Functional Interaction between Right Parietal and Bilateral Frontal Cortices during Visual Search Tasks Revealed Using Functional Magnetic Imaging and Transcranial Direct Current Stimulation

Abstract

The existence of a network of brain regions which are activated when one undertakes a difficult visual search task is well established. Two primary nodes on this network are right posterior parietal cortex (rPPC) and right frontal eye fields. Both have been shown to be involved in the orientation of attention, but the contingency that the activity of one of these areas has on the other is less clear. We sought to investigate this question by using transcranial direct current stimulation (tDCS) to selectively decrease activity in rPPC and then asking participants to perform a visual search task whilst undergoing functional magnetic resonance imaging. Comparison with a condition in which sham tDCS was applied revealed that cathodal tDCS over rPPC causes a selective bilateral decrease in frontal activity when performing a visual search task. This result demonstrates for the first time that premotor regions within the frontal lobe and rPPC are not only necessary to carry out a visual search task, but that they work together to bring about normal function.

Brain stimulation improves cognitive control by modulating medial‐frontal activity and preSMA‐vmPFC functional connectivity

“…In the tDCS literature, it is not uncommon to observe activation in areas other than the stimulation site [e.g., Ellison et al, ]. One plausible explanation for the current results is that offline atDCS may have facilitated neural activity within the preSMA and further transformed this facilitation effect via functional connectivity to the vmPFC.…”

Individual Differences and State-Dependent Responses in Transcranial Direct Current Stimulation

“…With this rationale, one potential factor is that tDCS may excite unintended frontal regions that then lead to the different findings across studies. Additionally, the asymmetrical nature of tDCS effect has been documented by many studies (e.g., Ellison et al, 2014). Here we also did not observe any cathodal-induced performance changes.…”

Transcranial Electrical Stimulation as a Tool to Enhance Attention

“…Ball et al (2013) investigated the effect of anodal and cathodal tDCS on both of these areas. They observed no effects of anodal tDCS, but cathodal stimulation to the right posterior parietal cortex increased reaction times, a finding later replicated by the same group (Ellison et al 2014). Interestingly, an earlier study did find that anodal stimulation over the parietal cortex decreased search time (Bolognini et al 2010a).…”