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Biomedical subjects

S M Sherman

Publications and source records attributed to S M Sherman.

At least 109 records · Page 6Linked to original sources
PubMed1978

Effects of early monocular lid suture upon neurons in the cat's medial interlaminar nucleus.

Single unit extracellular recordings, cell size measurements, and cell packing density measurements were made in the medial interlaminar nucleus (MIN) of nine adult cats that had been monocularly deprived by lid suture prior to natural eye opening. The electrophysiological properties of neurons in the nondeprived regions of MIN (areas receiving input from the non-deprived eye) remained unaffected by monocular lid suture. The latencies to optic chiasm stimulation and receptive field properties, including receptive field center size, were essentially the same as those found for MIN neurons of normal adult cats. In contrast, cells in the deprived regions were severely affected by monocular deprivation. We encountered in the deprived regions of MIN only about one half as many active neurons per mm of electrode penetration as we did in the nondeprived regions. Of the physiologically active cells remaining, about one half had abnormal receptive field and/or response properties. This resulted in a sampling density of 5.1 normal Y-cells per mm of penetration in nondeprived regions of MIN compared to 1.0 normal Y-cell per mm in deprived regions of MIN. Histological effects of deprivation were also seen. Deprived regions of MIN were distinguished from nondeprived regions in four cats by autoradiography following intravitreal injection of tritiated proline into the deprived or non-deprived eye (2 cats each). The mean cell size of deprived regions of MIN was 34% smaller than that of nondeprived regions. We did not find a difference in cell packing density between these two regions. It appears that the effects of monocular lid suture upon MIN are in most respects similar to the effects of monocular lid suture previously reported for the A laminae. Since MIN is composed solely of Y-cells, these data support the idea that the Y-pathways are more severely affected by visual deprivation than are the X-pathways. Further, since MIN projects largely outside the striate cortex, these data give the first demonstration of a primary effect of early lid suture upon extrastriate visual pathways.

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PubMed1978

Receptive-field properties of neurons in binocular and monocular segments of striate cortex in cats raised with binocular lid suture.

1. We studied the receptive fields of 171 striate cortical neurons from 17 cats raised with binocular lid suture. Of these, 102 fields were within 10 degrees of the area centralis and the remaining 69 were at least 38 degrees from the vertical meridian. 2. Based on their different response properties, cells were divided into three broad groups: the mappable cells (49%) had clearly defined receptive fields, the unmappable cells (31%) were activated by visual stimuli but had diffuse fields which could not be hand plotted, and the visually inexcitable cells (20%) could not be activated by visual stimuli. Very few (less than or equal to 12% of the total sample) normal simple or complex cells could be found. 3. Orientation selectivity was assessed in these cells. Only 12% displayed orientation selectivity within normal bounds, and these were all mappable cells. None of the unmappable cells had discernible orientation selectivity. 4. Ocular dominance was assessed for 62 of the centrally located receptive fields. Among mappable cells, there was an abnormally low proportion of binocular fields, while no such abnormality was seen for unmappable cells. 5. For 47 of the neurons, average response histograms were compiled for moving stimuli of various parameters in an effort to evoke the maximum discharge or peak response. This peak response was normal for mappable cells but reduced for unmappable cells. 6. We devised a technique for studying potential inhibitory receptive-field zones in these neurons, validated the method in normal striate cortex, and used it to test 20 mappable cells in the lid-sutured cats. None showed the pattern of strong inhibitory side bands seen in normal simple cells, although six showed weak or abnormal inhibitory zones. Interestingly, six of the seven visually inexcitable cells tested by this method had purely inhibitory receptive fields. 7. The effects of binocular suture were essentially identical for the binocular and monocular segments since the cell types and their response properties did not differ between these two areas of cortex. Furthermore, the cortical monocular segments of these cats seemed qualitatively different from the deprived cortical monocular segment after monocular suture. This extends an analogous difference for these cats reported for the monocular segments of the lateral geniculate nucleus. We thus conclude that monocularly and binocularly sutured cats develop by qualitatively different mechanisms. For the former, competition between central synapses related to each eye is a prominent feature of geniculocortical development, whereas, for the latter, such specific forms of geniculocortical development may not obtain.

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PubMed1977

Conditions for dominance of one eye during competitive development of central connections in visually deprived cats.

Three groups of visually deprived cats were studied for evidence that one eye gained a competitive advantage over the other during development of central connections. We attempted to detect such an advantage by measuring lateral geniculate cell sizes, by recording the proportion of lateral geniculate Y-cells and the ocular dominance of cortical neurons, and/or by testing visual orienting behavior. Three cats were raised with one eye covered by the lids, and the other, by the nictitating membrane. Lids reduce illumination by 3--4 log units, nictitating membranes, by about one log unit, and both eliminate spatial patterns. Neither eye in these cats appeared to develop with a competitive advantage over the other. Four cats raised with monocular nictitating membrane closure developed with a clear advantage to the open eye, and in all ways data from these cats were indistinguishable from those previously reported for monocularly lid sutured cats. Finally, 4 cats reared with binocular lid closure, but with additional, temporally modulated stimulation through the right lids, showed no evidence of a competitive advantate to either eye. We conclude that interocular differences in light intensity or temporal patterns do not confer a significant competitive advantage to either eye during development of central connections.

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PubMed1977

Loss of Y-cells in the lateral geniculate nucleus of monocularly deprived tree shrews.

In tree shrews (Tupaia glis) reared with one eye closed, Y-cells were almost entirely absent in the binocular segment of the lateral geniculate laminae receiving input from the deprived eye. Y-cells were found in the monocular segment of these laminae, and in the binocular segment of the laminae with input from the normal eye. X-cells were present in both the deprived and normal laminae and appeared unaffected by the deprivation. A number of abnormal cells were also found, and these were located primarily in the binocular segment where Y-cells were absent.

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PubMed1977

Visual discriminations of cats with cortical and tectal lesions.

Fourteen cats were trained on three visual discrimination tasks: light vs. dark, horizontal vs. vertical stripes, and upright vs. inverted triangles. Four of the cats then underwent large, bilateral occipito-temporal cortex ablations; postoperatively, they demonstrated little or no visually guided orienting behavior and solve only the brightness task and not the preoperatively learned pattern discriminations. Six other cats underwent the same cortical ablations plus a transection of the commissure of the superior colliculus; postoperatively, they demonstrated good visually guided orienting behavior (i.e., the Sprague effect) but still could solve only the brightness task. The final four cats were controls and underwent no surgery; they demonstrated good retention of the pattern task despite an extensive idle period corresponding to the postoperative period before retesting the above ten cats. These data indicate that, while a transection of the collicular commissure after visual decortication dramatically improves visual orienting, it does not obviously improve visual discrimination abilities.

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PubMed1977

The effect of cortical lesions upon visual discriminations in binocularly deprived cats.

Four cats were raised with binocular eyelid suture and, after their eyes were opened, were trained on a series of discrimination tasks. They performed at normal rates on the brightness task but indicated some difficulty with the pattern tasks. They then received large, bilateral occipito-temporal cortex ablations. Postoperatively, this in no observable way affected their visually guided orienting behavior, but it did destroy their capacity to perform the preoperatively learned pattern tasks. Postoperative performance on the brightness task remained good. These data indicate that, in these deprived cats, there is little or no cortical development for visual orienting, but cortex is necessary for visual discrimination learning.

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PubMed1977

Visual discriminations during eyelid closure in the cat.

We were able to train cats raised with sutured eyelids to perform simple brightness discriminations before their lids were parted. If, and only if, a small hole was present in a lid, could some of the cats also perform a grating orientation discrimination. By establishing their thresholds for the brightness discrimination before and after dark adaptation and before and after the lids were opened, we reached three main conclusions. (1) During dark adaptation (with pupils maximally dilated and retinae most sensitive, regardless of lid suture), the cats were 3-4 log units more sensitive with the lids open than with the lids closed. This indicates a 3-4 log unit attenuation for the lids which is in agreement with our photometric measurements. (2) During light adaptation, the sensitivity difference between the conditions of opened and closed lids was only 1-2 log units. We concluded that factors (such as pupil dilatation and retinal sensitivity) partially compensated for the lid attenuation, since the open eye could have a smaller pupil and less sensitive retina during light adaptation. (3) Given these potential compensatory features of the pupil and assuming consensual pupil sizes, the deprived eye of a monocularly sutured cat may suffer more photic deprivation (since the pupil behind the closed lid would be as constricted as the pupil in the open eye) than would either eye of a binocularly sutured cat (where both pupils can be relatively large).

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PubMed1977

The effect of superior colliculus lesions upon the visual fields of cats with cortical ablations.

The visual fields of 18 cats were measured before and after various lesions. Preoperatively, all cats had identical fields. With both eyes open, they saw from 90 degrees left to 90 degrees right; with one eye, from 90 degrees ipsilateral to 45 degrees contralateral. Thus the field for nasal retina extends from 90 degrees ipsilateral through to the midline; for temporal retina, from the midline through to 45 degrees contralateral. In summary, postoperative testing led to two major conclusions. (1) Large occipito-temporal cortical lesions produce a stable field blindness, but the blindness is alleviated by a transection of the commissure of the superior colliculus (or a unilateral collicular ablation). This transection yields the same result whether it occurs in an operation before, during, or after the cortical lesion. These data confirm and extend the Sprague effect. (2) Cats made dependent upon retinotectal pathways due to cortical ablations responded much better to stimulation of nasal retina than to stimulation of temporal retina. This presumably is related to the preponderance of nasal retina as a source of the retinotectal pathway. Since even smaller cortical lesions limited to areas 17, 18, and 19 produce this nasal/temporal retinal difference, it is concluded that integrity of the geniculocortical pathways is necessary for good temporal retinal vision as determined by these methods.

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PubMed1977

The effect of cortical and tectal lesions on the visual fields of binocularly deprived cats.

The visual fields of seven cats raised with binocular lid suture were measured before and after various neural lesions. Each of the cats preoperatively responded with each eye to stimuli from 90 degrees ipsilateral through to the midline. A transection of the optic chiasm rendered one cat blind on the visual field tests. Large bilateral occipito-temporal cortical ablations (4 cats) did not measurably affect orienting responses or the extent of visual field. Unilateral occipito-temporal cortical ablations (2 cats) also had no affect on the visual fields, but subsequent ablations of the contralateral superior colliculus produced permanent blindness in the hemifield contralateral to the ablated tectum. These two cats also were apparently blind with the eye contralateral to the ablated tectum; but with the other eye, the cats retained their preoperative orienting responses. These data are consistent with the hypothesis that, with early binocular deprivation, cats develop dependence upon retinotectal and not thalamocortical pathways for visually guided orienting behavior.

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PubMed1976

Receptive-field characteristics of neurons in cat striate cortex: Changes with visual field eccentricity.

1. Receptive-field properties of 214 neurons from cat striate cortex were studied with particular emphasis on: a) classification, b) field size, c) orientation selectivity, d) direction selectivity, e) speed selectivity, and f) ocular dominance. We studied receptive fields located throughtout the visual field, including the monocular segment, to determine how receptivefield properties changed with eccentricity in the visual field.2. We classified 98 cells as "simple," 80 as "complex," 21 as "hypercomplex," and 15 in other categories. The proportion of complex cells relative to simple cells increased monotonically with receptive-field eccenticity.3. Direction selectivity and preferred orientation did not measurably change with eccentricity. Through most of the binocular segment, this was also true for ocular dominance; however, at the edge of the binocular segment, there were more fields dominated by the contralateral eye.4. Cells had larger receptive fields, less orientation selectivity, and higher preferred speeds with increasing eccentricity. However, these changes were considerably more pronounced for complex than for simple cells.5. These data suggest that simple and complex cells analyze different aspects of a visual stimulus, and we provide a hypothesis which suggests that simple cells analyze input typically from one (or a few) geniculate neurons, while complex cells receive input from a larger region of geniculate neurons. On average, this region is invariant with eccentricity and, due to a changing magnification factor, complex fields increase in size with eccentricity much more than do simple cells. For complex cells, computations of this geniculate region transformed to cortical space provide a cortical extent equal to the spread of pyramidal cell basal dendrites.

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