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Biomedical subjects

S M Sherman

Publications and source records attributed to S M Sherman.

At least 91 records · Page 5Linked to original sources
PubMed1982

Linear and nonlinear W-cells in C-laminae of the cat's lateral geniculate nucleus.

1. We used standard, single-cell recording techniques to study the response properties of 34 W-cells in the C-laminae of the cat's lateral geniculate nucleus. By W-cell, we mean a poorly responsive geniculate neuron that receives slowly conducting retinal afferents; these are quite distinct from geniculate X- and Y-cells. Our measurements included response latency to optic chiasm stimulation, plots of the receptive-field center, time course of response, and responses to counterphased, sine-wave gratings. This last measurement also involved the determination of contrast sensitivity, which is defined as the inverse of the contrast needed to evoke a threshold response at a particular spatial and temporal frequency of the grating. Many of these responses were compared to those of geniculate X- and Y-cells recorded in the A-laminae. 2. Each of the W-cells responded with a latency of at least 2.0 ms to optic chiasm stimulation, and most (76%) exhibited a latency of at least 2.5 ms. However, only 26 of these W-cells responded to visual stimuli, and these responses were weak or "sluggish," as has been reported previously. Receptive fields of these W-cells tended to be large, compared to those of X- and Y-cells, and included 11 on-center, 13 off-center, and 2 on-off center fields. 3. W-cells exhibited either linear (12 cells) or nonlinear (14 cells) spatial and temporal summation, as determined from their responses to counterphased, sine-wave gratings. Linearity of spatial summation was determined by measuring contrast sensitivity as a function of the grating's spatial phase. The linear W-cells' responses were sinusoidally phase dependent, and the nonlinear W-cells' responses were independent of spatial phase. Linearity of temporal summation was determined by the presence or absence of harmonic distortion in the response relative to the grating's counterphase rate. Linear W-cells responded chiefly at the grating's fundamental temporal frequency, whereas much of the nonlinear W-cells' responses occurred at the second harmonic of the grating's temporal frequency. Thus, nonlinear W-cells exhibited many of the characteristics previously described for Y-cells. 4. Spatial and temporal contrast-sensitivity functions were determined for seven linear and eight nonlinear W-cells. Overall sensitivity values of the linear and nonlinear W-cells were comparable, but these groups differed in terms of the nature of the response component (linear or nonlinear) that was more sensitive. 5. The linear W-cells in our sample included both tonic (comparable to the "sluggish-transient" type of retinal ganglion cells) types, while all nonlinear W-cells were phasic. Otherwise, no difference between linear and nonlinear W-cells was seen for latency to optic chiasm stimulation, receptive-field size, overall contrast sensitivity, responsiveness to visual stimuli, overall spatial resolution, or temporal resolution. 6...

Animals↗
PubMed1982

Effects of monocular deprivation on the structure-function relationship of individual neurons in the cat's lateral geniculate nucleus.

The retino-geniculo-cortical pathways of the cat composed of at least three parallel channels. The neurons in these channels (W-, X-, and Y-cells) have different physiological properties. In earlier studies, we used a direct structure-function for analysis for individual geniculate neurons in normal cats. This was accomplished by electrophysiological characterization of the neuron followed by intracellular iontophoresis of horseradish peroxidase into the same neuron. By this technique, we demonstrated that W-, X-, and Y-cells have distinctive morphological features in the lateral geniculate nucleus of the act. We have extended this analysis in cats reared with monocular eyelid suture to 24 geniculate neurons innervated by the sutured eye in lamina A or A1. Ten of the 24 neurons (42%) had abnormal structure-function relationships. All but 1 of the normal cells were X-cells. Abnormalities included: (1) Y-cells with normal physiology but abnormally small somata; (2) Y-cells with abnormal physiology and morphology, including poor responsiveness and unusually thin, tortuous, and beaded dendrites; (3) visually unresponsive cells with morphology similar to that of the physiologically abnormal Y-cells; and (4) cells with the physiology of normal X-cells but the morphology of normal Y-cells. Furthermore, soma size measurements indicate that the abnormally small somata found in deprived geniculate laminae result from a selective effect on Y-cells.

Animals↗
PubMed1982

Development of the electrophysiological properties of Y-cells in the kitten's medial interlaminar nucleus.

Single unit, extracellular recordings were made in the medial interlaminar nucleus (MIN) of adult cats and of kittens at 2, 4, 6, 8, 12, and 16 weeks of age. MIN is part of the dorsal lateral geniculate nucleus, and nearly all of its recorded neurons are Y-cells in adult cats. We find that Y-cells in the MIN of younger kittens have long latencies to optic chiasm stimulation, large receptive fields without surrounds, low spatial and temporal resolutions, and nearly absent spontaneous activity. Responses to hand-held light stimuli are typically poor and inconsistent. Also, most of these immature Y-cells exhibit only linear response properties when tested with a counterphased modulated grating pattern. All of the above characteristics gradually develop to adult values over several months of the postnatal period. The percentage of cells with nonlinear response properties becomes adult-like near 8 weeks of age, while both spatial and temporal resolutions are still developing at 16 weeks of age. Latencies and receptive field center sizes achieve adult values at about 12 weeks of age. The immature properties of these neurons are similar to those recorded from abnormal cells in the area of the medial interlaminar nucleus innervated by the deprived eye of monocularly deprived adult cats. This indicates that the adult deprived Y-cells probably fail to develop and thus retain their immature properties.

Aging↗
PubMed1981

Further evidence of an early critical period in the development of the cat's dorsal lateral geniculate nucleus.

The concept of an early postnatal critical period of development for the lateral geniculate nucleus was assessed by determining in adult cats whether previously established properties of geniculate neurons could be altered by varying the cat's visual experience. The analysis was limited to lamina A1 and the binocular segment of lamina A, and the properties studied were the percentage of physiologically recorded Y-cells and cell soma size. Eleven experimental cats in four groups were studied, and three cats reared normally plus three cats reared with continuous monocular lid suture served as controls. Two cats raised first with monocular suture followed by a prolonged period in adulthood with both eyes open had cell size distributions and Y-cell proportions that were indistinguishable from cats raised with continuous monocular suture. Four cats raised first with one eye sutured underwent a reverse suture procedure in adulthood (i.e., the originally sutured eye opened and the other closed) and were maintained in this fashion for a prolonged period. These cats also had geniculate cell size distributions and Y-cell proportions that were indistinguishable from cats raised with continuous monocular suture. Two cats were raised first with binocular suture followed by a prolonged period in adulthood with one eye opened. Their geniculate cell size distributions and Y-cell proportions showed no effect on the adult monocular deprivation and were indistinguishable from previously published data concerning cats raised with continuous binocular suture. Finally, three normally raised cats underwent a prolonged period of monocular suture in adulthood. Their geniculate cell size distributions and Y-cell proportions showed no effects on the adult monocular deprivation. From these data, we conclude that an early critical period of development occurs for geniculate cell sizes and Y-cell proportions. Adult visual environments, whether normal or abnormal, had no detectable effect on geniculate neurons for these previously developed properties, whether normal or abnormal.

Age Factors↗
PubMed1981

Morphology of physiologically identified W-cells in the C laminae of the cat's lateral geniculate nucleus.

The projections from the retina through the lateral geniculate nucleus to the visual cortex in the cat are comprised of three parallel, independent pathways. These three pathways involve, respectively, W-, X-, and Y-cells in the retina and the lateral geniculate nucleus. In this study, we investigated the morphology of those neurons in the C laminae of the lateral geniculate nucleus that receive input from retinal W-cells. Micropipettes filled with horseradish peroxidase (HRP) were used to record the responses of single geniculate neurons identified as W-, X-, or Y-cells. Five W-cells in the C laminae then were stained intracellularly by impalement of the cell with the microelectrode followed by iontophoresis of HRP. Each of these neurons has a small to medium size soma and fine dendrites oriented roughly parallel to the plane of the geniculate laminar borders. These geniculate W-cells differ among themselves mainly in the detail of their dendritic processes. Three of these cells have virtually no dendritic appendages, while the other two have complex appendages not previously reported among neurons in the C laminae. Also, the degree of horizontal orientation of the dendrites differs considerably among these cells. Overall, the morphology of these W-cells is generally consistent with the class 4 cell briefly described by Guillery (Guillery, R. W. (1966) J. Comp. Neurol. 128: 21-50), and consequently, our data indicate that class 4 neurons are the morphological correlate of neurons physiologically classified as W-cells. Since greater morphological detail is presented by these HRP-filled cells than by previous Golgi-impregnated preparations, we can describe more completely the morphology of class 4 cells.

Animals↗
PubMed1979

Lateral geniculate nucleus in dark-reared cats: loss of Y cells without changes in cell size.

In cats reared in the dark from birth until 4 months of age, the dorsal lateral geniculate nucleus contained few normal Y cells in either the binocular or monocular segments. Although most of the neurons appeared to be normal X cells unaffected by light deprivation, many cells with abnormal receptive field and response charcteristics were encountered. These effects were permanent, since 1 to 2 years of normal visual experience following initial light deprivation did not lead to any functional recovery. The sizes of cell bodies in cats reared in the dark were similar to those of normal animals, an indication that changes in geniculate cell physiology need not be related to changes in cell size.

Animals↗
PubMed1979

Functional development of geniculocortical pathways in normal and amblyopic vision.

The geniculocortical pathways of many mammals, including primates, are largely comprised of two neuron types. These are known as X and Y cells. Their functional significance in unclear, but the following highly speculative hypothesis is suggested. Y cells, because of their broad sensitivity to the crucial lower spatial frequencies as well as to the higher ones, are involved in a basic analysis of form vision. X cells, because of their fairly selective sensitivity to higher spatial frequencies, add to this certain details (i.e. enhanced acuity, etc.). If an animal develops with ametropia, Y cells should be adequately stimulated and as the lower spatial frequencies remain undistorted many Y cells would develop and reasonable form vision with milk amblyopia would result. Only X cells would be greatly affected by such an environment. However, if the animal develops with cataracts or is reared in an environment which abolishes all spatial frequencies, then neither X nor Y cells will develop. This would result in poor form vision and a deep amblyopia. Many of these phenomena have been observed in experimental studies of cats. The present relevance for clinical problems of this suggested functional dichotomy for X and Y cells is at best tenuous, and it is offered merely as a working hypothesis for future studies.

Amblyopia↗