Prefrontal anodal High Definition-tDCS has limited effects on emotion regulation

This is the authors' abstract. We don't add key points for this paper.

Poor emotional regulation has been associated with core symptoms of a broad spectrum of mental health problems and neurodevelopmental disorders [1,2], and is a key cognitive ability to ensure psychological well-being. Indeed, healthy emotion regulation skills are a protective factor for the development of mental health conditions in young adulthood [3]. The ventrolateral prefrontal cortex (vlPFC) has been identified as one of the key brain regions underlying successful emotion regulation [4]. Diminished activity within this region has been linked to a reduced use of adaptive emotion regulation strategies such as cognitive reappraisal (i.e., the ability to reduce negative emotional states by generating positive interpretations) [5]. Thus, the vlPFC appears to be a promising target for non-invasive brain stimulation (NIBS) techniques to enhance emotion-regulatory function in patients with affective and social disorders. To date, only four studies have investigated the role of the vlPFC in cognitive reappraisal using transcranial direct current stimulation (tDCS [6e9]). In two of these studies, He et al., 2018, 2020 demonstrated that anodal tDCS over the right vlPFC improved reappraisal skills in the context of social exclusion in healthy participants [6], but failed to show improvements in individuals with high depressive traits [7]. Marques et al., 2018 found a reduction in the subjective valence ratings for negative imageswhen applying anodal tDCS over the left vlPFC. Conversely, Vieira et al., 2020 showed no improvements in the subjective valence ratings for negative images following the same stimulation protocol described in Marques et al., 2018. When it comes to the use of brain tDCS in emotion regulation, there is a need to integrate new procedures to improve the understanding of the effects of the stimulation over the vlPFC to modulate cognitive reappraisal skills. However, the current procedures fall short of achieving this due to four main challenges: (1) the lack of highly targeted stimulation protocols; (2) the need to reduce inter-individual variability among participants; (3) the need to apply brain stimulation protocols while engaging the targeted region; and (4) the selection of adequate biomarkers to accurately measure the modulation response. To achieve this, here we incorporated methods to i) reduce individual variability (i.e., withinsubjects vs. between-subjects design), ii) increase focality and targeted stimulation (i.e., high definition tDCS [HD-tDCS] vs. conventional tDCS), iii) produce more robust stimulation effects with the use of a cognitive task that specifically engages the vlPFC, and iv) utilise a reliable electrophysiological marker of emotion regulation (i.e., the late positive event-related potential [LPP]). Our study examined the effects of anodal HD-tDCS compared to sham (placebo) HD-tDCS over the right vlPFC in healthy young