The impact of brain lesions on tDCS-induced electric field magnitude

Abstract

Background: Transcranial direct current stimulation (tDCS) has been used to enhance motor and language rehabilitation following a stroke. However, improving the effectiveness of clinical tDCS protocols depends on understanding how a lesion may influence tDCS-induced current flow through the brain. Objective: We systematically investigated the effect of brain lesions on the magnitude of electric fields (e-mag) induced by tDCS. Methods: We simulated the effect of 630 different lesions - by varying lesion location, distance from the region of interest (ROI), size and conductivity - on tDCS-induced e-mag. We used current flow models in the brains of two participants, for two commonly used tDCS montages, targeting either primary motor cortex (M1) or Brocas area (BA44) as ROIs. Results: The effect on absolute e-mag change was highly dependent on lesion size, conductance and distance from ROI. Larger lesions, with high conductivity, close to the ROI caused e-mag changes of more than 30%. The sign of this change was determined by the location of the lesion. Specifically, lesions located in-line with the predominant direction of current flow increased e-mag in the ROI, whereas lesions located in the opposite direction caused a decrease. Conclusions: These results demonstrate that tDCS-induced electric fields are profoundly influenced by lesion characteristics. This highlights the need for individualised targeting and dose control in stroke. Additionally, the variation in electrical fields caused by assigned conductance of the lesion underlines the need for improved estimates of lesion conductivity for current flow models.

Applications of open-source software ROAST in clinical studies: A review

“…Ref. [ 44 ] achieved 0.16 V/m averaged electric field with high-definition electrodes Fp2-CCP3. For the frontal cortex, Ref.…”

In Vivo Measurements of Transcranial Electrical Stimulation in Lesioned Human Brain: A Case Report

“…The case report, for the first time, provides direct evidence for tES-induced EF in the lesioned human brain. Several previous modeling studies have studied the effect of lesions on tES-induced EF [ 9 , 12 , 13 , 14 , 28 , 29 , 30 ]. These simulated results mainly explore the situation of stroke patients and have found that lesions caused a shunt of stimulation current in target areas.…”

A Future of Current Flow Modelling for Transcranial Electrical Stimulation?

“…Structural changes that occur in degenerative disease such as dementia or ALS, or in acquired brain injury such as stroke, are also likely to have an impact on the distribution of current such that optimisation criteria for tES derived from healthy populations may no longer apply [60,61]. We know that changes in skull density, and in thickness of CSF and skull tissue [62,63], or the presence of lesions [61,64] will drastically alter E-field distribution.…”

“…We know that changes in skull density, and in thickness of CSF and skull tissue [62,63], or the presence of lesions [61,64] will drastically alter E-field distribution. For example, the presence of a lesion can result in either an increase or decrease in E-field magnitude in a region of interest, depending on the lesion location and size relative to the path of the current [60]. To add to this complexity, the conductances of lesioned tissue also remain unknown [60; 81].…”