White matter hyperintensities affect transcranial electrical stimulation in the aging brain

A Systematic Review and Meta-Analysis of Transcranial Direct Current Stimulation to Remediate Age-Related Cognitive Decline in Healthy Older Adults

“…88,[96][97][98][99][100] In older adults, age-related effects such as brain atrophy and white matter hyperintensities (WMH) were found as important factors that affect modeled field distribution following tDCS. 77,101 Brain atrophy is commonly described as a shrinkage of cortical structures that occurs with healthy aging. 102 The rate of atrophy is varied across individuals, and thus, the severity of brain atrophy found across older adult samples can vary.…”

“…77,81,108 In addition, another recent modeling study investigating WMH in 130 older adults found that the presence of WMH could reduce delivered current in intact brain up to 7%. 101 This occurrence suggests that it is difficult to recommend a standardized tDCS parameter that will work for all and, instead, tDCS applications in older adults may need to be tailored to each individual and account for various atrophy and WMH levels across older adult samples. For instance, adjusting current intensity level and using custom electrode placement to target desired brain region in each person.…”

The influence of white matter lesions on the electric field in transcranial electric stimulation

“…Our results augment the knowledge on accurate modeling of tDCS in the aging brain by investigations of sub-cortical alteration of the white matter fiber structure, leukoaraiosis. In contrast to previous studies on stroke lesions ( Wagner et al, 2007 , Datta et al, 2011 , Minjoli et al, 2017 ) and white matter lesions ( Indahlastari et al, 2021 ), we did not model white matter lesions using the physical properties of existing structures, for example, cerebrospinal fluid. Instead, we introduced the lesions as a new tissue type, with a distinct uncertainty in tissue conductivity.…”

“…Microstructural alterations like the disruption of white matter tracts, vessel impairments such as cerebral microangiopathy in the presence of vascular risk factors, inflammation, or the loss of myelination may cause atrophy and lesions of the white matter tissue. Despite their frequent manifestation in the aging brain ( De Leeuw et al, 2001 ), white matter lesions (WMLs), or leukoaraiosis, have only very recently gained attention in the context of tDCS simulations ( Indahlastari et al, 2021 ).…”

“…Even the conductivity of healthy tissue varies among subjects ( Katoch et al, 2018 ), rendering the conductivity of all tissues in the human head, but especially that of lesioned white matter, an uncertain input to the simulation. Fixed default conductivities, like the usage of cerebrospinal fluid for the physical modeling of lesions ( Wagner et al, 2007 , Datta et al, 2011 , Minjoli et al, 2017 , Indahlastari et al, 2021 ), may yield inaccuracies in the simulation results, which an uncertainty analysis can quantify.…”