Churning Better Transcranial Direct Current Stimulation Outcome with Accelerated Protocols: Understanding the Non-linear Dynamics through Metaplasticity.

Recent advances in the application of transcranial direct current stimulation in psychiatry include providing about five sessions of stimulation in a short period of time with an inter-session interval of 20 minutes. Such "accelerated" protocols may reduce treatment duration and have differential neurophysiological benefits. In this narrative review, we discuss the potential impact of such protocols on the temporal aspects of metaplasticity of the neurons, non-linear behaviour of the neuronal population and brain criticality. We discuss the potential neurophysiological mechanisms involved and how to translate these mechanisms to specific stimulation parameters like duration of session, inter-session interval and number of sessions in a day. The expected benefits and necessary precautions required for accelerated protocols are also discussed.