Eduardo Oswaldo-Cruz

Retinal ganglion cell distribution in the Cebus monkey: a comparison with the cortical magnification factors

The distribution of ganglion cells was determined in whole-mounted Cebus monkey retinae. Ganglion cell density along the horizontal meridian was asymmetric, being 1.2-4.3 higher in the nasal retinal region when compared to temporal retina at the same eccentricities. The total number of ganglion cells varied from 1.34 to 1.4 million. Ganglion cell density peaked at 49,000/mm2 about 0.5 mm nasal to the fovea. Comparison between ganglion cell density and areal cortical magnification factors for V1 and V2 reveals that the relative representation of the fovea increases in the visual cortex. This effect seems to be a general feature of the visual system of primates.

Visual receptive fields of units in the pulvinar of cebus monkey.

Visually driven units, isolated in the ventrolateral group -- Pv1g (109) and in subnucleus Pmu (33) of the pulvinar of the cebus monkey, were studied in acute and chronic preparations under nitrous oxide N2O/O2 anesthesia during periods of EEG arousal. Taking into consideration the response properties to static or moving stimuli as well as the organization of the receptive fields, units isolated in the pulvinar were subdivided into 8 groups. Units displaying dynamic properties predominate over static ones. Static units were classified in 3 groups; of these, one showed uniform receptive fields; the remaining two groups, with non-uniform RFs, were further subdivided in terms of orientation selectivity. By testing for directional sensitivity, organization of the RFs and orientation selectivity, the dynamic units were divided in 5 groups. Among these there was a predominance of directional units, displaying uniform RFs and showing orientation selectivity. Although the receptive fields would extend into the ipsilateral hemifield (up to 10 degrees), their centers were always located in the contralateral visual hemifield. Binocularly driven units predominate in both static and dynamic categories.

Visuotopic organization of the Cebus pulvinar: A double representation of the contralateral hemifield

The projection of the visual field in the pulvinar nucleus was studied in 17 Cebus monkeys using electrophysiological techniques. Visual space is represented in two regions of the pulvinar; (1) the ventrolateral group, Pvlg, comprising nuclei P delta, P delta, P gamma, P eta and P mu 1; and (2) P mu. In the first group, which corresponds to the pulvinar inferior and ventral part of the pulvinar lateralis, we observed a greater respresentation of the central part of the visual field. Approximately 58% of the volume of the ventrolateral group is concerned with the visual space within 10 degrees of the fovea. This portion of the visual field is represented at its lateral aspects, mainly close to the level of the caudal pole of the lateral geniculate nucleus (LGN). Projection of the vertical meridian runs along its lateral border while that of the horizontal one is found running from the dorsal third of the LGNs hilus to the medial border of the ventro-lateral group. The lower quadrant is represented at its dorsal portion while the upper quadrant is represented at the ventral one. In Pmu the representation is rotated 90 degrees clockwise around the rostrocaudal axis: the vertical meridian is found at the ventromedial border of this nucleus. Thus, the lower quadrant is represented at the later portion of Pmu and the upper at its medial portion. Both projections are restricted to the contralateral hemifield.

Distribution and size of ganglion cells in the retinae of large Amazon rodents

The topographical distribution of density and soma size of the retinal ganglion cells were studied in three species of hystricomorph rodents. Flat-mounted retinae were stained by the Nissl method and the ganglion cells counted on a matrix covering the whole retinae. Soma size was determined for samples at different retinal regions. The agouti, a diurnal rodent, shows a well-developed visual streak, reaching a peak density of 6250 ganglion cells/mm2. The total number of ganglion cells ranged from 477,427-548,205 in eight retinae. The ganglion-cell-size histogram of the visual streak region exhibits a marked shift towards smaller values when compared to retinal periphery. Upper and lower regions differ in both cell density and cell size. The crepuscular capybara shows a less-developed visual streak with a peak ganglion cell density of 2250/mm2. The shift towards small-sized cells in the visual streak is less marked. Total ganglion cell population is 368,840. In the nocturnal paca, the upper half of the fundus oculi includes a tapetum lucidum. The retina of this species shows the least-developed visual streak of this group, with the lowest peak ganglion cell density reaching 925/mm2. The total ganglion cell number (230,804) is also smaller than in the two other species. Soma-size spectra of this species are characterized by the presence, in the lower hemi-retina, of very large perikarya comparable in size to the cats alpha ganglion cells.

A schematic eye for the opossum

Abstract Schematic values were determined for the elements of the dioptric system of the eye of a marsupial. D. marsupialis aurita . Based on measurements on excised eyes a schematic eye was developed for this species. The following aspects of the opossums eye are discussed: real, entrance and exit pupils, retinal illumination and uniocular optical field. The extent of the retinal visual field was determined and the resulting cyclopic field established. The position of the blind and optic axes in space were indirectly determined by correlating the posture of the head under experimental and normal conditions, and the horizontal meridian was found to lie 4° below the blind axis.

Contrast sensitivity function and visual acuity of the opossum

The Modulation Transfer Function (MTF) of the visual system of the opossum, D. marsupialis aurita, was determined using the amplitude of Visually Evoked Cortical Potentials (VECP) as response indicator. Stimuli consisted of a 180 degrees phase reversal of sinusoidally modulated gratings with an average luminance of 2.4 cd/m2. Contrast sensitivity was determined for various spatial frequencies and the MTF was calculated by the least square fit of an exponential function. The average acuity value obtained was 1.25 c/deg. The Fourier transform of the MTF was considered an approximation of the Line Spread Function of the visual system. The lowest value observed was 14 min of arc. The visual acuity observed in the mesopic range was not altered when stimulus intensity was raised to photopic levels.

Single unit response types in the pulvinar of the Cebus monkey to multisensory stimulation.

Response to sensory stimulation was studied in 162 neurons in the pulvinar of Cebus monkeys in 4 acute and 5 chronic preparations. Two basic response patterns were observed: type I responses, similar to those obtained in primary relay centers, were only observed after visual stimulation. Type II responses were obtained after stimulation of more than one sensory modality. Characteristically these responses presented fatigue and habituation. Temporal relationship between stimulus and response was not as clear as in type I responses, afterdischarge frequently occurred. Taking these response types into consideration two groups of units were identified in the pulvinar. Units of group A (91 neurons) showed type I response to visual stimulation. For these units receptive fields similar to those found in other regions of visual projection could be defined. As a rule units of group A displayed type II responses to other sensory modalities. Units of group B (71) did not display type I responses; they always responded to visual, somatic, auditory and olfactory stimuli with type II responses. They could be activated by a single sensory modality (B, unimodal) or by more than one sensory modality (B, multimodal).

A Comparative Survey of Magnification Factor in V1 and Retinal Ganglion Cell Topography of Lateral-Eyed Mammals

Quantitative analysis of the geometrical transformations that the visual field undergoes when it is projected on central nuclei has been the object of many studies. From Daniel and Whitteridge (1961) until the present day the extent to which V1 cortical topography is determined by its retinogeniculate afferents (Orban, 1984; Pointer, 1986; Tolhurst, 1989; Whitteridge, 1973) has been a key question.