Long-Term Sheep Implantation of WIMAGINE®, a Wireless 64-Channel Electrocorticogram Recorder

Abstract

This article deals with the long-term preclinical validation of WIMAGINE ® (Wireless Implantable Multi-channel Acquisition system for Generic Interface with Neurons), a 64-channel wireless implantable recorder that measures the electrical activity at the cortical surface (electrocorticography, ECoG). The WIMAGINE ® implant was designed for chronic wireless neuronal signal acquisition, to be used e.g., as an intracranial Brain–Computer Interface (BCI) for severely motor-impaired patients. Due to the size and shape of WIMAGINE ® , sheep appeared to be the best animal model on which to carry out long-term in vivo validation. The devices were implanted in two sheep for a follow-up period of 10 months, including idle state cortical recordings and Somato-Sensory Evoked Potential (SSEP) sessions. ECoG and SSEP demonstrated relatively stable behavior during the 10-month observation period. Information recorded from the SensoriMotor Cortex (SMC) showed an SSEP phase reversal, indicating the cortical site of the sensorimotor activity was retained after 10 months of contact. Based on weekly recordings of raw ECoG signals, the effective bandwidth was in the range of 230 Hz for both animals and remarkably stable over time, meaning preservation of the high frequency bands valuable for decoding of the brain activity using BCIs. The power spectral density (in dB/Hz), on a log scale, was of the order of 2.2, –4.5 and –18 for the frequency bands (10–40), (40–100), and (100–200) Hz, respectively. The outcome of this preclinical work is the first long-term in vivo validation of the WIMAGINE ® implant, highlighting its ability to record the brain electrical activity through the dura mater and to send wireless digitized data to the external base station. Apart from local adhesion of the dura to the skull, the neurosurgeon did not face any difficulty in the implantation of the WIMAGINE ® device and post-mortem analysis of the brain revealed no side effect related to the implantation. We also report on the reliability of the system; including the implantable device, the antennas module and the external base station.

Minimal Tissue Reaction after Chronic Subdural Electrode Implantation for Fully Implantable Brain–Machine Interfaces

“…Results showed the dorsal encapsulation was thicker than both the ventral encapsulation and the control dural membrane. Consistent with previous studies in epidurally implanted ECoG electrodes [ 24 , 25 ], we demonstrated that the fibrosis encapsulation tissue proximal to the dural membrane was significantly thicker than that distal to the dural membrane for subdural electrode arrays. The subdural connective encapsulation tissue reported here would be expected of a long-term foreign body response to implants and/or a result of the acute wound healing reaction [ 16 , 27 ].…”

“…In this study, the cytomorphological characteristics of the cerebral cortex under the electrodes were not affected and were consistent with those in the contralateral hemisphere. Our neuronal density results in both hemispheres agreed with those of previous studies on rats, macaques, and human beings, which showed a mild inflammatory process with no significance in the brain region covered by subdural/epidural electrode arrays after 30 to 666 days [ 22 , 24 , 25 , 35 ]. Thus, considering the depression caused by the compression from the newformed dura fibrosis, it is plausible that the slight increase in cell density is most probably due to the pervasive mechanical deformation of brain tissue [ 36 ] rather than a response to foreign body inflammation.…”

“…Increased thickness of the dural membrane and fibrous encapsulation of the electrode array that were found in this study have been widely reported in other chronic ECoG implantation studies for both epidural and subdural placement [ 23 , 24 , 25 , 26 ]. We further quantitatively measured the thickness of the reactive tissues in the subdural space and found statistically significant differences compared with the control dural membrane.…”

“…There is only one skull-implantable device that is already medically approved: RNS. There are a few skull-implantable devices for BMIs previously reported [ 25 , 37 , 38 ]. The sizes of these devices are similar and small enough to be implanted in the large human skull, but too large to be implanted in the most of the experimental animals’ skulls.…”

Very High Bit Rate Near-Field Communication with Low-Interference Coils and Digital Single-Bit Sampling Transceivers for Biomedical Sensor Systems

“…As far as the system dimensions are considered, miniaturized neural probes are accompanied by coils [ 24 ] and circuit boards [ 25 , 26 , 27 ] measuring up to several centimeters, which is still feasible as they are embedded in upper tissue layers. Consequently, implant coils and prototype circuits for concept evaluation shall be realized with a maximum edge length of 10 mm, i.e., they shall cover a maximum circuit board area of 100 mm each.…”