Retinotopic mapping of the human visual cortex at a magnetic field strength of 7T

Responses for the phase-encoding paradigm of a single subject. Left-hand panels depict false-colour coded phase-map-overlays onto one EPI-plane obtained at a magnetic field strength of 7T (top) and 3T (bottom) for a coherence threshold of 0.35 and 0.20 (3T only), corresponding to a significance level of p⩽0.0001 and p⩽0.02, respectively. It should be noted that the slices could not be placed at identical positions for the 3 and 7T measurements, but that the depicted slices were chosen to cover corresponding regions of cortex. The 7T images were cropped less severely than the 3T images to illustrate the dominance of posterior signals, which is plausible for visually driven signals. The colour indicates response phase and hence the position of the stimulus in the visual field as indicated by the colour keys. The right-hand panels depict the mean times series (left) and average cycle (±SEM) for the ROIs indicated in the EPI-plane. (A) Eccentricity mapping data. (B) Polar angle mapping data. For colour keys and stimulus-schematics for eccentricity and polar angle mapping see insets in (A) and (B), respectively.

Retinotopic mapping data overlaid over flat maps of the right occipital lobe of a single subject for a coherence threshold of 0.30, corresponding to a significance level of p⩽0.0008; colour key as for Fig. 1. Data obtained with 2.5mm isotropic voxels in one single scan for eccentricity mapping and another single scan for polar angle mapping at a field strength of 7 and 3T are depicted on the left and right, respectively. Four early visual areas are labelled (V1–V4), the lines serve as guides to the locations of the visual area boundaries. In the left panel there is also an indication of the ROI used for the analysis shown in Fig. 3 (the depicted ROI is a result of the reprojection of the ROI from the T1-weighted anatomicals to the flattened representation).

Magnetic field strength comparison of the activity in V1 for three voxel sizes as determined for the same subject as for Fig. 2 for the section of the flat map highlighted in Fig. 2. A coherence threshold of 0.30, corresponding to a significance level of p⩽0.0008, was applied, the colour key is the same as for Fig. 1. (A) Eccentricity mapping results, (B) polar angle mapping results. In both panels, the voxel size used for the data acquisition in the EPI planes decreases from top to bottom (applied voxel sizes: 2.5³, 1.4³, and 1.1³mm³). In the two columns on the left the 7T maps are depicted, the 3T maps are depicted in the two columns on the right. Both unfiltered and spatially filtered (indicated by an “f”) data are depicted for each field strength in the respective left and right column.

Quantitative comparison of signal amplitude [left; mean+SEM of the amplitude of the sinusoid (half peak-to-peak-amplitude) with the fundamental frequency of the visual stimulus] and coherence [right; re-transformed mean+SEM of z-transformed values] obtained at 3 and 7T magnetic field strength, (A) for three different voxel sizes for an ROI in ventral V1 (see Fig. 2, left), (B) for a voxel size of 2.5³mm³ for ROIs comprising the different early visual areas. For the significance levels of the effects see text.

Right hemisphere polar angle maps obtained in experiment 2 (average of three 252s scans). The maps are thresholded at a coherence-value of 0.30, corresponding to a significance level of p⩽0.005. Only response phases corresponding to stimulation in the contralateral visual field are depicted. A great expanse of occipito-parietal cortex is activated by the retinotopic mapping stimulus and a number of hemifield and quadrant representations are evident. For subject A, the response phase is plotted as a function of position along trajectories intersecting the early visual areas in the occipital cortex (bottom) and recently identified areas in the parietal cortex (top). The phase reversals indicative of visual area boundaries are highlighted.