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Affective touch is a somatosensory modality involved in forming and consolidating positive social interactions. It is transduced in our skin presumably through C-Tactile mechanoreceptors, which are preferentially activated when touch is performed at speeds around 3cm/s (or CT-optimal speed). This increased activation, in turn, is related to greater pleasantness feelings. Given its social relevance, the observation of the affective touch can cause high empathic resonance in the observer. However, little is known whether the observation of CT-optimal touch is processed differently in our brain than at other CT-suboptimal speeds. In the present study, we evaluated the pleasantness ratings and the electroencephalogram of 30 healthy participants while they watched videos of affective touch at 3 speeds: static, slow (CT-optimal), and fast touch. We found that CT-optimal touch received higher evaluations of pleasantness and was related to a higher amplitude of the P3 component and desynchronization of beta activity compared to static or fast touch. Other frequency bands, such as theta and alpha, showed increased modulation to slow and fast touch compared to static touch, but did not allow us to distinguish between slow and fast conditions. Our results suggest that vicarious processing of affective touch at the optimal speed for CT receptors involves more processing resources and higher activation of somatosensory areas, evidencing that this modality of touch is a prioritized type of information.

Here we asked whether, similar to visual and auditory event-related potentials (ERPs), somatosensory ERPs reflect affect. Participants were stroked on hairy or glabrous skin at five stroking velocities (0.5, 1, 3, 10 and 20 cm/s). For stroking of hairy skin, pleasantness ratings related to velocity in an inverted u-shaped manner. ERPs showed a negativity at 400 ms following touch onset over somatosensory cortex contra-lateral to the stimulation site. This negativity, referred to as sN400, was larger for intermediate than for faster and slower velocities and positively predicted pleasantness ratings. For stroking of glabrous skin, pleasantness showed again an inverted u-shaped relation with velocity and, additionally, increased linearly with faster stroking. The sN400 revealed no quadratic effect and instead was larger for faster velocities. Its amplitude failed to significantly predict pleasantness. In sum, as was reported for other senses, a touch’s affective value modulates the somatosensory ERP. Notably, however, this ERP and associated subjective pleasantness dissociate between hairy and glabrous skin underscoring functional differences between the skin with which we typically receive touch and the skin with which we typically reach out to touch.

Touch plays an important role in the development of infants and children. In this review, we highlight the neural conditioning of affective touch and the related physiological responses, especially in the form of parasympathetic activation, pain suppression and stress relief. Based on recent studies, we show that the functionality of a population of C-tactile (CT) nerve fibers, hypothesized to provide the neurobiological substrate for the transmission of interpersonal touch, is already mature in the newborn and that the developmentally beneficial effects of such touch are already evident at this stage. We further aim to shed light on the role of nurturing touch in stimulating CT fibers. Based on this, we hypothesize that CT stimulation acts as a reinforcer that contributes to the development of newborns into social beings by means of conditioning.

Bridging the gap between the neurophysiology of C-tactile mediated touch and the psychology of how social touch makes us feel, we present a definition of affective touch as mediated through CT afferents. We clarify how gentle stroking activating the CT system communicates a signal for social exchange. We describe what is already known about the nature of this signal and how it is perceived as a function of multisensory input and individual differences. Reviewing sender-specific and receiver-specific effects, we bring these streams together to outline a hybrid communication model of affective touch. We propose that affective touch should not be operationalized by simply involving CT afferent activation and a narrow range of stimulation modes, but instead should consider the entire communication chain: signal, receiver, sender and the dynamic exchange between interacting agents. Such a complete communication model presents new research directions to disentangle bottom-up and top-down mediated effects on perception.

We report the impact of a Gentle Touch Stimulation (GTS) program. Forty-three mothers provided daily 10-min GTS with C-tactile (CT) afferent optimal stroking touch, for 4 weeks to their 3-12 weeks old infants. CT-afferents are cutaneous unmyelinated, low-threshold mechanosensitive nerves hypothesized to underly the regulatory impact of affective touch. We compared physiological and behavioral responses during a no-touch-baseline (BL), static-touch-baseline (BL-T), intervention/control (GTS/CTRL), Still Face (SF) and Reunion (RU) condition for GTS-infants versus a control-group (CTRL) at the start (T1) and end of (T2) of the program. We collected mother-infant ECG, respiration, cortisol, video-recordings, and diary-reports. At T1, physiological arousal significantly increased during SF in both groups, that is, decreased respiratory sinus arrhythmia (RSA) and R-R interval (RRI). At T2, GTS-infants showed significantly increased RSA, RRI, decreased respiration during GTS, buffering SF-arousal and allowing complete recovery during RU; CTRL-infants showed higher SF-arousal and small recovery, under initial BL-levels. Maternal cardio-respiratory showed a metabolic investment during RU. Cortisol and behavioral analyses showed higher arousal in CTRL-infants than GTS-infants at T2. We suggest that the combination of phasic short-term and tonic long-term responses to CT-optimal stroking touch, delivered in a structured daily manner, contribute to the building of infant stress regulation and resilience.Reportamos el impacto del programa de Estimulación Táctil Suave (GTS). Cuarenta y tres madres les dieron a sus infantes de 3-12 semanas 10 minutos de GTS con un toque táctil-C (CT) aferente óptimo de caricias por 4 semanas. Los aferentes CT son nervios cutáneos amielínicos mecano-sensibles de bajo impacto que según hipótesis rigen el impacto regulatorio del toque afectivo. Comparamos las respuestas fisiológicas y de comportamiento durante un momento de referencia no táctil (BL), un momento de referencia táctil estático (BL-T), intervención/control (GTS-CTRL), la Cara Seria (SF) y la condición de Reunión (RU) para infantes GTS versus un grupo de control (CTRL) al principio (T1) y al final (T2) del programa. Recogimos información ECG de madre-infante, respiración, cortisol, grabaciones en vídeo, y reportes de un diario. Al T1, la estimulación fisiológica significativamente aumentó durante SF en ambos grupos, v.g., una baja en la arritmia respiratoria paranasal (RSA) y el intervalo R-R (RRI). Al T2, los infantes GTS significativamente mostraron un aumento de RSA, RRI, una baja en la respiración durante GTS, amortiguando la estimulación SF y permitiendo un completo recobro durante RU; los infantes de CTRL mostraron una más alta estimulación SF y un pequeño recobro, bajo los niveles BL iniciales. El aspecto cardio-respiratorio materno mostró inversión metabólica durante RU. Los análisis de cortisol y de comportamiento mostraron más altas estimulaciones de infantes de CTRL que en infantes GTS al T2. Proponemos que la combinación de las respuestas fásicas a corto plazo y tónicas a largo plazo a las caricias táctiles óptimas CT, ofrecidas de una manera estructural diaria, contribuyen a moldear la regulación del estrés y capacidad de resistencia del infante.Cet article fait état de l'impact du programme Stimulation Toucher en Douceur (an anglais Gentle Touch Stimulation, que nous abrégeons ici GTS). Quarante-trois mères ont procédé chaque jour à un GTS de 10 minutes avec un toucher par caresse optimale C-tactile (CT) afférent, pendant 4 semaines à leurs nourrissons de 3-12 semaines. Les afférents CD sont des nerfs cutanés amyéliniques, à faible seuil et mécano-sensibles, dont on pense qu'ils sous-tendent l'impact régulatoire du toucher affectif. Nous comparons les réponses physiologiques et les réponses comportementales durant la condition à un niveau de référence NR sans toucher, un niveau de référence toucher statique (NR-T), un contrôle/intervention (GTS/CTRL), Visage Impassible (Still Face, soit SF) et la Réunion (RU) pour les bébés GTS par rapport aux bébés du groupe de contrôle (CTRL) au commencement (T1) et à la fin (T2) du programme. Nous avons recueilli l’électrocardiogramme mère-bébé, la respiration, le niveau de cortisol et les rapports-journaux. Au T1 la stimulation physiologique a augmenté de façon importante durant le SF pour les deux groupes, c'est-à-dire une arythmie des sinus respiratoires (RSA) décrue et un intervalle R-R décru (RRI). Au T2 les bébés GTS ont fait preuve d'une RSA et d'un RRI bien plus élevés, une respiration décrue durant le GTS, un éveil SF tampon et ont fait preuve d'un rétablissement complet durant la RU. Les bébés contrôle ont fait preuve de plus d’éveil SF et d'un petit rétablissement, moins élevés que les niveaux BL initiaux. La cardio-respiration maternelle a fait preuve un investissement métabolique durant la RU. Les analyses de cortisol et les analyses comportementales ont montré un éveil plus élevé chez les bébés-CTRL que chez les bébés GTS au T2. Nous suggérons que la combinaison de réactions phasiques à court terme et de réponses toniques à long terme au toucher caresse CT-optimal, donné chaque jour de manière structurée, contribue à la construction de la régulation du stress du bébé et de sa résilience.Warum sehnen wir uns nach Berührung? Die Auswirkungen täglicher sanfter Berührungsstimulation auf die physiologische und verhaltensbezogene Regulation sowie Resilienz von Mutter und Kind Wir berichten über die Auswirkungen eines Programms zur sanften Berührungsstimulation (Gentle Touch Stimulation; GTS). Dreiundvierzig Mütter wendeten bei ihren 3-12 Wochen alten Säuglingen 4 Wochen lang täglich 10 Minuten GTS an, d.h. eine C-taktile (CT) afferente optimale streichelnde Berührung. Bei den CT-Afferenzen handelt es sich um kutane, nicht-myelinisierte, niedrigschwellig mechanosensorische Nerven, von denen angenommen wird, dass sie den regulierenden Auswirkungen affektiver Berührungen zugrunde liegen. Wir verglichen die physiologischen und verhaltensbezogenen Reaktionen von GTS-Säuglingen im Vergleich zu einer Kontrollgruppe (CTRL) zu Beginn (T1) und am Ende (T2) des Programms während einer berührungsfreien Baseline (BL), einer statischen Berührungsbaseline (BL-T), einer Interventions-/Kontrollbedingung (GTS/CTRL), einer „Still Face“ Bedingung (SF) und einer Wiedervereinigung (RU). Erhoben wurden Mutter-Kind EKG, Atmung, Cortisol, Videoaufzeichnungen und Tagebucheinträge. Zu T1 nahm die physiologische Erregung während der SF in beiden Gruppen signifikant zu, d. h. die respiratorische Sinusarrhythmie (RSA) und das R-R-Intervall (RRI) nahmen ab. Zu T2 zeigten die GTS-Säuglinge signifikant erhöhte RSA, RRI und verringerte Atmung während der GTS, was die SF-Erregung abpufferte und eine vollständige Erholung während der RU ermöglichte. Die CTRL-Säuglinge zeigten eine höhere SF-Erregung und eine geringe Erholung unter den ursprünglichen BL-Werten. Die mütterliche kardio-respiratorische Aktivität zeigte eine metabolische Investition während der RU. Cortisol- und Verhaltensanalysen zeigten eine höhere Erregung bei CTRL-Säuglingen als bei GTS-Säuglingen zu T2. Die Ergebnisse weisen darauf hin, dass die Kombination von phasischen Kurzzeit- und tonischen Langzeitreaktionen auf CT-optimale streichelnde Berührungen, die täglich strukturiert durchgeführt werden, zum Aufbau der Stressregulation und Resilienz von Säuglingen beitragen.なぜ私たちはタッチングを希求するか−毎日の優しいタッチングの刺激が、母Ȁ子の身体生理および行動の調節と レジリエンス(復元力)に及ぼす影響 ジェントルタッチスティミュレーション(GTS)プログラムの効果について報告する。 43人の母親が、生後3〜12週の母親の乳児に、C-tactile(CT)求心性の最適ななでるタッチングを含む10分間のGTSを4週間毎日行った。CT求心性神経は、情緒的なタッチングの調整的な影響を過小評価していると仮定される皮膚の無髄鞘の低閾値のメカノセンシチブ神経である。GTSの非タッチベースライン(BL)、静的タッチベースライン(BL-T)、介入/制御(GTS / CTRL)、スティルフェイス(SF)、および再会(RU)状態での身体生理および行動の反応を、GTS-乳児と対照群(CTRL-乳児)で、プログラムの開始時(T1)と終了時(T2)に比較した。母と子の心電図、呼吸の状態、コルチゾール、ビデオ録画、および日記を記録した。T1では、両グループとも、SF中において身体生理的に有意に覚醒した。つまり、呼吸性洞性不整脈(RSA)とR-R間隔(RRI)が減少した。T2では、GTS-乳児は、RSA、RRIが有意に増加し、GTS中に呼吸数が減少し、SF覚醒は緩まり、RU中に完全に回復を示した。一方、CTRL-乳児は、初期のBLレベル下で、より高いSF覚醒とわずかな回復を示した。母親の心肺系は、RU中に代謝投資を示した。コルチゾールと行動分析では、T2ではGTS-乳児よりもCTRL-乳児でより高い覚醒を示した。構造化され毎日提供されるCT最適なストロークタッチングに対する相性の短期的および強壮性の長期的反応の組み合わせが、乳児のストレス調節と回復の構築に寄与するとした。.我们报告了一项“温和触摸刺激” (GTS) 项目的影响。43位母亲利用“C组触觉 (CT) 传入神经”的最佳轻抚触摸方式每天为其3-12周大的婴儿提供10分钟的GTS, 为期4周。C组触觉传入神经是皮肤无髓鞘、低阈值的机械敏感性神经, 被认为是情感触摸调节影响的基础。我们在项目开始 (T1) 和结束 (T2) 阶段比较了GTS-婴儿与对照组在无接触基线 (BL)、静态接触基线 (BL-T)、干预/对照 (GTS/CTRL)、静止面孔 (SF) 以及重聚 (RU) 条件下的生理和行为反应。我们收集了母婴心电图、呼吸、皮质醇、录像和日记报告。在T1阶段, 两组婴儿在SF期间的生理唤醒显著增加, 即呼吸性窦性心律不齐 (RSA) 和R-R间期 (RRI) 减少。在T2阶段, GTS-婴儿的RSA、RRI显著增加, GTS期间呼吸减少, SF-唤醒减缓, 并在RU期间呈现完全恢复;在初始BL水平下, CTRL-婴儿表现出更高的SF-唤醒和微小恢复程度。在RU期间, 母亲的心肺功能显示出代谢消耗。皮质醇和行为分析显示, 在T2阶段, CTRL-婴儿的唤醒程度高于GTS-婴儿。我们建议, 对CT的最佳轻抚触摸方式应结合阶段性短期反应和强直长期反应, 以结构化的日常方式开展, 这有助于建立婴儿压力调节和复原力。.لماذا نتوق إلى اللمس؟ تأثير تحفيز اللمسة اللطيفة اليومية على التنظيم الفسيولوجي والسلوكي للأم والطفل والمرونة نعرض في هذه الدراسة تأثير برنامج تحفيز اللمسة اللطيفة (GTS). اشتركت مجموعة من 43 أمًا في الدراسة حيث طلب منهم تقديم 10 دقائق يومياً من اللمسة المثالية مع التمسيد لمدة 4 أسابيع لأطفالهن الذين تتراوح أعمارهم بين 3-12 أسبوعًا. المستقبلات العصبية منخفضة العتبة في الحساسية الميكانيكية و يُفترض أنها تتحكم في التأثير التنظيمي لللمس العاطفي. قمنا بمقارنة الاستجابات الفسيولوجية والسلوكية خلال حالة عدم وجود اللمس (BL) ، واللمس الثابت (T-BL) ، ومجموعة التدخل / المجموعة الضابطة (GTS / CTRL) ، والوجه الثابت (SF) ، ومجموعة Reunion (RU) للأطفال في برنامج اللمسة اللطيفة (GTS) مقارنة بالمجموعة الضابطة (CTRL) في نقطة البداية (T1) ونقطة النهاية (T2) من البرنامج. قمنا بجمع بيانات رسم القلب ، والتنفس ، والكورتيزول ، وتسجيلات الفيديو ، وتقارير اليوميات. في نقطة البداية (T1) ، زادت الاستثارة الفسيولوجية بشكل ملحوظ خلال حالة الوجه الثابت (SF) في كلا المجموعتين ، أي انخفاض عدم انتظام ضربات القلب التنفسي (RSA) و (RRI). وفي نقطة النهاية (T2) ، أظهر الرضع في برنامج (GTS) زيادة ملحوظة في RSA ، RRI ، وانخفاض التنفس أثناء GTS ؛ بينما أظهر الرضع في المجموعة الضابطة استثارة أعلى للوجه الثابت (SF) وفترة انتعاش قصيرة ، تحت مستويات BL الأولية. وأظهرت تحليلات الكورتيزول والسلوكية إثارة أعلى عند الرضع في المجموعة الضابطة عن الرضع في مجموعة التدخل عند نقطة النهاية (T2). تقترح الدراسة أن الجمع بين الاستجابات المرحلية قصيرة المدى وطويلة المدى للمس التمسيدي الأمثل الذي يقدم بشكل يومي ونظامي ، يمكن أن يساهم في بناء المرونة وتنظيم الإجهاد لدى الرضع.

Affiliative tactile interactions buffer social mammals against neurobiological and behavioral effects of stress. The aim of the present study was to investigate the cutaneous mechanisms underlying such beneficial consequences of touch by determining whether daily stroking, specifically targeted to activate a velocity/force tuned class of low-threshold c-fiber mechanoreceptor (CLTM), confers resilience against established markers of chronic unpredictable mild stress (CMS). Adult male Sprague Dawley rats were exposed to two weeks of CMS. Throughout the CMS protocol, some rats were stroked daily, either at CLTM optimal velocity (5cm/s) or outside the CLTM optimal range (30cm/s). A third CMS exposed group did not receive any tactile stimulation. The effect of CMS on serum corticosterone levels, anxiety- and depressive-like behaviors in these three groups was assessed in comparison to a control group of non-CMS exposed rats. While stroking did not mitigate the effects of CMS on body weight gain, CLTM optimal velocity stroking did significantly reduce CMS induced elevations in corticosterone following an acute forced-swim. Rats receiving CLTM optimal stroking also showed significantly fewer anxiety-like behaviors (elevated plus-maze) than the other CMS exposed rats. In terms of depressive-like behavior, while the same velocity specific resilience was observed in a forced-swim test (FST) and social interaction test both groups of stroked rats spent significantly less time interacting than control rats, though they also spent significantly less time in the corner than non-stroked CMS rats. Together, these findings support the theory CLTMs play a functional role in regulating the physiological condition of the body.

This study explored whether a human-like feel of touch biases perceived pleasantness and whether such a bias depends on top-down cognitive and/or bottom-up sensory processes. In 2 experiments, 11 materials were stroked across the forearm at different velocities (bottom-up) and participants rated tactile pleasantness and humanness. Additionally, in Experiment 1, participants identified the materials (top-down), whereas in Experiment 2, they rated each material with respect to its somatosensory properties (bottom-up). Stroking felt most pleasant at velocities optimal for the stimulation of CT-afferents, a mechanosensory nerve hypothesized to underpin affective touch. A corresponding effect on perceived humanness was significant in Experiment 1 and marginal in Experiment 2. Whereas material identification was unrelated to both pleasantness and humanness, we observed a robust relation with the somatosensory properties. Materials perceived as smooth, slippery, and soft were also pleasant. A corresponding effect on perceived humanness was significant for the first somatosensory property only. Humanness positively predicted pleasantness and neither top-down nor bottom-up factors altered this relationship. Thus, perceiving gentle touch as human appears to promote pleasure possibly because this serves to reinforce interpersonal contact as a means for creating and maintaining social bonds. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Very preterm (VPT) infants requiring hospitalization in the Neonatal Intensive Care Unit (NICU) are exposed to several stressful procedural experiences. One consequence of NICU-related stress is a birth-to-discharge increased serotonin transporter gene (SLC6A4) methylation that has been associated with poorer stress regulation at 3 months of age. Maternal touch is thought to support infants’ stress response, but its role in moderating the effects of SLC6A4 methylation changes is unknown. The aim of this study was to assess the role of maternal touch in moderating the association between increased SLC6A4 methylation and stress response in 3-month-old VPT infants. Twenty-nine dyads were enrolled and at 3 months (age corrected for prematurity), participated in the Face-to-Face Still-Face paradigm to measure infants’ stress response (i.e., negative emotionality) and the amount of maternal touch (i.e., dynamic and static). Results showed that low level of maternal touch is associated with high level of negative emotionality during social stress. Furthermore, during NICU stay SLC6A4 methylation in VPT exposed to low level of maternal touch at 3 months was associated with increased negative emotionality. Thus, low levels of maternal static touch can intensify the negative effects of SLC6A4 epigenetic changes on stress response in 3-month-old VPT infants.

The sense of touch codes the detection and properties of physical objects on the body via mechanoreceptors within the skin. Technological advancements, such as ultrasonic haptic devices, are now able to ‘touch without touching’, claiming this is virtual touch. An initial aim of the study was to investigate subjective intensity and pleasantness ratings of ultrasound stimulation and the influence of top-down factors using the Touch Experience and Attitudes Questionnaire (TEAQ). Self-reported intensity and pleasantness ratings were measured in response to ultrasound stimuli. A second aim was to record from individual low threshold mechanoreceptors using the technique of microneurography in an attempt to determine which mechanoreceptors are activated by ultrasound stimulation of the skin. The major findings here were that microneurography found SAI and SAII units did not respond to ultrasound stimuli; intensity and pleasantness ratings were significantly different between age groups. Ultrasound can produce a variety of sensations with varying intensity and pleasantness ratings. A limitation of the study was the unexpected force difference generated between modulations. These findings have implications for mid-air haptics, somatosensory affective research, and virtual reality. Future research should focus on microneurography investigation of FA fibre responses to ultrasound.

OBJECTIVE The significance of the human sense of taste is typically underestimated until it is altered or even lost. Hypogeusia, a diminished capacity to taste, has an adverse influence on a patient's quality of life. Similar to interactions between the oral senses and between olfaction and intranasal trigeminal sensitivity, taste disturbance may also affect the mechanosensitivity of the tongue. In this study, we investigated the lingual tactile sensitivity of patients with subjective taste disturbance and people with normogeusia. STUDY DESIGN Prospective case-control study. METHODS Forty-six patients with subjective taste disturbance (mean age 60 years) and 43 participants with normogeusia (mean age 55 years) were enrolled and underwent a stereognostic test of edge and point sensitivity based on 3D-printed letters sized from 2 to 8 mm. Gustatory function and salivary production were also tested. RESULTS Patients with dysgeusia needed significantly bigger letters to recognize them compared with controls (P = .01). Apart from this, patients with dysgeusia had no significant association between gustatory function and salivary production. Duration of dysgeusia and age were not associated with the presently obtained measures of gustatory or oral mechanosensory function. CONCLUSIONS The results of this study indicate that taste dysfunction has a negative impact on oral mechanosensitivity and hence possibly on oral texture perception. LEVEL OF EVIDENCE 3 Laryngoscope, 131:2572-2577, 2021.

Current theory divides the human mechanical sense into discriminative and affective systems. A discriminative system supports tactile exploration and manipulation via fast Aß signaling, whereas an affective system supports the pleasure of friendly interpersonal touch via slow CT signaling. To probe this system segregation, we recorded the electroencephalogram from participants being stroked and reporting stroke pleasantness. We observed a somatosensory negativity that was maximal for CT optimal as compared with sub-optimal velocities, that predicted subjective pleasantness, and showed only for stroking of hairy skin known to be CT innervated. Importantly, the latency of this negativity preceded C fiber input to the brain by several hundred milliseconds and is best explained by interactions between CT and Aß processes in the spinal cord. Our data challenge the divide between discriminative and affective touch implying instead that both fast Aß and slow CT signaling play an important role in tactile pleasure.

Pain is a universal, multidimensional experience with sensory, emotional, cognitive, and social components, which is fundamental to our environmental learning when functioning typically. Understanding pain processing in psychiatric conditions could provide unique insight into the underlying pathophysiology or psychiatric disease, especially given the psychobiological overlap with pain processing pathways. Studying pain in psychiatric conditions is likely to provide important insights, yet, there is a limited understanding beyond the work in depression and anxiety. This is a missed opportunity to describe psychiatric conditions in terms of neurobiological alterations. To examine the research into the pain experiences of these groups and the extent to which a-typicality is present, a systematic review was conducted. An electronic search strategy was developed and conducted in several databases. The current systematic review included 46 studies covering five Diagnostic and Statistical Manual of Mental Disorders (5th ed.; DSM-5) disorders: autism, attention-deficit hyperactivity disorder (ADHD), schizophrenia, personality disorder, and eating disorders, confirming tentative evidence of altered pain and touch processing. Specifically, hyposensitivity is reported in schizophrenia, personality disorder and eating disorder, hypersensitivity in ADHD, and mixed results for autism. Review of the research highlights a degree of methodological inconsistency in the utilization of comprehensive protocols, the lack of which fails to allow us to understand whether a-typicality is systemic or modality specific.

Tactile sensitivities are common in Autism Spectrum Disorders (ASD). Psychophysically, slow, gentle stroking touch is typically rated as more pleasant than faster or slower touch. Vicarious ratings of social touch results in a similar pattern of velocity dependent hedonic ratings as directly felt touch. Here we investigated whether adults and children’s vicarious ratings vary according to ASD diagnosis and self-reported autistic traits. Adults’ scoring high on the AQ rated stroking touch on the palm as less pleasant than a Low AQ group. However, in contrast to our hypothesis, we did not find any effect of ASD diagnosis on children’s touch ratings despite parental reports highlighting significant somatosensory sensitivities. These results are discussed in terms of underpinning sensory and cognitive factors.

Affective sharing is a bottom-up process involving automatic processing of sensory inputs that facilitate vicarious experience of another’s emotional state. It is grounded directly in the prior experiences of the perceiver. In adults, vicarious ratings of affective touch match the known velocity tuning and hypothesized anatomical distribution of C-tactile afferents (CT), a subclass of C-fiber which respond preferentially to low force/velocity stroking touch, typically perceived as pleasant. Given the centrality of touch to early nurturing interactions, here we examined whether primary school aged children’s vicarious ratings of affective touch show the same anatomical and velocity specific patterns reported in adults. Forty-four children aged between 8 and 11 (mean age 9, 24 male) rated a sequence of video clips depicting one individual being touched by another on 5 different upper-body sites (palm, dorsal forearm, ventral forearm, upper-arm and back) at 3 different velocities (static, CT optimal, slow stroking and non-CT optimal, fast stroking). Immediately after viewing each clip, participants were asked to rate how pleasant they perceived the touch to be. While children rated the CT optimal velocity significantly higher than static or non-CT optimal touch, unlike adults their ratings did not vary across skin sites. This difference may reflect the fact children’s ratings are grounded in bottom-up affective resonance while adults also draw on top-down cognitive evaluation of the broader social context when rating the stimuli.

Ageing is accompanied by a steady decline in touch sensitivity and acuity. Conversely, pleasant touch, such as experienced during a caress, is even more pleasant in old age. There are many physiological changes that might explain these perceptual changes, but researchers have not yet identified any specific mechanisms. Here, we review both the perceptual and structural changes to the touch system that are associated with ageing. The structural changes include reduced elasticity of the skin in older people, as well as reduced numbers and altered morphology of skin tactile receptors. Effects of ageing on the peripheral and central nervous systems include demyelination, which affects the timing of neural signals, as well as reduced numbers of peripheral nerve fibres. The ageing brain also undergoes complex changes in blood flow, metabolism, plasticity, neurotransmitter function, and, for touch, the body map in primary somatosensory cortex. Although several studies have attempted to find a direct link between perceptual and structural changes, this has proved surprisingly elusive. We also highlight the need for more evidence regarding age-related changes in peripheral nerve function in the hairy skin, as well as the social and emotional aspects of touch.

Tactile sensitivities are common in Autism Spectrum Conditions (autism). Psychophysically, slow, gentle stroking touch is typically rated as more pleasant than faster or slower touch. Vicarious ratings of social touch results in a similar pattern of velocity dependent hedonic ratings as directly felt touch. Here we investigated whether adults and childrens vicarious ratings vary according to autism diagnosis and self-reported autistic traits. Adults scoring high on the AQ rated stroking touch on the palm as less pleasant than a Low AQ group. However, in contrast to our hypothesis, we did not find any effect of autism diagnosis on childrens touch ratings despite parental reports highlighting significant somatosensory sensitivities. These results are discussed in terms of underpinning sensory and cognitive factors. Funding Agencies|Linkoping University; Leverhulme TrustLeverhulme Trust [RPG-2013-058]; Liverpool John Moores University PhD studentship

Taste perception has been reported to vary with changes in affective state. Distortions of taste perception, including blunted recognition thresholds, intensity, and hedonic ratings have been identified in those suffering from depressive disorders. Serotonin is a key neurotransmitter implicated in the etiology of anxiety and depression; systemic and peripheral manipulations of serotonin signaling have previously been shown to modulate taste detection. However, the specific effects of central serotonin function on taste processing have not been widely investigated. Here, in a double-blind placebo-controlled study, acute tryptophan depletion was used to investigate the effect of reduced central serotonin function on taste perception. Twenty-five female participants aged 18–28 attended the laboratory on two occasions at least 1 week apart. On one visit, they received a tryptophan depleting drink and on the other, a control drink was administered. Approximately, 6 h after drink consumption, they completed a taste perception task which measured detection thresholds and supra-threshold perceptions of the intensity and pleasantness of four basic tastes (sweet, sour, bitter, and salt). While acutely reducing central levels of serotonin had no effect on the detection thresholds of sweet, bitter, or sour tastes, it significantly enhanced detection of salt. For supra-threshold stimuli, acutely reduced serotonin levels significantly enhanced the perceived intensity of both bitter and sour tastes and blunted pleasantness ratings of bitter quinine. These findings show manipulation of central serotonin levels can modulate taste perception and are consistent with previous reports that depletion of central serotonin levels enhances neural and behavioral responsiveness to aversive signals.

Recent evidence suggests that altered responses to affective touch - a pleasant interoceptive stimulus associated with activation of the C-Tactile (CT) system, may contribute to the aetiology and maintenance of mental conditions characterised by body image disturbances (e.g., Anorexia Nervosa). Here, we investigated whether tactile pleasantness and intensity differ across body sites, and if individual differences in dysmorphic appearance concerns and body awareness might be associated to touch perceptions across body sites. To this end, we measured perceived pleasantness and intensity of gentle, dynamic stroking touches applied to the palm, forearm, face, abdomen and back of 30 female participants (mean age: 25.87±1.17yrs) using CT-optimal (3 cm/s) and non-CT optimal (0.3 and 30 cm/s) stroking touch. As expected, participants rated CT-targeted touch as more pleasant compared to the two non-CT optimal stroking touch at all body sites. Nevertheless, CT-targeted touch applied to the abdomen elicited the lowest pleasantness ratings compared to all other body sites and to the two non-CT optimal stroking touch. Individual differences in body awareness and dysmorphic concerns significantly predicted preference for CT-optimal over non-CT optimal stroking touch applied to the forearm and the back. These findings begin to elucidate the link between CT sensitivity, dysmorphic appearance concerns and body awareness, which may have implications for future research looking to inform early interventions. Addressing impaired processing of affective interoceptive stimuli, such as CT-targeted touch, may be the key to current treatment approaches available for those populations at risk of disorders characterised by body image disturbance.

In the United Kingdom, the most common reasons for a child to come under the care of social services are neglect and abuse. Such early childhood adversity is a risk factor for social-isolation and poor mental health in adulthood. Touch is a key channel for nurturing interactions, and previous studies have shown links between early somatosensory input, experience dependent neural plasticity, and later life emotional functioning. The aim of the present study was to test the relationship between childhood neglect/abuse and later life experiences, attitudes, and hedonic ratings of affective touch. Here, affective touch is defined as low force, dynamic touch which C-Tactile afferents (CTs) respond optimally to. We hypothesized that a childhood lacking in early nurturing tactile stimulation would be associated with reduced sensitivity to socially relevant affective touch in adulthood. To test this, 19 care leavers (average 9.32 ± 3.70 years in foster care) and 32 non-care leavers were recruited through opportunity sampling (mean age = 21.25 ± 1.74 years). Participants completed a range of psychophysical somatosensory tests. First, they rated the pleasantness of CT-optimal (3 cm/s) and non-CT-optimal (0.3 and 30 cm/s) stroking touch applied to their forearm, both robotically and by an experimenter. They also made vicarious ratings of the anticipated pleasantness of social tactile interactions depicted in a series of videos. Finally, they filled in the Childhood Trauma Questionnaire (CTQ) and the Touch Experiences and Attitudes Questionnaire (TEAQ). As expected, care leavers reported significantly higher levels of childhood trauma than the control group. They also reported significantly lower levels of positive childhood touch compared to non-care leavers, but their attitudes and experiences of current intimate and affiliative touch did not differ. Across all psychophysical tests, care leavers showed specific reduction in sensitivity to the affective value of CT targeted 3 cm/s touch. The results of this study support the hypothesis that a lack of nurturing touch in early developmental periods leads to blunted sensitivity to the specific social value of affective touch. Future research should investigate the neural and physiological mechanisms underlying the observed effect.

Haptic devices can bring a sense of touch to virtual interactions, with substantial benefits for communication and health. Mid-air ultrasound can generate acoustic radiation forces for tailored tactile sensations - 'touch without touching'. To study the neuroscience of haptics, devices must be compatible with neural monitors. In this study, electromagnetic shielding with a Faraday was created. Our device creates a palpable focus of ultrasound with sufficient spatial resolution (5 mm diameter) and radiation pressure (1.56 or 1.76 Pa without or with Faraday cage lid, respectively) to stimulate small areas of skin. Magnetometer measurements showed minimal field strength variability around the system. Therefore, the proposed system could be compatible with neurological monitoring for neuroscience studies.

C-tactile afferents are hypothesized to form a distinct peripheral channel that encodes the affective nature of touch. Prevailing views indicate they project, as with other unmyelinated afferents, in lamina I-spinothalamic pathways that relay homeostatically relevant information from the body toward cortical regions involved in interoceptive processing. However, in a recent study, we found that spinothalamic ablation in humans, while profoundly impairing the canonical spinothalamic modalities of pain, temperature, and itch, had no effect on benchmark psychophysical affective touch metrics. These novel findings appear to indicate that perceptual judgments about the affective nature of touch pleasantness do not depend on the integrity of the lamina I-spinothalamic tract. In this commentary, we further discuss the implications of these unexpected findings. Intuitively, they suggest that signaling of emotionally relevant C-tactile mediated touch occurs in an alternative ascending pathway. However, we also argue that the deficits seen following interruption of a putative C-tactile lamina I-spinothalamic relay might be barely perceptible—a feature that would underline the importance of the C-tactile afferent in neurodevelopment.

Behaviors as ubiquitous as play, found throughout the animal kingdom, have clearly evolved to serve an evolutionary benefit to survival. From the perspective of a neuroethologist we can best understand such behaviors by teasing out the underlying neural mechanisms that drive them, and here we find that one sense in particular may well be playing an important role in the type of social bonding that play provides – the sense of touch. Recent research has identified a special class of touch nerves in the skin of the body, called the c-tactile afferent (CT), that code for the affective and emotional properties of touch, such as that experienced during play behaviors. The initial interest in CTs had focused on their role during early life nurturing care where tactile neglect is known to have a devastating effect on neurodevelopment. However, it appears there may be a second critical stage in brain development where CTs may also play a critical role – the play behaviors we see during adolescence.