Noninvasive Direct Stimulation of the Cochlear Nerve for Functional MR Imaging of the Auditory Cortex

Experimental setup and the different stimulation schemes used for the electrical stimulation of the auditory nerve during functional MR imaging. Stim. Sig., stimulation signal (stimulation information is transmitted from the control box of the Electro Audiometer, and the signal is generated in the receiver-stimulator); Rph, photo resistor impedance; Rdr, dark resistance of photo resistor; Pat. Sig., stimulation signal transmitted to patient; MR-Trig., MR-trigger signal; Im. Ac., image acquisition.

A, The entire stimulation setup is located within the shielded room. The electrode leads are disconnected by means of two photo resistors. The light for switching the photo resistors is transmitted via two optical fibers. The Electro Audiometer synchronizes the stimulator-receiver (receiver 2) and light source (receiver 1) by infrared transmission. Furthermore, the light source synchronizes the MR imager with the stimulation setup by applying an MR trigger signal to the imager after the photo resistors have disconnected the electrodes. State A (no stimulation) and state B (stimulation) are realized by a “beam shutter.”

B, Schematic diagram depicts synchronization between the current bursts used for electrical stimulation and image acquisition. The remaining time for safe imaging is 0.35 seconds for mode 1.

C, Schematic diagram depicts synchronization between the current bursts used for electrical stimulation and image acquisition. The remaining time for safe imaging is 0.7 seconds formode 2.