Long-term recording performance and biocompatibility of chronically implanted cylindrically-shaped, polymer-based neural interfaces

Abstract

Stereo-electroencephalography depth electrodes, regularly implanted into drug-resistant patients with focal epilepsy to localize the epileptic focus, have a low channel count (6-12 macro- or microelectrodes), limited spatial resolution (0.5-1 cm) and large contact area of the recording sites (~mm2). Thus, they are not suited for high-density local field potential and multiunit recordings. In this paper, we evaluated the long-term electrophysiological recording performance and histocompatibility of a neural interface consisting of 32 microelectrodes providing a physical shape similar to clinical devices. The cylindrically-shaped depth probes made of polyimide (PI) were chronically implanted for 13 weeks into the brain of rats, while cortical or thalamic activity (local field potentials, single-unit and multi-unit activity) was recorded regularly to monitor the temporal change of several features of the electrophysiological performance. To examine the tissue reaction around the probe, neuron-selective and astroglia-selective immunostaining methods were applied. Stable single-unit and multi-unit activity were recorded for several weeks with the implanted depth probes and a weak or moderate tissue reaction was found around the probe track. Our data on biocompatibility presented here and in vivo experiments in non-human primates provide a strong indication that this type of neural probe can be applied in stereo-electroencephalography recordings of up to 2 weeks in humans targeting the localization of epileptic foci providing an increased spatial resolution and the ability to monitor local field potentials and neuronal spiking activity.

A Critical Review of Microelectrode Arrays and Strategies for Improving Neural Interfaces

“…F4,F5) GFAP stains comparing resulting gliosis between two different geometries, including F4) floating and F5) Michigan MEAs are also provided. F1–F3) Adapted with permission under the Creative Commons Attribution BY‐NC‐ND 4.0 license . Copyright 2018, the Authors.…”

“…They found that small electrodes (15 µm Michigan electrodes and microwire electrodes) reduce glial scarring markers, while cylindrically shaped wire shanks help to mitigate long term FBR by limiting BBB breach. Another study demonstrated that cylindrically shaped neural probes are feasible for maintaining single unit and multiunit activity long‐term and were also shown to elicit a less severe FBR compared to other MEA geometries (Figure ,F1–F3), such as those utilized in focal epilepsy treatment. Floating, untethered MEAs (Figure A) have also shown promise in reducing FBR severity (Figure ,F4,F5) .…”

Recording site placement on planar silicon-based probes affects signal quality in acute neuronal recordings

“…In addition, spike sorting was performed on the recordings to extract the following single unit properties for comparison: single unit yield, amplitude of single unit spikes and isolation distance (see “ Spike sorting and calculation of single unit properties ” in the Methods section for more details). The latter is a measure commonly used to determine the quality of single unit clusters 59 , while the former are usual features used to assess the recording performance extracted under different conditions 27 , 61 . The unit yield as well as properties corresponding to the quality of single units (spike amplitude, isolation distance) are important measures that can demonstrate the practical usability of probes in electrophysiological experiments.…”

Recording site placement on planar silicon-based probes affects neural signal quality: edge sites enhance acute recording performance

“…In addition, spike sorting was performed on the recordings to extract various single unit properties for comparison, such as the single unit yield, the amplitude of single unit spikes and the isolation distance (see section 2.7 for more details). The latter is a measure commonly used to determine the quality of single unit clusters [59], while the former are usual features used to assess the recording performance extracted under different conditions [27,61]. Example recordings and single unit spike (table 3), the difference between site positions was most remarkable in the range corresponding to the largest spikes (from −300 μV to −1000 μV; figure 10(a)).…”