The goal of this project is to develop new micromachined silicon-probe technology with thin-film recording sites to acquire images of brain activity over three spatial dimensions plus the 4th dimension of time. Specifically, the applicants proposed to develop and test two new probe assemblies for chronic experimentation in the central auditory system. First, they would develop a chronic multishank recording probe with intrinsic drug-delivery microchannels and pumps to both assess and influence a 3-D tissue environment over time. Drug-delivery probes have been fabricated and used in acute experiments in the central nucleus of the inferior colliculus (CIC). The aim here is to adapt these probes to long-term chronic implantation and drug delivery to this deep auditory structure. Second, they would develop and test a new type of 3-D microelectrode array. It is based on the fabrication of two planar arrays that are connected by a forked silicon ribbon cable and that have recording sites which face inward and are mirror images of one another. This "Brain-in-a-Box" (B-I-B) probe will be used in semi-chronic studies in the auditory cortex of awake cats. Major issues to be addressed in this proposal concern 1) chronic recording and drug delivery, 2) flexible but stable interconnect cables and 3) high-channel-count percutaneous connectors. To help guide new directions and developments in fabrication and assembly, the applicants proposed to conduct two animal experiments as test beds for the maturation of the technology. The objectives of the first project are to use 32-site, drug-delivery probes to examine the extent and patterns ("images") of central neural activation in the CIC of guinea pigs to various spatial and temporal configurations of electrical stimulation of the auditory nerve, to correlate these neural patterns with behavioral measures in the same animal and to examine how the patterns and behavior are influenced by time after deafness, intervention and manipulation. The goal of the second project is to use B-I-B probes to characterize the spatio-temporal patterns of cortical activation associated with the coding of soundsource location in the auditory cortex of awake cats. A semi-chronic paradigm will be developed that will permit study of a population of units for some days or weeks, followed by explanation and replacement of the probe at a different cortical site. The probes would sample neurons simultaneously at up to 32 sites, with a spatial scale of some hundreds of micrometers and a temporal scale of milliseconds to hundreds of milliseconds. The practical and logistical information gained from both studies will help guide modifications and refinements of the technology.