Brain Dynamics Induced by Pleasant/Unpleasant Tactile Stimuli Conveyed by Different Fabrics

In this study, we investigated brain dynamics from electroencephalographic (EEG) signals during affective tactile stimulation conveyed by the dynamical contact with different fabrics. Thirty-three healthy subjects (16 females) were enrolled to interact with a haptic device able to mimic caress-like stimuli conveyed by strips of different fabrics moved back and forth at different velocities. Specifically, two velocity levels (i.e., 9.4 and 65 mm/sec) and two kinds of fabric (i.e., burlap and silk) were selected to deliver pleasant and unpleasant affective elicitations, according to subjects’ self-assessment. EEG power spectra and functional connectivity were then calculated and analyzed. Experimental results, reported in terms of <italic>p</italic>-value topographic maps, demonstrated that caresses administered through unpleasant fabrics increased brain activity in the <inline-formula><tex-math notation="LaTeX">$\theta$</tex-math></inline-formula> (4–8 Hz), <inline-formula><tex-math notation="LaTeX">$\alpha$</tex-math></inline-formula> (8–14 Hz), and <inline-formula><tex-math notation="LaTeX">$\beta$</tex-math></inline-formula> (14–30 Hz) bands, whereas the use of pleasant fabrics enhanced functional connections in specific areas (e.g., frontal, occipital, and temporal cortices) depending on the oscillations frequency and caressing velocity. Furthermore, we adopted K-NN algorithms to automatically recognize the pleasantness of the haptic stimulation at a single-subject level using EEG power spectra, achieving a recognition accuracy up to 74.24%. Finally, we showed how brain oscillation power in the <inline-formula><tex-math notation="LaTeX">$\alpha$</tex-math></inline-formula> and <inline-formula><tex-math notation="LaTeX">$\beta$</tex-math></inline-formula> bands over contralateral frontal- and central-cortex were the most informative features characterizing the pleasantness of a tactile stimulus on the forearm.