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Biomedical subjects

W Singer

Publications and source records attributed to W Singer.

At least 217 records · Page 12Linked to original sources
PubMed1980

Phasic electrodermal responses after visual stimulation in the cortically blind hemifield.

Phasic electrodermal responses were recorded after presenting targets within the blind part of the visual field to patients with damage to the geniculostriate pathway. The results suggest that the electrodermal component of the orienting response can also be elicited after damage to the visual cortex. The electrodermal responses are interpreted in terms of registration of a visual stimulus. This registration seems to be mediated by extrastriate pathways.

Dominance, Cerebral↗
PubMed1980

Pituitary adenomas in old age.

Pituitaries obtained at unselected autopsies of 152 men and women over 80 years of age, dying of different diseases, have been investigated histologically by using various staining procedures, including the immunoperoxidase technique. In 20 pituitaries, 22 adenomas were found providing evidence that these tumors are common in aging subjects. In 9 adenomas out of 17 cases, the immunoperoxidase technique revealed the presence of prolactin, indicating that prolactin-producing adenomas constitute the most frequently occurring pituitary tumor type in old age. The presence of growth hormone was demonstrated in one adenoma which also contained prolactin. No storage of ACTH, FSH, LH or TSH was found in the tumors. The biologic behavior of pituitary adenomas disclosed as incidental findings in old age remains to be elucidated. These neoplasms may have a slower growth rate, but more work is required to establish whether they differ from those found in younger age groups.

Adenoma↗
PubMed1980

Monocular activation of visual cortex in normal and monocularly deprived cats: an analysis of evoked potentials.

The unilaterally induced patterns of prominent excitatory post-synaptic activity within Areas 17 and 18 were investigated in normal and monocularly deprived cats. They were elicited by electrical stimulation of the optic nerves and evaluated with the one-dimensional current source-density method. 1. In Area 18 of normal cats the unilaterally and bilaterally induced current source-density patterns closely resemble each other. None of the mono-, di- or tri-synaptic activities is potentiated by binocular convergence. 2. In Area 18 of monocularly deprived cats the synaptic currents elicited by stimulating the nerve on the deprived side lead to approximately the same spatial and temporal distribution of sinks and sources as those induced from the normal eye; but the amplitudes are considerably smaller. This reduction is similar for mono-, di- and trisynaptic responses which indicates (a) that the imbalance between activity from the deprived and non-deprived eye is mainly due to reduced input to the cortical target cells from the deprived eye and (b) that the activity from the deprived eye still relayed to these cells is passed on to supra- and infragranular layers without diminution and in the same way as activity from the normal eye. 3. The imbalance of afferent activity from the deprived and non-deprived eye is apparent in the evoked potentials recorded from the white matter. This indicates that activity from the deprived eye is already strongly reduced in the thalamo-cortical fibres. 4. In monocularly deprived, but not in normal cats the monosynaptic activities from the two eyes are often segregated in depth within layer IV. 5. In Area 17 of both normal and deprived cats only a small fraction of the potential monosynaptic activity can be elicited by electrical stimulation of the optic nerves because of transmission failure in the lateral geniculate nucleus. Comparison of the current source-density patterns elicited from the normal and deprived nerve in monocularly deprived cats indicates that activity produced by fast conducting afferents is more affected (reduced) by deprivation that that conveyed by slower afferents.

Animals↗
PubMed1980

Silent corticotropic adenomas of the human pituitary gland: a histologic, immunocytologic, and ultrastructural study.

Among 300 surgically removed pituitary adenomas, 17 tumors containing immunoreactive 1-39 adrenocorticotropin (ACTH) and/or 19-39 ACTH, beta-lipotropin, and alpha-endorphin but unassociated with clinical signs of Cushing's disease have been detected. These neoplasms were divided into basophilic adenomas with strong periodic acid-Schiff (PAS) and lead-hematoxylin positivity and chromophobic tumors with moderate or no PAS and lead-hematoxylin positivity. The former were densely granulated tumors with a fine structure strikingly similar to that of functioning corticotropic cell adenomas. The latter were sparsely granulated with varying ultrastructural patterns. The marked morphologic diversity suggests that these adenomas, despite their similar immunocytologic characteristics, represent more than one entity. Clinically, the most common finding was a rapidly progressing visual defect. An unusually high incidence of infarction (5 cases) and recurrence (5 cases) was noted, underlining the importance of correct morphologic diagnosis and careful follow-up.

Adenoma↗
PubMed1979

Excitatory synaptic ensemble properties in the visual cortex of the macaque monkey: a current source density analysis of electrically evoked potentials.

The spatio-temporal distributions of excitatory synaptic ensemble activities in A17 and A18 of the visual cortex of the macaque monkey have been investigated. The synaptic activities were elicited by electrical stimulation of the primary efferents and were localized by applying the current source density analysis to the intracortically recorded field potentials. The principal results are as follows: 1. In A17, two groups of activity, evoked by fast and slow afferents, respectively, were distinguishable. 2. The fast afferents induced monosynaptic activity in layer IV C alpha and layer VI, disynaptic activity in layer IV C alpha and in the supragranular layers and trisynaptic activity in layer IV B. 3. The slow efferents induced monosynaptic activity in lower layers IV C beta and layer VI, disynaptic activity via strong connections in upper layer IV C beta, further disynaptic activity in layers III and IV B and trisynaptic activity in layers V A and II. 4. With the exception that the CSD data reveal more polysynaptic activity within layer IV, there is good agreement between the spatio-temporal distribution of synaptic activities and the cortical circuit diagrams proposed in anatomical studies. 5. In A18, activities from the slow and fast conducting afferent systems are revealed in layer IV, both most likely mediated by the monosynaptically activated target cells of A17. These activities are passed on to the supra-and infragranular layers. 6. In the lateral geniculate nucleus the safety factor of transmission is higher for activity conveyed by slow-than by fast-conducting retinal afferents. 7. The spatial distribution of monocularly evoked surface potentials failed to reveal the ocular dominance columns. 8. Comparison with the cat indicates that, with respect to the intracortical circuitry and LHN-transmission, there are more similarities between the fast-group activity in the monkey and the y-system in the cat and between the slow-group activity in the monkey and the x-system in the cat than vice versa.

Animals↗
PubMed1979

The role of binocular neurons in the cat striate cortex in combining information from the two eyes.

Cats were raised under conditions of daily alternating monocular exposure, so that each eye received normal input, but the animals were never allowed to use both eyes simultaneously. With single cell recording techniques it could be shown that this led to a severe disturbance of the normal binocularity of cortical neurons. The cats were trained by operant techniques in a two-choice box to discriminate with each eye non-retinotopic stimulus pairs. To test the ability to combine binocular signals it was tested whether the learned discrimination would transfer to red/green colored stimuli which were viewed dichoptically through appropriately colored contract lenses. The arrangement was such that the positive stimulus could be distinguished from the negative stimuli only when the signals from both eyes were combined and used simultaneously. All cats showed immediate transfer, from the monocularly learned discrimination task to the dichoptic paradigm. This indicates that the presence of a normal population of binocular cortical cells in area 17 is not a prerequisite for the ability to use binocular cues for the solution of a pattern discrimination task.

Animals↗
PubMed1978

Prominent excitatory pathways in the cat visual cortex (A 17 and A 18): a current source density analysis of electrically evoked potentials.

The current source density (CSD) method in its one-dimensional approximation is used to analyze the field potentials in visual areas 18 and 17 of the cat, which were elicited by stimulating electrodes in the optic chiasm (OX), the optic radiation (OR) or in the respective cortical area itself. The CSD analysis reveals the basic pattern of excitatory postsynaptic activity. 1. In both visual areas the basic specific excitatory activity flows along three different intracortical pathways, all starting in layer IV: The first pathway relays activity from layer IV to supragranular pyramidal cells via strong, local connections to layer III and from there through long-distance connections to layer II. The second pathway conveys activity from layer IV to layer V, where it mainly contacts apical dendrites of layer VI pyramidal cells. This infragranular polysynaptic activity is not clearly resolvable into separate components, suggesting that it is conveyed by various groups of axons, among them long-distance horizontal connections. The third pathway has one synaptic relay within layer IV and then conveys activity to layer III. In addition, monosynaptic activity is revealed in layers VI and I. 2. In A 18 one coherent, fast-conducting group of afferents induces this basic activity pattern. In A 17 no such fast conducting input is resolvable; the supragranular activity is induced by a small group of afferents with intermediate conduction velocity, which terminate in the upper part of layer IV. The infragranular activity is induced by afferents with slower and widely scattered conduction velocities, which terminate in the lower part of layer IV. The layer VI input is very prominent in A 17 and also has a wide latency scatter. 3. The supragranular activity is more prominent in A 18 than in A 17 and the respective layers appear thicker, in accordance with anatomy. In A 17 the infragranular activity prevails and layers IV and VI appear very broad, again in accordance with anatomy. 4. Comparison of the CSDs with the original evoked potentials shows that the surface evoked potentials over A 18 reflect the three dipolar sink/source distributions of the coherent monosynaptic activity in layer IV and of the two prominent polysynaptic activities in layers III and II. The widely scattered activity in the lower part of layer IV in A 17 and all infragranular activities in both areas generate smaller, partly closed-field potentials; those are not discernible from the strong far-field potentials which originate from the supragranular activity and--especially in A 17--from farther distant events.

Animals↗
PubMed1978

Association and dissociation of visual functions in a case of bilateral occipital lobe infarction.

A severe restriction of the visual field was observed in a patient suffering a bilateral occipital lobe infarction. Soon after the lesion, the visual field had an angle of approx. 4 degrees. Some recovery was observed within the following months. Within the restricted visual field, several visual functions were tested. Increment threshold, for instance, was found to be one log unit higher than would normally be expected. Color vision was completely lost soon after the lesion, but some recovery was later observed. Although binocular interaction was demonstrated by the interocular transfer of after-effects, the patient never experienced steropsis. He also seemed unable to recognize faces. Dsepite the small visual field, optokinetic nystagmus could be elicited. A notable slowing down of visual analyses was observed in experiments on visual reaction time, on the inversion of the Necker cube, and on binocular rivalry. The complete loss of certain functions like steropsis or face recognition in contrast to a quantitative reduction of other functions like visual acuity or color perception can be discussed in the light of two conceptual models of perceptual processing. One model suggests the representation of different visual functions within one neuronal network, each function represented by a different number of neurons or a different algorithm within the network. The second model suggests a spatial segregation of different visual functions in different cortical areas that receive input from one common structure, presumably the striate cortex.

Aged↗
PubMed1978

Ectopic ACTH syndrome: clinicopathological correlations.

Ten out of 164 cases of bronchogenic carcinoma showed pathological evidence at necropsy of the ectopic ACTH syndrome. All occurred in association with oat-cell carcinoma, constituting 19% of that group. The pathological features consisted of adrenocortical hyperplasia confined to the zona fasciculata and Crooke's hyaline change in the pituitary. Immunoperoxidase stainable ACTH was detected in the pituitary but not in the carcinoma tissue, a surprising finding, which may be due to the different nature of ACTH present in tumour tissue. The ectopic ACTH syndrome was diagnosed ante mortem in only four out of 10 patients on the basis of hypokalaemia and metabolic alkalosis. The lack of clinical pointers in all but terminal cases is discussed as well as possible measures for earlier diagnosis.

Adrenal Glands↗
PubMed1978

Intrasellar paraganglioma associated with hypopituitarism.

A 37-year-old with a history of postpubertal arrest of sexual development and delayed growth was found to have an enlarged sella turcica. The clinical and biochemical features were consistent with hypopituitarism. A tumor was removed transsphenoidally that, through light microscopy, histochemistry, and electron microscopy, proved to be a paraganglioma. We report the possible origin of intrasellar paraganglioma, as well as the pathogenesis of hypopituitarism.

Adult↗