What the dynamic between hemispheres can teach us about attention – a TMS-EEG study

Unilateral stroke can disrupt the equilibrium between hemispheres, which is necessary for efficient attentional deployment. Given the variability characterizing stroke patients’ cognitive profiles and the classical neuropsychological tools’ lack of sensitivity, we used a combination of behavioral and imaging techniques to identify biomarkers of interhemispheric equilibrium that predict attentional performance. Since the posterior parietal cortex (PPC) is a crucial node of the dorsal attention network and the PPC-to-PPC communication supports the interhemispheric equilibrium, we investigated whether the PPC-to-PPC communication predicts attentional performance. Given that the PPC is also a generator of alpha oscillations and alpha power correlated with attentional deployment, we tested whether interhemispheric asymmetries in alpha predict attentional performance.

The within-subjects experiment consisted of two sessions. In the first session, healthy participants underwent resting-state fMRI that allowed us to identify individualized TMS targets. In the second session, participants underwent both Rest- and TMS-EEG recordings, 100 TMS pulses at 65% of the maximum stimulator output over the right and 100 over the left PPC individualized target. EEG recordings were preceded by a set of behavioral tasks quantifying different components of attention such as visuospatial attention, attentional orienting and reorienting, and temporal selective attention.

Preliminary results showed that the interhemispheric signal propagation (IPS) from right to left PPC predicted participants’ performance in task quantifying spatial and temporal attention, while both the PPC and FEF alpha asymmetry index predicted participants’ search efficiency.

This is the first fMRI-guided TMS-EEG study to investigate ISP and alpha asymmetry index as possible biomarkers for attentional performance.