Transcranial electric stimulation of motor pathways: a theoretical analysis

The pattern of stimulation was only slightly dependent on the conductivity and the thickness of the CSF layer. Axons very close to the anode were stimulated with lowest threshold at the brain surface. Axons further away were stimulated with higher thresholds and the point of maximum stimulation moved nearer the center of the sphere. Near the cathode, stimulation was maximal about 5-7° away from the edge of the electrode but the peak magnitude of the activating function was generally 20 times lower than over the anode.