Mapping visual field with positron emission tomography by mathematical modeling of the retinotopic organization in the calcarine cortex

We developed an objective and quantitative method of mapping the human visual field with positron emission tomography (PET) and magnetic resonance imaging (MRI). The regional cerebral blood flow (rCBF) images were acquired with H ₂ ¹⁵O-PET under visual fixation as well as under visual stimulation with flickering diodes arranged along the ring at 0°, 3°, 7°, 14°, 21°, or 29° from the fixation point. After coregistration of PET and MR images, we extracted the surface of the calcarine cortex from the MR images and unfolded it to a two-dimensional (2-D) elliptic plane, on which the activated PET images were superimposed. Then we transformed the unfolded calcarine cortex into the visual field coordinates using the complex logarithmic function proposed by Schwartz. A large individual variation was observed in the retinotopical organization as well as in the morphology of the calcarine cortex. The formula was valid only within 15° from the center of the visual field. The constant parameter in the formula was estimated to be 1.5. The cortical linear magnification factor was 12.1, 2.8, and 1.6 at 0, 5, and 10°, respectively. The areas of the central 10° and 40° in the visual field correspond to 50% and 81% of the calcarine surface, respectively.