Characteristics of brain functional networks specific for different types of tactile perception

Tactile perception is a fundamental sensory system, playing a pivotal role in our understanding of the surrounding environment and aiding in motor control. In this study, we investigated the distinct neural underpinnings of discriminative touch, affective touch (specifically the C tactile system), and knismesis. We developed a paradigm of EEG experiment consisted of three types of touch tuned in terms of their force and velocity for different submodalities: discriminative touch (haptics or fast touch), affective touch (C-tactile or slow touch), and knismesis (alerting tickle or ultralight touch). Touch was delivered with a special high-precision robotic rotary touch stimulation device. Thirty nine healthy individuals participated in the study. Utilizing functional brain networks derived from EEG data, we examined the patterns of brain connectivity associated with fast, slow, and ultralight touches. Our findings revealed significant differences in functional connectivity patterns between these touch conditions, with the majority of variations occurring in the theta frequency range. Notably, connections in frontal, frontal-central, frontal-parietal, and occipitotemporal regions exhibited distinct activation strengths. Pairwise statistical comparisons further highlighted the unique characteristics of each touch modality. The theta band, in particular, played a prominent role in distinguishing ultralight from slow touches. These results shed light on the interplay between different touch submodalities and their distinctive processing in the brain, contributing to a comprehensive understanding of tactile perception. This research bridges a critical gap in our knowledge of the neural mechanisms underlying tactile perception and its role in shaping our perception of the world.