Does participant’s age impact on tDCS induced fields? Insights from computational simulations

Hannah Mccann,Leandro Beltrachini

doi:10.1088/2057-1976/ac0547

Hannah Mccann, Leandro Beltrachini

Open Access

https://doi.org/10.1088/2057-1976/ac0547

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Abstract

Objective: Understanding the induced current flow from transcranial direct current stimulation (tDCS) is essential for determining the optimal dose and treatment. Head tissue conductivities play a key role in the resulting electromagnetic fields. However, there exists a complicated relationship between skull conductivity and participant age, that remains unclear. We explored how variations in skull electrical conductivities, particularly as a suggested function of age, affected tDCS induced electric fields. Approach: Simulations were employed to compare tDCS outcomes for different intensities across head atlases of varying age. Three databases were chosen to demonstrate differing variability in skull conductivity with age and how this may affect induced fields. Differences in tDCS electric fields due to proposed age-dependent skull conductivity variation, as well as deviations in grey matter, white matter and scalp, were compared and the most influential tissues determined. Main results: tDCS induced peak electric fields significantly negatively correlated with age, exacerbated by employing proposed age-appropriate skull conductivity (according to all three datasets). Uncertainty in skull conductivity was the most sensitive to changes in peak fields with increasing age. These results were revealed to be directly due to changing skull conductivity, rather than head geometry alone. There was no correlation between tDCS focality and age. Significance: Accurate and individualised head anatomy and in vivo skull conductivity measurements are essential for modelling tDCS induced fields. In particular, age should be taken into account when considering stimulation dose to precisely predict outcomes.

Highlights

Transcranial direct current stimulation is a non-invasive technique that induces and modulates neural activity in the human brain
Between other parameters, on the electrical conductivity of head tissues, which vary throughout the literature [5] and uncertainty of which can result in calculation errors
Head models Standard structural T1 and T2-weighted magnetic resonance imaging (MRI)’s were obtained from the publicly available Neurodevelopmental MRI Database. This consisted of age-appropriate average MRI templates ranging from 2 weeks to 89 years old created from different databases of over 400 participants [40,41,42,43,44]

Summary

Introduction

Transcranial direct current stimulation (tDCS) is a non-invasive technique that induces and modulates neural activity in the human brain. The effect and application of tDCS on brain function is dependent on the applied region, frequency, duration, and intensity of stimulation. Altering these parameters allows individualised therapeutic and investigative intervention [3]. Between other parameters, on the electrical conductivity of head tissues, which vary throughout the literature [5] and uncertainty of which can result in calculation errors. Uncertain electrical conductivity, of the skull, has been revealed to influence tDCS electrical fields and substantially alter optimal tDCS stimulation protocol predictions [6]. Head model simplifications have been shown to play an important role in the determination of optimal tDCS doses.

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