A Multi-Channel Asynchronous Neurostimulator With Artifact Suppression for Neural Code-Based Stimulations

Abstract

A novel neurostimulator for generating neural code-based, precise, asynchronous electrical stimulation pulses is designed, fabricated, and characterized. Through multiplexing, this system can deliver constant current biphasic pulses, with arbitrary temporal patterns, and pulse parameters to 32 electrodes using one pulse generator. The design also features a stimulus artifact suppression (SAS) technique that can be integrated with commercial amplifiers. Using an array of CMOS switches, electrodes are disconnected from recording amplifiers during stimulation, while the input of the recording system is shorted to ground through another CMOS switch to suppress ringing in the recording system. The timing of the switches used to block and suppress the stimulus artifact are crucial and are determined by the electrochemical properties of the electrode. This system allows stimulation and recording from the same electrodes to monitor local field potentials with short latencies from the region of stimulation for achieving feedback control of neural stimulation. In this way, timing between each pulse is controlled by inputs from an external source and stimulus magnitude is controlled by feed-back from neural response from the stimulated tissue. The system was implemented with low-power and compact packaged microchips to constitute an effective, cost-efficient, and miniaturized neurostimulator. The device has been first evaluated in phantom preparations and then tested in hippocampi of behaving rats. Benchtop results demonstrate the capability of the stimulator to generate arbitrary spatio-temporal pattern of stimulation pulses dictated by random number generators (RNGs) to control magnitude and timing between each individual biphasic pulse. In vivo results show that evoked potentials elicited by the neurostimulator can be recorded ∼2 ms after the termination of stimulus pulses from the same electrodes where stimulation pulses are delivered, whereas commercial amplifiers without such an artifact suppression typically result in tens to hundreds of milliseconds recovery period. This neurostimulator design is desirable in a variety of neural interface applications, particularly hippocampal memory prosthesis aiming to restore cognitive functions by reinstating neural code transmissions in the brain.

Stimulation and Recording of the Hippocampus Using the Same Pt-Ir Coated Microelectrodes

“…Next, the electrodes were connected to a custom-built stimulator, design of which was described elsewhere ( Elyahoodayan et al, 2019 ). Charge-balanced, cathodic first, biphasic single pulses were delivered to the electrodes with each subsequent pulse having a larger total charge.…”

“…The output of a previously designed stimulator PCB ( Elyahoodayan et al, 2019 ) was connected to each electrode one at a time using a coaxial cable ending with hook cables. The voltage across the electrode in response to each stimulation pulse was digitized at 1 MHz sampling frequency and recorded.…”

“…Previously, we reported a stimulus artifact suppression technique that reduced the artifact down to ∼2 ms after the termination of the stimulation pulse from the stimulated electrode. The designed stimulus artifact suppression technique ( Elyahoodayan et al, 2019 ) was used here to record short latency neural response to stimulation. In short, the design uses a set of CMOS switches to disconnect the electrodes from the recording amplifiers during stimulation.…”

Advances in Neural Recording and Stimulation Integrated Circuits

“…Several stimulation artifact cancelation techniques have been reported previously. The blanking technique and digital signal processing (Erez et al, 2010) have been used to cancel the artifact (Olsson et al, 2005;Venkatraman et al, 2009;Kent and Grill, 2011;Myers et al, 2011;Zoladz et al, 2012;Wei-Ming et al, 2013;Yi et al, 2013;Bozorgzadeh et al, 2014;Elyahoodayan et al, 2019). In the blanking technique, the RFE is switched off or disabled (input is shorted to ground) during the stimulation period and turned on after the stimulation is completed to continue the recording.…”

An FPGA-Based Neuron Activity Extraction Unit for a Wireless Neural Interface

“…It creates a direct information pathway between the brain and the outside world [1] as a gateway component of neural devices. With the recent drastic advancement in experimental neuroscience, the neural interface is becoming sophisticated and miniaturized [2][3][4][5][6]. The longer-term procedure especially requires miniaturized and wireless devices to ensure patients' comfort and flexibility [7][8][9].…”