Inter-subject Variability in Electric Fields of Motor Cortical tDCS

Laakso, Ilkka; Tanaka, Satoshi; Koyama, Soichiro; Santis, Valerio De; Hirata, Akimasa

doi:10.1016/j.brs.2015.05.002

Cited by 323 publications

(338 citation statements)

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“…However, the acute effects are inconsistent across studies (Tanaka et al, 2009, 2011; Montenegro et al, 2015, 2016; Angius et al, 2016; Washabaugh et al, 2016) and seem dependent on tDCS protocols, training tasks, muscle groups, and subject populations. In this context, computational modeling would be useful to understand the different spatial distributions of the electric field induced by different tDCS protocols (electrode configuration, size, or current intensity; Laakso et al, 2015, 2016). …”

Section: Discussionmentioning

confidence: 99%

“…Twelve subjects per group seem underpowered, although 12 is close to the sample size (15 subjects per group) of Hendy and Kidgell's (2013) study. There is a large inter-individual variation in the outcome of tDCS over the hand motor cortex (Wiethoff et al, 2014; Laakso et al, 2015, 2016), with approximately one-half of subjects failing to respond to the stimulation in the expected manner (Wiethoff et al, 2014). Recently, such a large inter-individual variation was also observed in tDCS over the leg motor cortex (Madhavan et al, 2016; van Asseldonk and Boonstra, 2016).…”

Section: Discussionmentioning

confidence: 99%

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Transcranial Direct Current Stimulation Does Not Affect Lower Extremity Muscle Strength Training in Healthy Individuals: A Triple-Blind, Sham-Controlled Study

et al. 2017

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The present study investigated the effects of anodal transcranial direct current stimulation (tDCS) on lower extremity muscle strength training in 24 healthy participants. In this triple-blind, sham-controlled study, participants were randomly allocated to the anodal tDCS plus muscle strength training (anodal tDCS) group or sham tDCS plus muscle strength training (sham tDCS) group. Anodal tDCS (2 mA) was applied to the primary motor cortex of the lower extremity during muscle strength training of the knee extensors and flexors. Training was conducted once every 3 days for 3 weeks (7 sessions). Knee extensor and flexor peak torques were evaluated before and after the 3 weeks of training. After the 3-week intervention, peak torques of knee extension and flexion changed from 155.9 to 191.1 Nm and from 81.5 to 93.1 Nm in the anodal tDCS group. Peak torques changed from 164.1 to 194.8 Nm on extension and from 78.0 to 85.6 Nm on flexion in the sham tDCS group. In both groups, peak torques of knee extension and flexion significantly increased after the intervention, with no significant difference between the anodal tDCS and sham tDCS groups. In conclusion, although the administration of eccentric training increased knee extensor and flexor peak torques, anodal tDCS did not enhance the effects of lower extremity muscle strength training in healthy individuals. The present null results have crucial implications for selecting optimal stimulation parameters for clinical trials.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Transcranial Direct Current Stimulation Does Not Affect Lower Extremity Muscle Strength Training in Healthy Individuals: A Triple-Blind, Sham-Controlled Study

et al. 2017

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“…Even though 10 min of 2 mA tDCS has been shown to increase leg corticospinal tract excitability for at least 60 min (Jeffery et al, 2007), the use of imaging techniques such as fMRI would be useful to ensure that targeted areas had been effectively stimulated. Secondly, the experimental groups were not age-matched (post-stroke patients aged 52 ± 14 year vs. healthy controls 26 ± 7 years), which has been suggested to influence the response to electric fields induced by motor cortex tDCS (Laakso et al, 2015). However, since the aging process seems to negatively affect the recruitment activation of brain areas during motor tasks (Manan et al, 2015), the choice of healthy young individuals as controls is justified to ensure that tDCS effects upon motor performance were tested across groups really exhibiting opposite status in regards to motor cortex integrity (e.g., healthy vs. lesioned).…”

Section: Discussionmentioning

confidence: 99%

Bihemispheric Motor Cortex Transcranial Direct Current Stimulation Improves Force Steadiness in Post-Stroke Hemiparetic Patients: A Randomized Crossover Controlled Trial

Montenegro

Midgley

Massaferri

et al. 2016

Front. Hum. Neurosci.

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Post-stroke patients usually exhibit reduced peak muscular torque (PT) and/or force steadiness during submaximal exercise. Brain stimulation techniques have been proposed to improve neural plasticity and help to restore motor performance in post-stroke patients. The present study compared the effects of bihemispheric motor cortex transcranial direct current stimulation (tDCS) on PT and force steadiness during maximal and submaximal resistance exercise performed by post-stroke patients vs. healthy controls. A double-blind randomized crossover controlled trial (identification number: TCTR20151112001; URL: http://www.clinicaltrials.in.th/) was conducted involving nine healthy and 10 post-stroke hemiparetic individuals who received either tDCS (2 mA) or sham stimulus upon the motor cortex for 20 min. PT and force steadiness (reflected by the coefficient of variation (CV) of muscular torque) were assessed during unilateral knee extension and flexion at maximal and submaximal workloads (1 set of 3 repetitions at 100% PT and 2 sets of 10 repetitions at 50% PT, respectively). No significant change in PT was observed in post-stroke and healthy subjects. Force steadiness during knee extension (~25–35%, P < 0.001) and flexion (~22–33%, P < 0.001) improved after tDCS compared to the sham condition in post-stroke patients, but improved only during knee extension (~13–27%, P < 0.001) in healthy controls. These results suggest that tDCS may improve force steadiness, but not PT in post-stroke hemiparetic patients, which might be relevant in the context of motor rehabilitation programs.

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“…For a given stimulator output, current in a cortical target region may vary by up to 100% across individuals [7]. For the field to mature, and the clinical promise of tES to be rigorously tested, not knowing how much current we deliver or where this current might travel, will remain an unacceptable barrier.…”

mentioning

confidence: 99%

Are current flow models for transcranial electrical stimulation fit for purpose?

Bestmann

Ward

2017

Brain Stimulation

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Transcranial electrical stimulation (tES) enjoys a burgeoning reputation in basic and clinical research, and home-use. Even though Rush and Driscoll highlighted more than 40 years ago that "the amount of current entering the brain is of great consequence" [9], to this day tES studies generally do not control how much current is actually delivered to the brain. Instead, tES applications control the output of a stimulator, and so for most applications we do not control that comparable doses of current are delivered to the brain of different individuals. Yet we do know that the idiosyncratic properties of the head strongly influence how much of a fixed output current (e.g. 1mA) will reach the brain [1], and so we are in the extraordinary position of knowing that the effective dose of tES is highly variable across individuals (Figure 1), yet doing very little about it.The recent debate scrutinizing the efficacy, reliability and utility of tES [4,5,10] thus misses a vital point that likely contributes to variable outcomes. For a given stimulator output, current in a cortical target region may vary by up to 100% across individuals [7]. For the field to mature, and the clinical promise of tES to be rigorously tested, not knowing how much current we deliver or where this current might travel, will remain an unacceptable barrier. This is especially the case in clinical applications such chronic stroke where results have been rather mixed [3], and where the distortions of current flow that the lesions impose may amplify variability in effectively delivered current.

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Inter-subject Variability in Electric Fields of Motor Cortical tDCS

Cited by 323 publications

References 35 publications

Transcranial Direct Current Stimulation Does Not Affect Lower Extremity Muscle Strength Training in Healthy Individuals: A Triple-Blind, Sham-Controlled Study

Transcranial Direct Current Stimulation Does Not Affect Lower Extremity Muscle Strength Training in Healthy Individuals: A Triple-Blind, Sham-Controlled Study

Bihemispheric Motor Cortex Transcranial Direct Current Stimulation Improves Force Steadiness in Post-Stroke Hemiparetic Patients: A Randomized Crossover Controlled Trial

Are current flow models for transcranial electrical stimulation fit for purpose?

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