Influence of gender-related differences in transcranial direct current stimulation: A Computational Study

Gender-related anatomical differences have been reported with respect to brain and cerebrospinal fluid. The cortical induced electric field (EF) in transcranial direct current stimulation (tDCS) depends both on the dose (electrode montage and applied current) and the individual anatomical details. Therefore in spite of fixed dose, one can expect gender-related differences to impact induced EF which in turn would influence tDCS outcome. The abundance of promise with tDCS in both research and clinical domains is also accompanied with variability in response. The in-constant induced cortical EF is one of the main contributors of this variability. The aim of this study is to quantify the effects of the gender-related morphological changes on tDCS induced cortical EF. MRI data were obtained for 10 healthy individuals (5 males: M1-M5 and 5 females: F1-F5) spanning ages 27-47 years. Finite element models derived from the individual MRI and simulating the classic left motor cortex contralateral supraorbital (C3-SO) montage were used to predict the cortical EF. The percentage tissue volume were also determined to illustrate anatomical differences in the dataset considered. Findings indicate that induced EF is higher in female head models on an average than male head models across several metrics. While the average peak EF value in female head models was comparable to that of male head models, the mean and median values were 11.6% and 10% higher. On an individual basis, the highest peak value was observed in a female subject F3 (0.83 V/m) while the lowest peak value was observed in male subject M2 (0.34 V/m) -indicating a variation of similar to 2.4-fold across the dataset considered. The average gray matter percentage volume in females was 11.6% higher than in males. The average white matter percentage volume was 8.7% higher in females while negligible CSF percentage volume difference was noted across gender. The results of our study indicate gender-related differences in tDCS induced current flow and quantify the extent of this variation.