Fabrication And Application Of Flexible High-resolution ECoG Electrode

As the material basis of all cognitive functions,the brain governs all human life activities,consisting of approximately 85 billion neurons.Electroencephalogram(EEG)is a basic feature of neural activity and reflects the physiological state and information coding of neurons.Methods of neural activity recording mainly include invasive(implanted)and non-invasive(non-implanted).The common non-invasive method can obtain the scalp EEG signals generated by the simultaneous activities of a large number of neurons by connecting devices to the scalp surface,but the signal-to-noise ratio and spatial-temporal resolution are not high.One of the invasive methods can obtain the Stereoelectroencephalogram(SEEG)signals that consist of spike and local field potential(LFP)by implanting a set of the deep electrodes(Utah electrodes,microfilament electrodes or Michigan probe,etc.),which has a high spatial resolution,but is highly invasive and poorly stable,causing damage to brain tissue and rejection reactions.The cortical electrodes between the deep intracranial electrodes and the scalp electrodes have less invasive damage,and the collected signals(Electrocorticogram,ECoG)have advantages of high signal-to-noise ratio,high resolution,and a larger frequency range for signal acquisition,which contain extremely important cortical neural activity information.It could provide a powerful tool for diagnosis and intervention of central nervous system diseases(epilepsy,Parkinson’s disease,drug-resistant depression,etc.),neural coding and decoding as well as improvement of brain-computer interfaces(BCIs).The ECoG electrode is changing for the directions of smaller size,high density and ultra flexibility with the progress of MEMS(Micro-electro-mechanical systems)technology,aiming to obtain more abundant and accurate information of brain activity on the cortical surface.However,the existing ECoG electrodes still exist serious inadequacies.It mainly includes the following two aspects:on one hand,traditional ECoG electrodes cannot conformally cover over the highly convoluted brain surface,resulting in the loss of signal in the recording process.On the other hand,the existing ECoG electrodes cannot obtain high-throughput signals of brain activity on the cortical surface,due to their low density and low resolution.There are no over 256-channel cortical electrodes of independent research and development applied to clinical and neurophysiological experiments at home.To effectively solve the above problems,this paper focuses on the design,fabrication,characterization,performance testing and animal experimental verification of the flexible high-resolution ECoG electrodes on the basis of relevant research at home and abroad.The main work of the paper includes:1.During the evolution from primates to humans,the size of cerebral cortex is increased by forming more gyri and sulci,which is believed to be highly associated with cognitive abilities and the basis of higher brain functions in humans.Obtaining electrical signal in cerebral folds provides an important opportunity to obtain complete neural mapping.The conformal ultrathin brain electrode array was designed and fabricated based on MEMS technology and flexible materials,using a water-soluble silk film serving as the supporting layer to make the ultrathin device(with a total thickness of 2.2 microns)easier to manipulate during device assembly and installation.The ultrathin device can attach the folds of the curved brain and conformally wrap over the curved cortex after the dissolution of the silk protein film without generating hazardous byproducts.We applied ultrathin devices on different animal brain models,it performed well in the effective recording area of the signals compared to ordinary devices.Note that the complexity and number of brain sulcus are increasing from cat to sheep,and ultrathin devices can achieve the conformal attachment well.2.Based on the ultrathin device,we designed and fabricated a flexible ECoG electrode array with 1024-recording sites within 1×1 cm~2 through multilayer wiring for high-density and high-quality recording of neural activity.The epilepsy model of rats was established by using celiac injection of penicillin,and the brain electrical signals of part of the channel were collected by using flexible high-resolution ECoG electrode.The data of normal brain physiological state,induced epilepsy,high frequency seizure period,drug remission period and normal state were obtained.The preliminary brain decoding model were established.