Artikel
Functional and histological evaluation of µECoG in sheep
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Veröffentlicht: | 8. Juni 2016 |
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Gliederung
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Objective: Brain-Machine-Interfaces (BMI) require high temporal and spatial recordings of cortical neuroactivity. In opposition to invasive needle-electrodes, micro-electrocorticography (µECoG) is a promising technique with a limited extent of invasiveness. We recently developed a sheep model for µECoG-based BMI devices and demonstrated that somatosensory evoked potentials (SEP) and auditory evoked potentials (AEP) may be suitable for long-term functional testing of such devices in sheep. It was the aim of this study to (1) present first histological results of a 1-year-implantation period of µECoG-electrodes on 3 sheep’s cortices and (2) show a proof-of-concept that auditory evoked potentials can be used to perform chronic functional µECoG testing in an awake sheep.
Method: We implanted a µECoG grid made of medical silicon with platinum/iridium contacts on three sheep’s sensory cortices and performed regular SEP-analysis over 12 months during short anesthesia. Then, hematoxylin-eosine (HE) and glial fibrillary acidic protein (GFAP) staining of the cortices and HE staining of the dura were performed. For AEP recording, a similar electrode was implanted on the auditory cortex of one sheep and connected to a wireless infrared transmitter which was implanted subcutaneously in the shoulder area. A 3 s auditory signal with a peak frequency of 8 kHz and a noise of 125 Hz around that peak with 80 dB SPL was presented to the awake animal from a standardized distance.
Results: (1) Histological analysis: in all 3 animals we found signs of astroglioses and isolated hypoxic cells in the cortices and insular giant cells and siderophages in the adjacent dura above the grid. One animal showed slight dystrophic calcifications in the dura. (2) Proof-of-concept AEP: Auditory evoked potentials can reliably be recorded in the awake animal during the 2 months after implantation.
Conclusions: Histological analysis reveals slight reactive gliosis in the cortex the µEcoG grid was positioned on during 1 year. The neuronal integrity does not seem to be altered compared to tissue changes during implantation of invasive needle electrodes. AEP seem to be a gentle way to perform long-term functional evaluations of BMI devices in the awake animal. The present study demonstrates that the sheep is suitable to investigate tissue changes during chronic implantation of µECoG electrodes on the cortex and that AEP can be reliably used to perform long-term functional studies of µECoG based BMI devices.