Abstract:

PURPOSE: The primary visual cortex (V1) in primates performs a fine spatial analysis of the visual world, with the highest visual acuity in the cortical area corresponding to the fovea of the retina. Electrophysiological single-unit recordings have revealed an inverse proportionality between the receptive ?eld size, spatial frequency (SF) selectivity of V1 neurons and their eccentricities. As eccentricity is measured as the distance (degrees) from the fovea whereas cortical magnification factor (CMF) is calculated as cortical surface distance/visual angle (mm/degree), the correlation between the neural SF selectivity and CMF in macaque V1 has not yet been quantitatively de?ned.
METHODS: In this study by using intrinsic optical imaging, the SF selectivity of each pixel of the imaged area was measured in response to sinewave gratings with various combinations of orientation and SF. We quantitatively measured the relationship between CMF and SF selectivity, eccentricity as well as orientation domain size in macaque V1.
RESULTS: The ?ne cortical representation of the visual space was mapped and analyzed by using fast Fourier intrinsic optical imaging before the acquisition of the eccentricity and CMF maps with high spatial resolution. A physiometric function for SF selectivity and CMF was thus determined in the imaged areas of macaque V1. We also quantitatively measured the inverse proportionality between eccentricity and CMF and between the size of orientation domains and CMF.
CONCLUSIONS: These quantitative measurements of relationship among SF selectivity, eccentricity, orientation domains and CMF will be highly informative for future electrophysiological recording, other brain imaging studies and computational modeling in primates.

Key words: Cortical magnification factor, Spatial vision, Non-human primate