Effects of mid-frontal brain stimulation on sustained attention

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.