Chronic subdural electrocorticography in nonhuman primates by an implantable wireless device for brain-machine interfaces

Abstract Background Subdural electrocorticography (ECoG) signals have been proposed as a stable, good-quality source for brain-machine interfaces (BMIs), with a higher spatial and temporal resolution than electroencephalogram (EEG). However, long-term implantation may lead to chronic inflammatory reactions and connective tissue encapsulation, resulting in a decline in the signal recording quality. However, no study has reported the effects of the surrounding tissue on signal recording and device functionality thus far. Methods In this study, we implanted a wireless recording device with a customized 32-electrode-ECoG array subdurally in two nonhuman primates for 15 months. We evaluated the neural activities recorded and wirelessly transmitted to the devices and the chronic tissue reactions around the electrodes. Results Time-frequency analyses of the acute and chronic phases showed similar signal features. The average root mean square voltage and power spectral density remained relatively stable after chronic implantation. Histological examination revealed thickening of the reactive tissue around the electrode array; however, no evident inflammation in the cortex. In addition, we measured the gain factor of the newly formed ventral fibrous tissue in vivo. Conclusions This study suggests that subdural ECoG may provide stable chronic signal recordings for future clinical applications and neuroscience research and highlights the role of reducing the thickness of ventral tissue proliferation.