PubMed Health⌕ Search

Biomedical subjects

N Berman

Publications and source records attributed to N Berman.

At least 109 records · Page 6Linked to original sources
PubMed1977

The central projections in the retina in Necturus maculosus.

The projections of the retina in Necturus maculosus were studied by injecting radioactive proline into one eye. Labeling was seen in both the contralateral and ipsilateral diencephalon and tectum. The contralateral fibers are divided into three major tracts: the marginal, axial, and basal. The ipsilateral fibers separate into a marginal and an axial optic tract. The contralateral and ipsilateral axial optic tracts have a similar distribution. The contralateral and ipsilateral marginal optic tracts projecting to the diencephalon also have a similar distribution. However, in the tectum the ipsilateral marginal optic tract ends in the anterior third while the contralateral extends almost the entire length of the tectum. The retinotectal ipsilateral projection ends in clumps as has been described in other vetebrates. A direct ipsilateral retinotectal projection has not been described in any other amphibian.

Animals↗
PubMed1977

Comparison of the critical periods for monocular and directional deprivation in cats.

1. Earlier experiments rearing kittens with one eye closed and reversing the closure after a certain age, or rearing kittens in a rotating drum and reversing the direction after a certain age, suggest that the critical periods for ocular dominance and directional sensitivity may differ. Since these results were obtained by different investigators in different laboratories, we have made a direct comparison of the two types of visual deprivation. 2. Four pairs of litter-mate kittens (matched in weight) were reared. One animal in each pair was monocularly deprived with subsequent eye reversal; the other animal was directionally deprived with reversal of drum direction. All reversals took place at age 5 weeks. Both kittens in a given pair were either 'left first' (left eye open first or left direction first) or both were right first. One died prematurely. 3. Recordings were made from the visual cortex at some age after 4 months. Some recordings were made in the left cortex and some in the right. In all cases of monocular deprivation, the majority of cells were driven by the eye that was open last (i.e. open after 5 weeks of age). In all cases of directional deprivation, the majority of the cells preferred movement in the first direction of exposure (i.e. the direction before 5 weeks of age). 4. We conclude that the critical period for directional deprivation terminates earlier than the critical period for monocular deprivation.

Animals↗
PubMed1976

Early versus late visual cortex lesions: effects on receptive fields in cat superior colliculus.

Cats that sustain lesions of the visual cortex early in life appear to perform certain visual discrimination tasks better than those operated as adults. This study sought to determine whether this recovery is visual capacities was accompanied by reorganization of single cell responses at the level of the superior colliculus. Areas 17 and 18 were ablated in adult cats and in kittens at various times during the neonatal period. Responses of units in superior colliculus ipsilateral to the lesion were recorded following a prolonged recovery period. Following cortical lesions, collicular units rarely exhibited direction selectivity, binocularity was reduced in the majority of animals, and the ocular dominance distribution was biased toward the contralateral eye. The reduction of direction selectivity and binocularity were unrelated to the animal's age at operation.

Age Factors↗
PubMed1976

Recovery of function in cat visual cortex following prolonged deprivation.

Evidence that there is a critical period during which response characteristics of neurons in visual cortex of the cat may be influenced has been provided in several studied, which suggest that the period of influence is restricted to the first few months of life. Using a somewhat different experimental procedure, we have obtained evidence that cortical units retain plasticity long after the end of this period has passed. In our procedure prolonged visual deprivation was followed by exposure in a normal visual environment. The animals were maintained throughout the first year of life either in total darkness or in an enclosure illuminated intermittently by a strobe light. Following the period of deprivation, electrophysiologic recordings were taken from some of these animals. The remaining cats were permitted 6-12 months in a normally-illuminated environment prior to recording. Cats of the same age reared from birth in a normally lit environment were also recorded. Cortical neurons in cats deprived of any normal visual experience rarely show orientation selective responses. In animals allowed subsequent normal visual experience about one-half of the units studied exhibited this property. This level of response specificity is intermediate between that of normally-reared and recently-deprived animals. While most cortical units in normally-reared cats exhibited direction selectivity, this property is rarely observed in the "recovery" cats. A number of unit types which are rarely observed in either normal or totally deprived animals were encountered in cats that had normal exposure following prolonged deprivation. A convergent strabismus was observed, in contrast with the divergent strabismus often shown by cats immediately following prolonged visual deprivation. This shows that ocular alignment as well as cortical unit properties can remain plastic in the adult.

Blindness↗
PubMed1976

Halfway house residents: where do they go?

Three community-based nonmedical halfway houses for recently released mentally ill patients were surveyed to determine where the halfway house residents relocated following termination. Of 60 successful ex-residents, 36 were seen to relocate within 1 mile (street mileage) of the halfway house. This appeared to be significantly different from the number who may have lived within 1 mile of the halfway house before residence in the halfway house. The halfway house staff reported that the main determinant of the terminees remaining in the vicinity was the continuance of formal and informal supportive relationships that had been established during the period of residence. This finding was briefly discussed as to possible implications for planning and treatment related to halfway house programs.

Adult↗
PubMed1976

Cortical suppression of the ritino-collicular pathway in the monocularly deprived cat.

1. In nine cats monocularly deprived from birth, the responses of single neurones in the superior colliculus contralateral to the deprived eye were studied. 2. In six animals most units could be driven by visual stimuli only through the ipsilateral (experienced) eye despite the fact that this colliculus receives a major input from the contralateral (deprived) retina. 3. Immediately following removal of visual cortex, including areas 17, 18 and 19, the collicular units could be driven by the deprived eye. 4. We conclude that the cortex must exert a powerful suppression of the retino-collicular input, and we argue that this suppression occurs in normal as well as in monocularly deprived animals. 5. In three animals the retinal input from the deprived eye was not suppressed but instead dominated many collicular celld, apparently to the exclusion of the cortical input from the experienced eye.

Animals↗
PubMed1975

Cats raised in a one-directional world: effects on receptive fields in visual cortex and superior colliculus.

Cats were reared in a visual environment in which irregularly-shaped patches of luminescent paint moved constantly leftward. The distribution of preferred directions and orientations of cortical neurons in these cats was examined. Most cortical neurons encountered had leftward components in their preferred directions, and although no anisotropy of orientation was present in the rearing environment, most cortical neurons responded optimally to stimuli oriented at or near vertical. Variations in the strength of the induced bias of direction and orientation were noted among the different subclasses of cortical neurons. Preferred velocities of cortical neurons did not appear matched to the velocity of stimuli in the rearing environment. The ocular dominance distribution among cortical neurons in the unidirectional cats was skewed toward the contralateral eye relative to normal cats. The distribution of preferred directions in collicular neurons was largely unaltered by the rearing procedures employed. As in normal cats, units in the left colliculus more frequently responded best to rightward stimulus movement while those in the right colliculus preferred leftward movement. The ocular dominance distribution among collicular units was somewhat skewed toward the contralateral eye.

Animals↗
PubMed1975

Thrombotic thrombocytopenic purpura in childhood.

A survey was conducted among 46 pediatric institutions in the United States and Canada to evaluate the presentation, therapy and survival of children with thrombocytopenic purpura (TTP) seen since 1960. TTP is an uncommon disease in the pediatric age group, and the clinical and pathologic findings in adults and children are almost identical. It can be distinguished from haemolytic uraemic syndrome in that it usually occurs in older children, the renal disease is milder, and the central nervous system symptoms appear to be related to vascular occlusive disease, and not to the complications of severely compromised kidneys. Appropriate biopsy specimens which reveal typical widespread hyaline occlusion of arterioles may confirm the diagnosis. Combinations of corticosteroids, splenectomy, and heparin have been used as therapy. Prognosis has improved, and is probably related to improved supportive care.

Adolescent↗
PubMed1975

Receptive fields in cat superior colliculus after visual cortex lesions.

1. The superior colliculus has been studied in intact cats and in cats with visual cortex lexions by recording the responses of single tectal units to visual stimuli. 2. Three classes of units have been identified in the superficial layers of the colliculus in these visually decorticate cats. 3. One class, comprising 5% of the units studied, has receptive fields organized concentrically in a manner similar to retinal ganglion cells. 4. The second class, comprising 12% of the units studied, responds to stimulus velocities over 300/sec, responds well to both small and large stimuli, and can be driven by strobe flashes at frequencies up to 35--40/sec. These units are termed 'flicker' cells. 5. The third class comprising 83% of the units studied, responds best to stimuli which are not larger than the activating region of the receptive field, moving at relatively low velocities. These units show strong suppressive surrounds which are sensitive to higher velocities of stimulus movement than the central activating region. Responses from the activating region in these units are dramatically inhibited by flickering dhanges in the level of background illumination. 6. In intact cats few units are found which are strongly inhibited by background flicker. 7. It is suggested that a high-velocity sensitive element such as the 'flicker' cell or phasic retinal ganglion cell is responsible for the flicker-induced inhibition of collicular units in the visually decorticate cat.

Action Potentials↗
PubMed1975

Binocular interaction in the cat's superior colliculus.

1. Binocularly driven neurones with small receptive fields near the area centralis were recorded in the cat's superior colliculus. 2. Binocular interaction was tested by stimulating both eyes simultaneously with a single moving stimulus at various retinal disparities. 3. Collicular cells in general showed strong summation or even facilitation when the images of the stimulus were in exact correspondence on the receptive fields, sometimes with occlusion when they were out of register. The range of retinal disparity over which there was additive interaction could be as little as 1 or 2 deg, almost as narrow as for the most precisely tuned neurones in the visual cortex. Even cells with large receptive fields sometimes showed a narrow range of binocular interaction. 4. Non-directional cells generally exhibited weaker summation and broader disparity selectivity than did direction-selective cells. 5. Some neurones with virtually no response to a stimulus in one of the eyes can exhibit marked binocular interaction. Other apparently monocular cells show little or no binocular interaction. 6. The disparity of the centres of the receptive fields was measured after correcting for small eye movements, which were assessed by two different techniques. For 132 cells the measured distribution of horizontal disparity (range 4.5 deg; S.D. 0.93 deg) was significantly broader than that of vertical disparity (range 2.2 deg; S.D. 0.52 deg). Sources of error in these measurements are considered. 7. The results are discussed in relation to the known connexions between visual cortex and superior colliculus and the possible role of the latter in the regulation of eye movements.

Action Potentials↗
PubMed1973

Cats reared in stroboscopic illumination: effects on receptive fields in visual cortex.

Cats were reared in a light-tight box in which the only source of illumination was a 9-musec strobe flash every 2 sec. This allowed them to experience visual form but they did not experience visual movement. Receptive-field properties of single units in area 17 of the visual cortex of cats reared in stroboscopic illumination (strobe-reared) were compared with properties of units in area 17 of normally reared cats. In strobe-reared cats both direction selectivity and orientation selectivity were greatly reduced relative to normally reared cats, and some units in the strobe-reared cats responded only to strobe flashes.

Animals↗
PubMed1972

Comparison of receptive-field organization of the superior colliculus in Siamese and normal cats.

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 degrees 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 degrees 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 degrees 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.

Animals↗