MRM FOR MAPPING FUNCTIONAL ARCHITECTURE OF VISUAL CORTEX IN FERRETS

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Optical studies of the surface of the optical cortex of primates (cat, monkey, ferret) have shown that the neurons are organized in correlated groups having a 'blobby' appearance. Groups have a correlated response to, for example, stimuli by bar-shaped objects of a given orientation. Other, overlapped groups have similar response to differently oriented bars. The size of a group is on the order of 500 microns. The optical techniques are sensitive to the oxyhemoglobin-hemoglobin shift that occurs due to increased metabolism when the neurons are stimulated. The optical techniques are limited to viewing depths in the brain of about 100 microns. The goal of this research is to study this structure at a variety of depths in the cerebral cortex beyond those reached by optical means. Gradient echo 3D MR microscopy offers a unique opportunity as the only method to perform this kind of study. What is proposed is a pilot study to obtain 3D images (@ 7T) in the optical cortex of a ferret with 100 micron isotropic resolution while the animal is visually stimulated with an already validated stimulation protocol to evaluate the potential of MR microscopy in this application. The purpose of the pilot project will be to develop an MRI protocol for adequate functional imaging. We will try 3D projection imaging as well as 3D spin warp approaches. In addition, it will be necessary to ensure that the ferret can be adequately supported in the 7T system and that the optical stimulation system will function in/near the magnet. Note that the investigators already routinely use gas (halothane) anesthesia on these animals over the course of a several hour experiment and have experience and publications in the area.