The "Longing for Interpersonal Touch Picture Questionnaire": Development of a new measurement for touch perception.

Touch is a crucial factor of physiological and psychological health in humans. A lack of touch in contrast is associated with adverse implications on mental health. A new "Longing for Interpersonal Touch Picture Questionnaire (LITPQ)" was developed and tested for its concurrent, predictive, discriminant and face validity as well as its relation to psychological distress. Six different types of touch were depicted and touch frequency and touch wish concerning different interaction partners assessed. A sample of 110 participants aged 18-56 years completed the LITPQ as well as an existing touch deprivation questionnaire and a questionnaire on mental health. Frequency and wish for touch were higher for close interaction partners than for strangers. For 72.7% of the participants, their touch wish exceeded the reported touch frequency. The LITPQ correlated moderately with the existing questionnaire for touch deprivation and was independent of relationship status or gender but positively correlated with depressiveness, anxiety and somatization. Measuring longing for touch is a very complex task considering the many aspects of subjective touch perception and confounds in the method of self-report of touch. In our view, the LITPQ provides promising insights into this matter.

Olfactory Function Relates to Sexual Experience in Adults.

The olfactory system contributes significantly to human social behavior and especially to mate choice and empathic functioning. In this context, previous research examining individuals with impaired olfactory function indicated an influence of the sense of smell on different aspects of sexuality. However, the applied samples, methods, and results are diverse and an involvement of confounding factors, such as breathing problems, depression or social insecurity cannot be ruled out. The present study examined the potential correlation between odor threshold in healthy participants and their sexual desire, sexual experience, and sexual performance. In 70 adults (28 male, 42 female; mean age 24.8 ± 4.1 years), odor threshold was assessed using the "Sniffin' Sticks." The participants also responded to a battery of questions on sexual desire (Sexual Desire Inventory), sexual experience (orgasm frequency, perceived pleasantness of sexual activities on a visual analogue scale) as well as sexual performance (frequency of having sex, average duration of sexual intercourse). Odor sensitivity correlated positively with sexual experience: Participants with high olfactory sensitivity reported higher pleasantness of sexual activities. Further, women with high olfactory sensitivity reported a higher frequency of orgasms during sexual intercourse. These findings were exclusively present for sexual experience; no significant correlations were detected for sexual desire or sexual performance. The experience of sexual interactions appears to be enriched by olfactory input. We discuss that the perception of certain body odors may contribute to the concept of sexual pleasure by enhanced recruitment of reward areas.

Gender-Specific Relation Between Olfactory Sensitivity and Disgust Perception.

The perception of disgust is a powerful but yet puzzling emotion, aiming at the prevention of potential microbial pathogens and being directly linked to olfactory processing in its neurophysiological pathways via the anterior insular cortex. In sample of healthy participants with a natural variation in olfactory function, we investigated the relation between olfactory sensitivity and disgust perception. A total of 123 healthy individuals were surveyed with a disgust sensitivity questionnaire. Olfactory threshold was assessed in all participants using the Sniffin' Sticks. Additionally, tactile 2-point discrimination threshold was tested in a subgroup of the participants as a controlling factor for the specificity of the relationship between olfactory sensitivity and disgust. Only in men, a significant relation between disgust ratings and olfactory threshold was observed. Men with high olfactory sensitivity reported as high levels of disgust as female participants, while men with low olfactory sensitivity reported significantly lower disgust than women. There was no such relation for tactile sensitivity. Investigating sensory subscales of the disgust questionnaire, olfactory sensitivity was related to olfactory and tactile, but not to visual disgust ratings. In conclusion, there is a specific relation between the level of disgust and olfactory sensitivity in men, who generally present lower values of disgust than women. When disgust ratings are low, there seems to be an additional merit in the ability to perceive subtle olfactory stimuli. Thus high olfactory sensitivity may facilitate the perception of potential pathogenic threats and contribute to the evolutionary function of disgust as disease avoidance mechanism.

C-Tactile Mediated Erotic Touch Perception Relates to Sexual Desire and Performance in a Gender-Specific Way.

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.

Dynamics of Affective Habituation to Touch Differ on the Group and Individual Level.

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.

Right between the eyes: Corrugator muscle activity tracks the changing pleasantness of repeated slow stroking touch.

Subjective reports and physiological responses provide different appraisals of sensory input. The coherence between subjective and physiological responses to repeated pleasant stimuli remains largely unexplored, and is particularly important in situations where subjective responses are prone to cognitive or contextual bias. Here, we investigate how subjective and physiological responses to repeated gentle touch correspond at two separate sessions and compare these to responses obtained when smelling an odorant. Forty-eight participants underwent 60 trials of skin-to-skin slow stroking touch directed to the forearm. We collected subjective pleasantness reports, recorded facial electromyography (EMG) of the corrugator and zygomaticus muscles and heart-rate variability (HRV). With increasing touch repetitions, mean ratings of pleasantness decreased and corrugator muscle activity increased during session 1, whereas zygomaticus activity remained largely unchanged during both sessions. HRV was significantly higher during the first session, but did not increase from baseline during either sessions. Touch was rated as more pleasant than odor, and demonstrated greater resilience to satiety than the odor responses. Facial EMG recordings of the corrugator muscle appear to be a relevant measure for capturing satiety effects in skin-to-skin touch. Zygomaticus and HRV responses were independent of the subjective appraisal of the gentle touch. Rather than being blueprints of the subjective reports, physiological responses appear to reflect different parts of the subjective experience. As such, an improved understanding of the subjective and physiological responses to pleasant stimuli may improve our understanding of the dynamic interactions that take place in shaping complex emotional phenomena, such as aversion and pleasantness.

The individual preferred velocity of stroking touch as a stable measurement.

Affective touch is of fundamental importance in human social interactions and there is an increasing interest in using touch as a probe for general affective perception. To this end, we developed a test of preferred velocity (ToP-V) of touch and tested whether the individually preferred stroking velocity is a stable and valid measurement. In study one, thirty healthy participants (18-30years, 17 women) were examined with the ToP-V. Therefore, pairs of different slow stroking stimuli were presented by the Rotary Tactile Stimulator - a robotic device - on the forearm and the participants chose the velocity they preferred in a forced choice paradigm. A retest was conducted after about 12days. In study two, twenty-two healthy participants (20-43years, 11 women) were tested with a shorter version of the ToP-V on the forearm and also on the palm. Moreover, they rated the pleasantness and the intensity of the stroking stimulations on both body sites. Results suggest that humans possess an individual and stable preferred velocity of stroking touch (test-retest reliability r=0.86) which can be tested in a standardized procedure. A shortened 5min version of the ToP-V also exhibited reasonable test characteristics (split half reliability: r=0.7; test-retest reliability r=0.77). The ToP-V correlated well with the pleasantness ratings when tested on the forearm (r=0.65), but not when tested on the palm (r=-0.22), indicating that the ToP-V targets a C-tactile nerve fiber specific perception. Hence, the ToP-V can be used for reliably probing affective touch perception.

The relation between human hair follicle density and touch perception.

Unmyelinated low threshold C-tactile fibers moderate pleasant aspects of touch. These fibers respond optimally to stroking stimulation of the skin with slow velocities (1-10 cm/s). Low threshold mechanoreceptors are arranged around hair follicles in rodent skin. If valid also in humans, hair follicle density (HFD) may relate to the perceived pleasantness of stroking tactile stimulation. We conducted two studies that examined the relation between HFD and affective touch perception in humans. In total, 138 healthy volunteers were stroked on the forearm and rated the pleasantness and intensity. Stimulation was performed by a robotic tactile stimulator delivering C-tactile optimal (1, 3, 10 cm/s) and non-optimal (0.1, 0.3, 30 cm/s) stroking velocities. Additionally, a measure of discriminative touch was applied in study 2. HFD of the same forearm was determined using the Cyanoacrylate Skin Stripping Method (CSSM), which we validated in a pretest. Women had higher HFD than men, which was explained by body size and weight. Furthermore, women rated affective touch stimuli as more pleasant and had higher tactile acuity. Depilation did not affect touch perception. A weak relationship was found between the C-tactile specific aspects of affective touch perception and HFD, and the hypothesis of HFD relating to pleasant aspects of stroking only received weak support.