Abstract:

Emotion regulation is crucial to mental health and social life. Traditional view conceived emotion regulation as a deliberative process. However, there is growing evidence that emotion regulation can implement at an implicit level without or with limited involvement of the lateral prefrontal cortex (LPFC) that is responsible for cognitive control. Unlike explicit emotion regulation, we have few knowledge on the neural mechanisms underlying implicit emotion regulation. Here, we investigated the effect of excitatory the ventromedial prefrontal cortex (vmPFC) using transcranial direct current stimulation (tDCS) to provide causal evidence for the key role of the vmPFC in implicit emotion regulation.

This study had a mixed design, with group (anodal vs. sham) as the between-subject factor and priming type (reappraisal vs. baseline) as the within-subject factor. A total of 80 participants were recruited and randomly assigned to the anodal group and the sham tDCS group. The task was divided into two blocks, i.e., the implicit reappraisal block and the baseline block (Figure 1A). The order of the two blocks was counterbalanced within the participants in each group. At the beginning of each block, participants were required to complete a tDCS session (1.5 mA; 10 min for the active group and 1 min for the sham group). The anodal electrode was placed in the middle of Fz and Fpz and the ground electrode was placed under the chin). Then, participants completed six sessions of sentence unscramble task (10 trials per session) to prime the emotion regulation goal (Figure 1B). Each session of the sentence unscramble task was followed by a picture viewing task (5 trials) to evoke negative emotions (Figure 1C). The self-reported emotion rating and EEG signals were recorded during the picture viewing task. Half an hour after the end of the picture viewing task, participants were asked to rate the valence (1 = very unpleasant; 9 = very pleasant) of all viewed images in the picture viewing task.

The results showed that the experimental group (n = 40) reported lower negative emotional experience (experimental group: M = 0.32, SE = 0.01, control group: M = 0.28, SE = 0.01; F(1, 78) = 4.2, p = 0.043, η_p² = 0.051) and showed lower LPP amplitudes (experimental group: M = 0.80 µV, SE= 0.26, control group: M = 1.99 µV, SE = 0.26; F(1, 78) = 11.0, p = 0.001, η_p² = 0.124; Figure 2AC) when the vmPFC was activated in the cognitive reappraisal block compared to the control group (n = 40), indicating that excitatory vmPFC could effectively facilitate the ability of implicit emotion regulation. Furthermore, we also found that excitatory vmPFC can reduce the P1 amplitude (experimental group: M = 4.71 µV, SE = 0.40, control group: M = 6.12 µV, SE = 0.40; F(1, 78) = 6.1, p = 0.016, η_p² = 0.072; measured as the average amplitude of O1, O2) under both baseline and reappraisal conditions.

The above results indicated that activating the vmPFC could not only facilitate implicit emotion regulation but also reduce early attention distribution to negative stimuli. This study is the first attempt to use the tDCS technique to investigate priming-induced implicit emotion regulation. The results directly reveal the causal relationship between the vmPFC and implicit cognitive reappraisal, suggesting this brain region as a potential target of neural modulation to enhance the ability of implicit emotion regulation in clinical populations.

Key words: ventromedial prefrontal cortex, implicit emotion regulation, transcranial direct current stimulation, priming, cognitive reappraisal