Laminar specificity of functional MRI onset times during somatosensory stimulation in rat
- Laboratory of Functional and Molecular Imaging, National Institute of Neurological Disorders and Stroke, Bethesda, MD 20892
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Communicated by Leslie G. Ungerleider, National Institutes of Health, Bethesda, MD (received for review March 7, 2002)
Abstract
The blood oxygenation level-dependent (BOLD) response to somatosensory stimulation was measured in α-chloralose-anesthetized rats. BOLD fMRI was obtained at 40-ms temporal resolution and spatial resolution of 200 × 200 × 2,000 μm3 by using a gated activation paradigm in an 11.7 T MRI. Results show a consistent heterogeneity of fMRI onset times and amplitudes. The earliest onset time (0.59 ± 0.17 s, n = 9) corresponded anatomically to layer IV, with superficial and deeper layers starting significantly later (1.27 ± 0.43 s in layers I–III, and 1.11 ± 0.45 s in layer VI). The amplitude of BOLD signal changes also varied with the cortical depth from the pial surface. Changes in the supragranular layers (8.3%) were 44% bigger than changes in the intermediate layers (5.5%), located only ≈700 μm below, and 144% larger than the bottom layer (3.5%), located ≈1.4 mm below the pial surface. The data presented demonstrate that BOLD signal changes have distinct amplitude and temporal characteristics, which vary spatially across cortical layers.
Footnotes
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↵ * To whom correspondence should be addressed at: Laboratory of Functional and Molecular Imaging, National Institute of Neurological Disorders and Stroke, 10 Center Drive, Building 10/B1D118, Bethesda, MD 20892-1065. E-mail: silvaa{at}ninds.nih.gov.
- Abbreviations:
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BOLD, blood oxygenation level-dependent
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CCC, cross-correlation coefficient
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fMRI, functional MRI
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ROI, region of interest
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- Copyright © 2002, The National Academy of Sciences
