Effects of mid-frontal brain stimulation on sustained attention

Abstract

Vigilant attention is defined as the ability to sustain attention over longer periods of time in a non-stimulating environment. Previous studies have suggested an important role for the dorsomedial prefrontal cortex (mPFC) in vigilant attention. In this manuscript, we describe two experiments in which we aimed to enhance vigilant attention by applying transcranial electrical current stimulation over the mPFC. Specifically, we were interested in reducing the often observed decline in performance with time-on-task, the so-called vigilance decrement. In the first experiment, we applied transcranial direct current stimulation (tDCS) in a between-subject design (n=97): participants received either anodal, cathodal, or sham stimulation. In contrast to our prediction, we found no effect of stimulation on the vigilance decrement. In the second experiment, we applied transcranial alternating current stimulation (tACS). Participants received alpha and theta stimulation in two separate sessions (n=47, within-subject design). Here, we found a frequency-dependent effect on the vigilance decrement, such that contrary to our expectation, participants performance over time became worse after theta stimulation, compared to alpha stimulation. However, this result needs to be interpreted with caution given that at least part of this effect seems to be driven by the intensity of side effects experienced during the two stimulation frequencies. To conclude, across the two studies we were not able to reduce the vigilant decrement using tDCS or theta tACS.

Modulation of Sustained Attention by Theta-tACS over the Lateral and Medial Frontal Cortices

“…We stimulated both pMFC and LPFC, thereby providing novel evidence for the phase synchronization between the two areas. Another study showed no modulation effect of sustained attention when 4 Hz tACS was exerted between electrodes FCz and Cz and two reference electrodes were placed on the cheeks [ 14 ]. We argued that the complexity showed by these studies including ours highlighted the importance of electrode placements, which implied distinct underlying mechanisms.…”

“…For example, frontotemporal theta tACS with an in-phase protocol significantly improved working memory by synchronizing cortical oscillations [ 12 ]. TACS has also been demonstrated to modulate sustained attention through stimulating pMFC [ 13 , 14 ] or the occipitoparietal cortex [ 15 , 16 ], yet their effects were inconsistent. Given that pMFC-LPFC synchronization plays a crucial role in sustained attention, we expected that applying tACS could modulate theta-band pMFC-LPFC oscillations and ultimately affect sustained attention.…”