Fig 1.
A sponge was placed over the right dlPFC (F4) to stimulate the brain using weak electric current (2 mA) for 20 min. Another sponge was placed on the left cheek. This figure was adapted from the protocol summary panel in Starstim software NIC (copyright notice © Neuroelectrics SLU).
Fig 2.
Four types of stimuli were presented. Two stimuli were Pavlovian-congruent: go action to win reward and no-go action to avoid punishment. The remaining two stimuli were Pavlovian-incongruent: go action to avoid punishment and no-go action to win reward. Participants were instructed to maximize reward and minimize punishment by learning the correct action for each stimulus. Participants were asked to select an action when a target was presented. The reward was a picture of money, 1000 won (approximately US$ 1), whereas the punishment was an electric shock to the wrist. RT: response time, ITI: intertrial interval.
Table 1.
Descriptive statistics.
Fig 3.
Pavlovian bias in the punishment domain decreased in the anodal session (accuracy).
In the sham group, we found a significant difference in behavioral accuracy between the punishment conditions, which indicated the presence of Pavlovian bias, particularly in the punishment domain. This difference was not observed in the anodal group. The behavioral index of Pavlovian bias in the punishment domain also showed significantly lower bias in the anodal group than in the sham group. Error bars indicate SEM. *p < 0.05.
Table 2.
Model comparison (LOOIC).
Fig 4.
Pavlovian bias parameter in the punishment domain and other parameters decreased in the anodal session (modeling parameter).
We found lower parameter values in irreducible noise, go bias, and Pavlovian bias in the punishment domain in the anodal session, compared with the sham session. The decrease in Pavlovian bias in the punishment domain is consistent with the behavioral analysis. * 95% highest density interval of the posterior difference did not include zero.
Table 3.
Posterior mean (95% HDI highest density interval) of group mean parameters in anodal and sham groups.