The cutaneous senses: touch, temperature, pain/itch, and pleasure

Multisensory contributions to skin-cosmetic product interactions

The human face is one of the most salient regions of the body surface. Ratings of facial attractiveness, as well as judgements of a person's age, are influenced by the appearance of facial skin (not to mention the presence/absence of wrinkles). Unsurprisingly, many consumers spend huge amounts of money on trying to protect, maintain, and/or enhance their facial appearance. As highlighted by the evidence presented in this narrative review, both the skin and the cosmetic products that many consumers use are fundamentally multisensory in nature. The complex interaction between the particular skin site stimulated and the multisensory attributes of the product (e.g., when it is applied) can exert a number of effects on an individual's mood, their emotions, as well as on their self-perception (and self-confidence), over-and-above any functional effects that the cream or lotion may have on the skin itself. In this narrative historical review, the literature on the multisensory perception of facial skin is summarized and critically evaluated. Multisensory interactions taking place between the cosmetic product, its packaging, as well as its use/application at the sensory, cognitive, and emotional levels are all discussed.

Observational measures of caregiver's touch behavior in infancy: A systematic review

The caregiver's touch behavior during early infancy is linked to multiple developmental outcomes. However, social touch remains a challenging construct to operationalize, and although observational tools have been a gold standard for measuring touch in caregiver-infant interactions, no systematic review has been conducted before. We followed the PRISMA guidelines and reviewed the literature to describe and classify the main characteristics of the available observational instruments. Of the 3042 publications found, we selected 45 that included an observational measure, and from those we identified 12 instruments. Most of the studies were of infants younger than six months of age and assessed touch in two laboratory tasks: face-to-face interaction and still-face procedure. We identified three approaches for evaluating the caregiver's touch behavior: strictly observational (the observable touch behavior), functional (the functional role of the touch behavior), or mixed (a combination of the previous two). Half of the instruments were classified as functional, 25% as strictly observational, and 25% as mixed. The lack of conceptual and operational uniformity and consistency between instruments is discussed.

A Practice-Inspired Mindset for Researching the Psychophysiological and Medical Health Effects of Recreational Dance (Dance Sport)

“Dance” has been associated with many psychophysiological and medical health effects. However, varying definitions of what constitute “dance” have led to a rather heterogenous body of evidence about such potential effects, leaving the picture piecemeal at best. It remains unclear what exact parameters may be driving positive effects. We believe that this heterogeneity of evidence is partly due to a lack of a clear definition of dance for such empirical purposes. A differentiation is needed between (a) the effects on the individual when the activity of “dancing” is enjoyed as a dancer within different dance domains (e.g., professional/”high-art” type of dance, erotic dance, religious dance, club dancing, Dance Movement Therapy (DMT), and what is commonly known as hobby, recreational or social dance), and (b) the effects on the individual within these different domains, as a dancer of the different dance styles (solo dance, partnering dance, group dance; and all the different styles within these). Another separate category of dance engagement is, not as a dancer, but as a spectator of all of the above. “Watching dance” as part of an audience has its own set of psychophysiological and neurocognitive effects on the individual, and depends on the context where dance is witnessed. With the help of dance professionals, we first outline some different dance domains and dance styles, and outline aspects that differentiate them, and that may, therefore, cause differential empirical findings when compared regardless (e.g., amount of interpersonal contact, physical exertion, context, cognitive demand, type of movements, complexity of technique and ratio of choreography/improvisation). Then, we outline commonalities between all dance styles. We identify six basic components that are part of any dance practice, as part of a continuum, and review and discuss available research for each of them concerning the possible health and wellbeing effects of each of these components, and how they may relate to the psychophysiological and health effects that are reported for “dancing”: (1) rhythm and music, (2) sociality, (3) technique and fitness, (4) connection and connectedness (self-intimation), (5) flow and mindfulness, (6) aesthetic emotions and imagination. Future research efforts might take into account the important differences between types of dance activities, as well as the six components, for a more targeted assessment of how “dancing” affects the human body.

Temperature-Based Crossmodal Correspondences: Causes and Consequences

The last few years have seen an explosive growth of research interest in the crossmodal correspondences, the sometimes surprising associations that people experience between stimuli, attributes, or perceptual dimensions, such as between auditory pitch and visual size, or elevation. To date, the majority of this research has tended to focus on audiovisual correspondences. However, a variety of crossmodal correspondences have also been demonstrated with tactile stimuli, involving everything from felt shape to texture, and from weight through to temperature. In this review, I take a closer look at temperature-based correspondences. The empirical research not only supports the existence of robust crossmodal correspondences between temperature and colour (as captured by everyday phrases such as 'red hot') but also between temperature and auditory pitch. Importantly, such correspondences have (on occasion) been shown to influence everything from our thermal comfort in coloured environments through to our response to the thermal and chemical warmth associated with stimulation of the chemical senses, as when eating, drinking, and sniffing olfactory stimuli. Temperature-based correspondences are considered in terms of the four main classes of correspondence that have been identified to date, namely statistical, structural, semantic, and affective. The hope is that gaining a better understanding of temperature-based crossmodal correspondences may one day also potentially help in the design of more intuitive sensory-substitution devices, and support the delivery of immersive virtual and augmented reality experiences.

Shitsukan - the Multisensory Perception of Quality

We often estimate, or perceive, the quality of materials, surfaces, and objects, what the Japanese refer to as 'shitsukan', by means of several of our senses. The majority of the literature on shitsukan perception has, though, tended to focus on the unimodal visual evaluation of stimulus properties. In part, this presumably reflects the widespread hegemony of the visual in the modern era and, in part, is a result of the growing interest, not to mention the impressive advances, in digital rendering amongst the computer graphics community. Nevertheless, regardless of such an oculocentric bias in so much of the empirical literature, it is important to note that several other senses often do contribute to the impression of the material quality of surfaces, materials, and objects as experienced in the real world, rather than just in virtual reality. Understanding the multisensory contributions to the perception of material quality, especially when combined with computational and neural data, is likely to have implications for a number of fields of basic research as well as being applicable to emerging domains such as, for example, multisensory augmented retail, not to mention multisensory packaging design.

Intercostal nerve block of the anterior cutaneous branches and the sensibility of the female breast

Introduction

Better sensation in the reconstructed breast improves the quality of life. Sensory nerve coaptation is a valuable addition to autologous breast reconstruction. There are few publications concerning the sensory nerves of the breast and the nipple‐areola complex and reports are contradictory, so it is unknown which nerve is best suited as a recipient for coaptation. The current study serves as a proof of concept.

Materials and Methods

The areas innervated by the anterior cutaneous branches (ACBs) of the intercostal nerves (ICNs) were studied on two separate occasions in two healthy women. First, the ACBs of ICNs 2–5 were individually blocked using ultrasound. Next, the ACBs of all levels were blocked simultaneously. Sensation was measured using Semmes‐Weinstein monofilaments. The numbed areas corresponding to the ICNs were drawn in a raster of 2 × 2 cm.

Results

The largest area was supplied by the ACB of the 4th ICN, located in the upper (UIQ) and the lower (LIQ) inner quadrants of the breast. The 2nd‐largest area was supplied by the ACB of the 3rd ICN. Blockage of ACBs 2–5 affected sensation in the nipple and the areola.

Conclusions

Blockage of all levels 2–5 partially affected sensation in the nipple‐areola complex, suggesting innervation by a nerve plexus consisting of both ACBs and lateral cutaneous branches (LCBs). ACB4 supplied the largest area of the breast in the UIQ and LIQ and could be best suited for sensory nerve coaptation to optimize sensation in the autologously reconstructed breast.

Cutaneous immune responses mediated by dendritic cells and mast cells

In the skin, complex cellular networks maintain barrier function and immune homeostasis. Tightly regulated multicellular cascades are required to initiate innate and adaptive immune responses. Innate immune cells, particularly DCs and mast cells, are central to these networks. Early studies evaluated the function of these cells in isolation, but recent studies clearly demonstrate that cutaneous DCs (dermal DCs and Langerhans cells) physically interact with neighboring cells and are receptive to activation signals from surrounding cells, such as mast cells. These interactions amplify immune activation. In this review, we discuss the known functions of cutaneous DC populations and mast cells and recent studies highlighting their roles within cellular networks that determine cutaneous immune responses.

Introduction: Art and the brain: From pleasure to well-being

Empirical aesthetics in general, and neuroaesthetics in particular, have been very much influenced by Berlyne's psychobiological program. For him, aesthetic appreciation involved the brain's reward and aversion systems. From this point of view, art constitutes a set of potentially rewarding stimuli. Research has certainly made great advances in understanding how the process of artistic valuation takes places, and which brain circuits are involved in generating the pleasure we obtain from artistic practices, performances, and works. But it also suggests that pleasure is not the only effect of the arts. The evidence rather suggests that the arts have other cognitive and emotional effects which are closely related to human psychobiological health and well-being. These are: (1) attentional focus and flow, (2) affective experience, (3) emotion through imagery, (4) interpersonal communication, (5) self-intimation, and (6) social bonding. These effects are beneficial and contribute to the individual's biopsychological health and well-being. The fact that artistic practice has these effects helps explain why the arts are so important to human life, and why they developed in the first place, i.e., as ways to foster these effects. Therefore, a biopsychological science of the arts is emerging, according to which the arts can be conceptualized as an important system of external self-regulation, as a set of activities that contribute to our homeostasis and well-being.

Book Review: Our Senses: Gateways to Consciousness, written by Rob DeSalle

Charles Spence reviews Rob DeSalle’s (2018) new bookOur Senses: Gateways to Consciousness, a popular science look at the neuroscience behind the senses set in an evolutionary context.

Epigenetic correlates of neonatal contact in humans

Animal models of early postnatal mother–infant interactions have highlighted the importance of tactile contact for biobehavioral outcomes via the modification of DNA methylation (DNAm). The role of normative variation in contact in early human development has yet to be explored. In an effort to translate the animal work on tactile contact to humans, we applied a naturalistic daily diary strategy to assess the link between maternal contact with infants and epigenetic signatures in children 4–5 years later, with respect to multiple levels of child-level factors, including genetic variation and infant distress. We first investigated DNAm at four candidate genes: the glucocorticoid receptor gene, nuclear receptor subfamily 3, group C, member 1 (NR3C1), μ-opioid receptor M1 (OPRM1) and oxytocin receptor (OXTR; related to the neurobiology of social bonds), and brain-derived neurotrophic factor (BDNF; involved in postnatal plasticity). Although no candidate gene DNAm sites significantly associated with early postnatal contact, when we next examined DNAm across the genome, differentially methylated regions were identified between high and low contact groups. Using a different application of epigenomic information, we also quantified epigenetic age, and report that for infants who received low contact from caregivers, greater infant distress was associated with younger epigenetic age. These results suggested that early postnatal contact has lasting associations with child biology.

Multisensory modulation of experimentally evoked perceptual distortion of the face

BACKGROUND

Chronic oro-facial pain patients often perceive the painful face area as "swollen" without clinical signs, that is a perceptual distortion (PD). Local anaesthetic (LA) injections in healthy participants are also associated with PD.

OBJECTIVE

The aim was to explore whether PD evoked by LA into the infraorbital region could be modulated by adding mechanical stimulation (MS) to the affected area.

METHODS

Mechanical stimulation was given with a brush and a 128-mN von Frey filament. Firstly, sixty healthy participants were randomly divided into three groups: (i) LA control, (ii) LA with MS, (iii) isotonic solution (ISO) with MS as an additional control condition. To further examine the role of a multisensory modulation, an additional experiment was conducted. Twenty participants received LA with MS (filament) in addition to visual feedback of their distorted face. The results of the two experiments are presented together.

RESULTS

All three LA groups experienced PD; per contra, PD was not reported in the ISO group. MS alone did not change the magnitude of PD: brush (P = .089), filament (P = .203). However, when the filament stimulation was combined with additional visual information of a distorted face, there was observable decrease in PD (P = .002).

CONCLUSION

The findings indicate the importance of multisensory integration for PD and represent a significant step forward in the understanding of the factors that may influence this common condition. Future studies are encouraged to investigate further the cortical processing for possible implications for PD in pain management.

Not all about sex: neural and biobehavioral functions of human dance

This paper provides an integrative review of neuroscientific and biobehavioral evidence about the effects of dance on the individual across cultural differences. Dance moves us, and many derive aesthetic pleasure from it. However, in addition-and beyond aesthetics-we propose that dance has noteworthy, deeper neurobiological effects. We first summarize evidence that illustrates the centrality of dance to human life indirectly from archaeology, comparative psychology, developmental psychology, and cross-cultural psychology. Second, we review empirical evidence for six neural and biobehavioral functions of dance: (1) attentional focus/flow, (2) basic emotional experiences, (3) imagery, (4) communication, (5) self-intimation, and (6) social cohesion. We discuss the reviewed evidence in relation to current debates in the field of empirical enquiry into the functions of human dance, questioning the positions that dance is (1) just for pleasure, (2) all about sex, (3) just for mood management and well-being, and (4) for experts only. Being a young field, evidence is still piecemeal and inconclusive. This review aims to take a step toward a systematization of an emerging avenue of research: a neuro- and biobehavioral science of dance.

The Development of Tactile Perception

Touch is the first of our senses to develop, providing us with the sensory scaffold on which we come to perceive our own bodies and our sense of self. Touch also provides us with direct access to the external world of physical objects, via haptic exploration. Furthermore, a recent area of interest in tactile research across studies of developing children and adults is its social function, mediating interpersonal bonding. Although there are a range of demonstrations of early competence with touch, particularly in the domain of haptics, the review presented here indicates that many of the tactile perceptual skills that we take for granted as adults (e.g., perceiving touches in the external world as well as on the body) take some time to develop in the first months of postnatal life, likely as a result of an extended process of connection with other sense modalities which provide new kinds of information from birth (e.g., vision and audition). Here, we argue that because touch is of such fundamental importance across a wide range of social and cognitive domains, it should be placed much more centrally in the study of early perceptual development than it currently is.

Sensitivity of the Nipple-Areola Complex and Sexual Function Following Reduction Mammaplasty

BACKGROUND

The sensitivity of the nipple-areola complex (NAC) is very relevant to female sexuality.

OBJECTIVE

To evaluate NAC sensitivity and sexual function after breast reduction, and to assess whether altered NAC sensitivity is related to sexual dysfunction.

METHODS

The study included 80 patients, who were allocated to a control group with eutrophic breasts (CG, n = 20), a hypertrophy group without surgery (HG, n = 20), or a mammaplasty group (MG, n = 40). The MG was assessed preoperatively and 6 months postoperatively. The HG and CG were evaluated once. NAC sensitivity was assessed for touch, temperature, vibration, and pressure in four areola quadrants and the nipple. Sexual function was assessed with the Brazilian version of the Female Sexual Function Index, which has six domains (desire, arousal, lubrication, orgasm, satisfaction, and pain) and a total score that indicates the presence or absence of sexual dysfunction.

RESULTS

Compared to the CG, the MG had worse sensitivity to temperature and pressure in the nipple and areola medial quadrants postoperatively (P < 0.01). Compared to their preoperative assessment, the MG had reduced temperature and pressure sensitivity in the nipple and areola medial quadrants postoperatively (P < 0.05). Compared to the CG and HG, patients in the MG had higher postoperative scores of excitation (P = 0.0001), lubrication (P = 0.0004), orgasm (P < 0.0001), and satisfaction (P < 0.0001). There was an association between sexual dysfunction and low NAC sensitivity to temperature and vibration (P ≤ 0.041) in the MG's preoperative and postoperative scores, and to touch, temperature, and pressure across all three groups.

CONCLUSIONS

Breast reduction with a superomedial pedicle reduced NAC sensitivity but did not interfere with sexual function.

Embodied intersubjective engagement in mother-infant tactile communication: a cross-cultural study of Japanese and Scottish mother-infant behaviors during infant pick-up

This study examines the early development of cultural differences in a simple, embodied, and intersubjective engagement between mothers putting down, picking up, and carrying their infants between Japan and Scotland. Eleven Japanese and ten Scottish mothers with their 6- and then 9-month-old infants participated. Video and motion analyses were employed to measure motor patterns of the mothers’ approach to their infants, as well as their infants’ collaborative responses during put-down, pick-up, and carry phases. Japanese and Scottish mothers approached their infants with different styles and their infants responded differently to the short duration of separation during the trial. A greeting-like behavior of the arms and hands was prevalent in the Scottish mothers’ approach, but not in the Japanese mothers’ approach. Japanese mothers typically kneeled before making the final reach to pick-up their children, giving a closer, apparently gentler final approach of the torso than Scottish mothers, who bent at the waist with larger movements of the torso. Measures of the gap closure between the mothers’ hands to their infants’ heads revealed variably longer duration and distance gap closures with greater velocity by the Scottish mothers than by the Japanese mothers. Further, the sequence of Japanese mothers’ body actions on approach, contact, pick-up, and hold was more coordinated at 6 months than at 9 months. Scottish mothers were generally more variable on approach. Measures of infant participation and expressivity indicate more active participation in the negotiation during the separation and pick-up phases by Scottish infants. Thus, this paper demonstrates a culturally different onset of development of joint attention in pick-up. These differences reflect cultures of everyday interaction.

Tactile warning signals for in-vehicle systems

The last few years have seen growing interest in the design of tactile warning signals to direct driver attention to potentially dangerous road situations (e.g. an impending crash) so that they can initiate an avoidance maneuver in a timely manner. In this review, we highlight the potential uses of such warning signals for future collision warning systems and compare them with more traditional visual and auditory warnings. Basic tactile warning signals are capable of promoting driver alertness, which has been demonstrated to be beneficial for forward collision avoidance (when compared to a no warning baseline condition). However, beyond their basic alerting function, directional tactile warning signals are now increasingly being utilized to shift the attention of the driver toward locations of interest, and thus to further facilitate their speeded responses to potential collision events. Currently, many researchers are focusing their efforts on the development of meaningful (iconic) tactile warning signals. For instance, dynamic tactile warnings (varying in their intensity and/or location) can potentially be used to convey meaningful information to drivers. Finally, we highlight the future research that will be needed in order to explore how to present multiple directional warnings using dynamic tactile cues, thus forming an integrated collision avoidance system for future in-vehicle use.

The pleasurability of scratching an itch: a psychophysical and topographical assessment

BACKGROUND

Scratching an itch is perceived as being pleasurable. However, an analysis of topographical variations in itch intensity, the effectiveness of scratching to provide itch relief and the associated pleasurability has not been performed at different body sites.

OBJECTIVES

To examine the role of scratching pleasurability in providing itch relief by investigating whether itch intensity is perceived differently at three different sites and to assess a potential correlation between the pleasurability and itch attenuation induced by scratching.

METHODS

Itch was induced on the forearm, ankle and back using cowhage spicules in 18 healthy subjects. These sites were subsequently scratched by an investigator with a cytology brush immediately following itch induction. The intensity of itch with and without scratching at these sites and the pleasurability of scratching were recorded by taking visual analogue scale ratings at 30-s intervals.

RESULTS

Mean itch intensity and scratching pleasurability ratings at the ankle and back were significantly higher than on the forearm. For the forearm and ankle, the greater the itch while scratching, the higher was the pleasurability. A higher baseline itch was linked to a higher itch reduction secondary to scratching in all tested areas. Pleasurability paralleled the curve of itch reduction for the back and forearm; however, scratching pleasurability at the ankle remained elevated and only slightly decreased while itch was diminishing.

CONCLUSIONS

There are topographical differences in itch intensity, the effectiveness of scratching in relieving itch and the associated pleasurability. Experimental itch induced by cowhage was more intensely perceived at the ankle, while scratching attenuated itch most effectively on the back.

Vicarious responses to social touch in posterior insular cortex are tuned to pleasant caressing speeds

BACKGROUND

Affective touch carries strong significance for social mammals, including humans. Gentle, dynamic touch of a kind that occurs during social interactions is preferentially encoded by a distinct neural pathway involving tactile C (CT) afferents, a type of unmyelinated afferent nerve found exclusively in hairy skin. CT afferents increase firing when the skin is stroked at a pleasant, caress-like speed of ∼3 cm/s, and their discharge frequency correlates with the subjective hedonic experience of the caress. In humans, the posterior insula is a cortical target for CT afferents. Since the potential social relevance of affective touch extends to the touch interactions of others, we postulated that information from CT afferents in posterior insular cortex provides a basis for encoding observed caresses.

RESULTS

In two experiments, we exploited CT afferents' functionally unique tuning curve for stroking speed, demonstrating that a speed optimal for eliciting CT discharge (3 cm/s) also gives rise to higher BOLD responses in posterior insula than a nonoptimal speed (30 cm/s). When participants viewed videos of others' arms being stroked at CT-optimal versus -nonoptimal speeds, the posterior insula showed a similar response as to directly felt touch. Further, this region's response was specific for social interactions, showing no CT-related modulation for nonsocial dynamic-touch videos.

CONCLUSIONS

These findings provide direct evidence for a functional relationship between CT signaling and processing in posterior insular cortex. Such selective tuning for CT-optimal signals in insula may allow recognition of the hedonic relevance of a merely observed caress.

Time-lapse imaging and cell-specific expression profiling reveal dynamic branching and molecular determinants of a multi-dendritic nociceptor in C. elegans

Nociceptive neurons innervate the skin with complex dendritic arbors that respond to pain-evoking stimuli such as harsh mechanical force or extreme temperatures. Here we describe the structure and development of a model nociceptor, the PVD neuron of C. elegans, and identify transcription factors that control morphogenesis of the PVD dendritic arbor. The two PVD neuron cell bodies occupy positions on either the right (PVDR) or left (PVDL) sides of the animal in posterior-lateral locations. Imaging with a GFP reporter revealed a single axon projecting from the PVD soma to the ventral cord and an elaborate, highly branched arbor of dendritic processes that envelop the animal with a web-like array directly beneath the skin. Dendritic branches emerge in a step-wise fashion during larval development and may use an existing network of peripheral nerve cords as guideposts for key branching decisions. Time-lapse imaging revealed that branching is highly dynamic with active extension and withdrawal and that PVD branch overlap is prevented by a contact-dependent self-avoidance, a mechanism that is also employed by sensory neurons in other organisms. With the goal of identifying genes that regulate dendritic morphogenesis, we used the mRNA-tagging method to produce a gene expression profile of PVD during late larval development. This microarray experiment identified>2,000 genes that are 1.5X elevated relative to all larval cells. The enriched transcripts encode a wide range of proteins with potential roles in PVD function (e.g., DEG/ENaC and Trp channels) or development (e.g., UNC-5 and LIN-17/frizzled receptors). We used RNAi and genetic tests to screen 86 transcription factors from this list and identified eleven genes that specify PVD dendritic structure. These transcription factors appear to control discrete steps in PVD morphogenesis and may either promote or limit PVD branching at specific developmental stages. For example, time-lapse imaging revealed that MEC-3 (LIM homeodomain) is required for branch initiation in early larval development whereas EGL-44 (TEAD domain) prevents ectopic PVD branching in the adult. A comparison of PVD-enriched transcripts to a microarray profile of mammalian nociceptors revealed homologous genes with potentially shared nociceptive functions. We conclude that PVD neurons display striking structural, functional and molecular similarities to nociceptive neurons from more complex organisms and can thus provide a useful model system in which to identify evolutionarily conserved determinants of nociceptor fate.