Biomedical subjects

U Yinon

Publications and source records attributed to U Yinon.

At least 19 recordsLinked to original sources

PubMed2005

Columnar organization of the mammalian visual cortex and its vulnerability following lesion in adult cats.

It is well known that in the mammalian visual cortex the neurons, sharing similar response properties, are grouped together into functional units, known as cortical columns. The orientation and ocular dominance columnar organization is a fundamental element for both the anatomical and physiological features of the visual cortex. Nonetheless, little is known about the functional restoration of matured columnar columns following injury. In the present study, the visual cortex of adult cats was studied electrophysiologically, whereas the primary goal of the study was to reveal the functional stability of the columns, disconnected from the main visual input. Experiments were performed on the primary visual cortex (area 17) of 13 anaesthetized and paralyzed adult cats. The columnar distortion was produced by surgical incision perpendicular to the cortical columns. The single unit activity was recorded from 1186 visual cells (experimental groups) in areas proximal and distal to the lesion and, compared to data, received from intact visual cortex (control group). The results indicate that most of the visually responsive cells were found to be selective to specific orientation in all experimental groups (75-100%) similar to the normal control group (78%). Moreover, the distribution of orientation-specific cells was very similar in all experimental and control groups (p > 0.05), as well as in both recording areas (p > 0.05). The percentage of binocular cells was significantly lower in all experimental groups (23-49%) in comparison to the control (80%). However, the distribution of the binocular cells revealed the significant similarity between the experimental and control groups (p > 0.05). An additional finding of the study is that the visual responsiveness of cells was significantly reduced in all experimental groups: only 28-49% of cells were found to be responsive following injury, as compared to 86% in normal control group (p < 0.001). The distribution of cells has also been analysed in accordance with their directional specificity and it has been found that the majority of cells in the experimental groups were found to be bias and non-specific to light stimuli (52-84%) as compared normal controls (21%) (p < 0.001). It has been concluded that, despite the fact that no improvement in visual function was found, the inherent structure of the disrupted cortical columns in the visual cortex was generally preserved. Therefore, the disruption of the columnar connection does not lead to remarkable distortion of the connectivity pattern on the whole, though it does reduce the responsiveness level there. It was concluded that the columnar structure for both orientation and ocular dominance is characterized by high stability, which enables visual processing with minimal brain connections.

Animals↗

PubMed2002

Functional organization of columns in damaged visual cortex of adult cats.

OBJECTIVE: The objective of the present study was to reveal the amount of preservation of the most prominent features of the visual cortex: orientation and ocular dominance columns. It has been assumed that because of its inherent organization, the fragment of cells that would survive following lesioning would preserve the orientation and ocular dominance properties, despite the distortion of the connectivity pattern. EXPERIMENTAL: The experiments were carried out on 13 anesthetized and paralyzed adult cats from which 1,186 single cells were recorded. The animals were divided into the following three experimental (operated) groups to observe the time lapse of changes after operation: Acute (immediately); Short Chronic (2 to 3 months), and Long Chronic (5 to 7 months). The operations were performed using microsurgical, stereotaxic, electrophysiological, and histological techniques. The disconnection was produced by making a surgical incision into the visual cortex perpendicular to the cortical columns as accurately as possible. The single-unit activity of cells was recorded in the areas proximal and distal to the lesion. RESULTS: In all groups, the visual responsiveness of the cells was significantly reduced and the percentage of binocular cells was significantly lower in all recording sites. The distribution of the cells according to their ocular dominance was similar to that in the normal control group. Surprisingly, most of the cells, that remained visually active, were found selective to orientation in all experimental groups as well as in the normal control group. CONCLUSION: Even though no improvement in function occurred because mature cells were involved, the inherent structure of the disrupted cortical columns in the visual cortex was preserved. Therefore, the disruption of cortical connections does not lead to remarkable distortion of the inherent connectivity pattern on the whole in visually active cortical fragments.

Animals↗

PubMed2001

Responses to animated contours of neurons in visual cortex area 18 of the cat.

Given that cells in visual cortical area 18 in cats encode information of complex shapes, in addition to conventional stimuli like bars and gratings, we studied the capability of single cells in this area to 'identify' animated contours. The recorded cells were not selective to specific animated contours, whereas they were highly sensitive to the contour's degradation and to the orientation of its elements. The results indicate that cells in area 18 can encode information about many characteristics of complex animated patterns. The findings suggest the existence of a contour abstracting mechanism, which needs further study.

Animals↗

PubMed2000

Pathological and experimentally induced blindness induces auditory activity in the cat primary visual cortex.

Early blindness in humans and experimental visual deprivation in animal models are known to induce compensatory somatosensory and/or auditory activation of the visual cortex. An abnormal hydrocephalic cat with extreme malformation of the visual system, born in our breeding colony, rendered a good model system for investigating possible cross-modal compensation in such a pathological case. For comparison, we used normal and neonatally enucleated cats. When introduced to a novel environment, the abnormal cat behaved as if it was completely blind, yet it responded normally to auditory stimuli. As anticipated, single cells in the visual cortex of normal cats responded to visual, but not to auditory stimuli. In the visual cortex of enucleated cats, flashes of light did not elicit field-evoked potentials or single-unit responses. However, several cells did respond to various auditory stimuli. In the remnant visual cortex of the abnormal cat, auditory stimuli evoked field potentials and single-cell responses. Unexpectedly, however, unlike the enucleated cats, in the abnormal cat, flashes of light also elicited field-evoked potentials. Judging by its behavior, it is very likely that this deformed cat had completely lost its ability to perceive images, but had probably retained some sensitivity to light.

Abnormalities, Multiple↗

PubMed2000

[Visual, auditory, and bimodal activity in the banks of the lateral suprasylvian sulcus in the cat].

In addition to visually driven cells we found within the lateral suprasylvian visual cortex of cats a considerable number of auditory and/or bimodal cells. Most of the visually driven cells were direction and orientation selective with responses that were neither highly stimulus time locked nor very stable. Most of the auditory responses were also not very stable, had relatively high thresholds and were readily habituated. Previous studies have suggested that populations of cells within the lateral suprasylvian area are specialized for the analysis of optic flow fields. Given that a remarkable proportion of cells within this area can be also driven by auditory stimuli we hypothesize that the "optic flow" model may be extended to the bimodal domain rather than restricted to visual clues only. This, however, remains to be corroborated experimentally.

Animals↗

PubMed1999

Auditory activation of cortical visual areas in cats after early visual deprivation.

Auditory activation of the primary visual cortex (area 17) and two extrastriate visual cortical areas - the anterolateral lateral suprasylvian area (ALLS) and anteromedial lateral suprasylvian area (AMLS), was investigated in visually impaired cats. Impairment was accomplished shortly after birth by bilateral eyelid suturing (binocularly deprived cats, BD) or bilateral enucleation (binocularly enucleated cats, BE). In BE cats, the optic nerve and chiasm were entirely degenerated. No cortical atrophy or cytoarchitectural malformation was noticed in either BD or BE cats. In both normal and impaired cats we found auditory-responsive cells in the ALLS and AMLS, areas that are considered strictly visual. The most remarkable finding was an increase in the relative number of these auditory cells in the BD and BE cats, which was more prominent in the latter. Some auditory-responsive cells were also found in area 17 of BE cats. On the basis of formal calculation, it is tempting to suggest that the increase in relative number of auditory cells in these areas reflects the transformation of all the visual cells in the ALLS of BD and BE cats into auditory cells. In BE cats, all bimodal cells and an appreciable percentage of non-responsive cells also had transformed to auditory cells. In the AMLS of BD cats, it is primarily the bimodal cells that become auditory cells, whereas in BE cats all the visual and bimodal cells as well as non-responsive cells undergo this transformation. This assumption, however, is one possible interpretation of our results but not the only one. Other modes of neuronal plasticity that might yield similar results in the visually deprived cats can not be ruled out.

Acoustic Stimulation↗

PubMed1998

Electrophysiological studies on the effects on single cells of silver electrodes implanted in the visual cortex of cats.

We have studied whether the presence of an artificial metal conductor in the visual cortex has an effect on the responsiveness pattern of the cells there. The physiological properties of single cells have been characterized in the mammalian primary visual cortex, following the acute and chronic implantation of silver wire electrodes. The Experimental group was Chronic and Acute operated and implanted adult cats. The Control group consisted of operated, but not implanted, adult cats and intact (Normal) adult cats. A sagittal incision was unilaterally made in the primary visual cortex (area 17) and a silver wire was implanted. Single cells were extracellularly recorded in the pre- and postincision regions following anesthesia and paralysis, 4-8 weeks following the implantation in the Chronic and immediately in the Acute group. The responsiveness, ocular dominance, receptive field properties, orientation, and direction selectively of the cells were examined. The responsiveness level was different in the preincision (afferented) regions of all operated groups. I was consistently affected compared with their deafferented region. The main effect was found on the binocularity of cells in all operated groups. The following are the differences found between the preincision and postincision regions. Our findings show that although a metal wire conductor implanted in the mammalian visual cortex has an effect on the efficiency of the cells there, chemically inert metals may serve in the future as artificial conductors in the brain.

Afferent Pathways↗

PubMed1997

Delta and kappa opioid receptors in eyestalk ganglia of a crustacean.

Crustacean eyestalk ganglia are part of the protocerebrum and have been demonstrated to produce numerous neurohormones. 3H(2-D-Pen, 5-D-Pen)-enkephalin, 3H-(-)-ethylketocyclazocine and 3H(D-Ala2-NMePhe-Glyol5)-enkephalin were used as ligands for opioid receptors on neuronal membrane preparations of eyestalk ganglia under consideration of their stereospecific binding properties. In context with saturation binding isotherms, association and dissociation plots, we demonstrate here two opioid receptors; a delta-type receptor with high affinity (Bmax 68.5 fmol/mg protein, Kd = 4.0 nM) and low affinity (Bmax 493 fmol/mg, Kd = 83.6 nM) and a second receptor of kappa-type with Bmax of 3.1 pmol/mg protein and Kd = 68.6 nM.

Animals↗

PubMed1996

Nonlinear responses of simple cells to Mach band stimuli: evidence from early monocularly deprived cats.

We have previously shown that, cat simple cells respond linearly to edges of variable blur widths: cells with receptive fields (RFs) of even symmetry respond better to a luminance ramp (where Mach bands are observed); cells with RFs of odd symmetry respond better to a luminance step (where no Mach bands are perceived). Our evidence has also indicated the existence of inhibitory interaction between cells with RFs of even and odd symmetry as predicted by the Tolhurst-Ratliff Mach band model. Since monocular deprivation is known to impair cortical inhibitory mechanisms, we studied the responses of simple cells of adult cats monocularly deprived at the age of 8-10 weeks to Mach band stimuli in order to delineate specific changes in inhibitory interactions caused by monocular deprivation. In pattern-deprived cats, particularly for cells driven by the deprived eye, there were many cells that responded contrary to linear models: odd-symmetric cells responded maximally to blurred edges while even-symmetric cells responded maximally to sharp edges. Cells that responded maximally as predicted, responded, similarly to normal cat cells, less than expected at suboptimal widths. All cells in normal and light-deprived cats responded in a linear fashion to sinusoidal stimuli. We conclude, therefore, that intracortical inhibition shapes simple cells' responses to edges. Monocular deprivation impairs this mechanism, thus causing simple cells in monocularly deprived cats to respond nonlinearly to edges. All simple cells responded linearly to gratings since it is not the linear spatiotemporal RF of these simple cells that was impaired under monocular deprivation.

Animals↗

PubMed1995

Physiological studies of visual cortex reorganization following cortical deafferentation in neonatal cats.

Whether restoration takes place in the visual cortex of neonates was physiologically studied in cortical cells of cats following their deafferentation. Deafferentation was performed by a parasagittal incision made in the visual cortex, separating the medial part of it from the thalamocortical and other visual fibers. Responsiveness (percentage of responsive cells) in the middle zone (the middle sector along the cortical incision) of the deafferented region was 82.5%, compared with 91.7% in the afferented (lateral to the incision) region (p = 0.5). In comparison, the responsiveness level was 32.3 and 81.3% (p < 0.05) in the respective zones of the similarly deafferented adult controls. The ocular dominance distribution and binocularity were almost normal in the deafferented region of the neonatally operated cats, whereas binocularity was remarkably diminished in the adult controls. Recovery was also found in the specificity of the cells to orientation and direction in the neonatally operated cats, but not in the adult-operated cats. Thus, functional reorganization of the columnar organizations takes place in the neonatally deafferented but not in the adult-operated cats.

Age Factors↗

PubMed1994

Visual hemispheric dominance induced in split brain cats during development: a model of deficient interhemispheric transfer derived from physiological evidence in single visual cortex cells.

The effects of cancellation of both interhemispheric callosal transfer and interocular interactions, were studied in early monocularly deprived cats. The main purpose of this study was therefore to prove whether unilateral hemispheric dominance would result under these conditions and to what extent each hemisphere will be functionally independent. Secondly, we have attempted to establish such an experimental model physiologically, on the single cell level. Interhemispheric transfer was surgically canceled by sagittal transection of the corpus callosum. In addition, the ocular projections were separated by sagittal transection of the optic chiasm in the transbuccal approach. This condition had practically induced visual split brain condition in these cats. These manipulations were carried out concurrently with monocular deprivation (SBDK group) which was surgically done by eye closure during the critical period of development of the visual system. Thus, the hemisphere ipsilaterally to the visually deprived eye had developed under conditions of deficient visual experience while the hemisphere ipsilaterally to the normal eye had developed under conditions of unaltered visual experience. A group of cats (SBK) similarly operated but equally binocularly exposed during development was served as controls. In addition, adult cats similarly operated during adulthood either chronically or acutely were studied to evaluate the effects of interhemispheric and interocular separation. Other groups of cats were also studied for comparison, and included sham operated and normal adult cats. At adulthood, electrophysiological studies were done on these cats, in which action potentials were extracellularly recorded from single cells in the visual cortex (area 17-18 boundary) following anesthesia and paralysis. Stimulation was carried out manually and by a computer driven optical system, presenting on a tangent screen light bars at various spatial positions, orientations and directions. Receptive fields were thus mapped for all neurons and their dimensions and eccentricities were measured. The responsiveness, ocular dominance and other parameters were also studied for these cells. The results in the early deprived cats and in their controls, had shown a full separation between the two hemispheres, as reflected in the almost absolute ipsilateral eye responsiveness (> 97.0% cells). In comparison, in the sham operated and in the normal control cats only minor proportions of cells (13.0-18.7%) have been found as ipsilaterally and monocularly driven, showing almost full interhemispheric and interocular interaction. The main difference, however, in the results between the early monocularly deprived cats and their controls is that in the first group the two hemispheres were asymmetric concerning the amount of visual activation and in the second one they were very symmetric.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1994

Simple cells may lie at the basis of mach bands: evidence from physiological studies in the cat's visual cortex.

Mach bands are a visual illusion evoked by a luminance ramp dividing two luminance plateaux (blurred edges), but not by sharp edges. Recently, two physiology-based models have tried to cope with the psychophysical data concerning this phenomenon. The basic components of both models are neurons with even- or odd-symmetric receptive fields (RFs). Both models predict that odd-symmetric cells respond better to sharp edges, while even-symmetric cells respond better to blurred ones. We have measured the responses of 34 primary visual cortex simple cells of the cat to blurred edges of various degrees. Twenty-one cells had RFs of even symmetry, responding best to blurred edges than to sharp ones. The rest were odd-symmetric cells, of which 12 responded best to sharp edges, and only one exceptional cell responded best to a 0.85 degrees-wide edge. Thus, the different cell types responded as predicted by the two different Mach band models. Simple cells may thus serve as the physiological basis of the psychophysical phenomenon of Mach bands. Furthermore, our evidence suggests the existence of inhibition between odd- and even-symmetric cells, as predicted by one of the models.

Animals↗

PubMed1993

Physiological studies in deafferented visual cortex cells of cats following transplantation of fetal xenografts from the rat's cortex.

We have studied the physiological properties of cells (N = 822) in visual cortex area 17 of seven adult cats transplanted with visual cortex xenografts from fetal (E15-E17) rats. The transplants were assumed to induce recovery of adjacent neurons partially deafferented from visual input. The control group (eight cats, 564 cells) had just analogous sectioning in the cortex. The level of activity found, following visual stimulation, in the deafferented cortical region (medially to the graft) was 48.6% compared to the result (34.5%) obtained in the control cats, indicating the preservation of visual responsiveness. Furthermore, no disturbance could be found in the ocular dominance distribution or binocularity (64.4%) of the cells in the grafted region compared to those in the control cats, indicating preservation of the columnar organization. The deafferented cells in the grafted cortex thus demonstrated the absence of adverse immunological reaction there due to the presence of the xenogeneic tissue, indicating that the visual cortex is immunologically privileged.

Afferent Pathways↗

PubMed1992

Binocularity and excitability loss in visual cortex cells of corpus callosum transected kittens and cats.

The contribution of the corpus callosum to binocularity of visual cortex cells and to their responsiveness was studied in cats. Electrophysiological recordings of the responses of single cells to visual stimulation was performed in the callosal projection zone, visual cortex area 17-18 boundary in callosotomized cats. Callosotomy was carried out by transection of the visual segment of the corpus callosum in 6-7-week-old kittens and in acute and chronic adult cats (postoperative recovery time: 11 days-39 months). While in our normal cats the common proportion of binocularly driven cells (79.8%) was found (66.3% in the sham controls), a remarkable diminution (29.7%) was found in the callosotomized kittens, in the acute (39.7%) and in the chronic (50.6%)-operated cats. We have also found a change in the amount of binocularity as function of postoperative recovery time. While the proportion of binocular cells was conceivable (60.7%) in the short- and intermediate-term callosotomized cats (postoperative time: 0.3-5.5 months), it was diminished (36.9%) in the long-term (6.5-39 months) chronic cats. As to the responsiveness level, it was found that visual responsive cells constituted 88% of the cells in the normal and 80.3% in the sham controls. In comparison, they constituted 69.2% in the acute, 54.4% in the chronic and 52.8% in the callosotomized kittens. Furthermore, callosal transection had produced a symmetric effect in the two hemispheres, regarding binocularity and responsiveness. It has been thus concluded that the corpus callosum is essential for the mediation of binocular functions between the two hemispheres; in addition, cortical excitability has been also found to depend on callosal integrity.

Animals↗

PubMed1991

Isochronic transplantation of neonatal grafts in the visual cortex of cats: responsiveness, ocular dominance and specificity of cortical cells to visual stimulation.

The visual cortex of adult cats was studied physiologically following neonatal isochronic transplantation of grafts from areas 17,18, which were placed homotopically, in order to reveal their functional integration and thus possible repairing of damaged cortical neuronal circuits. Three homograft cats, in which transplantation was carried out between siblings (228 cortical cells) were compared to 4 animals receiving reimplanted autografts of the equivalent size (131 cells) as well as 3 animals with analogous sectioning of the visual cortex (162 cells) (pseudograft controls). The location of the boundaries between the transplant region and the host were determined using the Nissl's method for staining histological cross sections. Extracellular unit recording revealed typical waveform of the action potentials in the transplanted region and in the surrounding host tissue of all groups of cats. Visual responsiveness in the homograft cats was 17.5% in the transplanted region and 80.4% in the unoperated hemisphere; the corresponding results were 40.3% for the transplanted region and 82.2% for the unoperated hemisphere in the autografts and 23.1% and 73.4% in the pseudografts. The specificity of the cells to visual stimulation as expressed by their orientation and direction specificity, indicated preservation of these properties in the transplanted cats. While all responsive cells in the transplanted region of the homografts were orientation specific, their proportion was 60% in the autografts and 55.5% in the analogous region in the pseudograft controls. As to the direction specific cells, their performance in the grafted region of the grafted cats was even much higher than that of the pseudograft controls. The ocular dominance distribution of the cells showed preservation of binocularity in the transplanted region (90.0% binocular cells) of the homografts; it was however smaller in the equivalent region of the autografts (65.0%) and remarkably reduced (20.0%) in the pseudografts. It was concluded that despite the deafferentation induced during the transplantation procedure, a remarkable visual responsiveness was found in the transplanted region, indicating postoperative recovery. However, the cells there were mainly affected in their activity and less in their specificity to visual stimulation.

Animals↗

PubMed1991

Cortical cells' physiology following visual split brain in developing cats.

We have studied physiologically whether visual cortex cells in areas 17 and 18 of split-brain cats preserve their performance despite the blockage of both binocularity and of interhemispheric communication. The absolute majority of the cells in cats underwent split-brain surgery as kittens and adults and were driven by the ipsilateral eye, resulting in the absence of interhemispheric interaction. Similar results were found in cats and kittens that underwent only chiasm split surgery, although some recovery of callosal transfer was found in the latter. A remarkable loss of binocularity was found when only callosal transection was performed, both in adult cats and in kittens, although some ipsilateral eye dominance was observed in the latter. As to the deprived cats, while in the inexperienced hemisphere (ipsilateral to the deprived eye), the majority of the cells was visually unresponsive, in the contralateral (experienced) hemisphere, the majority was responsive. A considerable reduction in responsiveness was found in the callosally transected cats and kittens. Generally, a degradation of function was found in the various properties as a result of chiasmal and/or callosal transection. The main effect is the increased number of cells with diffuse and incomplete receptive fields. There was also a reduction in the proportion of orientation-selective cells, mainly in the split-brain cats. It was concluded that, despite the high amount of hemispheric independency in the normal brain, the integrity and simultaneous action of the two hemispheres are needed for the normal functioning of visual cortex cells.

Aging↗

PubMed1991

Intraocular retinal transplantation: a review.

This review covers intraocular transplantation of retinal tissue. This has importance both for theoretical understanding of retinal and neural development and for possible future clinical application. Transplantation sites have ranged from the anterior chamber through the retina to the subretinal space. Transplanted tissue has ranged from whole retina to specific retinal layers or specific types of retinal cells. Both within-species and inter-species transplants have been performed, and donor age has ranged from embryonic to adult. The ability of transplanted tissue to be accepted and to differentiate in host eyes has been studied. The conditions under which successful transplants are obtained, host-graft interactions, and transplantation methodologies have been explored. Morphological, and to a small extent, also functional characteristics of the transplants have been studied.

Animals↗

PubMed1990

Post-critical period plasticity of callosal transfer to visual cortex cells of cats following early conditioning of monocular deprivation and late optic chiasm transection.

We studied whether plasticity-induced callosal transfer exists after the critical period for sensitivity of visual cortex cells in kittens postnatally monocularly deprived and in which interocular competition was cancelled by chiasm transection during adulthood. Callosal transfer was studied acutely (n = 3 cats) and chronically (n = 7) following the chiasm transection (OCAMD). For comparison, adult cats in which chiasm transection only was performed (OCA) were also studied acutely (n = 3) and chronically (n = 9). The results were also compared to cats in which monocular deprivation and chiasm transection were simultaneously performed (OCKMD) during development (n = 6) and to normal control cats (n = 18). Unit recording was extracellularly carried out in visual cortex areas 17 and 18 and their boundary region, where the corpus callosum is represented. When no interocular competition was allowed between the non-deprived and the deprived eye via the thalamocortical direct visual pathways on cortical cells, such as in the OCKMD cats, the absolute majority of the cells were ipsilaterally driven, regardless of which hemisphere was studied. Only a minor proportion (4.1%) of the cells had some contralateral input from the non-deprived eye in the hemisphere ipsilateral to the deprived eye, indicating almost no interhemispheric callosal transfer. A slight increase in the proportion of cells callosally driven from the non-deprived eye (9.8%), was found in this hemisphere in cats in which interocular competition was allowed via the direct visual pathways prior to its cancellation by chiasm transection (OCAMD), if studied acutely after the chiasm transection. A remarkable increase in callosal transfer was found in this hemisphere under chronic conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗