Laminar Analysis of the BOLD Hemodynamic Impulse Response
We used high-resolution (&[le]1-mm voxels) to measure the BOLD hemodynamic impulse response function (HIRF) in early visual cortex. The measured data were then aligned with a segmented reference volume to permit examination of the data as a function of depth in the gray matter. The shape and timing of the HIRF change with depth. In particular, we find that the ""negative dip"" is generally evident only in tissue near the pial surface.