Neural Probes for Chronic Applications

Abstract

Developed over approximately half a century, neural probe technology is now a mature technology in terms of its fabrication technology and serves as a practical alternative to the traditional microwires for extracellular recording. Through extensive exploration of fabrication methods, structural shapes, materials, and stimulation functionalities, neural probes are now denser, more functional and reliable. Thus, applications of neural probes are not limited to extracellular recording, brain-machine interface, and deep brain stimulation, but also include a wide range of new applications such as brain mapping, restoration of neuronal functions, and investigation of brain disorders. However, the biggest limitation of the current neural probe technology is chronic reliability; neural probes that record with high fidelity in acute settings often fail to function reliably in chronic settings. While chronic viability is imperative for both clinical uses and animal experiments, achieving one is a major technological challenge due to the chronic foreign body response to the implant. Thus, this review aims to outline the factors that potentially affect chronic recording in chronological order of implantation, summarize the methods proposed to minimize each factor, and provide a performance comparison of the neural probes developed for chronic applications.

Mechanical characterization of compliant neural probes, their insertion regimes and a rule of thumb design

“…For a probe inserting into brain tissue, the base of the probe is considered to be clamped to the insertion tool and fixed (allowing for no translation or rotation), and the tip of the probe is pinned in the x-y plane as soon as it contacts brain tissue (only allows for rotation, not translation). Thus, the commonly accepted value of k is 0.7, validated experimentally in [12].…”

Does impedance matter when recording spikes with polytrodes?

“…Some coatings may help to promote cell health at the electrode surface and minimize the immune response of surrounding brain tissue. Strong neural attachment to implanted electrodes is desirable as it increases interface stability and improves electrical transfer across the tissue-electrode interface [3], [22], [39], [40]. We thus propose that we stop worrying about impedance magnitude (as long as it stays well below the input impedance of the amplifier) and start focusing on bio-compatible materials [39], [41], [42].…”

Multichannel Silicon Probes for Awake Hippocampal Recordings in Large Animals

“…Recent advances in high-density linear electrode arrays and wireless recording technology could tremendously enhance translational research studies of large-scale networks in species with large, gyrencephalic brains [20]. Ideally, the probes for electrophysiological recordings from deep brain structures must resolve laminar local field potentials (LFPs) and provide proper sampling densities to resolve single-units across channels for single unit spike-sorting and minimize damage to the neuro-electric interface (for review see [21]). For instance, multi-channel silicon probes with many contacts in a linear configuration can isolate units in a 2 -300 µm "sphere" around each electrode [22,23].…”