Proactive cognitive control enables individuals to anticipate and prepare for upcoming cognitive demands. Whereas prior research highlights the involvement of the dorsolateral prefrontal cortex (DLPFC) in proactive cognitive control, the lateralization of this function remains unclear. In this single-blind, sham-controlled, within-subject, randomized preregistered study, 31 healthy participants (mean age=22.26, SD=4.01; 18 women) received, in three separate sessions, sham and active high-frequency (20hz) repetitive transcranial magnetic stimulation (HF-rTMS) over the left and right DLPFC before performing a blocked version of the antisaccade task in combination with pupillometry to assess proactive cognitive control. Although preregistered analyses with saccade latency (i.e., time to initiate the first saccadic movement) did not show a significant effect of HF-rTMS, exploratory analyses with fixation latencies (i.e., time to fixate the gaze at the correct target location) in antisaccade trials were significantly shorter after both active left and right DLPFC stimulation compared to sham. Moreover, analyses accounting for tonic pupil size showed that the pupil constriction during the anticipatory phase (reflecting phasic resource allocation) was smaller after active left and right HF-rTMS (vs sham) on prosaccade trials, and a smaller pupil constriction was associated with shorter fixation latencies in antisaccade trials. Tonic pupil size, reflecting sustained resource allocation, was significantly larger after left DLPFC stimulation and was associated with longer saccade and fixation latencies after sham, but not active stimulation. These findings provide important evidence that helps reconcile mixed results in the field by supporting the involvement of both left and right DLPFC in proactive cognitive control via the regulation of anticipatory allocation of cognitive resources.

Transcranial direct current stimulation (tDCS) of the prefrontal cortex (PFC) modulates the autonomic nervous system by activating deeper brain areas via top-down pathway. However, effects on the nervous system are heterogeneous and may depend on the amount of current that penetrates the brain due to individual brain anatomical differences. Therefore, investigated the variable effects of tDCS on heart rate variability (HRV), a measure of the functional state of the autonomic nervous system. Using three prefrontal tDCS protocols (1.5mA, 3mA and sham), we associated the simulated individual electric field (E-field) magnitude in brain regions of interest with the HRV effects. This was a randomized, double-blinded, sham-controlled and within-subject trial, in which participants received tDCS sessions separated by two weeks. The brain regions of interest were the dorsolateral PFC (DLPFC), anterior cingulate cortex, insula and amygdala. Overall, 37 participants (mean age = 24.3 years, standard deviation = 4.8) were investigated, corresponding to a total of 111 tDCS sessions. The findings suggested that HRV, measured by Root Mean Squared of Successive Differences (RMSSD) and high-frequency HRV (HF-HRV), were significantly increased by the 3.0mA tDCS when compared to sham and 1.5mA. No difference was found between sham and 1.5mA. E-field analysis showed that all brain regions of interest were associated with the HRV outcomes. However, this significance was associated with the protocol intensity, rather than inter-individual anatomical variability. To conclude, our results suggest a dose-dependent effect of tDCS for HRV. Therefore, further research is warranted to investigate the optimal current dose to HRV.

The tendency to ruminate (i.e., repetitive, self-referential, negative thoughts) is a maladaptive form of emotional regulation and represents a transdiagnostic vulnerability factor for stress-related psychopathology. Vagally-mediated heart rate variability (HRV), reflecting parasympathetic nervous system activity, is commonly used as a physiological marker of stress regulation. Past research has suggested a link between trait rumination and resting HRV at baseline; however, inconsistent results exist in healthy individuals. In this study, we investigated the association between the tendency to ruminate and resting HRV measured at baseline in a healthy population using a large cross-sectional dataset (N = 1189, 88% women; mean age = 21.55, ranging from 17 to 48 years old), which was obtained by combining samples of healthy individuals from different studies from our laboratory. The results showed no cross-sectional correlation between resting baseline HRV and trait rumination (confirmed by Bayesian analyses), even after controlling for important confounders such as gender, age, and depressive symptoms. Also, a nonlinear relationship was rejected. In summary, based on our results in a large sample of healthy individuals, baseline resting HRV is not a trait marker of the tendency to ruminate.