This TI method provides precise amounts of neural activation within highly targeted areas of deep tissue using external electrodes. Neural membranes are low-pass filters of electrical signals; therefore, neurons are only excitable at low frequencies, such as 10Hz. Due to this property of neurons, the method applies high-frequency oscillating electric fields, in the kHz range, at multiple sites outside the brain so that the outer layers of tissue can remain unaffected. The applied high-frequency electric fields differ slightly in frequency, and interfere in time at the target location due to their slight difference in frequency. The interference produces a low-frequency electric field envelope capable of exciting neurons at a precise target point deep within the tissue. Additionally, the amplitude of the low-frequency envelope depends on the vector sum of the applied high-frequency electric fields at the target point; therefore, the amplitude can have a maximum at a point distant from the electrodes. Finally, this TI method allows for further spatial control of neural activation by varying the ratio of delivered currents between the different electrode pairs. The low-frequency envelope consequently moves toward and away from the electrodes as the ratio of currents varies. This enables “live steering” of neural activity, without having to physically move the electrodes.