Somatosensory electrical stimulation improves skill acquisition, consolidation, and transfer by increasing sensorimotor activity and connectivity

The interaction between the somatosensory and motor systems is important for normal human motor function and learning. Enhancing somatosensory input using somatosensory electrical stimulation (SES) can increase motor performance, but the neuronal mechanisms underlying these effects are largely unknown. With electroencephalography (EEG), we examined whether skill acquisition, consolidation, and interlimb transfer after SES was related to increased activity in sensorimotor regions as assessed by the N30 somatosensory evoked potential or rather increased connectivity between these regions as assessed by the phase slope index (PSI). Right and left-hand motor performance and EEG measures were taken before, immediately after, and 24 hours (Day 2) after either SES (n = 12; 5 males) or Control (n = 12; 5 males). The results showed skill acquisition and consolidation in the stimulated right hand immediately after SES (6%) and on Day 2 (9%) and interlimb transfer to the non-stimulated left hand on Day 2 relative to Control (8%, all p < 0.05). Increases in N30 amplitudes correlated with skill acquisition while PSI from electrodes that represent the posterior parietal and primary somatosensory cortex to the electrode representing the primary motor cortex correlated with skill consolidation. In contrast, interlimb transfer did not correlate with the EEG-derived neurophysiological estimates obtained in the present study, which may indicate the involvement of subcortical structures in interlimb transfer after SES. In conclusion, weak peripheral somatosensory inputs in the form of SES improve skill acquisition, consolidation, and interlimb transfer that coincide with different cortical adaptations including enhanced N30 amplitudes and PSI.