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Michael-Paul Schallmo, Cheng Qiu, Essa Yacoub, Cheryl Olman; Examining the Laminar Profile of Surround Suppression in V1 using High Resolution fMRI at 7 Tesla. Journal of Vision 2013;13(9):34. doi: https://doi.org/10.1167/13.9.34.
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© ARVO (1962-2015); The Authors (2016-present)
Surround suppression is an early visual cortical phenomenon believed to play an important role in processes such as figure-ground segmentation. This suppression from outside the classical receptive field is tuned to the relative orientation of center and surround stimuli; we refer to this specifically as orientation-dependent surround suppression (ODSS). Despite extensive investigation, the neural mechanisms of ODSS in early visual cortex are not well understood. Recent investigations using very high resolution spin-echo weighted fMRI have demonstrated that the laminar profile of the V1 BOLD signal is differentially sensitive to the configuration of visual stimuli. Due to the distinct patterns of local and long-range projections which exist at different cortical depths, the ability to examine the laminar profile of neural activity and its relationship to visual behavior can provide insight into the mechanisms of early visual processing. We investigated cortical depth-dependent profiles of BOLD activity in V1 during ODSS using high resolution fMRI at 7 Tesla. Data were acquired using both gradient echo (GE, 1 mm isotropic resolution) and 3D GRASE (GRadient And Spin-Echo, 0.8 mm isotropic resolution) sequences. V1 regions of interest (ROIs) representing center stimuli were defined retinotopically. Perceived contrast of center stimuli was lower with parallel than with orthogonal surrounds, as expected. Overall (throughout the cortical depth, both pulse sequences, all subjects), BOLD responses in V1 regions representing center stimuli were suppressed for parallel compared with orthogonal surrounds. GE data showed stronger overall BOLD responses near the pial surface compared to deeper layers, while GRASE data from anatomically matched ROIs did not. This may be attributed to larger BOLD effects from pial veins in GE compared with GRASE, with the latter being more sensitive to microvascular effects due to spin-echo weighting.
Meeting abstract presented at VSS 2013
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