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Thomas Lauritzen, Amitai Shenhav, Mark D'Esposito, Michael Silver; fMRI coherency analysis reveals feedforward progression of visual responses in human early visual cortex. Journal of Vision 2007;7(15):14. doi: 10.1167/7.15.14.
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Physiological and anatomical studies in animals are consistent with a hierarchical feedforward progression of visual responses in areas V1, V2, and V3. We have used fMRI and coherency analysis to measure the strength of coupling and relative response latencies to visual stimulation in human early visual cortex. Visual areas were defined using standard phase-encoded retinotopic mapping methods. In separate scanning sessions, subjects passively viewed a high-contrast, contrast-reversing checkerboard annulus for ten-second periods, alternating with ten seconds of gray screen visual fixation. Regions of interest were defined for portions of visual cortex that retinotopically represented the stimulus. Coherency analysis of the fMRI time series was performed to measure functional connectivity among these areas. Coherency magnitude was higher for adjacent (V1/V2 and V2/V3) than for non-adjacent (V1/V3) cortical areas, and coherency phase relationships showed V1 leading V2 and V3 and V2 leading V3. These data are consistent with feedforward hierarchical stimulus processing in early visual cortex and demonstrate that coherency analysis can measure temporal differences on the order of hundreds of milliseconds. Because many cognitive processes operate at a similar time scale, fMRI coherency analysis is likely to be useful for measuring functional connectivity for a variety of cognitive neuroscience applications.
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