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At least 631 records · Page 35Linked to original sources
PubMed1985

Modification of neuronal discharge along the ascending tectofugal pathway during visual conditioning.

Visually conditioned heart-rate change in the pigeon has been developed as vertebrate model system for analysis of associative learning. The visual pathways transmitting the conditioned stimulus information were identified, and neurophysiological analyses during conditioning were then undertaken to determine if these pathways behave merely as input lines or undergo training-induced modification. After finding that the retinal output is invariant with training, we investigated the central visual pathways, beginning with the tectofugal pathway. During conditioning single neurons in the nucleus rotundus and ectostriatum, the thalamic and telencephalic relays of the tectofugal pathway, showed enhancement of their phasic light-evoked responses. In contrast, the initial phasic responses attenuated during non-associative training. The rate at which these discharge modifications developed paralleled the development of the behavioral response. Thus, the tectofugal pathway shows plasticity during conditioning and does not behave merely as an input channel for the conditioned stimulus.

Action Potentials↗
PubMedDate not supplied

A VEP study of the visual pathway function in compressive lesions of the optic chiasm. Full-field versus half-field stimulation.

Changes of the pattern reversal visual evoked potentials (VEPs) to half- and full-field stimulation in 50 patients with compressive lesions of the optic chiasm are presented. Temporal half-field stimulation yielded abnormal responses in 85% of the eyes, showing non-recordable P100 in 50% of eyes, while in 35% the P100 was significantly attenuated or delayed. With nasal half-field the percentage of all detectable abnormalities was lower (36% of the eyes). Full-field stimulation revealed VEP abnormalities in 74% of eyes and therefore proved less sensitive than the half-field stimulation. This study adds new evidence that half-field stimulation can be an important adjunct for assessing the function of the optic chiasm.

Adolescent↗
PubMed1987

Residual vision in patients with retrogeniculate lesions of the visual pathways.

Twenty-five subjects have been studied who, as a result of damage to the striate cortex, were 'blind' in extensive areas (scotomata) of the visual fields. Of these 25 subjects, 5 exhibited residual vision in response to transient lights presented within the scotoma, which enabled them to locate the stimuli by hand-reaching or by eye movements; the latter have been measured by electro-oculography. The residual vision underlying their responses was characterized by low flicker-fusion and by sensitivity in detection of movement which increased as target speed was raised. Discrimination for the direction of target movement was poor, but spatial resolution in the discrimination of target displacement was essentially normal. The subjects were unable to recognize or discriminate the spatial structure of targets located within the 'blind' field, and the observed dissociation between spatial discrimination of displacement and pattern is examined in relation to the 'two systems' hypothesis of visual function. There is no obvious correlation between the extent of neuronal damage as revealed by CT scans and the existence of residual vision.

Adult↗
PubMed1987

Glucose utilization of visual cortex following extra-occipital interruptions of the visual pathways by tumor. A positron emission tomography study.

To assess the effect of extra-occipital lesions on the local cerebral glucose utilization of the primary and associative visual cortex, 29 patients were studied in the unstimulated state by positron emission tomography and [18F]2-deoxyglucose. Quantitative Goldmann perimetry was done in each patient at the time of the positron emission tomographic study. Nine patients showed homonymous defects, either hemianopsia or quadrantanopsia, whereas nine patients had heteronymous defects. Eleven control subjects, free of any neurological symptoms and with normal visual fields, were also studied with [18F]2-deoxyglucose positron emission tomography. In the normal control subjects and in patients with a heteronymous defect, left-to-right differences in the local cerebral metabolic rate for glucose of the visual cortex varied less than 10%. In patients with hemianopic defects, differences ranged from 8 to 38%, with the hypometabolic cortex always contralateral to the field defect. In patients with quadrantanopic defects, the visual cortex contralateral to the field defect demonstrated differences from 14 to 24% above and below the calcarine fissure, the cortex that received greater input from the affected field being hypometabolic.

Adult↗
PubMed1995

Comparison of colour discrimination and electroretinography in evaluation of visual pathway dysfunction in aretinopathic IDDM patients.

The slow progression of diabetic retinopathy makes it difficult to assess the effects of intervention therapy. There is thus a need for surrogate markers of visual change in diabetes. Colour vision tests and electroretinography (ERG) may be useful in this regard; yet little is known of their relative performance in the assessment of visual dysfunction in diabetes. The aim of the present study was to compare colour discrimination (100 hue test) and ERG indices (oscillatory potentials (OP) and pattern ERG (PERG)) in the evaluation of aretinopathic IDDM patients. Colour discrimination was abnormal in 10 aretinopathic IDDM patients when compared with nine age matched controls; mean square root 100 hue error scores were 10.38 (SD 2.89) versus 4.77 (1.87) respectively, p < 0.01. OP implicit times of the ERG were also abnormal; for example, for right eye, mean OP1 implicit time for diabetics versus OP1 implicit time for controls was 20.1 (2.0) versus 18.6 (1.4) ms, p = 0.03. Comparison of the two techniques suggested that the 100 hue test was more sensitive and more specific than ERG OP implicit times in the detection of diabetic visual dysfunction in these patients.

Adult↗
PubMed2005

Separate spatial scales determine neural activity-dependent changes in tissue oxygen within central visual pathways.

The relationship between oxygen levels and neural activity in the brain is fundamental to functional neuroimaging techniques. We have examined this relationship on a fine spatial scale in the lateral geniculate nucleus (LGN) and visual cortex of the cat using a microelectrode sensor that provides simultaneous colocalized measurements of oxygen partial pressure in tissue (tissue oxygen) and multiunit neural activity. In previous work with this sensor, we found that changes in tissue oxygen depend strongly on the location and spatial extent of neural activation. Specifically, focal neural activity near the microelectrode elicited decreases in tissue oxygen, whereas spatially extended activation, outside the field of view of our sensor, yielded mainly increases. In the current study, we report an expanded set of measurements to quantify the spatiotemporal relationship between neural responses and changes in tissue oxygen. For the purpose of data analysis, we develop a quantitative model that assumes that changes in tissue oxygen are composed of two response components (one positive and one negative) with magnitudes determined by neural activity on separate spatial scales. Our measurements from visual cortex and the LGN are consistent with this model and suggest that the positive response spreads over a distance of 1-2 mm, whereas the negative component is confined to a few hundred micrometers. These results are directly relevant to the mechanisms that generate functional brain imaging signals and place limits on their spatial properties.

Animals↗