Utah array characterization and histological analysis of a multi-year implant in non-human primate motor and sensory cortices

Abstract

Objective. The Utah array is widely used in both clinical studies and neuroscience. It has a strong track record of safety. However, it is also known that implanted electrodes promote the formation of scar tissue in the immediate vicinity of the electrodes, which may negatively impact the ability to record neural waveforms. This scarring response has been primarily studied in rodents, which may have a very different response than primate brain. Approach. Here, we present a rare nonhuman primate histological dataset (n=1 rhesus macaque) obtained 848 and 590 days after implantation in two brain hemispheres. For 2 of 4 arrays that remained within the cortex, NeuN was used to stain for neuron somata at 3 different depths along the shanks. Images were filtered and denoised, with neurons then counted in the vicinity of the arrays as well as a nearby section of control tissue. Additionally, 3 of 4 arrays were imaged with a scanning electrode microscope (SEM) to evaluate any materials damage that might be present. Main results. Overall, we found a 63% percent reduction in the number of neurons surrounding the electrode shanks compared to control areas. In terms of materials, the arrays remained largely intact with metal and Parylene C present, though tip breakage and cracks were observed on many electrodes. Significance. Overall, these results suggest that the tissue response in the nonhuman primate brain shows similar neuron loss to previous studies using rodents. Electrode improvements, for example using smaller or softer probes, may therefore substantially improve the tissue response and potentially improve the neuronal recording yield in primate cortex.

Chronic stability of a neuroprosthesis comprising multiple adjacent Utah arrays in monkeys

“…Our analysis of electrode integrity after the experiment revealed degradation of the IrOx deposition layer, electrode tip breakage, and pitting of the electrode surface. Similarly, across three arrays in an nonhuman primate (NHP), Patel et al found that their arrays remained largely intact but individual electrodes showed signs of tip breakage and cracking, 590-848 d after implantation [65].…”

Multimodal subspace identification for modeling discrete-continuous spiking and field potential population activity

“…Given its computational efficiency in training, the multiscale SID method can enable various future realtime learning applications in neuroscience and neural engineering. Tracking non-stationarity in neural representations is a major challenge in BMIs, which can happen due to various factors such as recording instability [101][102][103], learning and plasticity [58,67,98,[104][105][106][107][108][109][110][111][112][113][114], or a change in an internal state such as a psychiatric state [115]. These non-stationarities need to be addressed by relearning or updating the model parameters frequently, even potentially continuously at every time step [67].…”

Lifetime engineering of bioelectronic implants with mechanically reliable thin film encapsulations

“…Furthermore, an analysis of explanted Utah arrays indicated oxidation of the film as well as chlorine abstraction, which could contribute to embrittlement and cracking following swelling from fluid absorption [243]. A different study observed that parylene cracking was more common on the perimeter of implanted Utah arrays than toward the center, and theorized that lateral stresses on the outermost shanks due to micromotion or tugging from the wire bundle may have contributed [244]. In any case, other polymers are in need of investigation for long-term device stability.…”

“…Median lifespans for rigid and flexible substrates were found to be 216 and 108.5 d respectively. Ninety seven studies were included in the analysis, for which the supporting data can be found in supplementary data table 2 [12,17,30,90,94,96,97,101,114,115,121,131,136,142,153,168,170,223,241,242,244,331,379,389,390,393,394,.…”