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1.
Summary Anatomical studies have shown an extensive network of homotopic and heterotopic interhemispheric connections in area 19 of the cat visual cortex (Segraves and Rosenquist 1982a; 1982b). We have investigated their functional organization by recording visual responses in area 19 of cats following a midsagittal section of the optic chiasm. This operation interrupts all crossed optic fibers coming both from the nasal and the temporal retinae; as a result, each hemisphere receives optic fibers only from the lateral hemiretina of the ipsilateral eye which conveys information from the contralateral visual field. Visual information transmitted to the same hemisphere from the contralateral retina and the ipsilateral visual field must be attributed to an indirect, interhemispheric pathway. We found that a rather high proportion of neurons (31.8%) in area 19 of seven split-chiasm cats responded to visual stimuli presented to the contralateral eye. 1 — All neurons receiving this interhemispheric activation were also driven by the ipsilateral eye via an intrahemispheric pathway. 2 — The property of binocularity was significantly related to the visuotopic map in that both receptive fields of each binocular neuron adjoined or were in the immediate vicinity of the vertical meridian. 3 — Due to the small size of receptive fields in area 19, the contribution of the interhemispheric pathway to the representation of the visual field is rather limited and it is certainly less extensive than that predicted by anatomical studies. The representation of the ipsilateral visual field in area 19 of intact cats, as assessed electrophy-siologically, was comparable to that found in split-chiasm cats. Recordings in areas 17–18 of split-chiasm cats showed that the visual field represented through the corpus callosum in these visual areas is certainly not less and probably more, extensive than that found in area 19. The results support the conclusion that the relation to the vertical meridian and the receptive field size can explain the organization of the interhemispheric connections in the visual areas studied so far.  相似文献   

2.
1. The superior colliculus has been studied in Siamese and normal cats by recording the responses of single tectal units to visual stimuli.

2. The retinotopic organization of the superior colliculus has been compared in the two breeds. In the normal cat, the contralateral half-field is represented in the central and caudal part of the colliculus, and a vertical strip of the ipsilateral half-field, 15-20° wide, is represented at the anterior tip. The Siamese cat superior colliculus receives an abnormally large projection from the ipsilateral half-field so that units with visual receptive fields which extend as far as 40° into the ipsilateral half-field can be found. The area of the tectal surface devoted to the representation of the ipsilateral half-field is about twice as large in Siamese cats as in normal cats. The enhanced representation of the ipsilateral half-field in Siamese cats is reflected in a displacement of the vertical meridian and the area centralis on the tectal surface.

3. The area centralis in the Siamese cat is located at about the same point on the tectal surface as would be occupied by a point in the visual field about 6-7° contralateral to the area centralis in the normal cat. The smallest receptive fields in both breeds are located near the area centralis. The size of the receptive field for a tectal unit seems to be determined by the retinal location of the receptive field and not by the absolute position of the unit on the tectal surface.

4. The receptive-field characteristics of tectal units show many similarities in the two breeds. The receptive fields of individual units consist of activating regions flanked by suppressive surrounds. Units respond well to stimuli of different shapes and orientation provided they are moving. The optimum stimulus for a given unit can be much smaller than the size of the activating region. About two thirds of the units studied in both breeds show directional selectivity. Most of the units studied in normal cats can be activated by stimulation of either eye, while in Siamese cats, 80% of the units studied can be driven only by the contralateral eye. A few monocularly driven units with two separated receptive fields have been observed in Siamese cats.

5. In the left tectum of both breeds, units respond well to left-to-right stimulus movement. The reverse situation obtains in the right tectum. In Siamese cats, units located at the anterior tip of the tectum with their receptive fields located in the visual half-field ipsilateral to the tectum under study respond better to stimulus movement toward the area centralis than away from it. The preferred direction for a tectal unit seems to be determined by its tectal location rather than by the location of its receptive field in the retina.

6. Visual cortex lesions in both breeds increase the responsiveness of tectal units to flashing spots and almost entirely remove the directional selectivity exhibited by tectal units, although units with asymmetric surrounds are still found. In normal cats, the lesions change the ocular dominance distribution, skewing it more strongly toward the contralateral eye. In Siamese cats, the ocular dominance distribution remains unchanged after a visual cortex lesion.

7. The squint commonly exhibited by Siamese cats is regarded as a compensation for the anomalous retinotectal topography. It is suggested that, in the absence of an adaptive modification, the anomalous retinotectal projection would lead to mislocalization in Siamese cats just as it does in frogs and hamsters whose retinotectal projection has been experimentally altered. The convergent strabismus which Siamese cats commonly exhibit may be a cure for the abnormal retinal projections rather than a disease.

  相似文献   

3.
Summary We report electrophysiological data regarding the contribution of the corpus callosum to visual responses in the cortex around the anterior ectosylvian sulcus (AES). The experiments were performed in cats in which the optic input from each eye was surgically restricted to the ipsilateral hemisphere (split-chiasm cats), and where neuronal responses to stimulation of the contralateral eye were mediated by interhemispheric connections. A very high proportion of cells were driven by stimuli presented to either eye indicating that they were activated not only through an intrahemispheric pathway from the ipsilateral eye, but also through an interhemispheric pathway from the contralateral eye. With few exceptions, both receptive fields (RFs) of each binocular neuron abutted or were in the vicinity of the vertical meridian. All neurons responded well to moving stimuli and most of them showed directional selectivity. A few cells were activated by stimuli moving in depth. Following an additional section of the posterior half of the corpus callosum, cells in AES responded only to stimulation of the ipsilateral eye, demonstrating thus that the input from the contralateral eye was conveyed by this part of the corpus callosum. By contrast following a section of the anterior half of the corpus callosum, all visually responsive AES neurons were binocularly activated. These results suggest that the interhemispheric visual input to this ectosylvian region is conveyed via a polysynaptic loop involving visual cortical areas that are connected through the posterior portion of the corpus callosum.  相似文献   

4.
The development of intertectal neruonal connections has been investigated in Xenopus laevis. Contralateral eye grafts and enucleations were performed in embryos and the resultant visual projections to the optic tecta were mapped electrophysiologically after metamorphosis. In enucleated animals the ipsilateral projections were found to be normally organised retinotopically but consisted of visual units with abnormally large multi-unit receptive fields. In 10 animals with contralaterally grafted eyes a normal ipsilateral projection had developed from the abnormal eye and an abnormal projection from the normal eye, to produce congruent maps via the two eyes to one tectum. All the maps in these animals were retinotopically organised. In another 11 animals the ipsilateral projection from the operated eye was fragmentary or absent, while that from the unoperated eye resembled the pattern found after enucleation. Retinotopically abnormal contralateral projections had developed in 5 animals of this group. These results suggest that prefunctional specification determines the initial development of diffuse intertectal visual connections but these may be modified by a process of binocular interaction in the presence of a normal primary contralateral input.  相似文献   

5.
Aberrant visual projections in the Siamese cat   总被引:2,自引:2,他引:2       下载免费PDF全文
1. Guillery has recently shown that the Siamese cat has a grossly abnormal lateral geniculate body. His anatomical study suggested that certain fibres originating in the temporal retina of each eye cross in the chiasm instead of remaining uncrossed. They thus reach the wrong hemispheres, but in the geniculate they terminate in the regions that the missing fibres from the ipsilateral eye would normally have occupied. The result is that each hemisphere receives an input from parts of the ipsilateral field of vision, this input being entirely from the opposite eye. The purpose of the present work was to study the physiological consequences of this aberrant projection, in the lateral geniculate body and visual cortex.2. Single-cell recordings from the lateral geniculate body confirmed the presence of projections from the ipsilateral visual field of the contralateral eye. The part of layer A(1) receiving these projections was arranged so that the receptive fields of the cells were situated at about the same horizontal level and at the same distance from the vertical meridian as the fields of cells in the layers above and below (layers A and B), but were in the ipsilateral visual field instead of the contralateral. They thus occupied a region directly across the mid line from their normal position.3. In the cortex of all animals studied, we found a systematic representation of part of the ipsilateral visual field, inserted between the usual contralateral representations in areas 17 and 18. When the visual cortex was crossed from medial to lateral the corresponding region of visual field moved from the contralateral periphery to the mid line, and then into the ipsilateral field for 20 degrees . The movement then reversed, with a return to the mid line and a steady progression out into the contralateral field. The entire double representation was, with some possible exceptions, a continuous one. The point of reversal occurred at or near the 17-18 boundary, as judged histologically, and this boundary was in about the same position as in ordinary cats.4. Cells in the part of the cortex representing the ipsilateral fields had normal receptive fields, simple, complex, or hypercomplex. These fields tended to be larger than those in corresponding parts of the contralateral visual fields. Receptive-field size varied with distance from the area centralis, just as it does in the normal cat, so that cells with the smallest fields, in the area centralis projection, were situated some distance from the 17-18 border.5. Projections originating from the first 20 degrees from the midvertical in both visual half-fields had their origin entirely in the contralateral eye, as would be expected from the abnormal crossing at the chiasm. Beyond this visual-field region, and out as far as the temporal crescents, there were projections from both eyes, but we found no individual cells with input from the two eyes. The cells were aggregated, with some groups of cells driven by one eye and some by the other.6. From previous work it is known that ordinary cats raised with squint show a decline in the proportion of cells that can be driven binocularly, whereas animals raised with both eyes closed show little or no decline. A Siamese cat raised with both eyes closed had binocular cells in the regions of 17 and 18 subserving the peripheral visual fields, suggesting that the absence of binocular cells seen in the other Siamese cats was indeed secondary to the squint.7. In two Siamese cats there were suggestions of an entirely different projection pattern, superimposed upon that described above. In the parts of 17 and 18 otherwise entirely devoted to the contralateral visual field, we observed groups of cells with receptive fields in the ipsilateral field of vision. The electrode would pass from a region where cells were driven from some part of the contralateral visual field, to regions in which they were driven from a part of the ipsilateral field directly opposite, across the vertical mid line. The borders of these groups were not necessarily sharp, for in places there was mixing of the two groups of cells, and a few cells had input from two discrete regions located opposite one another on either side of the vertical mid line. The two receptive-field components of such cells were identical, in terms of orientation, optimum direction of movement, and complexity. Stimulation of the two regions gave a better response than was produced from either one alone, and the relative effectiveness of the two varied from cell to cell. These cells thus behaved in a way strikingly reminiscent of binocular cells in common cats.8. The apparent existence of two competing mechanisms for determining the projection of visual afferents to the cortex suggests that a number of factors may cooperate in guiding development. There seems, furthermore, not to be a detailed cell-to-cell specificity of geniculocortical connexions, but rather a tendency to topographic order and continuity, with one part of a given area such as 17 able to substitute for another. Whether or not these tentative interpretations are ultimately proved correct, it seems clear that this type of genetic anomaly has potential usefulness for understanding mechanisms of development of the nervous system.  相似文献   

6.
Cells in area 17 of the cortex are generally activated either directly through a retino-thalamic pathway or indirectly via a contralateral hemisphere-callosal pathway. The aim of the present experiment was to evaluate the effects of eliminating this second pathway on the binocular activation of cells in the primary visual cortex. The optic tract was sectioned on one side in 18 cats and unit activity was recorded in the contralateral hemisphere. This hemisphere should receive normal thalamo-cortical inputs but no visual callosal input. These animals were compared to 21 normal cats. Extracellular electrophysiological recordings were carried out in the conventional way using tungsten microelectrodes and N2O anaesthesia. Results indicated that the proportion of binocular cells found in the cortex of tract sectioned animals was lower than that found in normal animals. However, this decrease in binocularity could be essentially attributed to cells having receptive fields situated to within 4 degrees of the vertical meridian of the visual field. These results are interpreted as being congruent with the demonstrated anatomo-physiological projections of the callosal system.  相似文献   

7.
Summary Reference axes for the visuotopic study of the opossum's striate cortex were estimated from corresponding binocular response fields using multi-unit recording. These central binocular axes (CBA) were derived from experimental data based on the concept that corresponding receptive fields for each eye should be mostly in register under natural conditions. Vertical reference meridians, orthogonal to these axes, define a contralateral and an ipsilateral field for each eye with respect to the recording site. An ipsilateral field representation was observed for both eyes in the striate cortex at the transition zone with peristriate. Maximal values for the center and border of ipsilateral receptive fields were, respectively, 8 and 20 degrees for the contralateral eye and 6 and 14 degrees for the ipsilateral eye. An equivalent ipsilateral field representation was found in animals that had the anterior commissure cut prior to the recording session. This suggests that the ipsilateral field of both eyes may be represented in the striate cortex via the ipsilateral optic tract. Additionally, it was observed that the region of higher ganglion cell density in the retina shows a flattened distribution and that the CBA intersects the retina at the temporal aspect of this region.  相似文献   

8.
Summary The concept of corresponding retinal points was examined in terms of the binocular receptive fields of neurons in Area 17 of the cerebral cortex of the cat. Only a proportion of the binocular receptive field pairs can be accurately superimposed at the one time in a given plane. The fields which are not corresponding are said to show receptive field disparity. The attempt has been made to establish, on a quantitative basis, the parameters of the receptive field disparities that occur within 5° of the visual axis. A new method was used for defining the zero (vertical) meridian. Very effective paralysis of the extraocular muscles was achieved and the very small residual eye movements that occurred were regularly monitored so that corrections could be applied to the plotted positions of the receptive field pairs. The distribution of the receptive field disparities about the position of maximal correspondence has a range of about ±1.2° (S.D. 0.6°) in both the horizontal and vertical directions for fields in the vicinity of the visual axis. Panum's fusional area may represent the extent to which receptive fields in the one eye, all with the same visual direction, are linked to fellow members of a pair in the other eye over a range of receptive field disparities. A naso-temporal overlap of receptive fields occurs which is probably little if any more than can be accounted for on the basis of the disparity of receptive fields lying along the zero (vertical) meridian. When the extraocular muscles are paralyzed the eyes diverge and the binocular receptive field pairs are separated on the tangent screen. The distribution of the horizontal and vertical separations of the receptive field pairs have been examined.Selby Fellow of the Australian Academy of Sciences.  相似文献   

9.
Summary Visual fields of 15 monocularly deprived (MD) cats and 2 monocularly tested normal adult cats, were measured using stationary stimuli at fixed distances in the horizontal plane. Compared to the visual fields of monocularly tested normal cats, those of the deprived eyes of MD cats were found to be restricted to the ipsilateral hemifield up to the midline. This finding appeared to be permanent since it was measured both in cats tested early (4 cases) and late (11 cases) after deprivation. In addition, it seemed to be independent whether the nondeprived eye was closed by reverse suturing (13 cases), or was left open after deprivation and closed only temporarily during testing (2 cases).Visual fields were also found to be restricted to the ipsilateral hemifield, if MD cats were tested at several levels above the horizontal plane or in a hemisphere (23 cm radius) in which the superior and inferior segment of the visual space could be tested (6 cases).The results are controversial to those of Sherman (1973) who described the visual fields of MD cats to be restricted to the monocular (60–90 ° ipsilateral) segment. The differences observed in our results compared to those of Sherman could not be explained by experimental factors, since testing MD cats by the method employed by Sherman (8 cases) also resulted in visual fields covering the monocular as well as the binocular part of the ipsilateral side. Consequently, Sherman's hypothesis (1974b), that for MD cats the geniculocortical pathways dominate in the visual behavior and that retinotectal pathways are somehow suppressed, could not be confirmed by our results. In our experiments the visual behavior demonstrated by MD cats seemed to be developed mainly through retinotectal pathways. In MD cats in which after the deprivation period the non-deprived eye remained open, the monocular part seemed to be of more importance than the binocular segment; permanent closure of the normal eye seemed to lead to a further shift towards the binocular segment. Therefore, in non-reverse sutured MD cats some suppression of retinotectal pathways by imbalanced corticotectal pathways may be present, but not as elaborate as described by Sherman. This slight suppression is overcome by reverse suturing.The mechanism of release from suppression of retinotectal pathways is unknown, its possible localisation is discussed.  相似文献   

10.
Summary In young cats, the posterior portion of the corpus callosum was sectioned 13–29 days after birth. The animal's eyes were photographed at weekly intervals for six months using the pupil-reflex method. From the corneal reflection evident in the photographs the degree of alignment for the optical axes of each cat was estimated (Sherman, 1972). The 17 experimental cats all showed a significant tendency toward permanent divergent strabismus, as compared to six normal cats. The limits of the visual field were determined for both groups of cats using a perimetry technique similar to that of Sprague and Meikle (1965) and Sherman (1973). With one eye open normal cats responded from 90 ° ipsilateral to 45 ° past the vertical midline into the contralateral visual field. With either eye the experimental cats responded from 90 ° ipsilateral to approximately the vertical midline. The loss of visual responsiveness is within the contralateral region of the normally binocular zone. Three cats received the same operation at 9, 13, or 20 months old. Eye alignment and visual field perimetry were unaffected by the surgery. It is not known whether the observed abnormalities result from arrested development, or disruption of intrinsically determined ocular alignment.  相似文献   

11.
Summary Visual fields of ten cats which had one or both eyes rotated at 8 days of age were measured by two forms of perimetry and compared to visual fields of two normal cats and of four cats with monocular rotations at 16 days, 3 months or 6 months of age. All animals showed excellent localization of visual stimuli and responded to the actual location of stimuli in space rather than to the retinal locus normally associated with that location. In cats with monocular rotations, the field of the normal eye was always normal, extending from 90 ° ipsilateral to 30 ° contralateral. Cats with rotations of one eye at 3 or 6 months of age had essentially normal fields in the rotated eye as well, while cats with surgery at 8 or 16 days had restricted horizontal fields. They responded only to stimuli in the ipsilateral hemifield; they were blind in the contralateral hemifield. Their superior and inferior visual fields were normal. The field deficits related consistently to visual field coordinates and not to the angle or direction of rotation. In cats with binocular rotations the visual field of at least one eye extended across the midline. Thus, the extent of the field depended upon sensorimotor experiences of the cat both before and after surgery. It is argued that these monocular field deficits have a central origin, not a retinal one.When tested with both eyes open, seven of 14 experimental animals did not respond throughout the visual field seen by each eye alone. The total visual field with both eyes open was less than the sum of the two monocular fields; greatest losses were most pronounced in the extreme periphery of the field ipsilateral to the rotated eye. Since changes in eye position (e.g., convergence during bincocular viewing) were not observed, it is suggested that the binocular losses indicate suppression of the deviated eye which has a central origin.All animals were tested for visual following, visually-triggered extension (placing), and visually-guided reaching. Cats which had been routinely encouraged to use the rotated eye(s) by occlusion of the other eye showed skilful performance within a few weeks after surgery as previously reported by Peck and Crewther (1975), Mitchell et al. (1976) and others. In contrast, two cats reared with both eyes open after unilateral rotation in infancy were profoundly handicapped, as previously reported by Yinon (1975, 1976).This research was supported by Grant NS 14116 from the US Public Health Service  相似文献   

12.
The effect of visual deprivation upon the maturation of the ipsilateral visuotectal projection has been studied in Xenopus laevis. This topographically ordered projection is polysynaptic. The first stage involves the retinal projection to the contralateral optic tectum. The tectum projects to the nucleus isthmi on the same side. The final stage is the crossed isthmotectal projection from the nucleus isthmi to the tectum ipsilateral to the eye. The topographic precision of connections at various points in this polysynaptic pathway has been investigated by quantifying single-unit and multi-unit receptive field sizes in the contralateral and ipsilateral visuotectal projections. Observations have been made on normal animals of different ages to plot the normal maturational course of events. The effects of visual deprivation on this maturational process has been studied. Between one week and one year after metamorphosis there is an increase in the precision of connections in both the contralateral and ipsilateral visuotectal projections. Visual deprivation had no effect upon the parameters of the contralateral visuotectal projection. Ipsilateral visuotectal single units in dark-reared animals had normal receptive field sizes. Ipsilateral multi-unit receptive fields in dark-reared animals were considerably larger than in normal animals. It was concluded that the effects of visual deprivation are limited to effects on the crossed isthmotectal component of the intertectal system. In this component, however, visual experience seems to play an important role in the normal development and modification of connections. It is suggested that visual experience is utilized to accommodate changes in the system required to respond to normal changes in interocular geometry that take place with development in Xenopus.  相似文献   

13.
Summary The visual representation in the uncrossed retinal projection to the superior colliculus (SC) was examined electrophysiologically by recording multiunit responses in paralysed, anaesthetised adult rats (both pigmented and albino), which had been monocularly enucleated either prenatally or soon after birth. This manipulation partially stabilises an exuberant neonatal projection from the remaining eye to the ipsilateral SC. Neuronal responses were also stronger and the multi-unit receptive fields larger than in intact animals. Many of the visual fields recorded on penetrations in caudal SC were located in the peripheral ipsilateral visual hemifield, corresponding to nasal retina. Such receptive fields are not seen in normal animals and were not found in animals enucleated on day 3 or later. The topographic representation of the dorso-ventral retinal axis, lateral to medial in the SC, was normal in all experimental animals. The representation of the naso-temporal retinal axis was abnormal and more variable. In all operated animals as the recording electrode was moved caudally away from the rostral pole of the SC, the corresponding receptive fields moved gradually from up to 40° in the ipsilateral visual hemifield to about 40° into the contralateral hemifield (a location corresponding to the peripheral edge of the temporal retina). This is the mapping polarity found in the normal uncrossed retinal projection. In the enucleated animals, the map was expanded and frequently displayed a clustering of fields arising from far temporal retina. In animals enucleated prenatally or on the day of birth, visual responses could be recorded in more caudal SC. The corresponding receptive fields now moved nasally on the retina, generating reversals in the map. The most caudal penetrations in these early enucleates frequently gave receptive fields located in retina nasal to the optic disc, up to 90 degrees into the ipsilateral visual hemifield. These results demonstrate that a temporal relationship exists between the order and mapping polarity of the visual field in SC and the time of enucleation. Prenatal enucleation produces reversals of the mapping polarity in caudal SC while neonatal enucleation produces an expanded map but one with a mapping polarity appropriate for an uncrossed projection  相似文献   

14.
Summary All cells in the nucleus of the optic tract (NOT) of the cat, that Bcould be activated antidromically from the inferior olive, were shown to be direction-specific, as influenced by horizontal movements of an extensive visual stimulus. Cells in the left NOT were activated by leftward and inhibited by rightward movement, while those in the right NOT were activated by rightward and inhibited by leftward movement. Vertical movements did not modulate the spontaneous activity of the cells. The mean spontaneous discharge rate in 50 NOT cells was 30 spikes/s.This direction-specific response was maintained over a broad velocity range (<0.1 ° – >100 °/s). Velocities over 200 °/s could inhibit NOT cells regardless of stimulus direction.All cells in the NOT were driven by the contralateral eye, about half of them by the ipsilateral eye also. In addition, activation through the contralateral eye was stronger in most binocular units. Binocular cells preferred the same direction in the visual space through both eyes.An area approximately corresponding to the visual streak in the cat's retina projected most densely onto NOT cells. This included an extensive ipsilateral projection. No clear retinotopic order was seen. The most sensitive zone in the very large receptive fields (most diameters being >20 °) was along the horizontal zero meridian of the visual field.The retinal input to NOT cells was mediated by W-fibers.The striking similarities between the input characteristics of NOT-cells and optokinetic nystagmus are discussed. The direction selectivity and ocular dominance of the NOT system as a whole can provide a possible explanation for the directional asymmetry in the cat's optokinetic nystagmus when only one eye is stimulated.This work was supported by DFG-Grants No 450/3 and 450/7 to K.-P. Hoffmann  相似文献   

15.
Summary In adult cats that had previously undergone surgical section of the posterior corpus callosum at 13–18 days after birth, the striate cortex was examined using extracellular single unit recordings. The receptive fields of the cells examined were located from the vertical meridian to 39 ° peripherally, and ranged from above to below the horizontal meridian. Cells were classified according to type (simple, complex), ocular dominance, receptive field size and location. Callosum sectioned cats had 53% of striate cells activated monocularly as compared to 25% for control cats. This increase in monocularly activated units primarily occurred for receptive fields in the paracentral region of the visual field, from 4–39 °. The age at which the neonatal surgery had occurred was correlated with the individual cat's proportion of monocularly activated cells.Therefore, the increase in monocular activation of striate units occurred within a large portion of the normal binocular visual field. This physiological change was partially predicted by a previous behavioral study showing a substantial loss in the extent of the binocular visual field following neonatal corpus callosum section (Elberger 1979).Support for this research was received from Training Grant No. T-32 EY 07035-02 awarded to the University of Pennsylvania. Additional support was provided by the Department of Neurobiology and Anatomy, University of Texas Medical School at Houston, No. 1-11321-215001-10  相似文献   

16.
We examined the retinae of two monkeys whose left striate cortex had been removed eight years previously and compared the transneuronally degenerated hemiretina of each eye with the normal hemiretina, and with the retinae of normal monkeys. All retinae were prepared as whole mounts. One from each pair was stained with Cresyl Violet; the other was reacted for horseradish peroxidase two days after placing pellets of the enzyme in the optic nerve. Measurements of ganglion cell density in the Nissl-stained retina of the contralateral right eye showed that approximately 80% of retinal ganglion cells were missing in the central 30 degrees of the degenerated hemiretinae. More peripherally the percentage loss was less extensive. Measurements of cell soma size and dendritic field size of peroxidase-labelled classified surviving cells in the degenerated temporal hemiretina of the ipsilateral eye showed them to be morphologically normal. In comparison with the normal hemiretina, however, the mean soma size at three selected eccentricities was larger than normal, suggesting selective loss of smaller ganglion cells. Classification of peroxidase-labelled ganglion cells in the normal and degenerated hemiretinae revealed that the population of P beta cells was reduced by as much as 85% in the degenerated region. There was comparable change in the density of P alpha or P gamma cells. The degeneration of the great majority of P beta cells, which are believed to be the morphological substrate of ganglion cells with small and colour-opponent receptive fields, must set limits on the visual sensitivity and discrimination that survive damage to striate cortex.  相似文献   

17.
Summary Cats reared with their visual world restricted to vertical lines for one eye and horizontal lines for the other had, in their visual cortices, units with elongated receptive fields that were either vertically or horizontally oriented. These receptive fields could be mapped only using that eye which had seen lines of the same orientation during development. Other units had diffuse, unresponsive receptive fields (Hirsch and Spinelli, 1970). Six cats, from the group above, were revived and allowed normal binocular viewing in an attempt to determine the possibility and extent of adding other types of receptive fields by giving other experiences to their visual systems. After exposure to a normal environment for up to 19 months it was found that indeed there had been a massive increase in the percentage of those classes of receptive fields that were either absent or weak at the end of the selective visual experience. Significantly, these receptive fields, acquired during binocular viewing, were very often binocular.The results, however, show that units whose response characteristics mimic the stimuli viewed during development were almost completely unaffected by normal binocular visual experience, i. e., they were monocularly activated and had the orientation appropriate for the stimuli viewed by the eye from which they could be mapped. Most impressive are a few units whose receptive field shape is almost a carbon copy of the pattern viewed during development. The data provide evidence that visual experience has a direct continuing and lasting effect on the functional connectivity of cells in the visual cortex.  相似文献   

18.
Summary Thirty-four kittens reared by allowing each eye patterned visual input, but on alternate days and for unequal periods of time (unequal alternating monocular exposure (AME)), were tested for their ability to orient to targets at different positions in visual space. In all unequal AME cats, the visual field of the more experienced eye (MEE) was normal, while that of the less experienced eye (LEE) was restricted. In contrast, in 14 cats reared with equal AME, the fields of both eyes were equal and of normal size. The field deficits observed in the unequal AME cats must therefore be due to the imbalance in stimulation and thus result from a competitive interaction between the afferents from the MEE and the LEE.The field deficits observed in the unequal AME cats differed from those observed in two monocularly deprived (MD) cats. Neither of the MD cats ever responded to targets presented in the region of normal binocular overlap when tested with the deprived eye (DE). The unequal AME cats all showed a nasal field loss in the LEE, but responded normally to targets throughout the temporal portion of the binocular visual field. When the imbalance in stimulation was large (8 to 1) or moderate (8 to 4), there was an abrupt drop in responsiveness (from 100% to zero) as the position of the target was changed from temporal to nasal. When the imbalance was slight (8 to 7), the drop in responsiveness was more gradual and occurred within the nasal field. Our results demonstrate that (1) the paradigm of unequal AME is a useful one for studying binocular competition quantitatively, (2) even the slightest imbalance in stimulation of the two eyes can affect the outcome of the competitive interaction, and (3) the pathways serving binocular vision are not uniformly affected by binocular competition: the ipsilateral pathway is more sensitive than the contralateral pathway.Supported by NIH grants EYO1268 to HVBH and EYO2609 to SBT  相似文献   

19.
Summary Pretectal cells of the European fire salamander were recorded extracellularly during binocular and monocular horizontal optokinetic stimulations. The locations of the individual units within the pretectal nucleus were verified with Alcian blue injections. The particular anatomical properties of single cells were demonstrated after single-unit recordings by means of horseradish peroxidase preparations.Direction selective pretectal cells were found to be predominantly (2/3) sensitive to temporo-nasal movements in the visual field of the contralateral eye. They usually possessed large receptive fields centered on the visual equator with restricted diameters in the dorso-ventral axis. Their resting discharge was low, and in some cells no spontaneous discharges were observed. The cells preferred low stimulus velocities, most of them being optimally stimulated with velocities of 1 to 10 deg/s. A group of units was exclusively sensitive to accelerated movements. A subclass of them was transiently responsive when the stimulus stopped.In the anterior and most dorsal part of the pretectal nucleus, binocularly influenced units were found. These cells responded best with binocular optokinetic stimulations and less vigorously or with less pronounced direction selectivity if only the contralateral eye was stimulated. With ipsilateral stimulations alone no response could be elicited. This response type could be explained by inhibitory inputs from the ipsilateral eye via direct ipsilateral projections or crossing pretectal fibers. The responses of these cells are well correlated to behavioral results showing that OKN performance in salamanders, as in some other vertebrates, is different with binocular as compared to monocular stimulations.The direction-sensitive pretectal cells usually possess extensive dendritic arborizations within the ipsilateral pretectal neuropil. Most of the cell bodies were scattered in the white substance or in the superficial layers of the periventricular gray. In the cases where the efferent fiber of a particular cell could be clearly recognized, the axon projected to the basal optic neuropil of the accessory optic system, the contralateral pretectum or, in two cases, to the medulla oblongata into a region which might be homologous to the inferior olive of higher vertebrates.  相似文献   

20.
1. To compare the spatial organization of the direction selectivity of neurons in the medial terminal nucleus (MTN) of the accessory optic system with that of neurons in the adjacent ventral tegmentum, extracellular single-unit recordings were made in the anesthetized rabbit. The ventral tegmental neurons were located in a region called the visual tegmental relay zone (VTRZ), which is defined by the ventral tegmental terminal field of contralaterally projecting MTN neurons. 2. Some of the present sample of MTN neurons (5 of 34) had monocular receptive fields composed of two parts distinguished by a marked difference in the orientation of their respective direction-selective tuning curves. For one part of the receptive field the preferred excitatory direction was "up," while for the other part it was "down." Such receptive fields for one eye were called bipartite, whereas the more usually encountered MTN receptive fields, which could be characterized by a single direction-selective tuning curve, were called uniform. 3. Of the 16 neurons recorded from the VTRZ, all but one were binocular. For these neurons, both uniform and bipartite receptive fields were found for each eye alone. The only monocular neuron encountered in the VTRZ had a contralateral, bipartite receptive field. 4. The spatial organization of the direction selectivity of bipartite receptive fields strongly suggests that they are suited to represent rotation of the visual field about a horizontal axis located in the vertical plane that divides the receptive field into two parts. 5. The boundary between the two parts of the bipartite receptive fields was found using handheld visual stimuli at one of two azimuthal locations, either close to 45 degrees or between 95 and 125 degrees (the 0 degree reference was rostral in the midsagittal plane). This particular structure of the bipartite receptive fields suggests that their preferred rotation axes have a close spatial relation to the best-response axes of the semicircular canals. 6. Seven VTRZ neurons were antidromically activated by electrical stimulation of the ipsilateral dorsal cap of the inferior olive. Since the receptive fields of VTRZ neurons have many of the structural features characteristic of the receptive fields of rostral dorsal cap neurons we conclude that the spatial organization of the receptive fields of dorsal cap neurons is, for the most part, synthesized prior to the inferior olive.(ABSTRACT TRUNCATED AT 400 WORDS)  相似文献   

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