Thin Film Neural Interfaces For Brain Computer Interface And Electroretinography Applications

THIN-FILM NEURAL INTERFACES FOR BRAIN-COMPUTER INTERFACE AND ELECTRORETINOGRAPHY APPLICATIONS Sanitta Thongpang Under the supervision of Associate Professor Justin C. Williams At the University of Wisconsin-Madison The brain, and more precisely the central nervous system (CNS), is an extremely complex organ responsible for controlling essential sensorimotor functions of the human body. These functions rely on nerves running all-throughout the organism, transporting the sensory information from the body towards the CNS and the motor information from the CNS to the muscles. However, when severed, these functions can be durably lost, provoking paralysis and significant loss of quality of life. Neuroprosthesis is a promising approach to allow the patient to regain some of the quality of life lost through the control of a computer directly from measuring brain activity. Unfortunately, current methods are either too invasive, risk a decrease of performance over time and require extreme precision to place (i.e. single-unit electrode) or non-invasive but imprecise and limited (e.g. electroencephalogram). Electrocorticogram interfaces (ECoG and micro-ECoG) have been developed to measure brain activity as close as possible to the neurons while minimizing invasivity and long-term effects. These are placed on between the cortex and the cranium and allow good improvements in signal quality and spatial resolution. Here, I present the improved electrode designs and fabrication methods for reliable micro-ECoG electrode arrays using flexible insulating materials such as polyimide and parylene C. Furthermore, we characterize the long-term effect of chronic implantation of the device both on the electrical and material properties as well as the biological response of the brain of the micro-ECoG arrays. In addition, leveraging recent developments in optogenetics, two-way neural interface devices were developed. By integrating these methods with cranial window imaging techniques, I demonstrated that very powerful tools for optimizing micro-ECoG electrode arrays, as well as answering fundamental biological question on the function of the brain, can be developed. Finally, the flexible thin-film bio-MEMS fabrication methods demonstrated were readily expanded to many other applications such as electroretinogram (ERG) recording.