HRFs extracted from the random-ISI experiment by : whole-volume (a) and region-specific (b)

×: extracted HRF coeffcients. Dashed lines: function HRFfitted to ×. 95% prediction intervals for the fitted functions are shown as error bars.<p><b>Copyright information:</b></p><p>Taken from "Data-driven haemodynamic response function extraction using Fourier-wavelet regularised deconvolution"</p><p>http://www.biomedcentral.com/1471-2342/8/7</p><p>BMC Medical Imaging 2008;8():7-7.</p><p>Published online 10 Apr 2008</p><p>PMCID:PMC2409308.</p><p></p

HRFs extracted from the fixed-ISI data by selective averaging (top row) and (bottom row)

Left: whole-volume, right: region-specific. The extracted coeffcient are the × at each TR. Dotted lines: fits of HRFto the coeffcients. Error bars show the 95% confidence intervals for the fitted function.<p><b>Copyright information:</b></p><p>Taken from "Data-driven haemodynamic response function extraction using Fourier-wavelet regularised deconvolution"</p><p>http://www.biomedcentral.com/1471-2342/8/7</p><p>BMC Medical Imaging 2008;8():7-7.</p><p>Published online 10 Apr 2008</p><p>PMCID:PMC2409308.</p><p></p

Box plot of the temporal HRF properties of the GE HRF across the cortical depth and SE HRF across all subjects.

<p>A) Onset time (s), B) TTP (s) C) FWHM (s), and D) PSC (%). Comparing the SE HRF with surface gray matter GE HRF (0–1 mm cortical depth) shows that all temporal properties are significantly increased (P<0.01, Wilcoxon signed–rank test). This indicates that the surface gray matter GE contrast probes a different part of the vascular system upon activation than the SE contrast. Surface gray matter in V1 contains mainly postcapillary veins (diameters ∼70 μm) and much less capillaries (diameters ∼5 μm) than deep gray matter regions <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0054560#pone.0054560-Duvernoy1" target="_blank">[20]</a>. Looking at the deep gray matter GE HRFs (>1 mm cortical depth) and the SE HRF we found that the TTP, FWHM and PSC were all significantly increased for the GE HRF. The onset times, however, did not differ significantly. These findings suggest that the earlier part of the deep gray matter GE HRF is in close correspondence to the SE HRF and hence is weighted towards the microvasculature. ^*** denotes significant difference between the two compartments (Wilcoxon signed–rank test for P<0.01, ** for P<0.05, * for P<0.1).</p

Spatial activation maps and time courses of the GE and SE HRF upon short visual stimulation.

<p>A) Percent signal change (PSC) map of the visual cortex V1 for the GE (top) and SE (bottom) HRF data with isotropic voxel sizes of 1 mm and 2 mm, respectively. As expected the SE contrast shows reduced sensitivity. B) Closer examination of the cortical surface and pial vasculature on the 0.5 mm T2*-weighted anatomical scan. The cortical surface (white) was manually delineated in 3D and from this surface the cortical depth profiles were computed: black; 0–1 mm, red; 1–2 mm, and green; 2–3 mm. The high-resolution T2*-weighted scan was also used to identify the larger pial draining veins, which were excluded from the GE BOLD analysis. C) GE HRFs across cortical depth (0–1, 1–2, and 2–3 mm) and the SE HRF for a representative subject (subject 4 as indicated in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0054560#pone-0054560-t001" target="_blank">Table 1</a>). As the GE and SE BOLD do not measure from the exact same vasculature there should be no exact spatial match in their activation patterns from the functional localizer. We therefore focused on the temporal evolution of the estimated HRFs, with the following parameters of interest: onset time, time-to-peak (TTP), full-width-at-half-maximum (FWHM), and maximum percent signal change (PSC). Onset times of the SE and GE HRF in deep gray matter (>1 mm cortical depth) are very comparable while the FWHM and TTP are increased for the GE HRF for all cortical depths indicating that the earlier part of deep gray matter GE HRF is weighted toward microvascular dynamics. Shaded areas denote the standard error of the mean (SEM). The black bar indicates the stimulus onset and duration (250 ms).</p