Laminar specificity of functional MRI onset times during somatosensory stimulation in rat.
The blood oxygenation level-dependent (BOLD) response to somatosensory stimulation was measured in alpha-chloralose-anesthetized rats. BOLD fMRI was obtained at 40-ms temporal resolution and spatial resolution of 200 x 200 x 2,000 microm(3) 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 approximately 700 microm below, and 144% larger than the bottom layer (3.5%), located approximately 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.
Silva
Afonso C
AC
Laboratory of Functional and Molecular Imaging, National Institute of Neurological Disorders and Stroke, Bethesda, MD 20892, USA. silvaa@ninds.nih.gov
Koretsky
Alan P
AP
D000818:Animals; D001931:Brain Mapping; D002560:Cerebrovascular Circulation / Q000502:physiology*; D004558:Electric Stimulation; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D010100:Oxygen / Q000097:blood; D051381:Rats; D017207:Rats, Sprague-Dawley; D013003:Somatosensory Cortex / Q000502:physiology*
D010100:Oxygen