Montages for tCS

In this page we provide some examples of montages used in the literature for several applications. Readers are encouraged to search the literature for other options.

We recall here the logic regarding anodal versus cathodal stimulation. Anodal stimulation over an area produces electric fields directed generally inward into the brain in the subjacent cortex. The direction of the electric field with respect to the orientation of the neuron is a significant parameter in the alteration of the trans-membrane potential, especially of elongated neurons such as pyramidal cells. For this reason we may loosely say that anodal stimulation is excitatory, since long cortical neurons are generally aligned perpendicular to the cortical surface, etc. The opposite applies to cathodal stimulation. However, these are approximate statements. The geometry of the cortical surface is complex, as are the generated electric fields. For this reason, biophysical modeling of electric fields an their interactions with neurons is an important tool to carefully define montages. If interested in the topic, see this paper on biophysical modeling and this one on the electric field generated by focal tDCS.

If interested, contact us for our StimWeaver service: we can produce the best tCS montage for your targeting problem.

Stroke

Please see our blog (| Stroke Jan 2013 and | Recent Highlights Sept 2013) for a review of the literature on tCS for Stroke.

A stroke that affects the cerebral cortex may have a wide range of effects depending on the location of the lesion. The clinical strategies for treating stroke typically involve stabilization of the patient, preservation of function in the brain area and adaptation of the patient to diminished function. There are some hints that electrical stimulation of the brain may in itself promote recovery or preservation of brain tissue <ref> Kanzaki S, Stöver T, Kawamoto K, Prieskorn DM, Altschuler RA, Miller JM, Raphael Y., | Glial cell line-derived neurotrophic factor and chronic electrical stimulation prevent VIII cranial nerve degeneration following denervation, J Comp Neurol. 2002 Dec 16;454(3):350-60. </ref>, although to date a relatively small number of published studies have focused on improving specific functions through the use of single or repeated sessions of anodal stimulation.

The main motivation behind the use of non-invasive brain stimulation for stroke recovery is to support relearning of compromised abilities by enhancement of pathologically-reduced cortical excitability and activity, directly by excitability-enhancing brain stimulation of the lesioned area, or indirectly, by reducing excitability of the non-lesioned contralateral hemisphere – since this has inhibitory connections with the lesioned one <ref> Wittenberg GF, Schaechter JD., | The neural basis of constraint-induced movement therapy , Curr Opin Neurol. 2009 Dec;22(6):582-8. </ref>. Specifically, the respective excitability enhancements are thought to promote relearning of functions by enhancing learning-related long-term potentiation (LTP) (which is the likely physiological basis of learning and memory formation <ref> Rioult-Pedotti MS, Friedman D, Donoghue JP., | Learning-induced LTP in neocortex., Science. 2000 Oct 20;290(5491):533-6 </ref>. ) and via this mechanism promote recovery.

A typical montage using large, traditional sponges will result in large affected areas by the stimulation. It would look like this:

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An alternative is to put the "reference" electrode over the "contralateral supraorbital region". Again, we see large effects over widespread areas of the cortex:

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A more modern version, using StarStim and targeting only the left hemisphere (i.e., trying to avoid stimulating other sites) may look like this:

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Pain

For a NEs White Paper on a literature review related to tCS in Central Pain, please see our Central Pain / tCS White Paper.

Typical montages for Pain focus on the primary motor cortex. A montage for central pain from an interesting study<ref> Study: F. Fregni, P. S. Boggio, M. C. Lima, M. J. Ferreira, T. Wagner, S. P. Rigonatti, A. W. Castro, D. R. Souza, M. Riberto, S. D. Freedman, M. A. Nitsche, and A. Pascual-Leone. 2006. | A sham-controlled, phase II trial of transcranial direct current stimulation for the treatment of central pain in traumatic spinal cord injury. Pain 122 (1-2):197-209. </ref> is as follows. The target was the motor cortex, and it relied on the use of large sponge electrodes. The "nuissance" electrode was place on the contralateral orbit. Here we provide a visualization of these montages using StimViewer.

In this study the authors found that there was a significant pain improvement after active anodal stimulation of the motor cortex, but not after sham stimulation. These results were not confounded by depression or anxiety changes. Furthermore, cognitive performance was not significantly changed throughout the trial in both treatment groups. The results of our study suggest that this new approach of cortical stimulation can be effective to control pain in patients with spinal cord lesion.

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As was the case in Stroke, the use of small electrodes could provide much more focal, controlled stimulation:

File:MotorMultichannel2.png

Multichannel solution for motor cortex

References

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