Does non-invasive brain stimulation modulate emotional stress reactivity?

Abstract

Excessive emotional responses to stressful events can detrimentally affect psychological functioning and mental health. Recent studies have provided evidence that non-invasive brain stimulation (NBS) targeting the prefrontal cortex (PFC) can affect the regulation of stress-related emotional responses. However, the reliability and effect sizes have not been systematically analyzed. In the present study, we reviewed and meta-analyzed the effects of repetitive transcranial magnetic (rTMS) and transcranial direct current stimulation (tDCS) over the PFC on acute emotional stress reactivity in healthy individuals. Forty sham-controlled single-session rTMS and tDCS studies were included. Separate random effects models were performed to estimate the mean effect sizes of emotional reactivity. Twelve rTMS studies together showed no evidence that rTMS over the PFC influenced emotional reactivity. Twenty-six anodal tDCS studies yielded a weak beneficial effect on stress-related emotional reactivity (Hedges' g = -0.16, CI95% = [-0.33, 0.00]). These findings suggest that a single session of NBS is insufficient to induce reliable, clinically significant effects but also provide preliminary evidence that specific NBS methods can affect emotional reactivity. This may motivate further research into augmenting the efficacy of NBS protocols on stress-related processes.

Keywords: emotion; repetitive transcranial magnetic stimulation; review; stress; transcranial direct current stimulation.

Fig. 1

Example of simulated images of induced electric fields by an rTMS and a tDCS montage (SimNIBS 2.1, Thielscher et al., 2015). Note the difference in focality and magnitude of the electric fields induced by the two NBS techniques. The depicted rTMS-induced field simulation is based on a pulse with a current change of 40 A/μs, corresponding to 40% maximum stimulator output of a rapid rate stimulator, from a figure-of-eight double 70 mm coil placed over the 10–20 system electrode position F3 (left DLPFC). The depicted tDCS-induced field simulation is based on a direct current with an intensity of 2.0 mA flowing between a 5x7 cm anode and a 5x7 cm cathode, placed over electrode position F3 (left DLPFC) and Fp2, respectively.

Fig. 2

PRISMA flow diagram.

Fig. 3

Forest plot of the separate outcomes of anodal tDCS studies. The figure additionally depicts for each study the sample sizes of active tDCS and sham tDCS conditions (sham sample size is left blank for crossover studies), the target area for anodal stimulation, the type of stress induction in the experiment and the outcome measure.

Fig. 4

Funnel plot of anodal tDCS studies. Note: because two studies reported many separate outcomes (Marques et al., 2018; Rêgo et al., 2015), the standard errors of their effects were increased by the RVE correction. These effects therefore appear at the bottom of the plot.

Fig. 5

Methodological quality and risk of bias of the included studies.