Tomographic and spatio-temporal correlates of short-term plasticity in human primary somatosensory cortex from magnetoencephagraphic (MEG) data

We trained humans to detect changes in the frequency of 21 Hz electrical stimulation applied to the right-hand digits 2+3+4 and recorded the MEG signal before, during and after the training. We evaluated changes for each digit and observed: (1) activations in the left primary somatosensory (L-SI) and medial parietal precuneus (PCu) areas; (2) after the training in L-SI, the 21 Hz spectral power increased for digits 3 and 4 over the stimulation period, while the 10 Hz spectral power increased for digit 3 only around the stimulus onset and offset; (3) only digit 3 showed significant change in the correlation between the two areas around the stimulus onset and offset, at the same latency ranges of increased 10 Hz spectral power. During the training, we found that the L-SI activation reflects the input frequencies of stimuli at early latencies but correlates with the subject's perception between low and high frequencies at later latencies.