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Biomedical subjects

C Veraart

Publications and source records attributed to C Veraart.

At least 37 records · Page 2Linked to original sources
PubMed1997

Brain energy metabolism in early blind subjects: neural activity in the visual cortex.

As an attempt to better understand the metabolic basis for the previously reported increases in glucose metabolism in the visual cortex of congenitally blind subjects, cerebral blood flow, oxygen consumption and glucose utilization were investigated with multitracer positron emission tomography. Measurements were carried out in three subjects who became blind early in life and in three age-matched blindfolded controls. Regional analysis of cerebral blood flow, metabolic rates for oxygen and glucose utilization revealed that these parameters were relatively higher in the visual cortex in case of early blindness (109.7 +/- 2.4%; 114.3 +/- 1.5%; 118.0 +/- 5.5%, respectively) than in controls (98.1 +/- 3.9%; 108.6 +/- 3.6%; 105.2 +/- 4.8%). There were slight differences, albeit statistically not significant, between early blind and control subjects in terms of oxygen-to-glucose metabolic ratios. The relatively preserved stoichiometry in the visual areas of blind subjects points to the lack of variation in the yield of glucose oxidation in this cortex. Those observations suggest that the high level of energy metabolism disclosed in early blind visual cortex is related to neural activity.

Adult↗
PubMed1993

High metabolic activity demonstrated by positron emission tomography in human auditory cortex in case of deafness of early onset.

Glucose metabolism has been studied in the auditory cortex of human subjects with deafness of early onset, and compared to normal subjects with ears plugged. The metabolism in the auditory cortex and in the association auditory cortex was higher in deaf subjects than in normal subjects. This result is compared to similar observations that we made previously in the visual cortex of human subjects with blindness of early onset.

Adolescent↗
PubMed1993

Selective control of muscle activation with a multipolar nerve cuff electrode.

Acute experiments were performed on adult cats to study selective activation of medial gastrocnemius, soleus, tibialis anterior, and extensor digitorum longus with a cuff electrode. A spiral nerve cuff containing twelve "dot" electrodes was implanted around the sciatic nerve and evoked muscle twitch forces were recorded in six experiments. Spatially isolated "dot" electrodes in four geometries: monopolar, longitudinal tripolar, tripolar with four common anodes, and two parallel tripoles, were combined with transverse field steering current(s) from an anode(s) located 180 degrees around from the cathode(s) to activate different regions of the nerve trunk. To quantify the degree of selectivity, a selectivity index was defined as the ratio of the force in one muscle to the force in all four muscles in response to a particular stimulus. The selectivity index was used to construct recruitment curves for a muscle with the optimal degree of selectivity. Physiological responses were correlated with the anatomical structure of the sciatic nerve by identifying the nerve fascicles innervating the four muscles, and by determining the relative positions of the electrodes and the nerve fascicles. The results indicated that the use of transverse field steering current improved selectivity. We also found that tripoles with individual dot anodes were more selective than tripoles with four common dot anodes. Stimulation with two parallel tripoles was effective in activating selectively fascicles that could not be activated selectively with only a single tripole. The multipolar cuff proved an effective method to control selectively and progressively the force in muscles innervated by fascicles that were well defined at the level of the cuff.

Animals↗
PubMed1992

Use of an ultrasonic echolocation prosthesis by early visually deprived cats.

The aim of this study was to design an animal model of sensory substitution in the case of blindness. Six kittens were binocularly enucleated; as adults, they were fitted with an ultrasonic echolocation prosthesis. This device provided the animals with auditory signals that coded distance and direction of obstacles. Animals were trained by operant conditioning to use the prosthesis in various behavioral situation. The results showed that visually deprived animals tried to solve the task using natural information and that they only used artificial information provided by the prosthesis when they were unable to succeed with natural cues. Under these conditions, it was asserted that in a jumping test these animals evaluated depth by means of the prosthesis; in a locomotion task in a maze, it was also demonstrated that they could use the prosthesis for avoiding obstacles.

Animals↗
PubMed1990

Glucose utilization in human visual cortex is abnormally elevated in blindness of early onset but decreased in blindness of late onset.

Glucose utilization has been studied in the visual cortex of blind human subjects, by comparison with normal volunteers, using positron emission tomography. In 6 subjects who became blind early in life ('early blindness'), metabolism in visual cortex was elevated, comparable to that of normal subjects studied with the eyes open. By contrast, glucose utilization in visual areas of 6 human subjects who became blind after completion of visual development ('late blindness') was decreased, slightly lower than in normal volunteers studied with the eyes closed. This unexpected difference between early and late blind subjects might reflect the persistence, in early blindness, of supranumerary synapses which would escape the normal developmental decrease in synaptic density during infancy.

Adult↗
PubMed1988

High metabolic activity in the visual cortex of early blind human subjects.

Glucose metabolism has been studied in the visual cortex of early blind human subjects. In the forebrain of these subjects, regional glucose utilization was the highest in the striate and prestriate cortical areas. Furthermore, this activity was higher than in blindfolded sighted subjects, whether at rest or during an auditory or tactile task. These observations raise the question of the functionality of the blind's visual cortex.

Blindness↗
PubMed1986

Effects of deprivation of vision and vibrissae on goal-directed locomotion in cats.

The locomotor behaviour of adult cats blinded soon after birth was compared to that of control cats by measuring running time in a maze. The effects of vibrissae deprivation in trained blind and control cats and of visual deprivation in control cats was studied. The performance of the control cats decreased in darkness to the level reached by the blind cats. Deprivation of vibrissae affected the performance of the control cats only in darkness and had no effect on the blind cats. The role played by various sensory systems in locomotion during development and in adulthood is discussed.

Animals↗
PubMed1984

Development of the air righting reflex in cats visually deprived since birth.

Classical experiments on the ability of cats to turn in the air during a free fall, the air righting reflex, have shown that vestibular and visual cues can play a role in this behavior. The development of this air righting reflex in kittens blinded since birth has been studied. The results show that the development in the blinded kittens is the same as in normal kittens with vision: mature by 33 days. This result and the comparison with other studies confirm that the air righting reflex is primarily a vestibular controlled reaction.

Animals↗
PubMed1984

A simple and inexpensive device for applying a calibration pulse when performing intracellular recording.

A simple and low-cost device is described which facilitates the calibration of intracellular DC recordings in amplitude and time. A current source, optically coupled to a conventional stimulator, injects a pulse of current, across a 1-omega resistor connecting the preparation to ground. Amplitude and duration of the current pulse are determined by adjusting the voltage output of the conventional stimulator. By linking the preparation to ground through a resistor of 1 omega the background noise and the DC shifts in the voltage trace of the intracellular recording are kept to a minimum.

Animals↗
PubMed1981

Wiener kernels determination in the cats lateral geniculate nucleus as a function of velocity of a sinusoidal grating: preliminary results.

The aim of this work was to develop a mathematical model which could describe information collected in the lateral geniculate body in response to the movement of a specific stimulus in an animal's visual field. To do this, a visual stimulation technique was developed, as well as a group of computer programs for processing the information recorded during the experiments. This group of programs is a method of non-linear identification based on the Wiener Kernels method, with the speed of an image's motion in the visual field as the systems entry variable. Preliminary results have shown that non-linearities in visual information processing would also be involved in speed coding. Thus a further utilization of the Wiener method seems useful and could contribute a great deal to visual system analysis.

Animals↗
PubMed1978

Possible role of acetylcholine in the mediation of non-retinal input to the lateral geniculate nucleus region.

In these series of experiments, the effects of acetylcholine and related substances administered by iontophoresis or by intravenous injection, have been examined on neurones of the lateral geniculate nucleus region to see whether non-retinal inputs on these cells use acetylcholine as a mediator. Quantitative analysis has shown that the somatic induced facilitation of the visual responses evoked in the lateral geniculate nucleus is suppressed after intravenous administration of atropine. This observation favors the intervention of muscarinic cholinergic receptors in the mediation of non-retinal inputs to the lateral geniculate nucleus region.

Acetylcholine↗