Biomedical subjects

U Yinon

Publications and source records attributed to U Yinon.

At least 37 records · Page 2Linked to original sources

PubMed1990

The ocular dominance and receptive field properties of visual cortex cells of cats following long-term transection of the optic chiasm and monocular deprivation during adulthood.

Plasticity-induced interhemispheric transfer of visual information to cortical cells was studied in adult cats. The direct contralateral visual pathway was surgically eliminated permitting binocularity only by callosal transfer. In order to enhance the interhemispheric transfer, one hemisphere was made less visually active by depriving it chronically from visual input. Single cell recording was made in areas 17-18 boundary, the callosal projection zone, of operated (OC), operated and deprived (OCMD), and normal control cats. In the OCMD cats, greater than 90% of the cells in each hemisphere reacted ipsilaterally to the deprived or non-deprived eye. Only 3.1% of the cells in both hemispheres of the OCMD cats and 3.9% in the OC cats had contralateral input via the corpus callosum. The two hemispheres were similar in the selectivity of their cells to stimulus orientation and direction. The average receptive field area of the OCMD cats was also similar for the ipsilaterally driven cells in the two hemispheres; it was 1.2 degrees 2 for the deprived eye and 1.1 degrees 2 for the normal eye. The receptive fields (greater than 95%) of both eyes of the OCMD cats were found in the nasal visual hemifields and greater than 70% of them were at eccentricities of less than 5 degrees from the vertical meridian. The disappearance of the temporal (contralateral) hemifields in these cats and the physiological properties of their cortical cells were determined merely by the chiasm transection which had thus induced nearly complete interhemispheric separation. No effect of the monocular deprivation, in normal adult cats or in cats with chiasm transection was found, even after long periods (greater than 7 months). Therefore, plasticity-induced interhemispheric transfer of visual information was not found during adulthood.

Animals↗

PubMed1990

Hydrocephalus in developing cats: physiological properties of visual cortex cells.

We have studied electrophysiologically by single cell recording in the visual cortex, whether modification of the visual system in developing and in adult cats by hydrocephalus has an effect on processing of visual information. One of our cats (H1) had developed a complete hydrocephalus and the others partial, as proved by either complete or partial dilation of the lateral ventricles, respectively and by the thinning of the cortex. Despite this, the horizontal lamination and the vertical organization of the cortex were fully preserved. Except for the optic radiation and the corpus callosum which was remarkably modified, the optic tract, chiasm, nerve and retina were morphologically and histologically normal. The visual behavior of the hydrocephalic cats was normal. This was also reflected, by and large, in the physiological properties of the visual cortex. However, in cat H1 there were many more visually unresponsive cortical cells in comparison to its matched controls (C1) and the normal cats. A reduced responsiveness was also found in cat H2 with partial hydrocephalus but not in the other partial hydrocephalic cats. Similarly, the ocular dominance distribution of the cells was affected in cat H1 in comparison to the control cats as indicated by the changes found in the relative proportions of contralaterally and ipsilaterally driven cells in the two hemispheres. No change was, however, found in the partially hydrocephalic cats. Most of the cells in the hydrocephalic cats were orientation specific, similarly to the result of their matched controls. Direction specific cells were much smaller in proportion in cat H1 but not in the other cats, in comparison with their matched controls. In keeping with this, a large increase was found in the receptive field area of cat H1, a smaller one in cat H2 and none in the other hydrocephalic cats in comparison to the matched controls. The eccentricity distribution of the receptive fields in the hydrocephalic cats was the same as expected under normal conditions. It was concluded that in the way hydrocephalus had modified the brain of several of our cats, a quantitative effect was induced in visual cortex cells leading to some degradation of function; this change, however, did not interfere with their basic visual properties.

Animals↗

PubMed1988

Corpus callosum transection reduces binocularity of cells in the visual cortex of adult cats.

The possible involvement of the corpus callosum in binocular functions of the visual cortex was studied in adult cats. Unit recording was made in areas 17, 18 boundary following posterior or complete transection of the corpus callosum, acutely as well as chronically, after short (3-4 months) and long (5.5-39 months) survival periods. A considerable reduction of binocularly driven cells was found in the posteriorly callosally transected cats (acute: 41% cells; short-chronic: 65%; long-chronic: 32%). Similar results, albeit smaller in the long-survival group, were found following complete callosal transection. In comparison, the proportion of binocular cells in the normal cats was 85%. It was concluded that the corpus callosum is involved in interhemispheric integration and enhancement of binocularity in visual cortex cells. No recovery occurs as function of time following cancellation of the interhemispheric interaction by callosal transection.

Animals↗

PubMed1988

Split chiasm developmentally induced in kittens: plasticity of interhemispheric transfer in visual cortex cells.

Visual callosal transfer during development was studied in order to reveal plasticity-related compensation for the absence of direct contralateral inputs. The optic chiasm was midsagittally sectioned in 6-8 weeks old kittens (OCK) and for comparison, in adult cats (OCA). Unit recording was made during adulthood in the border area between visual cortex areas 17 and 18, namely the callosal projection zone. The proportion of cells showing interhemispheric transfer in the OCK group, as indicated by the presence of visual input from the contralateral eye was 10.5%; in the OCA cats their proportion was 4.0%. Moreover, 2.3% of the cells showed a pure transfer of input from the contralateral eye in the OCK, although none was seen in the OCA cats. Thus, during the developmental period, a plasticity induced process, albeit limited, takes place in the enhancement of interhemispheric transfer of visual information.

Animals↗

PubMed1988

Midsagittal transection of the optic chiasm and the corpus callosum induces visual split brain in cats: the effect on ocular dominance and responsiveness to cells in the visual cortex.

The geniculocortical pathways from the contralateral eye and the callosal pathway were interrupted in cats in order to study how cortical cells are influenced by changes induced in the interhemispheric transfer of visual information. Unit recording was carried out from areas 17 and 18 boundary, the callosal projection zone. The ocular dominance distribution of cortical cells showed absence of interhemispheric interaction. The visual areas in the two sides of the brain thus functioned independently, presenting a condition of visual split brain. This also has been reflected by the absence of compensatory visual inputs via an alternative commissural pathway. Furthermore, remarkable diminution in the excitability level was found as indicated by the reduction in the proportion of visually responsive cells. Finally, the results of the split brain cat reflect the condition of the individual operations from which it is composed.

Animals↗

PubMed1988

Unilateral interruption of geniculate and callosal inputs to the visual cortex of cats: ocular dominance and responsiveness of cells in the deafferented and in the intact hemispheres.

In order to study the ocular dominance and responsiveness of cells in the deafferented visual cortex, the geniculate and the callosal inputs were interrupted in adult cats by either simultaneous (OTCCX) or separate surgical transection of the optic tract (OTX) and the posterior corpus callosum (CCX). Unit recording was chronically carried out mainly in the boundary of areas 17-18, the callosal projection zone. A small proportion of visually responsive cells was encountered in the deafferented hemisphere of the OTCCX (8.3%) and the OTX (6.3%) cats. In the intact hemisphere, 59.7% of the cells were visually responsive in the OTCCX cats and 57.0% in the OTX cats; they were 61.6% of the cells in the CCX cats and 85.6% in the normal controls (both hemispheres). The majority of the cells in the deafferented hemisphere of the OTCCX (88.9%) and the OTX (82.4%) cats were binocularly driven. In the intact hemisphere of the OTCCX cats, 85.1% of the cells were binocularly driven, in comparison to 77.6% in the OTX cats, 48.8% in the CCX cats, and 81.5% in the normal controls. We therefore concluded that following unilateral elimination of the geniculate input as well as the callosal transection, binocularity in the intact hemisphere was preserved despite the remarkable diminution in the responsiveness level there. Furthermore, the supply of visual input to the deafferented hemisphere was not affected after callosotomy, suggesting an alternative transfer, albeit minor, via an anterior callosal or another commissural pathway.

Afferent Pathways↗

PubMed1988

Visual split brain and monocular deprivation in kittens: differentiation between the effects of disuse and of binocular competition in visual cortex cells.

To differentiate between the resulting effect of disuse, developmentally induced by deprivation, and the binocular competition effect on cortical cells, visual split brain was performed concurrently with monocular deprivation in kittens. In the experienced hemisphere of the split brain deprived cats (ipsilaterally to the non-deprived eye), there were twice as many visually responsive cortical cells than found in their inexperienced hemisphere (ipsilaterally to the deprived eye); however, these cells were equal in number to that found in the split brain controls. In the monocularly deprived control cats a relation of 3.2 was found between cells driven by the non-deprived and the deprived eye. Visual disuse, therefore, resulting from monocular deprivation, affects cortical cells under complete absence of binocular competition but is greatly enhanced by the latter.

Animals↗

PubMed1988

Enhanced electroretinogram in cats induced by exposure to mercury acetate.

The present study was undertaken in order to verify whether, and how, retinal functions are affected by subacute poisoning with organic mercury. Mercury acetate in various concentrations (0.025-0.25 mg/kg per day) was injected subcutaneously every second day to adult cats (N = 20) throughout a 2.5-4.0-week period. The electroretinogram (ERG) was recorded and the Hg2+ concentrations in the blood were determined. In nearly 90% of the intoxicated cats an enhanced electroretinogram (scotopic b-wave amplitude) was found as compared to its level in the normal control cats (N = 10). The latency of the ERG was found to be appropriately shorter, up to a maximal difference of nearly 20% in comparison to the controls. Hg2+ was present in the blood of the exposed cats during a 2.5-month period following the exposure. It is concluded that exposure to mercury acetate induces a permanent increase in the excitability level of the cat's retina.

Animals↗

PubMed1988

The deafferented visual cortex and interhemispheric relationships: a physiological approach.

A condition of asymmetrical activation in the visual system, induced by unilateral optic tract section (OTX) was examined in nine adult cats, four of which had been reared after early onset of monocular deprivation (MD-OTX) during the critical developmental period. Their results were compared to those of monocularly deprived (MD) and normal control cats. Extracellular single-unit recordings from areas 17, 18 and their border were performed at various intervals after OTX to study the effects of this isolation of one hemisphere from direct geniculo-cortical input. Electrophysiological results from the isolated hemispheres of both OTX and MD-OTX cats revealed that contralateral input via the corpus callosum was virtually undetectable in the majority of cats. Only in the cats in which the deprivation was ipsilateral to the OTX, 3.5% of the cells exhibited visual activity in the isolated hemisphere. In the intact hemisphere of the OTX group, binocularity was unaffected overall in comparison to the normal control animals, except for a slight decrease within the 0-4 degrees region from the vertical meridian. In the MD-OTX group, the cats with onset of deprivation prior to natural eye opening possessed an increase in deprived eye responsiveness compared to the control MD cats. No such an increase was seen in later onset of deprivation (3-4 weeks following natural eye opening) in the MD-OTX cats. Overall, visual responsiveness was reduced in all of the OTX and MD-OTX cats, with a return towards normal control values seen only in one animal with extended recovery (6 months). Orientation and direction selectivity were dramatically decreased in the OTX and MD-OTX cats. As the majority of receptive fields mapped from the OTX cats were in the ipsilateral visual field to the section, the remaining small number of receptive fields in the contralateral "blind" visual fields adds further support for a nasotemporal overlap in the retina of the cat. The conclusion from these results is that an asymmetrical level of direct geniculo-cortical input in the visual system of the adult cat yields a physiological bidirectional inactivation of the callosal pathway for the transfer of visual information. Thus, activation of the callosal pathway connecting the cortical visual areas has been postulated to be dependent upon simultaneous, reciprocal interaction between the two hemispheres.

Animals↗

PubMed1988

Split brain acutely and chronically induced in cats causes ipsilateral eye dominance and reduced excitability of cells in the visual cortex.

The ocular dominance distribution and the excitability level of single cells in the callosal projection zone of the visual cortex (area 17-18 boundary), were electrophysiologically studied in acute and in chronic cats following simultaneous (OCX-CCX) and separate transections of the optic chiasm (OCX) and corpus callosum (CCX). Except for a few cells (3.4%) in the acute OCX-CCX cats showing an interhemispheric transfer, as expressed by their contralateral eye response, all other cells had a monocular response to the ipsilateral eye. An ipsilateral monocular response was found in the chronic OCX-CCX cats, even for long survival periods (17.0 months). The result for the OCX cats was similar, as indicated by the major ipsilateral response and the small proportion of cells showing an interhemispheric transfer. No improvement was found with postoperative time; acute OCX cats had 5.0% cells with contralateral input and 1-7 months chronic cats had 1.7-6.5% of these cells. These animals have thus split brain from point of view of the visual cortex; each hemisphere is therefore independent of the other one as far as neuronal functions are concerned. A remarkable reduction in binocularity was found following callosal transection (CCX) both in acute (41.4% binocularly driven cells) and in 3-39 months chronic cats (45.5% cells), in comparison to the control cats (74.2%). This indicates that elimination of the corpus callosum as itself enhances the binocularity diminution in split brain cats. The reduction found in visual responsiveness in our split brain cats (total: 63.2% unresponsive cells), is attributed to the summation of the individual effects of the optic chiasm and corpus callosum transections. A consistent tendency was found in the long chronic in comparison to the acute OCX-CCX, OCX, and CCX cats for a decrease in the responsiveness level with survival time; however, the short chronic OCX-CCX and CCX cats had the maximal proportion of unresponsive cells. It was concluded that the split brain induced in adult cats has a permanent effect on interhemispheric transfer to visual cortex cells. The absence of interhemispheric interaction under these conditions is not compensated by either transfer through anterior parts of the corpus callosum or through other commissures.

Animals↗

PubMed1987

Unilateral visual cortex deafferentation induces changes in receptive field properties of cortical cells in the intact hemisphere of normal and of monocularly deprived cats.

Receptive field properties and the selectivity of cortical cells to visual stimulation were studied in the visual cortices (the boundary between areas 17 and 18) of both hemispheres following unilateral deafferentation in normal and in early monocularly deprived cats. Almost no visual activity was encountered in the deafferented hemisphere and a considerable diminution in visual responsiveness was found in the intact hemisphere of all experimental cats. Responsiveness had increased with recovery time; unresponsive cells had consisted 44.6% of the cells in the intact hemisphere of the acute, 34.7% in the 3-month chronic and 14.5% in the normal cats. Disregarding the bias due to an early monocular deprivation, the ocular dominance distribution of the cells in the intact hemispheres of these cats was unaffected. Selectivity was markedly reduced in the intact hemisphere of the deafferented cats as expressed mainly in the increased orientation tuning range and in the proportion of orientation-selective cells. The proportion of these cells was 45.5% in the deafferented cats, 38.6% in the deafferented monocularly deprived cats, 65.3% in the monocularly deprived and 81.9% in the normal control cats. A similar trend, although less prominent, was found in respect to the proportion of direction-selective cells. The size of receptive fields was only slightly affected in the deafferented deprived cats. Receptive fields were considerably larger in size (length) in the deafferented cats in comparison to their respective normal and monocularly deprived controls. It is concluded that the absence of visual input from the deafferented hemisphere is bidirectionally affecting the corpus callosum.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗

PubMed1987

The deafferented visual cortex: neuronal activity and visual evoked potentials.

The callosal transfer of information to the visual cortex following its unilateral deafferentation from its geniculate input was studied in both hemispheres. Deafferentation was performed in adult cats by sectioning the optic tract. Action potentials of single cortical cells and visual evoked potentials were recorded from area 17-18 boundary in acute and chronic operated cats. In the deafferented hemisphere, cortical cells were usually visually inactive. However, some recovery of function took place in this hemisphere in the chronic cats, as expressed by the increase in the proportion of S-cells. In the intact hemisphere diminution of responsiveness and reduction of selectivity to the stimulus orientation and direction were found. The responsiveness and selectivity level in the intact hemisphere increased with postoperative time. The ocular dominance distribution in this hemisphere was similar to that of our normal control cats. The characteristics of the visual evoked potentials were in keeping with the hemispheric dominance of the cortical cells found in the experimental cats. It was concluded that a plasticity related mechanism is involved in the recovery of callosal activation of visual cortical cells following deafferentation.

Animals↗

PubMed1986

Hypermetropia in dark reared chicks and the effect of lid suture.

Two experimental groups of domestic fowl chicks were reared in darkness. One group was normal (DR) and the second had unilateral lid closure (DRC). A control group was reared in normal illumination (LR). The optical components of the eye were examined by retinoscopy, keratometry and phacometry while physical measurements were made using ultrasonography and micrometry. The DR chicks developed a significant hyperopia (+3.11 D) compared to the LR chicks (+0.65 D), attributed to a significant decrease in corneal height and lens thickness. A significant increase in the anteroposterior axis of the DR chicks tends to reduce the dark induced hyperopia. Lid closure in the DRC chicks increases the hyperopic effect by +3.07 D due to additional corneal flattening. These results reinforce our proposal of the chick eye as a model for research in the various forms of ametropia.

Animals↗

PubMed1985

Optic chiasm split and binocularity diminution in cortical cells of acute and of chronic operated adult cats.

The ocular dominance, responsiveness level and receptive field properties of single cortical cells were studied in 12 acute and chronic split chiasm adult cats (729 cells) and in 13 normal controls (544 cells). Recording was made from the border between visual areas 17/18. Responsive cells in the operated cats were obtained exclusively (87.1%) following stimulation of the ipsilateral eye, except for a very few cells (2.5%) which were binocularly driven. In comparison, only few (10.9%) of the cells in the normal control cats were driven ipsilaterally and the majority of them (74.5%) were binocularly driven. Relatively small proportions of cells (46.1%) were visually responsive in the acute (less than 1 week postoperatively) and in the most chronic (greater than 6 months) cats, in comparison to the normal cats (87.3%). No consistent change was found in the responsiveness level of cortical cells as function of length of the survival time (correlation coefficient: -0.45). Only a very slight tendency for a relative increase in binocularly driven cells with survival time was found as well as a reduction in the proportion of nonspecific cells. However, in view of the general absence of binocularity and responsivity in these cats, it was concluded that no recovery was found, even long after the elimination of the contralateral inputs.

Animals↗

PubMed1984

Properties of visual cortical cells of the intact and the deafferented hemisphere of unilateral optic tract sectioned acute and chronic adult cats.

Single unit recording from visual cortex areas 17 and 18 and in the border region between them was performed on adult cats with unilateral optic tract section (OTX) either on the day of the operation (acute) or three to six months postoperatively (chronic). Visual activity from both hemispheres was analyzed with respect to the responsiveness level, the ocular dominance distribution and selectivity to orientation and direction. The results showed almost a complete absence of visual responsiveness in the deafferented hemisphere and a considerable reduction of responsiveness in the intact hemisphere. Following surgery an increase in visually responsive cells was found in the intact hemisphere as postoperative recovery continued. In addition, a reduction in the proportion of cells selective for orientation and direction was also found in the intact hemisphere of the OTX animals as compared to the control cats. Furthermore, cortical binocularity was not affected in the intact hemisphere of all OTX cats. We conclude that an almost total absence of interhemispheric callosal transfer of visual functions from the intact to the deafferented hemisphere is induced as a result of the unilateral OTX in adult cats. Moreover, the fact that the absence of cortical binocularity in the hemisphere receiving direct geniculate input was not disrupted, indicates the absence of callosal transfer from the deafferented to the intact hemisphere.

Animals↗

PubMed1984

Ocular dominance of cortical cells in cats dark-reared into maturity after short postnatal monocular deprivation.

We studied the preservation of the early monocular deprivation effect by rearing kittens in complete darkness for long periods (9.5 to 20 months) after a monocular deprivation period of 4 weeks that was initiated at the age of 1 month (MDDR cats). For comparison, four groups of kittens were used: monocularly deprived as those described above and then reared in normal light conditions (MDN), monocularly deprived at the age of 1 month (MD), and dark-reared (DR) or normally light-reared (NOR) from birth. Recordings from the visual cortex of MDDR and MDN cats showed that there was a clear preference for cells driven only by the experienced eye compared with the deprived eye. This preference was found whether, subsequent to the monocular deprivation period, these cats were dark- or light-reared (P less than 0.005 for MDDR and MDN compared with NOR cats). The difference between the MDDR, MDN, and MD groups of cats was reflected in the proportions of binocularly driven cells; the largest number of binocularly driven cells was found in the MDDR cats. There was no bias toward either eye in the ocular dominance distribution of cortical cells in cats that were reared in total darkness (DR) or in the light under normal conditions (NOR). We thus conclude that the long-term dark period during development did not erase the effect of early monocular deprivation on the cat visual cortex provided that the latter lasted 4 weeks prior to the dark period.

Animals↗

PubMed1984

Deafferentation of the visual cortex: the effect on cortical cells in normal and in early monocularly deprived cats.

The optic tract was unilaterally transected and receptive field mapping and unit recordings were made for cells in the boundary of areas 17-18 in the deafferented and in the intact visual cortex of adult cats monocularly deprived during the critical developmental period. Three groups of adult animals served as controls: normal cats, early monocularly deprived (MD) cats, and optic tract transected cats. In contrast to the activity found in the intact hemisphere, the deafferented hemisphere of the experimental group was almost completely unresponsive. The ocular dominance distribution in the intact hemisphere of the experimental group (75.0% cells monocularly driven by the normal eye) was similar to that of the control MD cats (78.1%). This indicates that cutting the optic tract after the critical period does not affect the ocular dominance distribution of cortical cells induced in the intact hemisphere by early monocular deprivation. The reduction found in the proportion of visually responsive cells and the orientation and direction selective cells in the intact hemisphere of the experimental group, is mainly due to the isolation of the fellow hemisphere from its direct visual input, and the subsequent inactivation of the callosal pathway interconnecting the two visual areas.

Afferent Pathways↗

PubMed1984

Survival of early monocular deprivation effects in cortical cells of kittens following prolonged dark rearing.

To study whether early visual experience survives the absence of consequent visual stimulation during development, experimental kittens were reared in the dark for 5-13.5 months following monocular deprivation (MD) periods of 2-11 weeks which were initiated at the time of natural eye opening (MD-dark). For comparison, experimental kittens, normally reared after equivalent MD periods (MD-bino.), were also studied. Cats raised with permanent MD, dark-reared cats and normal cats, served as controls. The proportion of responsive cells was considerably reduced by the dark-rearing. It was especially reduced for the MD-dark kittens following monocular deprivation limited to the first postnatal month (58.3% responsive cells) in comparison to the equivalent group of MD-bino. kittens (80.5%). This is also in keeping with the diminution in cortical responsiveness obtained in the kittens which were dark-reared from birth (55.5%). The responsiveness level found in the normal control cats was 87.3%. It was found that the duration of the MD period prior to the dark-rearing period was directly related to the ocular dominance (OD) distribution of cortical cells. The susceptibility period to MD in both MD-dark and MD-bino. groups ends at approximately 3 months of age; the lower limit for the susceptibility period is at approximately 1-2 weeks after natural eye opening. The main period of sensitivity within this period of time is the first 4 postnatal weeks following natural eye opening. It is concluded that once the effect of monocular deprivation has been established, it will survive for the rest of the cat's life, even under conditions of complete absence of consequent visual stimulation. Furthermore, a certain degree of consolidation of the MD effect takes place in the light (i.e. in MD-bino. cats) despite their return to normal binocular vision. A somewhat opposite occurrence takes place in the dark (in MD-dark cats) with a tendency for masking of the MD effect previously induced in the light to be found.

Aging↗