Model 2200 isolator

Electrical stimuli were delivered through the intracranial electrodes using a battery-driven isolated constant current stimulator (IZ-2H stimulator, Tucker-Davis technology’s, Alachua, FL, USA, and Model 2200 isolator, A-M systems, WA, U.S.A.). The stimulus waveforms were designed using OpenEx software in the Tucker-Davis RZ2 processing base station (sampling rate of 48 kHz) and sent to the stimulator for generation of the actual electrical stimulus. Hardware RF filters (Mini-Circuit, Brooklyn, NY, BLP-1.9+, passband: DC - 1.9 MHz) were installed on the patch-panel of the scanner room and inserted between electrodes and the stimulator in order to avoid noise contamination of the MR images. The stimulator, battery and stimulus controlling equipment were all in the control room adjacent to the MR scanner. Electrode tail leads were kept parallel to the scanner’s B0 field orientation. The experimental setup is shown in Fig. 1A.

Bipolar electrical stimulation was delivered through the intracranial electrodes using a battery-driven isolated constant current stimulator (IZ-2H stimulator, Tucker-Davis technology’s, Alachua, FL, USA, and Model 2200 isolator, A-M systems, WA, U.S.A.). We used biphasic charge-balanced constant current stimulus waveforms of +9/-3 or +12/-4 mA, delivered at 100 Hz (5 to 9 pulses; see Figure 5, andTable S3). Mean in-situ electrode impedance measured at the time of the experiments was 4.08 (sd = 1.65) k Ω for 100 Hz stimulation.