Quantifying long-term microelectrode array functionality using chronicin vivoimpedance testing

Abstract

Long-term acquisition of high-quality neural recordings is a cornerstone of neuroprosthetic system design. Mitigating the experimental variability of chronically implanted arrays has been a formidable task because the sensor recording sites can be influenced by biotic and abiotic responses. Several studies have implicated changes in electrical interface impedance as a preliminary marker to infer electrode viability. Microelectrode impedance plays an important role in the monitoring of low amplitude and high-resolution extracellular neural signals. In this work, we seek to quantify long-term microelectrode array functionality and derive an impedance-based predictor for electrode functionality that correlates the recording site electrical properties with the functional neuronal recordings in vivo. High temporal resolution metrics of this type would allow one to assess, predict, and improve electrode performance in the future. In a large cohort of animals, we performed daily impedance measurements and neural signal recordings over long periods (up to 21 weeks) of time in rats using tungsten microwire arrays implanted into the somatosensory cortex. This study revealed that there was a time-varying trend in the modulation of impedance that was related to electrode performance. Single units were best detected from electrodes at time points when the electrode entered into the 40-150 KΩ impedance range. This impedance trend was modeled across the full cohort of animals to predict future electrode performance. The model was tested on data from all animals and was able to provide predictions of electrode performance chronically. Insight from this study can be combined with knowledge of electrode materials and histological analysis to provide a more comprehensive predictive model of electrode failure in the future.

The Use of a Bone-Anchored Device as a Hard-Wired Conduit for Transmitting EMG Signals From Implanted Muscle Electrodes

“…In vitro impedance measurements were made using the EVAL-AD5934EBZ (Analog Devices, MA, USA) using the potentiostatic method [14].…”

Polymer Fiber Probes Enable Optical Control of Spinal Cord and Muscle Function In Vivo

“…The spinal cord is highly viscoelastic (elastic modulus of 0.5-1 MPa) and experiences up to ~10% of repeated strain during motion [25,26] , presenting a challenge to combined intraspinal neural recording and optical stimulation, since the majority of neural probes and light-delivery devices are comprised of brittle materials [27][28][29] that may cause damage to the neural tissue and fail under repeated deformation [30] . To overcome these limitations, we engineered highly flexible biomimetic all-polymer fiber probes that combine an optical core for optogenetic stimulation and conductive electrodes for simultaneous neural recording.…”

Intracranial neuronal ensemble recordings and analysis in epilepsy

“…The relationship between the size of the electrode surface and the impedance is inversely proportional, with electrodes with larger area exhibiting lower impedance (Butson et al, 2006;Ludwig et al, 2006). Prasad et al found that the ideal resistance for SUA detection is between 40-150kΩ (Prasad and Sanchez, 2012). : A: black dots: average extracellular spike amplitude (±SE) vs. tetrode tip distance from 19 labeled pyramidal cells.…”

“…This leads to decreasing neuronal signal quality and SNR (Ludwig et al, 2006;Plenk, 2011;Wang et al, 2005). The microelectrode impedance fluctuates (Ward et al, 2009) and increases over time after contacting the biological tissue (Prasad and Sanchez, 2012). There are studies however, demonstrating long term biocompatibility of microelectrodes.…”

“…The impedance of the electrode depends on the surface area that comes into contact with the biological tissue, but for the typical 12.5-200µm diameter the impedance of Pt/Ir electrodes are in the 0.1-5MΩ range (Prasad, 2014) and tungsten electrodes in the 30-400kΩ range (Prasad and Sanchez, 2012).…”