FEF Excitability in Attentional Bias: A TMS-EEG Study

Abstract

The role of distinct cortical regions in guiding social orienting needs further investigation. Our aim was to explore the contribution of the frontal eye field (FEF) in early orienting of attention towards stimuli with social value. We used a TMS-EEG approach to investigate event related potentials (ERPs; no-TMS block) and TMS evoked potentials (TEPs; TMS block) during the cueing phase of a modified version of the dot-probe task, comparing competing (face vs. house) and not competing (house vs. house) conditions. Our results revealed an increased amplitude of ERP components in the competing condition, showing greater posterior N170 and fronto-central vertex positive potential (VPP) and an enhanced frontal negative component at 250-270 ms from cue onset. TMS pulses over the FEF induced similar N170 and VPP amplified components. In addition, in the ERPs, a reduced positivity at 400 ms was shown when the face appeared on the left side vs. the right side of space. In contrast, in the TMS blocks, we found lateralized effects on N170 depending on the side of face presentation. The enhanced cortical excitability induced by TMS over the right FEF significantly correlated with the performance on the behavioral task, suggesting a link between the FEF activity during the cueing phase of the dot-probe task and the subsequent behavioral response times to the targets.

Keywords: EEG; TMS; attention; competition; face; frontal eye field; social.

Figure 1

Experimental procedure and conditions of the dot-probe task. Following presentation of a fixation cross for 1,500 ms, cues were presented simultaneously for 500 ms. Reaction times (RTs) were measured from the onset of the target, which followed the cues until the button press. In TMS blocks, TMS was delivered over the right frontal eye field (FEF) at 140 ms from cue onset. The represented face picture is from the Karolinska Directed Emotional Faces database (AM08ANS).

Figure 2

Multichannel butterfly plot and topoplot of the competition (blue trace) and no competition (red trace) conditions for average event related potentials (ERPs; A) and TMS evoked potentials (TEPs; B). The gray bars define the time window where cluster-based analyses evidenced significant results. Topoplots show the signal topography at waves’ peaks (ERPs: 170 ms and 240 ms; TEPs: 160 ms and 185 ms). Significant clusters are evidenced in the topoplot of the cluster analysis (C).

Figure 3

Multichannel plot and topoplot of the left face (blue trace) and right face (red trace) conditions for ERPs (A) and TEPs (B). The gray bars define the time window where cluster-based analyses evidenced significant results. Topoplots show the signal topography at waves’ peaks (ERPs: 440 ms; TEPs: 160 ms and 185 ms). Significant clusters are evidenced in the topoplot of the cluster analysis (C).

Figure 4

Scatterplot of the correlations between the bias score and the Δglobal mean field power (ΔGMFP) in the significant time window of the TEP cluster analysis. (A) ΔGMFP refers to the difference in GMFP in the competition and no competition conditions in the time window of the positive cluster (120–195 ms from cue onset); bias (ms) refers to the difference in RTs in incongruent − congruent trials. (B) ΔGMFP refers to the difference in GMFP for left and right face presentation in the time window of the positive and negative clusters (150–200 ms from cue onset); bias refers to the difference in corrected RTs in incongruent − congruent trials for left face cues.