Background~Transcranial direct current stimulation encompasses the induction of a relatively weak constant current flow through the cerebral cortex via scalp electrodes . Dependent on stimulation polarity, this results in a modulation of cortical excitability and spontaneous neural activity. The technique was established in the 1950s and 1960s primarily in animals. In these early studies it was shown that subthreshold DC stimulation increases spontaneous neuronal activity if the anode is placed above or within the cortex, while exposure to cathodal polarity results in reduced activity. This is caused by a subthreshold membrane depolarization by anodal and a hyperpolarization by cathodal stimulation. It was demonstrated in humans that the after-effects of tDCS depend on modifications of NMDA receptor-efficacy. The after-effects of tDCS are blocked by the NMDA receptor antagonist dextromethorphan, and prolonged by the partial NMDA receptor-agonist D-cycloserine. This tDCS polarity-dependent alteration of NMDA receptor function seems to be initiated by the respective membrane potential shift and probably by the accompanying cortical activity modification,because it is prevented by the sodium channel blocker carbamazepine. Intraneuronal calcium concentration also contributes, because calcium channel antagonists eliminate the excitability-enhancing after-effects of anodal tDCS. Recently, tDCS has been reported to be a novel, non-invasive and safe therapeutic tool to treat neuropsychiatric disorders including depression. This therapeutic tool has been reported to show promising effect in treating unipolar and bipolar depression. However, the sample sizes have been small. Further work is needed to see if these early promising studies replicate. Much evidence has indicated that patients with depression show hypoactivity over left dorsolateral prefrontal cortex (DLPFC) and hyperactivity over right DLPFC. We therefore hypothesize that tDCS over DLPFC with anode placed at left DLPFC and cathode placed at right DLPFC would reduce depressive symptoms in patients with unipolar depression and bipolar depression.~The study aimed to investigate whether tDCS over DLPFC could modify depressive symptoms, neurocognitive function and heart rate variability of unipolar and bipolar depression.~Study design: open-label study.~Participants: 60 patients with unipolar depression and 60 with bipolar depression.~Others: see Arms and Interventions, Eligibility Criteria or Outcome Measures.
The study aimed to investigate whether transcranial direct current stimulation could improve depressive symptoms, neurocognitive function and modulate heart rate variability in unipolar and bipolar depression.