Perceptual plasticity is mediated by connectivity changes of the medial thalamic nucleus

It is well known that the threshold for somatosensory perception may adapt to different inputs. Recent studies suggest the presence of a modulating effect of somatosensory inputs on the spinal dorsal horn. However, the effects of somatosensory inputs on cerebral processing and, in particular, on the functional and effective connectivity of the somatosensory brain network, are poorly understood. In this study, we investigated the longitudinal impact of somatosensory stimuli on the resting-state functional connectivity and effective connectivity of the somatosensory brain network. We performed resting-state functional magnetic resonance imaging (fMRI) in 12 healthy subjects before and after unilateral electrical median nerve stimulation. We combined this analysis with a psychophysiological examination of changes of the perception threshold. We found that the unilateral median nerve stimulation increased the perception thresholds bilaterally and increased the resting-state functional and effective connectivity between most cortical areas of the somatosensory network. The major finding, however, was a decreased resting-state functional connectivity between both secondary somatosensory cortices and the bilateral medial nuclear complex of the thalamus. This decreased connectivity was correlated with increased perception thresholds. These findings emphasize the importance of the medial thalamic nucleus for the perceptual awareness of somatosensory stimuli.