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Altered cortical inhibition after electroconvulsive therapy (ECT), repetitive transcranial magnetic stimulation (rTMS) and vagus nerve stimulation (VNS)
It has been suggested that the GABA neurotransmitter system may contribute to the mechanism of action in the treatment of major depressive disorders. Reports demonstrating increased GABA-ergic activity after administration of different classes of clinically effective antidepressants and electroconvulsive therapy led to the anticonvulsant hypothesis of antidepressant mechanism of action. Diagnostic transcranial magnetic stimulation (dTMS) has been used to demonstrate at least two different cortical inhibitory processes: the postexcitatory inhibition (PI) and the intracortical inhibition (ICI). Using dTMS we investigated excitatory and inhibitory cortical functions after a treatment course of ECT, rTMS or VNS in patients with major depressive disorder. The main findings of the present study were an increase of PI and ICI in patients responding to one of these therapeutic interventions. These findings indicate an enhanced activity of inhibitory circuits in human motor cortex after successful antidepressant therapy.