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).