Cortical responses to tactile imagery: a high-density EEG study of the μ-rhythm event-related desynchronization and somatosensory evoked potentials

Tactile imagery (TI) engages somatosensory cortices in both hemispheres, along with widespread brain regions associated with the imagery process itself. Actively simulating touch can influence the processing of actual tactile stimuli, as reflected by modulations in somatosensory evoked potentials (SEPs) components. This study uses high-density electroencephalography (EEG) and sLORETA-based source localization to analyse cortical sources of SEPs components susceptible to active skin sensations imagery. Twenty healthy participants performed TI and tactile attention (TA) tasks. TI enhanced early SEP components (P100), indicating engagement of primary somatosensory cortical networks. This was accompanied with robust μ-rhythm event-related desynchronization (ERD) localized to the postcentral gyrus. While TA also elicited μ-ERD, its cortical distribution was broader, suggesting involvement of more distributed and possibly non-specific attentional mechanisms. Notably, sensor-space analysis revealed an enhanced late frontal P200 peak during TI, potentially indicating increased frontal activation. However, source-space analysis confirmed the absence of frontal pole involvement in SEPs during TI, underscoring the importance of accurate source localization. Thus, TI was found to significantly activate primary somatosensory cortices, influencing early stages of real tactile stimulus processing. Its effects were more spatially focused compared to those induced by TA. These findings suggest that TI could be a prospective approach for sensorimotor rehabilitation. On the other hand, TA could provide an effortless method for modulating sensorimotor rhythms in BCI control.