State-of-art neuroanatomical target analysis of high-definition and conventional tDCS montages used for migraine and pain control

Abstract

Although transcranial direct current stimulation (tDCS) studies promise to modulate cortical regions associated with pain, the electric current produced usually spreads beyond the area of the electrodes' placement. Using a forward-model analysis, this study compared the neuroanatomic location and strength of the predicted electric current peaks, at cortical and subcortical levels, induced by conventional and High-Definition-tDCS (HD-tDCS) montages developed for migraine and other chronic pain disorders. The electrodes were positioned in accordance with the 10-20 or 10-10 electroencephalogram (EEG) landmarks: motor cortex-supraorbital (M1-SO, anode and cathode over C3 and Fp2, respectively), dorsolateral prefrontal cortex (PFC) bilateral (DLPFC, anode over F3, cathode over F4), vertex-occipital cortex (anode over Cz and cathode over Oz), HD-tDCS 4 × 1 (one anode on C3, and four cathodes over Cz, F3, T7, and P3) and HD-tDCS 2 × 2 (two anodes over C3/C5 and two cathodes over FC3/FC5). M1-SO produced a large current flow in the PFC. Peaks of current flow also occurred in deeper brain structures, such as the cingulate cortex, insula, thalamus and brainstem. The same structures received significant amount of current with Cz-Oz and DLPFC tDCS. However, there were differences in the current flow to outer cortical regions. The visual cortex, cingulate and thalamus received the majority of the current flow with the Cz-Oz, while the anterior parts of the superior and middle frontal gyri displayed an intense amount of current with DLPFC montage. HD-tDCS montages enhanced the focality, producing peaks of current in subcortical areas at negligible levels. This study provides novel information regarding the neuroanatomical distribution and strength of the electric current using several tDCS montages applied for migraine and pain control. Such information may help clinicians and researchers in deciding the most appropriate tDCS montage to treat each pain disorder.

Keywords: HD-tDCS; finite-element modeling; neuromodulation; pain; transcranial direct current stimulation.

Figure 1

Three different conventional tDCS montages are illustrated (first column, from the top to the bottom): M1-SO motor (cortex-supraorbital), DLPFC (dorsolateral prefrontal cortex bilateral) and Cz-Oz (vertex-occipital cortex). Electric field maps generated in outer cortical regions and inner structures (insula, cingulate gyrus, thalamus and brainstem) are illustrated in the next five columns (from the left to the right).

Figure 2

Electric field maps produced by two methods of high-definition (HD)-tDCS: HD-tDCS 4 × 1 and H.O.P.E. HD-tDCS 2 × 2 (first column from the top to the bottom) in outer (second column) and inner structures (third to sixth, from the left to the right).