| The large variations in microelectrode performance need to be understood and controlled to objectively evaluate new electrode designs, implantation protocols, and intervention strategies. In this study, performance of microelectrodes was studied by examining electrical, neural, histological, and mechanical properties of acute and chronic preparations. Electrical Impedance Spectroscopy (EIS) was used to investigate and to reduce the variations of microelectrode impedance in bench, acute and chronic experiments. Controlled in-vivo indentation of the meninges was developed as an acute model of the encapsulation process, and was used to study the electrical and mechanical properties of the brain tissue. The indention test revealed that the pia mater could be dragged down by the tips of the blunt microelectrodes during implantation. The EIS of the pia mater was highly sensitive to the applied stress. A thin layer of tissue staining comparably to the pia mater was also found around chronically implanted microelectrodes, and may be a major source of in-vivo impedance variations.;The chronic experiments showed that the longer the microelectrodes were implanted, the more resistive the encapsulation tissue became. While microelectrode impedance was not linked to the recording quality, increase in ground resistance was related to the susceptibility to common mode interference such as radio frequency interference and motion artifacts.;Noise estimation algorithms and signal quality metrics were developed to assess the quality of neural recordings without classification of neural spikes. Data from acute and chronic experiments suggested that a large portion of noise was from neural activities, because (1) Noise and signal strength were correlated; (2) The noise could be event related; (3) The noise level reduced considerably when the animals were anesthetized; (4) The bandwidth of the noise was related to the level of neural activities.;New approaches in improving the performance of chronic neural microelectrodes were proposed based on the findings. |
