We will build a visible light spectroscopy (VLS) system to probe the neocortex of mice and immature rats. This system will use multiple optical fibers placed on the exposed skull and measure complete attenuation spectra from 500 to 630nm between pairs of fibers using white light illumination and a multi-channel imaging spectrograph equipped with a cooled CCD detector. We have developed and validated a novel algorithm to calculate the concentration of reduced cytochrome c and reduced cytochrome oxidase as well as absolute hemoglobin concentration and saturation directly from these attenuation spectra. We will use this algorithm to reconstruct a topographic map of the cortex between pairs of optodes and extend this algorithm to reconstruct a full 3 dimensional tomographic image of the cortex. The topographic system will consist of 25 transmit fibers and 16 receive fibers with a spacing of 1.25mm allowing us to span 7x7mm of the neocortex. We will use nearest neighbor pairs of optodes to map the neo cortex with a spatial resolution of 1.56mm 2. Temporal resolution will be 1 second. ? ? The tomographic system will consist of an array of 36 fibers spaced lmm apart spanning an area x5mm across the neocortex. We will sequence through all 36 fibers making each one in turn a transmit fiber and the remaining 35 receive fibers. We will apply a tomographic reconstruction based on a Monte-Carlo simulation of the transport of light through the tissue to reconstruct the gray matter of the cortex in 3 dimensions. We expect sufficient signal to make measurements up to fourth nearest neighbor allowing an in-plane resolution of lmm 2 and a depth resolution of 0.25mm. Temporal resolution will be 1.5 seconds. The ability to directly image signals from the mitochondria will make this system unique and will be invaluable in following the metabolic consequences of spreading depression and seizure propagation as well probing the mechanisms of ischemic and excitotoxic cell death. ? ?
