Targeted multielectrode tDCS increases functional connectivity within the arcuate fasciculus network: An exploratory study and analysis

Abstract

Non-invasive electrical stimulation can modulate not only targeted local intrinsic brain activity, but also activity in remote, yet connected brain regions. Such modulation of connected regions and/or entire networks may account for some of the treatment-induced changes in complex behaviors and cognitive processes. The current study tested whether strategically-placed electrodes delivering transcranial direct current stimulation (tDCS) to single or several nodal cortical regions within a structurally-defined network, the arcuate fasciculus network (AF-network), have the potential to strengthen functional connectivity between network regions more effectively than a single electrode placed over an individual nodal region within that same network. Concurrent tDCS-MR imaging was utilized to acquire resting-state fMRI while delivering 4 mA of direct current in multiple OFF-ON-OFF epochs with either a single- or multielectrode anodal montage over nodal cortical regions of the AF-network. Multielectrode anodal stimulation significantly changed functional connectivity between ipsilateral AF-network nodes while no single anodal electrode placed over one nodal region of the right AF-network did so. This significant change in functional connectivity was specific to the targeted right AF-network and could not be seen in other unrelated networks in the same hemisphere (e.g., the inferior longitudinal fasciculus). Functional connectivity measures were compared with electric field modeling measures to estimate target engagement. Regional homogeneity of current tangential to the cortical surface of the AF-network-targeted cortical nodes (J tangent) significantly predicted functional connectivity between these cortical nodes. Taking the anatomy and the drivers of a targeted network into account will help advance the efficacy of an intervention and precision medicine in general.