ERP evidence of tactile texture processing: Effects of roughness and movement

Psychological and neurophysiological studies have investigated the peripheral neural mechanisms implicated in tactile roughness perception. However, the cortical mechanisms involved in roughness processing are not well understood. In the present study, we used behavioural data and event-related evoked potentials (ERPs) to investigate the extent to which two tactile stimuli varying in roughness (triangular gratings peak-to-peak spacing of 1.6 mm and 2.8 mm) and movement (the time available for tactile contact with the surface) modulate early stages of brain activation. Behavioral results showed that participants discriminate the two levels of roughness at the three velocities explored in the study but they were judged as equivalent in pleasantness. The ERP results showed a biphasic early-fast N1-P2 deflection. The N1 and P2 peaks to the smoother texture occur earlier than that of the rougher texture. Considering velocity, the N1 onset occurs later for the slowest velocity, followed by the intermediate velocity and earlier for the fastest velocity and the three velocities differ significantly. LORETA analysis showed that N1 and P2 components of surface roughness are both related to the activation produced in the somatosensory cortex and posterior cingulated respectively, suggesting that these areas might be involved in the sensory processing of roughness.