Brain oscillatory dynamics during discriminative vs CT-optimal touch

The affective dimension of touch is conveyed by low-threshold mechanoreceptors known as C-Tactile (CT) afferents. Literature has shown that the stimulation of these fibers appears to have an important modulatory function in neural oscillations. However, much remains to be explored in this field. This study aims to provide background knowledge about the brain oscillatory dynamics and spatial field distributions of CT stimulation, by comparing the brain's spectral power and the microstates to affective (stroking) vs discriminative touch (vibration) conditions. Thirty-four healthy participants (18 female) received tactile stimulation with a cosmetic brush at CT-optimal speeds or vibrotactile stimulation (at around 200 Hz) on the left forearm's dorsum. They evaluated the pleasantness and intensity ratings of the stimulation while an electroencephalogram was recorded. Stroking stimulation was rated as more pleasant than the vibrotactile stimuli, with no significant differences in the intensity ratings. Power spectral density results revealed reduced power in alpha/mu and beta bands in central/Rolandic areas for the stroking condition compared to the vibration condition. Microstates analysis showed a reduced prevalence of class A and an increased prevalence of classes B and D during stroking. These findings indicate that CT-tuned stroking increased sensorimotor cortical excitability and engaged greater attentional resources, suggesting that this form of touch may be a prioritised type of information.