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In-Depth Information
In human visual pathway, visual information passes from retina to lateral genicu-
late nucleus and then to human primary visual cortex. Therefore, human primary
visual cortex (V1) contains a map of visual space. To a good approximation, each
two-dimensional (2D) location in the visual field is represented at a single physical
location within V1. Area V1 is the human visual cortical area with the most well-
defined anatomical boundaries, agreed on by virtually all previous studies, both his-
torical and more recent [3, 4].
Previous retinotopic studies of humans by fMRI have identified the V1 [5], placing
it between the occipital pole and the lateral end of the parieto-occipital sulcus (POS)
[6]. Andrews et al. (1997) measured the size of the lateral geniculate nucleus (LGN)
and the optic tract as well as the surface area of striate cortex. They observed that the
surface area correlates closely with the cross-sectional area of the optic tract as well
as with the area and volume of the lateral geniculate nucleus (LGN). Given that pho-
toreceptor density also varies by up to a factor of three across individuals [7], it is
possible that this density is a key variable that leads to the variation in size of the
central representations found in the LGN and V1. To what extent do the sizes of other
visual areas follow the size of V1? This question has not been answered precisely.
Amunts et al. (2000) measured the volume of Brodmann's areas 17 and 18 in ten
brains (post-mortem). However, they did not report on a correlation between the sizes
of these areas. Also, the correspondence between Brodmann's area 18 and visual area
V2 is not as clear as that between striate cortex and V1 [8].
In this study, we investigated the quantitative relationship between the V1 surface area
and human peripheral visual field and estimated the cortical surface area of the V1, V2,
V3. We used a newly developed visual presentation system to examine the V1, V1, V2,
V3 surface area and
areal
cortical magnification for 0° to 60° of eccentricity. Therefore
human V1 appeared to be an ideal location to test for addition functional features within a
well defined, well accepted cortical area, by using functional MRI (fMRI).
2 Method and Materials
2.1 Subjects and Stimuli
Eight healthy subjects without previous neurological or psychiatric disorders (age 19-
31 years, mean 25 years; two women, six men) participated in the study. The subjects
had normal or corrected-to-normal vision and were right-handed. Visual stimuli were
created on a display using a resolution of 800 × 600 pixels. The display stimulus was
brought to the subject's eyes within the scanner by a wide-view optical-fiber presenta-
tion system. Monocular (right eye) presentations were accomplished; the optical-fiber
screen (surface-curved with a curvature radius of 30 mm) was placed in the center of
the 30 mm from a subject's eye. The visual field of stimulus was a 120° horizontal ×
120° vertical. Because the screen so was close to the eye, subjects wore a contact lens
(Menicon soft MA; Menicon, Japan. with +20, +22, +25 magnification) to retain their
length of focus. We obtained written informed consent from all subjects before the
experiment. The study was approved by the Institutional Research Review Board of
Kagawa University, Japan.
