Polarity-specific changes in the E-field and focality in mild cognitive impairment patients for HD-tDCS and reverse HD-tDCS

Abstract

Objective: This study analyzed polarity-specific changes in the electric field (E-field) and the focal point of tDCS stimulation for both High-Definition tDCS (HD-tDCS) and reverse HD-tDCS considering the head geometry of Mild Cognitive Impairment (MCI) patients. The distance between the left preauricular (LPA) and right preauricular points as well as the inion and nasion were calculated in 3D to measure correlations.

Methods: T1-weighted structural MRI images were obtained from the Alzheimer's Disease Neuroimaging Initiative (ADNI). We utilized SimNIBS 3.2.6 for MRI image processing, 3D head model generation, application of HD-tDCS and reverse HD-tDCS, E-field analysis, and other relevant parameters.

Results: Electric field analysis was conducted on all 10 MCI subjects to examine the distribution and focality of the peak electric field. Despite using uniform stimulation for all subjects, variation was observed in the peak electric field (at the 99.9th, 99th, and 95th percentiles) and focality (at the 75th and 50th percentiles). However, the peak electric field and focality values remained consistent when comparing HD-tDCS and reverse HD-tDCS. The only differing quantities were associated with the normal component influenced by the changing direction of the current in HD-tDCS and reverse HD-tDCS.

Conclusion: HD-tDCS and reverse HD-tDCS exhibited distinct values for the electric field strength and focality. HD-tDCS demonstrated more positive fields and inflow current compared to reverse HD-tDCS, making it suitable for excitatory effects. Conversely, reverse HD-tDCS would be more appropriate for inhibitory effects due to the prevalence of more negative fields and outflow current.