Transcranial Alternating Current and Random Noise Stimulation: Possible Mechanisms

Figure 4

Translation of tACS intensity to intracranial voltage gradients allows a comparison to thresholds for eliciting spikes in animal research. The left axis represents tACS intensity. Neuling et al. [35] applied 1 mA intensity (peak-to-peak value: translates to a sine wave of 0.5 mA amplitude). In their FEM, they could show that this intensity results in a number of current densities in different parts of the brain with a maximum of 0.1 A/m² (axis: current density). The third axis represents the tissue resistivity of gray matter (tissue conductivity given on the left of the axis in brackets). Values in the range from 2.84 to 3.03 Ωm result in voltage gradients from 0.284 to 0.303 V/m being in the range of thresholds for neural firing or phase-locking (axis: voltage gradient). Note that for voltage gradients 1 mV/mm is equal to 1 V/m.