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Mapping ocular dominance columns in human V1 using fMRI
ABSTRACTS
Mapping Ocular Dominance Columns in Human V1 using fMRI R.S. Menon, S. Ogawa and K. Ugurbil Advanced Imaging Laboratories, The John P. Robarts Research Institute, London, Canada, AT&T Bell Laboratories, Murray Hill, USA and Centre for Magnetic Resonance Research, University of Minnesota, Minneapolis, USA In humans, the ocular dominance columns (ODCs) have been demonstrated post-mortem in striate cortex by histochemical staining for cytochrome oxidase (1), but a noninvasive technique for examining human striate cortex organization on the scale of cortical functional subunits has not been available. The hemodynamic-response mechanism that allows visualization of orientation columns and ODCs in awake monkeys by optical imaging of intrinsic signals demonstrates that corticovascular responses to visual stimuli can be localized to the columnar level in several mammalian species (2). The Blood Oxygen Level Dependent (BOLD) technique (3) upon which the vast majority of cortical mapping using functional Magnetic Resonance Imaging (fMRI) is based, is also sensitive to the hemodynamic changes in the local vasculature, which suggests that, in principle, cortical columns could be mapped noninvasively using fMRI as well. SUBJECTS AND ACTIVATION TASK 13 normal subjects (ages 20-59, 4 females) gave written consent prior to participating in this study. Ten of the subjects had previous MRI or fMRI experience. GRASS goggles (Quincy, MA) flashing at 10 Hz were used for photic stimulation, modified so that all light emitting diodes (LEDs) but one [middle line, most medial] were masked out on each side. Each LED subtended about 1.2 degrees of the horizontal and vertical visual field. Binocular stimulation ("B" state) sandwiched between periods of darkness ("D" state), was used to identify primary visual cortex. Monocular stimulation using the left ("L" state) or right ("R" state) flashing LED was used to deliniate ocular dominance columns. Each of the states, B, D, L and R were typically 1 minute in duration. MRI STUDIES All fMRI experiments were performed using an in-plane resolution of 391 by 391 microns and a slice thickness of 3 mm on a 4 T whole-body human imager [Varian (Palo Alto, CA)/Siemens (Erlangen, Germany)] [TE=30 ms, TR=50 ms, slice thickness=3 mm, Flip Angle-22 ~ 256x256]. Subject head motion was restrained with various combinations of bite bars, rigid foam pads, straps and neck braces. Since the columns are expected to be 5 to 10 mm in length in humans and 0.8 to 1 mm on a side, it is expected that they will be perpendicular to the 3 mm thick slice chosen parallel to the calcarine fissure in at least a few local regions, but not necessarily in the whole slice. Cross-correlation analysis (>0.5) was used to identify pixels that responded to left or right eye photic input as well as binocular input. Only the images with the alternating monocular stimulation were used for the correlation with the reference waveforms. 44 left ocular dominance columns RESULTS right ocular dominance columns We found that in certain areas of V1, the correlation 43 analysis detected pixels that oscillated in synch with the left-right stimulus paradigm. At the correlation values 42 used, NO pixels were detected outside the brain suggesting these are not random. In addition, these pixels are found as alternating clumps of pixels along =~ 41 the line of Gennari visible in some of our images, suggesting that they are confined to layer 4C of V1. We note that the BOLD signal within a column does ~ 4o not return to zero during stimulation of the alternate eye suggesting that there are both specific and non-specific 39 4 8 12 16 20 24 28 32 36 40 44 components to the fMRI maps. ACKNOWLEDGEMENTS Image Number Supported by an operating grant and a salary support award from the Medical Research Council of Canada (R.S.M) and NIH grant RR08079 (K.U.). 1. Horton, J. C. and Hedley-White, E. T. Phil. Trans. R. Soc. Lond. 1984, B304:255-272. 2. Grinvald, A., Lieke, E., Frostig, R. D., Gilbert, C. D. and Wiesel, T. N. 1986, Nature, 324:361-364. 3. Ogawa, S. , Lee, T. M., Nayak, A. S. and Glynn, P. 1990, Magn. Reson. Med. 14:68-78. -"
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Mapping Ocular Dominance Columns in Human V1 using fMRI R.S. Menon, S. Ogawa and K. Ugurbil Advanced Imaging Laboratories, The John P. Robarts Research Institute, London, Canada, AT&T Bell Laboratories, Murray Hill, USA and Centre for Magnetic Resonance Research, University of Minnesota, Minneapolis, USA In humans, the ocular dominance columns (ODCs) have been demonstrated post-mortem in striate cortex by histochemical staining for cytochrome oxidase (1), but a noninvasive technique for examining human striate cortex organization on the scale of cortical functional subunits has not been available. The hemodynamic-response mechanism that allows visualization of orientation columns and ODCs in awake monkeys by optical imaging of intrinsic signals demonstrates that corticovascular responses to visual stimuli can be localized to the columnar level in several mammalian species (2). The Blood Oxygen Level Dependent (BOLD) technique (3) upon which the vast majority of cortical mapping using functional Magnetic Resonance Imaging (fMRI) is based, is also sensitive to the hemodynamic changes in the local vasculature, which suggests that, in principle, cortical columns could be mapped noninvasively using fMRI as well. SUBJECTS AND ACTIVATION TASK 13 normal subjects (ages 20-59, 4 females) gave written consent prior to participating in this study. Ten of the subjects had previous MRI or fMRI experience. GRASS goggles (Quincy, MA) flashing at 10 Hz were used for photic stimulation, modified so that all light emitting diodes (LEDs) but one [middle line, most medial] were masked out on each side. Each LED subtended about 1.2 degrees of the horizontal and vertical visual field. Binocular stimulation ("B" state) sandwiched between periods of darkness ("D" state), was used to identify primary visual cortex. Monocular stimulation using the left ("L" state) or right ("R" state) flashing LED was used to deliniate ocular dominance columns. Each of the states, B, D, L and R were typically 1 minute in duration. MRI STUDIES All fMRI experiments were performed using an in-plane resolution of 391 by 391 microns and a slice thickness of 3 mm on a 4 T whole-body human imager [Varian (Palo Alto, CA)/Siemens (Erlangen, Germany)] [TE=30 ms, TR=50 ms, slice thickness=3 mm, Flip Angle-22 ~ 256x256]. Subject head motion was restrained with various combinations of bite bars, rigid foam pads, straps and neck braces. Since the columns are expected to be 5 to 10 mm in length in humans and 0.8 to 1 mm on a side, it is expected that they will be perpendicular to the 3 mm thick slice chosen parallel to the calcarine fissure in at least a few local regions, but not necessarily in the whole slice. Cross-correlation analysis (>0.5) was used to identify pixels that responded to left or right eye photic input as well as binocular input. Only the images with the alternating monocular stimulation were used for the correlation with the reference waveforms. 44 left ocular dominance columns RESULTS right ocular dominance columns We found that in certain areas of V1, the correlation 43 analysis detected pixels that oscillated in synch with the left-right stimulus paradigm. At the correlation values 42 used, NO pixels were detected outside the brain suggesting these are not random. In addition, these pixels are found as alternating clumps of pixels along =~ 41 the line of Gennari visible in some of our images, suggesting that they are confined to layer 4C of V1. We note that the BOLD signal within a column does ~ 4o not return to zero during stimulation of the alternate eye suggesting that there are both specific and non-specific 39 4 8 12 16 20 24 28 32 36 40 44 components to the fMRI maps. ACKNOWLEDGEMENTS Image Number Supported by an operating grant and a salary support award from the Medical Research Council of Canada (R.S.M) and NIH grant RR08079 (K.U.). 1. Horton, J. C. and Hedley-White, E. T. Phil. Trans. R. Soc. Lond. 1984, B304:255-272. 2. Grinvald, A., Lieke, E., Frostig, R. D., Gilbert, C. D. and Wiesel, T. N. 1986, Nature, 324:361-364. 3. Ogawa, S. , Lee, T. M., Nayak, A. S. and Glynn, P. 1990, Magn. Reson. Med. 14:68-78. -"
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