The impact of brain morphometry on tDCS effects on GABA levels

Transcranial direct current stimulation (tDCS) applied over both dorsolateral prefrontal cortices (DLPFCs) can change neurotransmitter levels when measured with concurrent magnetic resonance spectroscopy (MRS) [1,2]. For instance, tDCS elevated prefrontal GABA levels in adults with gambling disorder (GD) [1]. Such effect may be clinically meaningful as medications targeting the GABAergic system can reduce craving [3] and impulsivity in GD [4]. However, there are still several unknowns on how tDCS influences brain activity. One factor that may influence tDCS effects is brain morphometry. This is of particular interest for populations known to display altered morphometry, such as GD [5]. Further, animal studies showed that neuron morphology influences electric field stimulation in brain slices. Direct current is thought to favor depolarization of pyramidal neurons in layer V [6]. Considering that a greater number of neurons are found in areas of larger volume [7], one could predict that brain areas with greater cortical volume have more pyramidal neurons that respond to tDCS. The goal of this exploratory study was to investigate the impact of brain morphometry on tDCS effects on GABA levels in adults with GD. We hypothesized that greater tDCS-induced elevation of GABA levels will correlate with greater volume and thickness of the DLPFCs.