EG: sample size of the experimental group; CG: sample size of the control group; NT: no treatment; PLA: placebo intervention; AT: alternative treatment; TAU: treatment as usual; Y: yes (criterion fulfilled); Y/N: yes/no (criterion partly fulfilled); C: clinical outcome measure; P1: well-established subjective test of depression; M: test of mood; Cog: cognitive feature of depression; Positive: individual regions of interest active while positive vs. neutral stimuli observed; L: left; DLPFC: dorsolateral prefrontal cortex; ACC: anterior cingulate cortex; FαA, FβA: EEG frontal alpha/beta asymmetry; ↑: upregulation; ↓: downregulation.