fMRI measurements of visual areas and retinotopic maps in monkey

We have measured visual field maps in several distinct visual areas of anaesthetized macaque monkeys using functional magnetic resonance imaging (fMRI). The maps were measured using phase-encoded retinotopic methods that have also been applied to human subjects. Expanding ring and rotating wedge phase-encoded measurements were acquired (8-shot EPI, TE= 20ms, and TR=750, 16 plane, voxel 1x1x2 mm). In addition, higher resolution anatomical scans were obtained (3D MDEFT; 0.5x0.5x0.5mm). The anatomical scans were used to register data from different functional scans. Also, these anatomical scans were segmented into white matter and gray matter to produce flat maps of the activation data in order to visualize retinotopic maps. Strong signals were observed in area V1 and several other areas known to be connected directly to V1. The retinotopic maps produced clear definitions of the boundary between areas V1 and V2 in all animals. These maps parallel closely the results in humans using similar methods. In addition, retinotopic organization in a region on the posterior bank of the STS, probably corresponding to area MT, could be observed. The cortical magnification function in V1 was in close agreement with the function obtained in similar human fMRI measurements. In different animals, the foveal representation of V1 and V2 fell at significantly different positions with respect to the main anatomical landmarks