Hi Martin,

I think that placement of cathode anywhere over the head would affect the expected results from anodal stimulation. By placing cathode over motor or Wernicke's  area , you are essentially inhibiting these areas and that should have clinical consequences.

So I suppose that cathode should be placed on an extra cephalic site preferably the shoulder.

likewise if your active electrode is the cathode for example in cases of dystonia, then you'd better place the anode extra cephalic.

Nevine, thank you for your comment, it is, indeed, correct.

We consider Wernicke are for cathode since our experiments involves another placement, to be specific:

1) Sham - randomly A or B.

2) Placement A: anode - left PFC, cathode - ???

3) Placement B: anode - right Wernicke, cathode - left Wernicke

So, if we choose left Wernicke (CP5) as cathode, the only difference between A and B is the anode placement (which is of the interest). As for motor cortex, I was considering it because lexical-semantic functions are of the interest.

Thank you,

M.

Dear Martin

by placing anode on rt Wernicke's and cathode on the left homologous area then you are stimulating the non dominant speech area and inhibiting the dominant one. thus reversing the normal state.

Is this what your research is about?

Yes, such effects are intended,

the problem is that I would like to see the predicted current flow but don't have a suitable software for that (Bonsai has just a few positions; Simnibs requires Mac or Linux).

M.

Dear Martin

if I understood correctly, you want to maximize the induced current between cathode and anode? If yes you shoukd place cathode somewhere close to the anode and for ankde on F3  you should place cathode on F4. But, there is two points: first the physiological and neurophysiological effects, I mean inhibiting or exciting effect you are seeking and second the direction and distribution of indiced current you like. 

If ou place cathod on shoulder or extra cephalic then you would have most of indiced current under Anode and if you put cathod on contra hemishphere on symmetrical place, then the current flow beneath anode-cathode.

also to increase the current density under an electrode you can chose smaller electride as active against a big electrode size as reference.

Dear Martin,

Regarding the stimulation of the left DLPFC (F3), we have previously applied the cathode over the right orbitofrontal area (AF8) for the treatment of fatigue and pain in multiple sclerosis. You can find the details in the following articles:

Chalah MA, Riachi N, Ahdab R, Mhalla A, Abdellaoui M, Créange A, Lefaucheur JP, Ayache SS. Effects of left DLPFC versus right PPC tDCS on multiple sclerosis fatigue. J Neurol Sci. 2017 Jan 15;372:131-137. doi: 10.1016/j.jns.2016.11.015. Epub 2016 Nov 10.

Ayache SS, Palm U, Chalah MA, Al-Ani T, Brignol A, Abdellaoui M, Dimitri D, Sorel M, Créange A, Lefaucheur JP. Prefrontal tDCS Decreases Pain in Patients with Multiple Sclerosis. Front Neurosci. 2016 Apr 8;10:147. doi: 10.3389/fnins.2016.00147. eCollection 2016.

On another note, you can contact the tDCS companies. Engineers are availables and they can help you in simulating the shape of current depending on the design you pick. 

Best regards,

Moussa 

Following.