Figure 2
In vivo intracranial electric field induced by subcutaneous and transcutaneous stimulation. Measuring induced intracranial electric fields at the location of subdural strips. (A) Intracranial electric field induced by subcutaneous stimulation (R = 0.856, P < 0.001, n = 28 in four different arrangements in 3 beagles) was several times larger compared to transcutaneous stimulation (R = 0.760, P < 0.001, n = 28 in four different arrangements in 3 beagles). Error bars represent SD. (B) The ratio of induced intracranial electric field and stimulus intensity with subcutaneous and transcutaneous stimulation (P < 0.001, n = 140 in four different arrangements in 3 beagles). To induce 1 mV/mm intracranial electric field in transcutaneous stimulation, approximately 5 mA scalp-applied current is needed. (C) As the stimulus frequency from 20 to 2000 Hz increased, the induced field decreased by about 20% (n = 18 in two different arrangements in 3 beagles, R = −0.204, P = 0.034 for subcutaneous, and n = 20 in two different arrangements in 3 beagles, R = −0.279, P = 0.002 for transcutaneous stimulation). Error bars represent SD. (D) The ratio of intracranial gradients induced by subcutaneous and transcutaneous stimulation was almost constant with stimulus frequency between 20 and 2000 Hz (one-way ANOVA; F(5, 102) = 0.052, P = 0.998, n = 18 in 3 beagles for subcutaneous, and n = 20 in 3 beagles for transcutaneous stimulation). Error bars represent SD.
