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Abstract

Transcranial magnetic stimulation (TMS) is a non-invasive technique to modulate brain activity. Previously, we leveraged biophysical modeling of the induced electric field (E-field) to map causal structure-function relationships in the primary motor cortex. Here, we transfer this localization approach to attention network, which helps to understand the TMS effect on a higher cognitive function. Pinpointing the cortical stimulation target to modulate attentional processes will ultimately allow for an optimized stimulation scheme, and thus, boost the effectiveness of TMS mapping.

Thirty right-handed healthy subjects (15 female, mean age 30.8 ± 5.3 years) were recruited to participate in one MRI and two TMS experiments. the fMRI peak activity within the rIPL (right inferior parietal lobe) during a Posner-like attention task provided the center target for TMS (Figure 1). First, subjects underwent 500 Posner-task trials with 5 TMS pulses at 10 Hz each to potentially impact attentional processing. Importantly, the stimulation site was randomly selected for each trial to induce a selection of different cortical exposures. By analyzing the effect of the local E-field exposure on the attentional performance we then identify the true cortical target. These targets are then validated in a second TMS experiment and with respect to the fMRI activation peak.

The fMRI results show that during the stimulus-driven reorienting of attention, distributed brain regions from different networks were activated, especially the reorientation network. The locations with the highest goodness of fit (R2) are different from the activation peaks among subjects (Figure 2). This potentially identifies differences in BOLD-measured activity and TMS-evoked neuronal effects.