Electric field dependent effects of motor cortical TDCS

Laakso, Ilkka; Mikkonen, Marko; Koyama, Soichiro; Ito, Daisuke; Yamaguchi, Tomohiko; Hirata, Akimasa; Tanaka, Satoshi

doi:10.1101/327361

Cited by 4 publications

(5 citation statements)

References 51 publications

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“…A major issue facing the adoption of brain stimulation techniques into clinical practice is the large interindividual variability in responses (Hordacre et al, 2021). This variability is likely to be driven, at least in part, by differences in current flow through the regions of interest (Laakso et al, 2018). In addition to the high degree of variability seen across healthy individuals (Evans et al, 2020;Laakso et al, 2015), here we show that large lesions will further increase this variability by up to 30%.…”

Section: Implications For Clinical Applicationsmentioning

confidence: 63%

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

Johnstone

Zich

Evans

et al. 2021

Preprint

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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.

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Section: Implications For Clinical Applicationsmentioning

confidence: 63%

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

Johnstone

Zich

Evans

et al. 2021

Preprint

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“…A major issue facing the adoption of brain stimulation into clinical practice is the large inter-individual variability in responses 55 . This variability is likely to be driven, at least in part, by differences in how much current is delivered and where to 24,56 . In addition to the high degree of variability seen across healthy individuals 15,16,22 , here we show that large lesions can alter E-field magnitude by around 30%, compared to non-lesioned brains.…”

Section: Implications For Clinical Applications Of Tdcsmentioning

confidence: 99%

The impact of brain lesions on tDCS-induced electric fields

Evans,

Johnstone,

Zich

et al. 2023

Sci Rep

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Transcranial direct current stimulation (tDCS) can enhance motor and language rehabilitation after stroke. Though brain lesions distort tDCS-induced electric field (E-field), systematic accounts remain limited. Using electric field modelling, we investigated the effect of 630 synthetic lesions on E-field magnitude in the region of interest (ROI). Models were conducted for two tDCS montages targeting either primary motor cortex (M1) or Broca’s area (BA44). Absolute E-field magnitude in the ROI differed by up to 42% compared to the non-lesioned brain depending on lesion size, lesion-ROI distance, and lesion conductivity value. Lesion location determined the sign of this difference: lesions in-line with the predominant direction of current increased E-field magnitude in the ROI, whereas lesions located in the opposite direction decreased E-field magnitude. We further explored how individualised tDCS can control lesion-induced effects on E-field. Lesions affected the individualised electrode configuration needed to maximise E-field magnitude in the ROI, but this effect was negligible when prioritising the maximisation of radial inward current. Lesions distorting tDCS-induced E-field, is likely to exacerbate inter-individual variability in E-field magnitude. Individualising electrode configuration and stimulator output can minimise lesion-induced variability but requires improved estimates of lesion conductivity. Individualised tDCS is critical to overcome E-field variability in lesioned brains.

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“…To add to this complexity, the conductances of lesioned tissue also remain unknown [60; 81]. The likely impact of these brain differences on dose and target engagement poses a challenge to the efficacy of stimulation in clinical practice [62,65].…”

Section: How Generalisable Are Cfms?mentioning

confidence: 99%

A Future of Current Flow Modelling for Transcranial Electrical Stimulation?

Lee

Bestmann

Evans

2021

Curr Behav Neurosci Rep

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Purpose of Review Transcranial electrical stimulation (tES) is used to non-invasively modulate brain activity in health and disease. Current flow modeling (CFM) provides estimates of where and how much electrical current is delivered to in the brain during tES. It therefore holds promise as a method to reduce commonplace variability in tES delivery and, in turn, the outcomes of stimulation. However, the adoption of CFM has not yet been widespread and its impact on tES outcome variability is unclear. Here, we discuss the potential barriers to effective, practical CFM-informed tES use. Recent Findings CFM has progressed from models based on concentric spheres to gyri-precise head models derived from individual MRI scans. Users can now estimate the intensity of electrical fields (E-fields), their spatial extent, and the direction of current flow in a target brain region during tES. Here. we consider the multi-dimensional challenge of implementing CFM to optimise stimulation dose: this requires informed decisions to prioritise E-field characteristics most likely to result in desired stimulation outcomes, though the physiological consequences of the modelled current flow are often unknown. Second, we address the issue of a disconnect between predictions of E-field characteristics provided by CFMs and predictions of the physiological consequences of stimulation which CFMs are not designed to address. Third, we discuss how ongoing development of CFM in conjunction with other modelling approaches could overcome these challenges while maintaining accessibility for widespread use. Summary The increasing complexity and sophistication of CFM is a mandatory step towards dose control and precise, individualised delivery of tES. However, it also risks counteracting the appeal of tES as a straightforward, cost-effective tool for neuromodulation, particularly in clinical settings.

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Electric field dependent effects of motor cortical TDCS

Cited by 4 publications

References 51 publications

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

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

The impact of brain lesions on tDCS-induced electric fields

A Future of Current Flow Modelling for Transcranial Electrical Stimulation?

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