Abstract
Objective. This paper describes the design, testing and use of a novel multichannel block-capable stimulator for acute neurophysiology experiments to study highly selective neural interfacing techniques. This paper demonstrates the stimulator’s ability to excite and inhibit nerve activity in the rat sciatic nerve model concurrently using monophasic and biphasic nerve stimulation as well as high-frequency alternating current (HFAC). Approach. The proposed stimulator uses a Howland Current Pump circuit as the main analogue stimulator element. 4 current output channels with a common return path were implemented on printed circuit board using Commercial Off-The-Shelf components. Programmable operation is carried out by an ARM Cortex-M4 Microcontroller on the Freescale freedom development platform (K64F). Main results. This stimulator design achieves ± 10 mA of output current with ± 15 V of compliance and less than 6 µA of resolution using a quad-channel 12-bit external DAC, for four independently driven channels. This allows the stimulator to carry out both excitatory and inhibitory (HFAC block) stimulation. DC Output impedance is above 1 M Ω. Overall cost for materials i.e. PCB boards and electronic components is less than USD 450 or GBP 350 and device size is approximately 9 cm × 6 cm × 5 cm. Significance. Experimental neurophysiology often requires significant investment in bulky equipment for specific stimulation requirements, especially when using HFAC block. Different stimulators have limited means of communicating with each other, making protocols more complicated. This device provides an effective solution for multi-channel stimulation and block of nerves, enabling studies on selective neural interfacing in acute scenarios with an affordable, portable and space-saving design for the laboratory. The stimulator can be further upgraded with additional modules to extend functionality while maintaining straightforward programming and integration of functions with one controller. Additionally, all source files including all code and PCB design files are freely available to the community to use and further develop.
Highlights
Acute Ex-Vivo and In-Vivo Experiments are a cornerstone of research in neurophysiology as they enable a quick exploratory experimental cycle
Work on high-frequency alternating current (HFAC) block has been exploratory in nature, with experimental setups used to modulate waveforms or combine multiple current sources in order to achieve specific effects [16, 17, 18, 19, 20]
Keithley received current was measured as a function of stimulator output node voltage to determine the compliance limits of the stimulator, with results on Figure 7 showing voltage compliance of ±15 V before noticeable output error
Summary
Acute Ex-Vivo and In-Vivo Experiments are a cornerstone of research in neurophysiology as they enable a quick exploratory experimental cycle. This reduces the risk of failure when committing to lengthy chronic in-vivo experiments before an animal model is well-understood by the experimenter. A large number of stimulators are available from commercial and academic sources, these are generally designed for specific applications. Work on HFAC block has been exploratory in nature, with experimental setups used to modulate waveforms or combine multiple current sources in order to achieve specific effects [16, 17, 18, 19, 20]
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