Open Hardware for neuro-prosthesis research: A study about a closed-loop multi-channel system for electrical surface stimulations and measurements

Abstract

Abstract Recent progress in neuro-prosthetic technology gives rise to the hope that in the future blind people might regain some degree of visual perception. It was shown that electrically stimulating the brain can be used to produce simple visual impressions of light blobs (phosphenes). This technology, using electrodes placed on top of the visual cortex, was successfully used to give blind people some degree of visual impression of their surrounding. However, this perception is very far away from natural sight. For developing the next generation of visual prostheses, real-time closed-loop stimulators are required. Such a stimulator measures the actual neuronal activities and on this basis determines the required stimulation pattern. In addition, there is a desire to shrink the diameter of the applied electrodes and increase their spatial density. This leads to the challenge of designing a system that can produce arbitrary stimulation-patterns with up to ± 70 V and with up to 25 mA while measuring neuronal signals with amplitudes in the order of mV. Furthermore, interruptions of the measurements during stimulation should be as short as possible and the system needs to scale to hundreds of electrodes. We discuss how such a system and especially its current pumps and input protection need to be designed and which problems arise. We condense our findings into an example design for which we provide all design files (boards, firmwares and software) as open-source. This is a first step in taking the existing open-source www.open-ephys.org recording system and converting it into a closed-loop experimental setup for neuro-prosthetic research.