Quantittative measurement of changes in 23Na MRI associated with transcranial direct current stimulation (tDCS) of the motor cortex

Abstract

Studies from both animal and humans indicate that tDCS changes in brain function are likely mediated via changes in membrane permeability. The underlying mechanisms of these processes, however, are not well understood. The goal of this study was to investigate changes in total sodium concentration (TSC), measured with 23Na MRI, following tDCS of the motor cortex area in healthy volunteers. The motivation stemmed from the central role Na plays in neuronal permeability and brain activation. The study's primary aim was to measure changes in TSC in the motor area before and after tDCS in each tissue.

We enrolled seven subjects, each particpating in 3 separate randomized sessions (one week apart): sham, anodal, or cathodal tDCS application preceded and followed by the MRI acquisition. For tDCS, a direct current of 2 mA (0.057 mA/cm2) was delivered for 20 minutes via two surface electrodes (5 x 5 cm2) positioned over the left M1 area and the contralateral orbito-frontal cortex. Tissue-specific images, [NA]GM, [NA]WM, [NA]CSF, were obtained using the spatial linear regression partial volume correction (SLR PVEc) algorithm originally developed for ASL MRIr.

There was an increase of [Na] following anodal stimulation in the areas underneath of the site of the stimluation, such as BA4, BA6, corresponding to the motor cortex stimulated. Moreover, we found widespread changes following a pattern similar across subjects after anodal stimulation.

This is the first work that combines NA-MRI with non invasive brain stimulation techinques (NIBS). Using an "offline" experimental design we measured changes in [NA] in the motor area under anodal stimulation. The [Na] images were corrected for PVE using an algorithm previously applied in ASL MRI.

The preliminary findings from the present work can be importnat for better understanding the effect of NIBS in clinical application

Research Category and Technology and Methods

Translational Research: 9. Transcranial Direct Current Stimulation (tDCS)