Fig. 1

Principle of multipolar temporal interference and increased focality in non-human primates. A TI: Adding two frequencies to create an envelope – Two equal amplitude sinusoidal signals at 1975 Hz and 2025 Hz interact to create a 50 Hz amplitude modulated signal. B mTI: Adding two envelopes to create a greater envelope – The first 50 Hz envelope signal is created from the interaction of 1975 and 2025 Hz signals, the second from 2975 and 3025 Hz. When the two envelopes are added, a larger 50 Hz envelope is created. The maximum modulation occurs at the center of the circle (yellow area). C mTI: Reducing the amplitude to that of the original TI envelope increases focality – The amplitude from the electrode pairs is reduced to create an envelope amplitude equal to the original standard TI envelope with only two frequencies. The focality will increase compared to the standard TI, while maintain the AM maximum of the standard TI. D Classic TI and measurements a macaque monkey – 3D reconstruction of the skull of the macaque monkey (CT scan) with depth electrodes used to record the TI amplitude modulation. The region of strong amplitude modulation is found to be subcortical with TI using two high frequencies, but the focality is limited. Modulation index is calculated as follow MI = 1-(min/max)), also illustrated in Fig. 2A. Position of stimulation electrodes (skin) are shown as pink circles around the skull. Red arrow shows the contact of the electrode which recorded the maximum MI. E. mTI and measurements in a macaque monkey – The focality of the AM signal compared to D is improved with mTI using 8 frequencies to create 4 overlapping envelopes, where the amplitude from the pairs of carrier frequencies have been reduced to create an envelope with equal amplitude to D, which results in a more focal spatial profile. As in 1D, the position of stimulation electrode (skin) are shown as pink, blue, red and green circles around the skull. Red arrow shows the electrode which recorded the maximum MI