Abstract
Brain–computer interfaces (BCI) are reliant on the interface between electrodes and neurons to function. The foreign body reaction (FBR) that occurs in response to electrodes in the brain alters this interface and may pollute detected signals, ultimately impeding BCI function. The size of the FBR is influenced by several key factors explored in this review; namely, (a) the size of the animal tested, (b) anatomical location of the BCI, (c) the electrode morphology and coating, (d) the mechanics of electrode insertion, and (e) pharmacological modification (e.g., drug eluting electrodes). Trialing methods to reduce FBR in vivo, particularly in large models, is important to enable further translation in humans, and we systematically reviewed the literature to this effect. The OVID, MEDLINE, EMBASE, SCOPUS and Scholar databases were searched. Compiled results were analysed qualitatively. Out of 8388 yielded articles, 13 were included for analysis, with most excluded studies experimenting on murine models. Cats, rabbits, and a variety of breeds of minipig/marmoset were trialed. On average, over 30% reduction in inflammatory cells of FBR on post mortem histology was noted across intervention groups. Similar strategies to those used in rodent models, including tip modification and flexible and sinusoidal electrode configurations, all produced good effects in histology; however, a notable absence of trials examining the effect on BCI end-function was noted. Future studies should assess whether the reduction in FBR correlates to an improvement in the functional effect of the intended BCI.
Highlights
The brain–computer interface (BCI), often described as a neural interface, is of growing interest to neuroscientists and clinicians, as well as material and bioelectrical engineers
Public interest grows in Brain–computer interfaces (BCI) and early studies demonstrating the success of stimulatory probes in spinal cord injury are promising, they remain exceedingly rare [35], a further study will be required before they may be used for a restorative or enhancing intent
Public interest grows in BCI and early studies demonstrating the success of stimulatory probes in spinal cord injury are promising, they remain exceedingly rare [35], a finding supported by the low acceptance rate of our own study, which suggests there is not enough evidence to draw any meaningful conclusions far
Summary
The brain–computer interface (BCI), often described as a neural interface, is of growing interest to neuroscientists and clinicians, as well as material and bioelectrical engineers. Interfacing neurons with a sensor or probe offers exciting new avenues in the treatment of neurological disease [1,2]. In its simpler form, it is already employed through deep brain stimulation (DBS), where electrodes deliver current to a specific region of the brain, with improvements in symptoms in pathologies such as Parkinson’s disease [3]. Like those in retinal and cochlear implants, can ameliorate impaired vision, and restore some function to perceptive faculties previously thought irreparable [4,5]. The scope of application is wide, demonstrated by the recent STIMO trial, where patients with partial spine transection were able to regain some motor function in their lower limbs using simple electrode stimulators applied to target spinal nerves [6]. The ability to accurately record and actuate the nervous system may create new treatment modalities, and give life to a new generation of sophisticated robotic prostheses
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