Search PubMed⌕ Search

Biomedical subjects

P Stoerig

Publications and source records attributed to P Stoerig.

35 records · Page 2Linked to original sources
PubMed1994

Retinal ganglion cells labelled from the pulvinar nucleus in macaque monkeys.

In order to study the distribution and morphological classes of retinal ganglion cells that can be retrogradely labelled from the pulvinar nucleus, we made two iontophoretic injections of horseradish peroxidase into the pulvinar in each hemisphere of five macaque monkeys. The retrogradely labelled ganglion cells projecting to or through the pulvinar nucleus were examined in retinal whole-mounts. They comprise all three major ganglion cell classes. Primate gamma cells formed the great majority of classifiable cells and, like the primate alpha cells that were found in much smaller numbers, they were already known to send axons to the superior colliculus and to the pretectal complex. In contrast, the primate beta cells were hitherto thought to project solely to the dorsal lateral geniculate nucleus. This primate beta cell projection to an extrageniculate target could account in part for the substantial number of primate beta cells that escape transneuronal retrograde retinal degeneration following striate cortical ablation, and might contribute to the residual visual sensitivity that survives destruction of striate cortex and the degeneration of the lateral geniculate nucleus.

Animals↗
PubMed1993

The visual system and levels of perception: properties of neuromental organization.

To see whether the mental and the neural have common attributes that could resolve some of the traditional dichotomies, we review neuroscientific data on the visual system. The results show that neuronal and perceptual function share a parallel and hierarchical architecture which is manifest not only in the anatomy and physiology of the visual system, but also in normal perception and in the deficits caused by lesions in different parts of the system. Based on the description of parallel hierarchical levels of active information processing in the visual brain, we suggest a concept of dissociable levels of perception, advocating that the phenomenal perception and recognition is realized in the functional integrity of a network of reciprocal cortico-cortical connections. The properties shared by neuronal and perceptional functions provide a basis for a neuromental monism in which both functions are attributed a causal role.

Cerebral Cortex↗
PubMed1992

Wavelength discrimination in blindsight.

In the circumscribed, long-standing, clinically absolute visual field defects of three patients with vascular lesions that involved the optic radiation and visual cortex, forced-choice discrimination between coloured stimuli was tested. Paired stimuli were matched for luminous efficiency on the basis of previous measurements of increment-threshold spectral sensitivity made in the same patients and at the same retinal positions. To different extents all patients could discriminate between narrowband wavelength stimuli. The results imply that despite the effects of retrograde degeneration on thalamic and retinal colour-processing channels, neurons which process wavelength information are still functional, although the information they transmit is not consciously perceived.

Adult↗
PubMed1991

Direct and indirect retinal input into degenerated dorsal lateral geniculate nucleus after striate cortical removal in monkey: implications for residual vision.

We removed the striate cortex of one cerebral hemisphere in a macaque monkey, causing almost total retrograde degeneration of the corresponding dorsal lateral geniculate nucleus (dLGN) and extensive transneuronal degeneration of ganglion cells in the corresponding hemi-retina of each eye. The rare surviving geniculate projection neurons were retrogradely labelled by horseradish peroxidase (HRP) from extra-striate cortex and retinogeniculate terminals were labelled by an intraocular injection of HRP. Retinal terminals in the degenerated dLGN made synaptic contact exclusively with the dendrites of interneurons immunopositive for gamma-aminobutyric acid (GABA) in both parvocellular and magnocellular regions of dLGN. As well as being post-synaptic to retinal terminals these vesicle-containing dendrites were pre- and postsynaptic to other similar dendrites, and presynaptic to relay cells. Surviving labelled projection neurons received retinal input indirectly, via both the GABA-immunopositive interneurons and GABA-immunonegative terminals characteristic of those from the superior colliculus. In the degenerated, as opposed to the normal dLGN, about 20% of retinal terminals were GABA-immunopositive and GABA-immunoreactivity was prominently elevated in the ganglion and amacrine cell layers of the degenerated half of the retina. The optic nerve also contained numerous GABA-immunopositive axons but very few such axons were found in a normal optic nerve processed in identical manner. The surviving pathways from the retina must underlie the visual abilities that survive striate cortical removal in monkeys and human patients and may involve the degenerated dLGN as well as the mid-brain.

Animals↗
PubMed1991

The neurobiology of blindsight.

Some patients can respond to visual stimuli presented within their clinically absolute visual field defects that have been caused by partial destruction of striate cortex. This puzzling phenomenon of looking, pointing, detecting and discriminating without seeing has been called blindsight, and has fascinated philosophers and neuroscientists alike as a spotlight on the nature of unconscious or covert awareness, and the means it provides of studying the visual information carried by pathways other than the major route through the striate cortex.

Animals↗
PubMed1991

Increment-threshold spectral sensitivity in blindsight. Evidence for colour opponency.

In the circumscribed visual field defects of 3 patients, increment-threshold spectral sensitivity was measured with a guessing paradigm. Nine 116', 200 ms narrowband stimuli with maximum transmission between 450 and 660 nm were presented on a white background of photopic or scotopic luminance. Sensitivity measured in the blind field was compared with that at matched positions in the patients' normal hemifield, and with that at corresponding positions in 2 control subjects. Results show that spectral sensitivity in the blind field, albeit reduced by up to 1 log unit, shows normal dependence on adaptation level, reflecting rod activity under scotopic, and cone activity under photopic conditions. Characteristic discontinuities in the spectral sensitivity curve seen under light adaptation are evidence for colour-opponent processes, presumably involving primate beta retinal ganglion cells.

Adult↗
PubMed1989

Projection patterns of surviving neurons in the dorsal lateral geniculate nucleus following discrete lesions of striate cortex: implications for residual vision.

In four monkeys with long-standing partial ablation of the striate cortex pellets of horseradish peroxidase were placed in either the striate cortex immediately adjacent to the ablation, or in the extrastriate cortex of the ventral prelunate gyrus, i.e. in visual area V4. We examined the dorsal lateral geniculate nucleus to see whether surviving neurons, within the region that shows retrograde degeneration as a result of the cortical lesion, project to remaining striate cortex and/or to extrastriate cortex. Neurons labelled from extrastriate cortex were found throughout the degenerated region, whereas neurons labelled from striate cortex were confined to the border between the normal and degenerated region of the nucleus. This shows that isolated neurons found within the degenerated region survive striate cortex damage because they project to an extrastriate visual area, and not because their terminals depart from the otherwise strict topographic representation of the lateral geniculate nucleus on to striate cortex.

Animals↗
PubMed1989

Transneuronal retrograde degeneration of retinal ganglion cells after damage to striate cortex in macaque monkeys: selective loss of P beta cells.

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

Animals↗
PubMed1989

Residual target detection as a function of stimulus size.

In the visual field defects of 5 patients with damage in the postgeniculate part of the primary visual system, residual detectability of an achromatic intensity target was tested as a function of target diameter, which was 10, 27, 44, 69 and 116 min of arc of visual angle. The set of 5 targets was presented at 3 different intensity ranges on a background of low photopic luminance. Within this size range residual detectability was a V-shaped function of target size with a dip at 44 min of arc. This result is discussed in relation to the centre/surround organization of receptive and perceptive fields.

Adult↗
PubMed1987

Plasticity and rigidity in the representation of the human visual field.

Neuronal plasticity in the mammalian visual system has been studied with a variety of experimental methods like induction of artificial squint and eye rotation. To investigate neuronal plasticity in the human visual system, we examined a patient with a congenital convergent squint of his left eye, who later suffered a vascular lesion in his left occipital lobe that led to an incomplete hemianopia in his right visual field. The examination revealed that the visual field representation in the striate cortex is rigidly prewired with reference to the anatomical fovea. In contrast, plasticity in the oculomotor system enables the patient to use a functional visual axis that does not correspond to the anatomical fovea. Local alterations of sensitivity within the visual field that indicate interactions among non-corresponding retinal points provide additional evidence of functional plasticity.

Esotropia↗
PubMed1987

Chromaticity and achromaticity. Evidence for a functional differentiation in visual field defects.

In the visual field defects of 10 patients who had suffered lesions in the postgeniculate part of the primary visual projection, red-green discrimination and achromatic target detection was tested. In addition, 8 of these patients were tested for detection of red and green targets. Targets were presented on a low photopic achromatic background, so that the red and green targets differed from the background both in intensity and in wavelength, whereas the achromatic target differed in intensity only. Six patients showed evidence of discriminating between red and green targets, 5 patients could also detect the colour targets, but none could detect the achromatic one that was presented at the same retinal position. These results imply that wavelength and intensity information are treated differentially, and suggest that these patients possess residual colour-opponent channels that subserve the defective part of the visual field.

Color Perception↗
PubMed1986

Eccentricity-dependent residual target detection in visual field defects.

Lesions in the postgeniculate part of the visual system lead to visual field defects in the corresponding parts of the contralateral visual field. In some patients these field defects, though blind according to perimetry, have been observed to still be sensitive to visual stimulation. This report is based on studies of five such patients, whose ability to detect a small visual target presented tachistoscopically within the blind field was tested. Receiver-Operating-Characteristic curves were measured for three different retinal positions: a relatively central one, an eccentric one, and one within the natural Blind Spot that serves as a control. Results show that the four patients who could detect the target did so exclusively at the eccentric position.

Aged↗
PubMed1985

Signal detection analysis of residual vision in a field defect due to a post-geniculate lesion.

A patient's ability to discriminate between 'blank trials' and small visual targets presented tachistoscopically within his blind hemifield was tested at five positions within the scotoma. For each position a Receiver-Operating-Characteristic curve (ROC) was determined. Results show the patient's discrimination between the target and no-target conditions to be better than expected by guessing at three positions along the horizontal meridian, whereas in the natural Blind Spot within the scotoma no significant discrimination is found. Thus, light scatter produced by the visual target cannot explain the observed residual vision. At least three anatomical pathways could be responsible for the discrimination: the retino-collicular projection, the retino-geniculo-striatal projection, and the retino-geniculo-extrastriatal projection.

Aged↗
PubMedDate not supplied

Spatial summation in blindsight.

Spatial summation curves were determined in the circumscribed visual-field defects of five patients with blindsight. Under light-adapted conditions that favor the color-opponent system, increment thresholds for white and red targets presented on a white background were measured as a function of stimulus size which ranged from 9-110 min arc. In both normal and defective hemifields, summation was linear for the red stimuli. In contrast, the curves measured with the white stimuli showed some nonlinearity in the normal hemifield, and a pronounced eccentricity-dependent notch in the field defect. The results indicate that the neurons mediating sensitivity differ in their summation properties for wavelength and intensity information.

Adult↗
PubMedDate not supplied

Wavelength sensitivity in blindsight.

Blindsight--the residual visual functions observed in visualfield defects resulting from destruction of part of the primary visual cortex (striate cortex) even though visual stimuli presented in the field defect are not consciously perceived--has generated new insights into the nature of consciousness and the role of the extrastriate pathways in visual processing. Some patients can detect and localize unseen stimuli when they are required to guess. Discrimination of movement, flicker and orientation may also be present, but residual colour discrimination is controversial. Negative results imply that only the pathways from eye to striate cortex can transmit information about colour in primates. By measuring sensitivity to light of different wavelengths in patients with blindsight we show that spectral sensitivity in the blind fields is surprisingly high, with a reduction of only 1 log unit or less across the visible spectrum. It is also essentially normal in form, whether the patients are adapted to light or dark. The shift in peak sensitivity from medium to shorter wavelengths in adaptation to the dark (the Purkinje shift) and the presence of discontinuities in the light-adapted curve together show that blindsight involves both rod and cone contributions, and that some colour opponency remains. As colour opponency requires input from primate beta retinal ganglion cells, two-thirds of which degenerate transneurally after a striate cortical lesion in juvenile monkeys, our results show that the surviving subpopulation of primate beta cells is functional.

Amblyopia↗