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.

Im Fokus der vorliegenden kumulativ angefertigten Arbeit stehen vier wissenschaftliche Untersuchungen, deren Thematik die Vibrationssensorik des Menschen darstellt. Die aus Vibrationen gewonnenen Informationen führen zu wichtigen Regulationsmechanismen zum Beispiel zur Aufrechterhaltung des Gleichgewichtes und des Ganges. Die Ermittlung von sogenannten Vibrationswahrnehmungsschwellen stellt eine Möglichkeit zur Quantifizierung des Funktionszustandes des somatosensorischen Systems dar. In diesem Zusammenhang ist die Kontrolle und Standardisierung einflussnehmender Messbedingungen auf die Bewertung der Vibrationssensorik wichtig. Im ersten Beitrag der vorliegenden Arbeit rückt die Rolle der Auflagekraft, mit welcher der Stößel der Messgeräte die zu untersuchende Hautpartie belastet, in den Fokus (Studie I). In den sich anschließenden Beiträgen werden die Wirkmechanismen der mechanischen Hauteigenschaften auf die Wahrnehmung von Vibrationen aus evolutionsbiologischer (Studie II) und pathologischer (Studie III) Sichtweise betrachtet. Im letzten Beitrag wird die potentielle Wirkung von unterschwelligen Rauschstimulationen als mögliche bewegungstherapeutische Maßnahme zur Verbesserung der sensorischen Leistungsfähigkeit untersucht (Studie IV). Am Ende der Arbeit erfolgt die übergreifende Diskussion der einzelnen Beiträge. Mit Hilfe der gewonnen Erkenntnisse werden Handlungsempfehlungen zur Verbesserung der Quantifizierung der Vibrationssensorik in klinischen und wissenschaftlichen Bereichen abgeleitet. Das erweiterte Verständnis über die Wirkmechanismen verschiedener Einflussgrößen auf die Vibrationssensorik unterstützt die gezielte Erforschung von bewegungstherapeutischen Maßnahmen zur Steigerung der sensorischen Leistungsfähigkeit des Menschen. / The focus of the present cumulative dissertation is on four scientific investigations that deal with the human vibration sensory system. The information obtained from vibrations leads to important regulatory mechanisms, for example to maintain balance and gait. Determining so-called vibration perception thresholds represents a possibility to quantify the functional condition of the somatosensory system. In this context, it is important to control and standardize the measurement conditions that influence the evaluation of the vibration sensory system. The first article of the present dissertation focuses on the role of the contact force with which the probe of a measuring device loads the skin area to be examined (Study I). In the subsequent contributions, the action mechanisms of mechanical skin properties regarding vibration perception are considered from an evolutionary (Study II) and pathological (Study III) point of view. In the last paper, the potential effect of subliminal noise stimulation is examined as a possible exercise therapy intervention to improve sensory performance (Study IV). A comprehensive discussion of the individual contributions is included at the end of the present dissertation. Using the gained knowledge, recommendations are derived to improve the quantification of vibration sensation in clinical and scientific areas. The broadened understanding of the mechanisms of action of different influencing variables regarding vibration sensation supports the targeted research of exercise therapy interventions to increase sensory performance in humans.

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.