A flexible parylene probe for in vivo recordings from multiple subregions of the rat hippocampus.

The hippocampus is crucial to the formation of long-term memory and declarative memory. It is divided into three sub-fields the CA1, the CA3 and the DG. To understand the neuronal circuitry within the hippocampus and to study the role of the hippocampus in memory function requires the collection of neural activities from multiple subregions of the hippocampus simultaneously. Micro-wire electrode arrays are commonly used as an interface with neural systems. However, recording from multiple deep brain regions with curved anatomical structures such as the thin cell body layers of the hippocampus requires the micro-wires to be arranged into a highly accurate, complex layout that is difficult to fabricated manually. In this work, we designed and developed a flexible parylene-C based neural probe which can be easily micro-machined to the desired dimensions. Sixty-four electrical recording sites are micromachined on to 8 parylene shanks and spaced according to the distribution of hippocampal principal neurons in different hippocampus subregions. Together with our collaborators, we developed and optimized the implantation procedure of the flexible parylene probe and tested the insertion method both in brain tissue phantom and in vivo with a sham device. Immunohistochemistry (IHC) staining post-implantation of the sham probe was used to verify the location of the probe and to evaluate immune responses to the probe. Fully functional devices were fabricated and, in future studies, functional probes will be chronically implanted into the rat hippocampus, and neural activities will be recorded and compared with signals obtained with micro-wire arrays.