From scalp to cortex, the whole isn’t greater than the sum of its parts: introducing GetTissueThickness (GTT) to assess age and sex differences in tissue thicknesses

Abstract

Noninvasive techniques to record and stimulate the brain rely on passing through the tissues in between the scalp and cortex. Currently, there is no method to obtain detailed information about these scalp-to-cortex distance (SCD) tissues. We introduce GetTissueThickness (GTT), an open-source, automated approach to quantify SCD, and unveil how tissue thicknesses differ across age groups, sexes and brain regions (n = 250). We show that men have larger SCD in lower scalp regions and women have similar-to-larger SCD in regions closer to the vertex, with aging resulting in increased SCD in fronto-central regions. Soft tissue thickness varies by sex and age, with thicker layers and greater age-related decreases in men. Compact and spongy bone thickness also differ across sexes and age groups, with thicker compact bone in women in both age groups and an age-related thickening. Older men generally have the thickest cerebrospinal fluid layer and younger women and men having similar cerebrospinal fluid layers. Aging mostly results in grey matter thinning. Concerning SCD, the whole is not greater than the sum of its parts. GTT enables rapid quantification of the SCD tissues. The distinctive sensitivity of noninvasive recording and stimulation modalities to different tissues underscores the relevance of GTT.

An electric field modeling study with meta-analysis to understand the antidepressant effects of transcranial direct current stimulation (tDCS)

“…It is expected that electrode position would vary from person to person in order to account for interindividual variability, which might be caused by individual brain volume, cortical thickness, or even scalp-brain distance due to age-related atrophy, for instance. 63 , 64 In this sense, it is optimal that individual models be simulated prior to the tDCS session to ascertain optimal electrode placement for each patient, with special attention to older adults, who might exhibit higher heterogeneity in brain structures. 65 Nonetheless, the optimized montages proposed herein suggest that unilateral stimulation may be more beneficial compared to bilateral stimulation to target the DLPFC.…”