Inter-individual variability in current direction for common tDCS montages
The direction of applied electric current relative to the cortical surface is a key determinant of transcranial direct current stimulation (tDCS) effects. Inter-individual differences in anatomy affect the consistency of current direction at a cortical target. However, the degree of this variability...
| Main Authors: | , , , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
Elsevier
2022-10-01
|
| Series: | NeuroImage |
| Subjects: | |
| Online Access: | http://www.sciencedirect.com/science/article/pii/S1053811922006176 |
| _version_ | 1811216605178232832 |
|---|---|
| author | Carys Evans Catharina Zich Jenny S.A. Lee Nick Ward Sven Bestmann |
| author_facet | Carys Evans Catharina Zich Jenny S.A. Lee Nick Ward Sven Bestmann |
| author_sort | Carys Evans |
| collection | DOAJ |
| description | The direction of applied electric current relative to the cortical surface is a key determinant of transcranial direct current stimulation (tDCS) effects. Inter-individual differences in anatomy affect the consistency of current direction at a cortical target. However, the degree of this variability remains undetermined. Using current flow modelling (CFM), we quantified the inter-individual variability in tDCS current direction at a cortical target (left primary motor cortex, M1). Three montages targeting M1 using circular electrodes were compared: PA-tDCS directed current perpendicular to the central sulcus in a posterior-anterior direction relative to M1, ML-tDCS directed current parallel to the central sulcus in a medio-lateral direction, and conventional-tDCS applied electrodes over M1 and the contralateral forehead. In 50 healthy brain scans from the Human Connectome Project, we extracted current direction and intensity from the grey matter surface in the sulcal bank (M1BANK) and gyral crown (M1CROWN), and neighbouring primary somatosensory cortex (S1BANK and S1CROWN). Results confirmed substantial inter-individual variability in current direction (50%–150%) across all montages. Radial inward current produced by PA-tDCS was predominantly located in M1BANK, whereas for conventional-tDCS it was clustered in M1CROWN. The difference in radial inward current in functionally distinct subregions of M1 raises the testable hypothesis that PA-tDCS and conventional-tDCS modulate cortical excitability through different mechanisms. We show that electrode locations can be used to closely approximate current direction in M1 and precentral gyrus, providing a landmark-based method for tDCS application to address the hypothesis without the need for MRI. By contrast, ML-tDCS current was more tangentially orientated, which is associated with weaker somatic polarisation. Substantial inter-individual variability in current direction likely contributes to variable neuromodulation effects reported for these protocols, emphasising the need for individualised electrode montages, including the control of current direction. |
| first_indexed | 2024-04-12T06:41:59Z |
| format | Article |
| id | doaj.art-ec9fda1d1cd64fc19b4e7f3c85f70a83 |
| institution | Directory Open Access Journal |
| issn | 1095-9572 |
| language | English |
| last_indexed | 2024-04-12T06:41:59Z |
| publishDate | 2022-10-01 |
| publisher | Elsevier |
| record_format | Article |
| series | NeuroImage |
| spelling | doaj.art-ec9fda1d1cd64fc19b4e7f3c85f70a832022-12-22T03:43:41ZengElsevierNeuroImage1095-95722022-10-01260119501Inter-individual variability in current direction for common tDCS montagesCarys Evans0Catharina Zich1Jenny S.A. Lee2Nick Ward3Sven Bestmann4Department for Clinical and Movement Neurosciences, UCL Queen Square Institute of Neurology, 33 Queen Square, London, WC1N 3BG, United Kingdom; Corresponding author.Department for Clinical and Movement Neurosciences, UCL Queen Square Institute of Neurology, 33 Queen Square, London, WC1N 3BG, United Kingdom; Wellcome Centre for Integrative Neuroimaging, FMRIB, Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, United KingdomDepartment for Clinical and Movement Neurosciences, UCL Queen Square Institute of Neurology, 33 Queen Square, London, WC1N 3BG, United KingdomDepartment for Clinical and Movement Neurosciences, UCL Queen Square Institute of Neurology, 33 Queen Square, London, WC1N 3BG, United KingdomDepartment for Clinical and Movement Neurosciences, UCL Queen Square Institute of Neurology, 33 Queen Square, London, WC1N 3BG, United Kingdom; Wellcome Centre for Human Neuroimaging, UCL Queen Square Institute of Neurology, United KingdomThe direction of applied electric current relative to the cortical surface is a key determinant of transcranial direct current stimulation (tDCS) effects. Inter-individual differences in anatomy affect the consistency of current direction at a cortical target. However, the degree of this variability remains undetermined. Using current flow modelling (CFM), we quantified the inter-individual variability in tDCS current direction at a cortical target (left primary motor cortex, M1). Three montages targeting M1 using circular electrodes were compared: PA-tDCS directed current perpendicular to the central sulcus in a posterior-anterior direction relative to M1, ML-tDCS directed current parallel to the central sulcus in a medio-lateral direction, and conventional-tDCS applied electrodes over M1 and the contralateral forehead. In 50 healthy brain scans from the Human Connectome Project, we extracted current direction and intensity from the grey matter surface in the sulcal bank (M1BANK) and gyral crown (M1CROWN), and neighbouring primary somatosensory cortex (S1BANK and S1CROWN). Results confirmed substantial inter-individual variability in current direction (50%–150%) across all montages. Radial inward current produced by PA-tDCS was predominantly located in M1BANK, whereas for conventional-tDCS it was clustered in M1CROWN. The difference in radial inward current in functionally distinct subregions of M1 raises the testable hypothesis that PA-tDCS and conventional-tDCS modulate cortical excitability through different mechanisms. We show that electrode locations can be used to closely approximate current direction in M1 and precentral gyrus, providing a landmark-based method for tDCS application to address the hypothesis without the need for MRI. By contrast, ML-tDCS current was more tangentially orientated, which is associated with weaker somatic polarisation. Substantial inter-individual variability in current direction likely contributes to variable neuromodulation effects reported for these protocols, emphasising the need for individualised electrode montages, including the control of current direction.http://www.sciencedirect.com/science/article/pii/S1053811922006176Transcranial electrical stimulationCurrent flow modellingInter-individual variabilityBrain stimulation |
| spellingShingle | Carys Evans Catharina Zich Jenny S.A. Lee Nick Ward Sven Bestmann Inter-individual variability in current direction for common tDCS montages NeuroImage Transcranial electrical stimulation Current flow modelling Inter-individual variability Brain stimulation |
| title | Inter-individual variability in current direction for common tDCS montages |
| title_full | Inter-individual variability in current direction for common tDCS montages |
| title_fullStr | Inter-individual variability in current direction for common tDCS montages |
| title_full_unstemmed | Inter-individual variability in current direction for common tDCS montages |
| title_short | Inter-individual variability in current direction for common tDCS montages |
| title_sort | inter individual variability in current direction for common tdcs montages |
| topic | Transcranial electrical stimulation Current flow modelling Inter-individual variability Brain stimulation |
| url | http://www.sciencedirect.com/science/article/pii/S1053811922006176 |
| work_keys_str_mv | AT carysevans interindividualvariabilityincurrentdirectionforcommontdcsmontages AT catharinazich interindividualvariabilityincurrentdirectionforcommontdcsmontages AT jennysalee interindividualvariabilityincurrentdirectionforcommontdcsmontages AT nickward interindividualvariabilityincurrentdirectionforcommontdcsmontages AT svenbestmann interindividualvariabilityincurrentdirectionforcommontdcsmontages |