fMRI ABILITY TO MAP COLUMNAR STRUCTURES IN HUMANS

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DESCRIPTION (provided by applicant): Functional magnetic resonance imaging offers an unmatched combination of spatial and temporal resolution that continues to be pushed to new levels. Recently, the limits of BOLD fMRI have been challenged to the level of sub-millimeter structures. The reliability and reproducibility of these maps, as well as the optimization of the fMRI methods to acquire these maps has not yet been established, especially in humans. Differential mapping using gradient echoes, which may not be reliable in the general case because of the well known large vessel artifacts (more significantly at low fields), has been used in humans. We have recently demonstrated, made possible by funding from an R21 proposal, at sub-millimeter spatial resolutions, the advantages of high field Hahn spin echo (HSE) BOLD signals. Differences in specificity to neural activity between GE and HSE BOLD signals at high fields has not yet been addressed. Optimized BOLD signals to map brain function could allow for mapping of functional architecture without apriori knowledge of orthogonal conditions (i.e. single condition mapping). This would be an invaluable tool for many neuroscience applications where orthogonal conditions and columnar organizations in general are not known. This work will advance the foundation of our previous R21 proposal which investigated T2 weighted fMRI at high magnetic fields. The central hypothesis of this application is that HSE based BOLD fMRI signals at high fields (7 Tesla) can be used to attain a higher spatial specificity and therefore more reliable maps of cortical columns, in awake humans, than at lower fields (4 Tesla) and/or with gradient echoes. Finally, the existence of orientation columns in humans, which has never been shown, can be addressed using fMRI techniques developed in this work.