Human brain processing of gentle touch investigated with time-resolved methods
Résumé
Gentle touch of the hairy skin in humans activates both Aβ-and C-tactile (CT) mechanoreceptive afferents. Due to the different conduction velocities of Aβ-and CT afferents, their impulses reach the central nervous system with different latencies: Aβ afferents are fast conducting, and CT afferents are slowly conducting. Using the time-resolved neuroimaging methods of magnetoencephalography (MEG), and stereotactic electroencephalography (SEEG) we have investigated the spatiotemporal dynamics of brain activity elicited by concomitant activation of Aβ and CT afferents during gentle stroking touch. Our results from MEG indicate that Aβ afference rapidly activates the posterior insula (within ~100 ms post onset of the tactile stimulus) and that CT afference reaches the posterior insula with a delay. This finding suggests that Aβ and CT afference is co-processed within the posterior insula, and that both afferent types play a role in affective processing of tactile events. We also have preliminary SEEG results that indicate that Aβ afference induces gamma synchronization in the posterior insula during gentle touch of the forearm. Together, results from both MEG and SEEG highlight the importance of considering Aβ afferents in the affective processing of gentle stroking touch of the hairy skin in humans.