING) of 25 mothers and 25 fathers (unrelated to one another) on their infants, aged 4–16 weeks. We registered infant electrocardiogram (ECG) and respiration to calculate infant RR-interval (RRI), respiration rate (f R) and (respiratory corrected) RSA (RSA corr). Based on video-recordings, we analyzed the stroking speed. Infants' RSA corr significantly increased during and after stroking, no matter whether touch was delivered by fathers or mothers. This effect was mediated by both heart rate (HR) and respiration. However, respiratory mediation occurred later when delivered by fathers than by mothers. Both mothers' and fathers' stroking speed occurred within the optimal stimulation range of c-tactile (CT) afferents, a particular class of cutaneous unmyelinated, low-threshold mechano-sensitive nerves hypothesized to be involved in inter-personal bonding. The discussion builds on the idea to mitigate fathers' doubts about their paternal capabilities and proposes a research agenda regarding the further examination of the role of nurturing touch and its underlying mechanisms within the development of infants' physiological self-regulation. Finally, the importance of respiratory measurements in infant physiological research is emphasized. [ABSTRACT FROM AUTHOR]

The beneficial effects of touch in development were already observed in different types of skin-to-skin care. In the current study, we aimed at studying potential underlying mechanisms of these effects in terms of parasympatho-inhibitory regulation. We examined the specific impact of affective maternal stroking versus non-stroking touch on the cardio-respiration of both mothers and infants in terms of respiratory sinus arrhythmia (RSA). We compared a 3-min TOUCH PERIOD (stroking or non-stroking touch) with a baseline before (PRE-TOUCH) and after (POST-TOUCH) in 45 dyads (24 stroking/21 non-stroking touch) with infants aged 4–16 weeks. We registered mother-infant ECG, respiration and made video-recordings. We calculated RR-interval (RRI), respiration rate (f R) and (respiratory corrected) RSA and analyzed stroking mean velocity rate (MVR) of the mothers. ANOVA-tests showed a significant different impact on infants' respiratory corrected RSA of stroking touch (increase) versus non-stroking touch (decrease). Further, during and after stroking touch, RRI significantly increased whereas f R significantly decreased. Non-stroking touch had no significant impact on infants' RRI and f R. In the mothers, RRI significantly decreased and f R significantly increased during the TOUCH PERIOD. The mothers' MVR occurred within the range of 1–10 cm/s matching with the optimal afferent stimulation range of a particular class of cutaneous unmyelinated, low-threshold mechano-sensitive nerves, named c-tactile (CT) afferents. We suggest CT afferents to be the a potential missing link between the processing of affective touch and the development of physiological and emotional self-regulation. The results are discussed with regard to the potential role of CT afferents within the building of early self-regulation as part of a multisensory intuitive parenting system and the importance to respect this ecological context of an infant in research and clinical applications. • Impact of maternal affective touch on infants' parasympathetic regulation. • Stroking touch increased infants' RSA, RRI and decreased their f R. • Non-stroking touch decreased infants' RSA and had no impact on their RRI, f R. • Mothers stroked intuitively at an optimal CT afferent stimulation range (1–10 cm/s). • CT afferents may link affective touch and the development of self-regulation. [ABSTRACT FROM AUTHOR]

Social touch is important for interpersonal interaction. Gentle touch and slow brushing are typically perceived as pleasant, the degree of pleasantness is linked to the activity of the C-tactile (CT) fibers, a class of unmyelinated nerves in the skin. The inability to experience pleasure in general is called anhedonia, a common phenomenon in the chronic pain condition fibromyalgia. Here, we studied the perception and cortical processing of gentle touch in a well-characterized cohort of fibromyalgia. Patients and controls participated in functional brain imaging while receiving tactile stimuli (brushing) on the forearm. They were asked to provide ratings of pleasantness of the tactile stimulus and ongoing pain. We found high distress, pain catastrophizing, and insomnia, and a low perceived state of health in fibromyalgia. Further, patients rated both slow (CT-optimal) and fast (CT-suboptimal) brushing as less pleasant than healthy participants. While there was no difference in brain activity during touch, patients showed deactivation in the right posterior insula (contralateral to the stimulated arm) during pleasantness rating and activation during pain rating. The opposite pattern was observed in healthy participants. Voxel-based morphometry analysis revealed reduced grey matter density in patients, in the bilateral hippocampus and anterior insula. Our results suggest anhedonia to gentle touch in fibromyalgia with intact early-stage sensory processing but dysfunctional evaluative processing. These findings contribute to our understanding of the mechanisms underlying anhedonia in fibromyalgia.

For centuries, scholars have been puzzled by the distinct human prosociality. A variety of explanations have been proposed to unveil the mystery of it and nearly all these explanations have focused on the role of complex cognitive processes. In this paper, we propose a novel hypothesis that human prosociality is touch-scaffolded. We argue that early tactile stimulation such as maternal touch serves as the basic component that enables the emergence of nascent human prosociality. During this process, C-tactile afferents along with many neuropeptides, such as oxytocin and endogenous opioids, play pivotal roles in the touch – prosociality connection by facilitating the formation of an intimate caregiver-infant bond and the development of a positive social schema. Our model provides a different perspective on the development of human prosociality and builds a bridge between the human tactile system and high-level psychology – human prosociality. [ABSTRACT FROM AUTHOR]

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Background Unmyelinated low-threshold mechanoreceptors—the so-called C-tactile (CT) afferents—play a crucial role in the perception and conduction of caressing and pleasant touch sensations and significantly contribute to the concept of erotic touch perception. Aim To investigate the relations between sexual desire and sexual performance and the perception of touch mediated by CT afferents. Methods Seventy healthy participants (28 men, 42 women; mean age ± SD = 24.84 ± 4.08 years, range = 18–36 years) underwent standardized and highly controlled stroking stimulation that varied in the amount of CT fiber stimulation by changing stroking velocity (CT optimal = 1, 3 and 10 cm/s; CT suboptimal = 0.1, 0.3, and 30 cm/s). Participants rated the perceived pleasantness, eroticism, and intensity of the applied tactile stimulation on a visual analog scale, completed the Sexual Desire Inventory, and answered questions about sexual performance. Outcomes Ratings of perceived eroticism of touch were related to self-report levels of sexual desire and sexual performance. Results Pleasantness and eroticism ratings showed similar dependence on stroking velocity that aligned with the activity of CT afferents. Erotic touch perception was related to sexual desire and sexual performance in a gender-specific way. In women, differences in eroticism ratings between CT optimal and suboptimal velocities correlated positively with desire for sexual interaction. In contrast, in men, this difference correlated to a decreased frequency and longer duration of partnered sexual activities. Clinical Implications The present results lay the foundation for future research assessing these relations in patients with specific impairments of sexual functioning (eg, hypoactive sexual desire disorder). Strengths and Limitations The strength of the study is the combination of standardized neurophysiologic methods and behavioral data. A clear limitation of the study design is the exclusion of exact data on the female menstrual cycle and the recruitment of an inhomogeneous sample concerning sexual orientation. Conclusion The present results provide further evidence that unmyelinated CT afferents play a role in the complex mechanism of erotic touch perception. The ability to differentiate between CT optimal and suboptimal stimuli relates to sexual desire and performance in a gender-specific way. Bendas J, Georgiadis JR, Ritschel G. C-Tactile Mediated Erotic Touch Perception Relates to Sexual Desire and Performance in a Gender-Specific Way. J Sex Med 2017;14:645–653. [ABSTRACT FROM AUTHOR]

Osteopathic medicine is a system of manual diagnosis and treatment. While there is growing evidence that osteopathy is effective in a range of clinical conditions, the underlying biological basis of its therapeutic effects remain largely unknown. Given that the sense of touch plays a critical role in osteopathy, in this perspective article, with a particular focus on perinatal care, we explore the potential mechanisms by which stimulation of the skin senses can exert beneficial physiological and psychological effects, aiding growth and development. We propose that a class of low threshold mechanosensitive c-fibre, named c-tactile afferents, which respond optimally to gentle, slow moving touch are likely to play a direct and significant role in the efficacy of manual therapies. A greater understanding of the impact the type and quality of touch plays in therapeutic tactile interventions and in particular the neuroscience underpinning these effects will aid the development of more targeted, population specific interventions. [ABSTRACT FROM AUTHOR]

C-tactile (CT) afferent fibers are optimally stimulated by slow gentle stroking, and an inverted U-shaped relationship exists between stroking velocity and pleasantness ratings of this type of touch. This study investigated whether an additional and potentially important variable, touch avoidance, interacts with this relationship. While a typical U-shaped velocity-pleasantness relationship was expected, those high in touch avoidance were expected to rate CT-targeted touch (1-10 cm/s) as less pleasant than those low in touch avoidance. Thirty-five participants rated the pleasantness of a brush stroked across their forearm at five velocities (0.3, 1, 3, 10, 30 cm/s) administered by a custom-built touch stimulator (''the touch device''). Participants also completed two self-report measures of touch avoidance. There was an inverted U-shaped relationship between velocity and pleasantness ratings, and high touch avoidance resulted in a downward shift of this curve. The downward shift was across all velocities, including those that do not maximally engage CTafferents. It appears that touch avoidance reduces the pleasantness of all kinds of touch in a similar way, and it is unlikely to be specifically related to CTafferent functioning. Other potential mechanisms leading to touch avoidance are discussed. [ABSTRACT FROM AUTHOR]

• Effects of nurturing maternal touch were studied in dyads of mothers and preterm infants. • Nurturing maternal touch is suited to target C-tactile fibres in the preterm infant. • Nurturing maternal touch significantly decreased infants' mean heart rate. • Heart rate decrease appeared delayed compared to term born children. • The C-tactile system is immature in preterm children and infantile maturation relates to reactivity to C-tactile targeted touch. Preterm infants are challenged to adapt to an extrauterine milieu, while their interoceptive system and autonomic regulation capacity is still immature. Caressing parental touch is known to foster parasympathetic regulation in infants by stimulating C-tactile (CT) afferents and in preterm infants, slow stroking stimulation also leads to a heart rate decrease. The particular impact of maternal stroking has not yet been investigated and factors influencing the maturation of the CT system in preterm infants remain unclear. We therefore analysed 53 standardized events in which preterm infants (24 to 36 weeks gestational age at birth) were stroked by their mothers. Video analysis revealed that mothers use CT optimal velocities to stroke their preterm child. Analysis of pulse oximetric data showed no effect of stroking on infantile blood oxygenation, but a significant decrease of the heart rate. Compared to term-born children, this decrease was delayed by about two minutes. Furthermore, our data suggested that more immature preterm infants benefited less from stroking than more mature ones. We conclude that maternal stroking touch targets CT afferents in preterm infants and that the preterm CT system is not yet mature. [ABSTRACT FROM AUTHOR]

Pleasant, affective touch provides various health benefits, including stress and depression relief. There is a dichotomy between mechanoreceptive afferents that predominantly signal discriminative (myelinated A-beta) and affective (unmyelinated C-tactile) aspects of touch. It is well documented that discriminative abilities of touch decline with age. However, a thorough investigation of how the pleasant aspects of touch develop with age has not been previously attempted. Here, we investigated the relationship between age and psychophysical ratings in response to gentle stroking touch. One hundred twenty participants (60 males, 60 females) ages 13-82 years were presented with C-tactile optimal and suboptimal stroking velocities, and rated pleasantness and intensity. Moreover, to examine the specificity of age effects on touch perception, we used olfactory stimuli as a cross-sensory comparison. For all ages, we found that C-tactile optimal stimuli were rated significantly more pleasant than C-tactile suboptimal stimuli. Although, both touch and olfactory intensity ratings were negatively correlated with age, a positive correlation between pleasantness ratings of touch (but not olfactory stimuli) and age was found. We conclude that the affective, but not the discriminative, aspects of touch are enhanced with increasing age. The increase of pleasantness of all touch stimuli in late adulthood is discussed in relation to cognitive modulations. [ABSTRACT FROM AUTHOR]

Highlights: [•] We have studied touch perception in a human model of experimental allodynia. [•] Both discriminative and affective touch processing was affected in allodynia. [•] Tactile allodynia is signaled by Aβ afferents. [•] The contribution of CTs seems to be the loss of a pain inhibiting role. [Copyright &y& Elsevier]

Abstract: The social brain hypothesis proposes that the demands of the social environment provided the evolutionary pressure that led to the expansion of the primate brain. Consistent with this notion, that functioning in the social world is crucial to our survival, while close supportive relationships are known to enhance well-being, a range of social stressors such as abuse, discrimination and dysfunctional relationships can increase the risk of psychiatric disorders. The centrality of the social world to our everyday lives is further exemplified by the fact that abnormality in social behaviour is a salient feature of a range of neurodevelopmental and psychiatric disorders. This paper aims to provide a selective overview of current knowledge of the neurobiological basis of our ability to form and maintain close personal relationships, and of the benefits these relationships confer on our health. Focusing on neurochemical and neuroendocrine interactions within affective and motivational neural circuits, it highlights the specific importance of cutaneous somatosensation in affiliative behaviours and psychological well-being and reviews evidence, in support of the hypothesis, that a class of cutaneous unmyelinated, low threshold mechanosensitive nerves, named c-tactile afferents, have a direct and specific role in processing affiliative tactile stimuli. [Copyright &y& Elsevier]

Abstract: Human unmyelinated (C) tactile afferents signal the pleasantness of gentle skin stroking on hairy (nonglabrous) skin. After neuronal injury, that same type of touch can elicit unpleasant sensations: tactile allodynia. The prevailing pathophysiological explanation is a spinal cord sensitization, triggered by nerve injury, which enables Aβ afferents to access pain pathways. However, a recent mouse knockout study demonstrates that C-tactile afferents are necessary for allodynia to develop, suggesting a role for not only Aβ but also C-tactile afferent signaling. To examine the contribution of C-tactile afferents to the allodynic condition in humans, we applied the heat/capsaicin model of tactile allodynia in 43 healthy subjects and in 2 sensory neuronopathy patients lacking Aβ afferents. Healthy subjects reported tactile-evoked pain, whereas the patients did not. Instead, patients reported their C-touch percept (faint sensation of pleasant touch) to be significantly weaker in the allodynic zone compared to untreated skin. Functional magnetic resonance imaging in 18 healthy subjects and in 1 scanned patient indicated that stroking in the allodynic and control zones evoked different responses in the primary cortical receiving area for thin fiber signaling, the posterior insular cortex. In addition, reduced activation in the medial prefrontal cortices, key areas for C-tactile hedonic processing, was identified. These findings suggest that dynamic tactile allodynia is associated with reduced C-tactile mediated hedonic touch processing. Nevertheless, because the patients did not develop allodynic pain, this seems dependent on Aβ signaling, at least under these experimental conditions. [Copyright &y& Elsevier]

Social touch is important for interpersonal interaction. Gentle touch and slow brushing are typically perceived as pleasant, the degree of pleasantness is linked to the activity of the C-tactile (CT) fibers, a class of unmyelinated nerves in the skin. The inability to experience pleasure in general is called anhedonia, a common phenomenon in the chronic pain condition fibromyalgia. Here, we studied the perception and cortical processing of gentle touch in a well-characterized cohort of fibromyalgia. Patients and controls participated in functional brain imaging while receiving tactile stimuli (brushing) on the forearm. They were asked to provide ratings of pleasantness of the tactile stimulus and ongoing pain. We found high distress, pain catastrophizing, and insomnia, and a low perceived state of health in fibromyalgia. Further, patients rated both slow (CT-optimal) and fast (CT-suboptimal) brushing as less pleasant than healthy participants. While there was no difference in brain activity during touch, patients showed deactivation in the right posterior insula (contralateral to the stimulated arm) during pleasantness rating and activation during pain rating. The opposite pattern was observed in healthy participants. Voxel-based morphometry analysis revealed reduced grey matter density in patients, in the bilateral hippocampus and anterior insula. Our results suggest anhedonia to gentle touch in fibromyalgia with intact early-stage sensory processing but dysfunctional evaluative processing. These findings contribute to our understanding of the mechanisms underlying anhedonia in fibromyalgia. [ABSTRACT FROM AUTHOR]

Previous behavioral research points to a positive relationship between maternal touch and early social development. Here, we explored the brain correlates of this relationship. The frequency of maternal touch was recorded for 43 five-year-old children during a 10 min standardized play session. Additionally, all children completed a resting-state functional magnetic resonance imaging session. Investigating the default mode network revealed a positive relation between the frequency of maternal touch and activity in the right posterior superior temporal sulcus (pSTS) extending into the temporo-parietal junction. Using this effect as a seed in a functional connectivity analysis identified a network including extended bilateral regions along the temporal lobe, bilateral frontal cortex, and left insula. Compared with children with low maternal touch, children with high maternal touch showed additional connectivity with the right dorso-medial prefrontal cortex. Together these results support the notion that childhood tactile experiences shape the developing "social brain" with a particular emphasis on a network involved in mentalizing., (© The Author 2016. Published by Oxford University Press.)