Mgp. Rosa et al., RETINOTOPIC ORGANIZATION OF THE PRIMARY VISUAL-CORTEX OF FLYING FOXES(PTEROPUS-POLIOCEPHALUS AND PTEROPUS-SCAPULATUS), Journal of comparative neurology, 335(1), 1993, pp. 55-72
The representation of the visual field in the occipital cortex was stu
died by multiunit recordings in seven flying foxes (Pteropus spp.), an
esthetized with thiopentone/N2O and immobilized with pancuronium bromi
de. On the basis of its visuotopic organization and architecture, the
primary visual area (V1) was distinguished from neighboring areas. Are
a V1 occupies the dorsal surface of the occipital pole, as well as mos
t of the tentorial surface of the cortex, the posterior third of the m
esial surface of the brain, and the upper bank of the posterior portio
n of the splenial sulcus. In each hemisphere, it contains a precise, v
isuotopically organized representation of the entire extent of the con
tralateral visual hemifield. The representation of the vertical meridi
an, together with 8-15-degrees of ipsilateral hemifield, forms the ant
erior border of V1 with other visually responsive areas. The represent
ation of the horizontal meridian runs anterolateral to posteromedial,
dividing V1 so that the lower visual quadrant is represented medially,
and the upper quadrant laterally. The total surface area of V1 is abo
ut 140 mm2 for P. poliocephalus, and 110 mm2 for P. scapulatus. The re
presentation of the central visual field is greatly magnified relative
to that of the periphery. The cortical magnification factor decreases
with increasing eccentricity, following a negative power function. Co
nversely, receptive field sizes increase markedly with increasing ecce
ntricity, and therefore the point-image size is approximately constant
throughout V1. The emphasis in the representation of the area central
is in V1 is much larger than that expected on the basis of ganglion ce
ll counts in flat-mounted retinas. Thus, a larger degree of convergenc
e occurs at the peripheral representations in the retino-geniculo-cort
ical pathway, in comparison with the central representations. The mark
ed emphasis in the representation of central vision, the wide extent o
f the binocular field of vision, and the relatively large surface area
of V1 reflect the importance of vision in megachiropterans. (C) 1993
Wiley-Liss, Inc.