gms | German Medical Science

Objective: We have recently shown that tiny magnetic coils can robustly activate neurons and that activation with such an approach has some significant advantages over conventional electrode-based methods. Here, we describe efforts to translate micro-coil based stimulation into an implantable cortical visual prosthesis.

Material and Methods: Two types of micro-coils were developed, micro-fabricated and ‘bent-wire’ designs, and each was tested for their ability to activate pyramidal neurons (PNs) of the primary visual cortex in mouse brain (coronal) slices in vitro. Electrophysiology helped to establish the threshold levels required for activation and calcium imaging experiments were used to help establish the selectivity of activation. Ongoing in vivo testing is being used to compare the stability of coil implants vs. that of micro-electrodes.

Results: Coil-based stimulation robustly activates PNs without also activating nearby passing axons. As a result, activation is confined to focal regions around the coil tip. PNs from both layer 5 and layer 2/3 can be activated and certain forms of repetitive stimulation can induce ‘state’ changes in the underlying circuits. Coils implanted in vivo reliably drive behavioral circuits.

Discussion: Our results suggest that coil-based implants may be an attractive alternative to conventional micro-electrode based devices. Ongoing psychophysical experiments in primate and long-term implantation studies will be discussed.

Acknowledgement: This work was supported by the Dept. of Veterans Affairs (RR&D: RX001663) and the NIH (NINDS: U01-NS099700 and NEI: R01-EY023651).