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

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.

Population-level insights into temporal interference for focused deep brain neuromodulation

“…However, the effects of aging on conductivity may impact the estimated electric fields. One study found a reduction in intracranial electric field intensity due to a reduction in skull conductivity with age (McCann and Beltrachini, 2021). Thus, incorporating age-appropriate skull conductivity in the models may enhance the observed electric field magnitude reduction in the elderly population (due to the loss of grey matter volume), as shown in our study and others (Antonenko et al, 2021).…”

Addressing the inconsistent electric fields of tDCS by using patient-tailored configurations in chronic stroke: Implications for treatment

“…Finally, our individualized head models assumed known conductivities for all tissue types in the model. Literature shows that skull conductivity is highly variable ( McCann et al, 2019 ) and negative correlation with electric field strengths ( McCann and Beltrachini, 2021 ). Furthermore, we assumed CSF conductivity for the lesion, which might not represent all subjects in our sample, although commonly used ( Datta et al, 2011 , Minjoli et al, 2017 ).…”

Personalized tDCS for Focal Epilepsy—A Narrative Review: A Data-Driven Workflow Based on Imaging and EEG Data

“…In [101], a relation is found between certain tissue conductivities, like the skull and age. This was further investigated in [103], in which the effect of this age dependency on the tDCS fields is underlined. There are several more reasons for variability in tissue conductivities, such as the measurement method used, the tissue temperature, and inter-individual variations.…”