Induction of LTD-like plasticity by paired associative stimulation is blocked by intracortical inhibition

Objective/Aims: Paired associative stimulation (PAS) of the hand motor cortex (M1) may induce depressant effects on corticospinal excitability. It has been likened to the long-term depression of excitatory synapses as studied in vivo animal work. We hypothesized that activation of inhibitory and/or facilitatory interneurons during PAS may modulate LTD-like plasticity. Methods: 60 subjects were examined (20 in every condition). PAS10 was performed by combining repetitively electric stimulation of the median nerve with subsequent TMS of the contralateral M1 (interstimulus interval 10 ms, 180 pairs, 0.1 Hz). Effect…