Modelling the differential effects of age on transcranial magnetic stimulation induced electric fields

Objective. The therapeutic application of noninvasive brain stimulation modalities such as transcranial magnetic stimulation (TMS) has expanded in terms of indications and patient populations. Often neurodevelopmental and neurodegenerative changes are not considered in research studies and clinical applications. This study sought to examine TMS dosing across time points in the life cycle. Approach. TMS induced electric fields with a figure-of-eight coil was simulated at left dorsolateral prefrontal cortex regions and taken in vertex as a control region. Realistic magnetic resonance imaging-based head models (N = 48) were concurrently examined in a cross-sectional study of three different age groups (children, adults, and elderlies). Main results. Age had a negative correlation with electric field peaks in white matter, grey matter and cerebrospinal fluid (P < 0.001). Notably, the electric field map in children displayed the widest cortical surface spread of TMS induced electric fields. Significance. Age-related anatomical geometry beneath the coil stimulation site had a significant impact on the TMS induced electric fields for different age groups. Safety considerations for TMS applications and protocols in children are warranted based on the present electric field findings.