Using EEG (SS-EPs) to characterize the brain activity in response to textured stimuli in passive touch

When sliding our fingertip on a surface, complex vibrations are produced in the skin. In the present study, we used electroencephalography (EEG) to record steady-state evoked brain potentials (SS-EPs) and characterize the cortical activity related to the passive tactile exploration of textured surfaces. In a first experiment, the right index fingertip was passively scanned against square-wave gratings having a spatial period (SP) ranging between 0.4 and 1.6 mm, using a constant normal force (1.5N) and two constant exploration velocities (17.6 mm/s, 48 mm/s). The movement of the grating was achieved using a robot with a feedback force sensor. Depending on the SP, we expected that these dynamic stimuli would elicit SS-EPs at frequencies ranging between 11 and 120 Hz and, possibly, their harmonics. We found that consistent SS-EPs can be recorded at the lowest frequency (11 Hz). In a second experiment, the fingertip was scanned against a 3.52 mm sinusoidal grating onto which a textured fabric was glued. We found that periodically modulating the magnitude of texture-induced high-frequency vibrations can elicit a measurable SS-EP in the recorded EEG. Our results suggest that SS-EPs could be used to isolate and study the brain responses related to the tactile exploration of textures.