Brain Imaging:: Lab Page

INTRODUCTION: It is well known that the relationship between visual field eccentricity and cortical distance from the fovea can be described approximately by a log function. The function describing the increase in width of visual areas with eccentricity is not known, however. The complete mapping between visual space and cortex is a combination of these two functions. Before the human cortex was measured by fMRI, Schwartz (1980 Biol.Cybernetics) proposed a complex-logarithmic mapping function as a model for human visual cortex. We examined the fit of this function to V1/2 mapping data.
METHODS: We collected retinotopic mapping data using advanced fMRI procedures. We are using the atlas fitting functions from the VISTA-toolbox (Dougherty et al., 2003 J.Vis. 3:586-598) to semi-automatically define the borders between visual areas together with their iso-eccentricity and iso-polar lines on the reconstructed 3D cortical manifold.
RESULTS: Using retinotopic procedures with a log-scaled eccentricity stimulus and a fine fixation cross to optimize the stability of fixation, we could reliably map the representation of the eccentricity down to 0.3° radius, which is substantially closer to the foveal center than previous studies. We find an increase in V1 width up to 8° eccentricity (by a factor of 3.1, from 17.4 ± 3.4 mm at 0.37° to 54.5 ± 2.8 mm at 8°, with no significant increase thereafter). 
CONCLUSIONS: The combined measurements of eccentricity magnification functions and width magnification functions define the amount and isotropy of cortical area devoted to visual space at any eccentricity. This analysis provides a detailed framework to compare with theoretical treatments of the mapping of visual space to cortex. In detail, these results are inconsistent with the mapping function log(z+a) with an estimated a<0.8°, proposed by Schwartz and constrain more elaborated models such as the conformal dipole mapping (Balasubramanian et al. 2002 Neural Netw. 15:1157-1163).