Electroencephalographic spectral correlates of caress-like affective haptic stimuli

This paper describes how brain dynamics, as estimated through spectral analysis of electroencephalographic (EEG) oscillatory rhythms, is modified by quantifiable, affective haptic stimuli. Specifically, 32 healthy subjects (16 females) interacted with a haptic device able to convey caress-like stimuli while varying force and velocity of the device itself. More specifically, 2 values of force (i.e., "strength of the caress") and 3 velocity levels (i.e. "velocity of the caress") were combined to control the device during the experiment. Subjects were also asked to self-assess the haptic stimuli in terms of arousal (activation/ deactivation) and valence (pleasure/displeasure) scores. Results, shown in terms of p-values topographic maps, revealed a suppression of the oscillations over the controlateral somatosensory cortex, during caresses performed with the lowest force (2N) and the highest velocity (65 mm/s). This occurred in all of the frequency bands considered, α, β, and γ. Lower velocities (9.4 mm/s and 37 mm/s) did not significantly modify EEG reactivity in such bands. Concerning caresses administered at high force (6N), there was a significant decrease of EEG oscillatory activity focused on mid-frontal electrodes, in all of the considered frequency bands, when the velocity of the caresses was the lowest one. Significant sparse decrease of EEG power spectra, in all of the considered frequency bands, occurred at higher strength and velocity of the caress.