Acute social and somatic stress alters cortical metaplasticity probed with non-invasive brain stimulation in humans.

Studying the neuronal mechanisms that govern the cortical adaptations to acute stress is critical for understanding the development of neuropsychiatric diseases. Homeostatic plasticity stabilizes the neural activity in which a previous synaptic event drives subsequent synaptic plasticity. In this study, we evaluated the effect of acute stress induced with the socially evaluated cold pressor test (SECPT) on cortical metaplasticity in humans using a non-invasive brain stimulation protocol. After being exposed to the SECPT and control stress conditions, 30 healthy participants were tested for cortical metaplasticity assessed with changes in the amplitude of the motor evoked potential (MEP) induced by a single-pulse transcranial magnetic stimulation (TMS). Cortical metaplasticity was induced by combining priming with cathodal tDCS (cTDCS) followed by a sub-threshold 1-Hz repetitive stimulation (rTMS) test session. Our results showed that SECPT induced cardiovascular adaptations (increase in systolic, diastolic blood pressure, and heart rate), indicating that SECPT effectively induced acute stress. Also, in our experiments stimulation of subjects with 1-Hz rTMS after they had undergone the SECPT condition induced inhibition of MEP whereas 1-Hz rTMS administered after the control condition induced a facilitatory (physiologic) response pattern. Here we observed that acute stress impairs homeostatic metaplasticity. The dysfunctional regulation of cortical plastic changes after stress could play a pivotal role in the pathogenesis of neurological and psychiatric diseases.