Abstract
Transcranial direct current stimulation (tDCS) has been recognized as a promising tool for investigating the causal relationship between specific brain areas of interest and behavior. However, the reproducibility of previous tDCS studies is often questioned because of failures in replication. This study focused on the effects of tDCS on one cognitive domain: beauty perception. To date, the modulation of beauty perception by tDCS has been shown in two studies: Cattaneo et al. (2014) and Nakamura and Kawabata (2015). Here, we aimed at replicating their studies and investigating the effects of tDCS on beauty perception using the following parameters: (1) cathodal stimulation over the medial prefrontal cortex (mPFC) (Nakamura and Kawabata, 2015); (2) anodal stimulation over the left dorsolateral prefrontal cortex (lDLPFC) (Cattaneo et al., 2014). We also performed a more focal stimulation targeting the orbitofrontal cortex (OFC) to determine the optimal stimulation site for modulating beauty perception (3). Participants rated the subjectively-perceived beauty of the images before and after the tDCS administration. We divided images into four clusters according to the obtained scores in our preliminary study and examined changes in beauty ratings in each image cluster separately to exclude factors, such as stimuli attributions that may reduce tDCS effects. The results showed no strong effects of tDCS with the same parameters as in previous studies on beauty rating scores in any image cluster. Likewise, anodal stimulation over the OFC did not result in a change in rating scores. In contrast to previous studies, the current study did not corroborate the effects of tDCS on beauty perception. Our findings provide evidence regarding the recent reproducibility issue of tDCS effects and suggest the possible inflation of its effects on cognitive domains.
Highlights
Transcranial direct current stimulation is a major method that compensates for the drawbacks of neuroimaging techniques, i.e., the inability to prove causality between changes in brain activation and observed behaviors
Contrary to the finding of Nakamura and Kawabata (2015), we found no strong effects of cathodal Transcranial direct current stimulation (tDCS) over the medial prefrontal cortex (mPFC) on beauty perception compared to the sham stimulation condition in any clusters (Figure 5A)
This finding was consistent across all image clusters (BF > 1). In this series of studies, we evaluated the effects of tDCS on beauty perception using three different electrode montage on beauty perception: (1) cathodal tDCS over the mPFC (Nakamura and Kawabata, 2015), (2) anodal tDCS over the lDLPFC (Cattaneo et al, 2014), and (3) anodal tDCS over the orbitofrontal cortex (OFC)
Summary
Transcranial direct current stimulation (tDCS) is a major method that compensates for the drawbacks of neuroimaging techniques, i.e., the inability to prove causality between changes in brain activation and observed behaviors. By delivering a low-intensity, direct current to cortical areas, tDCS is considered to facilitate or inhibit spontaneous neuronal activity and modulate cortical area excitability localized below the stimulating electrode (Nitsche and Bolognini, 2013), inducing modulation of behavioral performance (Nitsche et al, 2008). Researchers have used tDCS to report causal evidence that a stimulated brain region is involved in the behavior of interest (Filmer et al, 2014). A sizeable number of studies have reported the effectiveness of prefrontal area stimulation in improving cognitive performance (Gladwin et al, 2012; Nelson et al, 2014; Ferrari et al, 2015; Abend et al, 2018). Researchers may have selectively reported only significant results, they conducted many preliminary studies with various electrode placements
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