Abstract:

Significance The perception of wetness is a crucial sensory experience that significantly influences human comfort and our interaction with the environment. Despite its importance, the underlying neural mechanisms of wetness perception remain not fully understood. Most existing studies focus on the peripheral neural pathways, which involve receptors and afferent neurons responsible for sensing temperature, pressure, and humidity. Understanding these mechanisms is essential for advancing fields such as sensory neuroscience, neurophysiology, and clothing design, where precise sensory feedback is critical. The value of this research lies in bridging the gap in our knowledge about how different sensory pathways collaborate to create a unified experience of wetness and how this information is integrated at the brain level. Investigating the neural circuits involved in wetness perception will offer deeper insights into sensory processing, with applications in ergonomics, healthcare, and the development of smart wearable technologies.

Progress Recent studies have increasingly emphasized the crucial role of thermoreceptors and mechanoreceptors in the perception of wetness. These peripheral sensory receptors, responsible for detecting temperature changes and tactile pressure, respectively, work in concert to transmit signals that the brain interprets as moisture on the skin. Specifically, heat-sensitive neurons respond to cooling-often associated with the evaporation of water-while mechanosensitive neurons detect the pressure and texture of stimuli contacting the skin. Research has shown that wetness perception is not mediated by a dedicated "wetness receptor" but rather emerges from the integration of cold and tactile information. This multimodal encoding occurs at the peripheral level, yet the precise mechanisms through which these different neuronal populations interact remain poorly understood.

While significant advances have been made in mapping peripheral responses to wet stimuli, notably through microneurography and psychophysical experiments, relatively less attention has been directed toward understanding how the central nervous system processes and integrates these sensory inputs. Some neuroimaging studies have proposed that the brain interprets wetness through the convergence of thermal and tactile inputs in somatosensory and higher-order integrative regions, such as the parietal and prefrontal cortices. However, empirical evidence remains scarce, and the exact neural circuits involved in wetness perception are yet to be clearly delineated. Theoretical models suggest a collaborative encoding process between thermosensitive and mechanosensitive pathways, but this hypothesis requires further validation through functional neuroimaging and electrophysiological studies. Bridging this knowledge gap is essential for advancing our understanding of multisensory integration in somatic perception and may have important implications for neurorehabilitation and tactile interface design.

Conclusion and Prospect This review highlights a growing consensus that wetness perception arises from the integration of multiple sensory pathways, primarily involving thermoreceptors and mechanoreceptors that encode temperature changes and tactile stimuli. While peripheral mechanisms of wetness perception have been relatively well characterized, significant gaps remain in our understanding of how the central nervous system processes and integrates these multisensory signals. In particular, it remains unclear how the brain transforms separate inputs, such as cooling sensations and mechanical deformation of the skin, into a unified perception of wetness. To address these knowledge gaps, future research should prioritize the use of advanced neuroimaging techniques, such as functional near-infrared spectroscopy (fNIRS), functional magnetic resonance imaging (fMRI), and electroencephalography (EEG), to monitor cortical responses during wetness-related stimulation. These approaches can provide insights into the temporal dynamics and spatial localization of neural activity associated with wetness perception. Special attention should be given to the roles of the primary and secondary somatosensory cortex, as well as the insular cortex, which are known to be involved in the integration of sensory inputs and in the perception of bodily states. Moreover, identifying the specific neural circuits and characterizing the behavior of individual neuron populations involved in wetness processing will be essential for constructing a comprehensive model of multisensory integration. A deeper understanding of these mechanisms could inform the development of innovative tactile interfaces, improve textile design for thermal and moisture comfort, and enhance user experience in wearable technology.

Key words: neurophysiology, thermal and moisture comfort, somatosensory cortical response, tactile sensation, wetness perception