Transcranial direct current stimulation for empathy: a systematic review and meta-analysis.

Bahji, Anees; Forth, Evan; Yang, Cheng-Chang; Khalifa, Najat

BACKGROUND Transcranial Direct Current Stimulation (tDCS) has been used to modulate empathy, but no studies have meta-analyzed the evidence base for its efficacy. OBJECTIVES This study aimed to determine the efficacy of tDCS at modulating empathy. METHODS We conducted a systematic review and meta-analysis of randomized controlled trials involving anodal or cathodal versus sham tDCS to modulate empathy in healthy adults and clinical populations. Random-effects modelling was applied to pooling overall efficacy estimates using standardized mean differences (Hedge's g) and 95% confidence intervals. Outcome measures for tasks designed to measure empathy were reaction time and accuracy. RESULTS We identified 20 trials (from 28 reports), involving 1013 participants (55% male; mean age 31.2 years; range 21-69 years). Most studies involved healthy volunteers. Anodal tDCS improved lab-based computerized measures of cognitive empathy by way of reduced reaction time after we excluded one outlier (g = -0.19, 95% CI: -0.33 to -0.06, k=21, I2 <0.1%) and improved lab-based computerized measures of accuracy (g = 0.37; 95% CI 0.19 to 0.56, p < 0.001, k = 13) on related tasks. However, cathodal tDCS did not impact performance on any of these tasks. CONCLUSION Anodal tDCS appears to improve lab-based computerized measures of cognitive empathy in healthy adult volunteers. While the evidence provided by this review may be of relevance to individuals with impaired empathic capabilities, the generalizability of our findings is geared towards nonclinical populations given the preponderance of healthy volunteers in our review. Hence, it is not clear if moderate improvements in speed and accuracy on lab-based computerized empathy measures would lead to meaningful clinical improvements. Future studies should consider the use of tDCS to modulate empathy in clinical populations.