MEG study of short-term plasticity following multiple digit frequency discrimination training in humans

We trained four right-handed male subjects to detect small changes in the frequency of 21 Hz electrical stimulation applied to digits 2+3+4 of the right hand for 4 hours. Before and after the training, we recorded magnetoencephalographic (MEG) signals when the stimulation was applied to digit 2-5 separately using a whole-head MEG system. We applied tomographic analysis to the MEG data to track the evolution of activity over the entire brain every 1.6 ms and evaluated the change for each digit before and after the training. In summary: (1) subjects improved in discrimination performance with training; (2) activations were identified in the left primary somatosensory (L-SI) and medial parietal precuneus (PCu) areas, but no systematic changes were observed in location and strength of activation of these two areas; (3) after 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 around stimulus onset and offset; (4) only digit 3 showed significant change of correlation between L-SI and PCu areas around the stimulus onset and offset, coincident with the increased 10 Hz spectral power. Our results suggest that short-term plasticity is associated with changes in timing and interaction between cortical areas.