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C Bonnet

Publications and source records attributed to C Bonnet.

At least 73 records · Page 4Linked to original sources
PubMed1996

Illusory form with inducers of opposite contrast polarity: evidence for multistage integration.

The perception of brightness differences in Ehrenstein figures and of illusory contours in phase-shifted line gratings was investigated as a function of the contrast polarity of the inducing elements. We presented either continuous lines or line-like arrangements composed of aligned dashes or dots whose spacing was varied. A yes/no procedure was used in which naive observers had to decide whether or not they perceived a brightness difference in a given Ehrenstein figure or an illusory contour in a phase-shifted line grating. The results show that brightness differences are perceived to some extent in Ehrenstein figures with inducers of opposite polarity of contrast; however, the percentage of yes response was systematically lower and response times were longer than for figures with inducers of the same polarity. Phase-shifted line gratings with lines of opposite polarity of contrast yielded stronger illusory contours and shorter response times than those with lines of the same polarity. When the sign of contrast was not the same within a given line of induction, neither differences in brightness nor illusory contours were perceived. The results suggest that the mechanisms that lead to apparent differences in brightness are more sensitive to input of the same contrast polarity, the mechanisms generating illusory contours more sensitive to input of opposite polarity. The data are discussed in the light of a multistage approach to illusory form perception and some implications for cortical models of illusory contour integration are discussed.

Adult↗
PubMed1996

On the relation between stimulus intensity and processing time: Piéron's law and choice reaction time.

Piéron (1914, 1920, 1952) demonstrated that simple reaction time (SRT) decays as a hyperbolic function of luminance in detection tasks. However, whether such a relationship holds equally for choice reaction time (CRT) has been questioned (Luce, 1986; Nissen, 1977), at least when the task is not brightness discrimination. In two SRT and three CRT experiments, we investigated the function that relates reaction time (RT) to stimulus intensity for five levels of luminance covering the entire mesopic range. The psychophysical experiments consisted of simple detection, two-alternative forced choice (2 AFC) with spatial uncertainty, 2 AFC with semantic categorization, and 2 AFC with orientation discrimination. The results of the experiments showed that mean RT increases with task complexity. However, the exponents of the functions relating RT to stimulus intensity were found to be similar in the different experiments. This finding indicates that Piéron's law holds for CRT as well as for SRT. It describes RT as a power function of stimulus intensity, with similar exponents, regardless of the complexity of the task.

Adult↗
PubMed1996

Fluoroquinolone induced tendinopathy: report of 6 cases.

We describe 6 cases of fluoroquinolone induced Achilles tendinitis in 4 women and 2 men, mean age 68.6 years. Patients presented with pain and swelling of sudden onset, which was most often bilateral. Tendon rupture was frequent, accompanied by nodules and ecchymoses. The diagnosis was clinical, occasionally ultrasonography was helpful; the role of magnetic resonance imaging has yet to be defined. Certain risk factors were found, particularly association with longterm steroid therapy, and close surveillance of high risk subjects is mandatory. Although proper dosage and duration of treatment were respected, the principal fluoroquinolones were clearly incriminated. We found no correlation between treatment duration and the degree of involvement. Nevertheless, immediate discontinuation of the antibiotic and placement of both Achilles tendons at rest is essential. Early and appropriate management did not prevent prolonged recovery times and there was always a risk of functional sequelae. This side effect is class related and rare. Its physiopathologic mechanism is poorly understood.

Adult↗
PubMed1996

Bovine collagen induced systemic symptoms: antibody formation against bovine and human collagen.

We describe the first case of systemic symptoms after injection of bovine collagen and silicone polymers associated with antibodies to both native type I and II bovine and human collagen that varied with clinical features. Joint inflammation, edema at the injection site of bovine collagen implant and fever appeared 6 months after injection. Our patients history raises the question of whether the injection of animal derived collagen, particularly combined with silicone, induces or exacerbates autoimmune disease.

Adult↗
PubMed1996

Synovial cyst at the C1-C2 junction and spondyloarthropathy.

A spinal synovial cyst is a rare extradural benign tumor generally located at the lumbar spine, arising at the facet joint capsule, and usually associated with degenerative changes. We describe a 64-year-old woman with a synovial cyst involving the quadrate ligament of the odontoid process, which caused neurologic signs. Her family history was positive for spondyloarthropathy. The radiologic investigations, preoperative differential diagnosis, and association of spondyloarthropathy with this rare benign foramen magnum tumor are of particular interest.

Cervical Vertebrae↗
PubMed1996

Evaluation of magnetic resonance imaging for the detection of sacroiliitis in patients with early seronegative spondylarthropathy.

A prospective study was conducted in 23 patients to evaluate magnetic resonance imaging versus computed tomography and plain film radiography for the early detection of sacroiliitis in patients with spondylarthropathy and an Amor score of less than 6. Computed tomography was significantly better than the other two techniques despite some false-positive results, particularly in patients older than 40 years. Magnetic resonance imaging lacked sensitivity for detecting elementary lesions, particularly of the cartilage, but demonstrated clearly that the earliest abnormality was edema of the subchondral bone.

Adult↗
PubMed1995

Subthreshold summation with illusory contours.

Results from three experiments using spatial forced-choice techniques show that an illusory contour improves the detectability of a spatially superimposed, thin subthreshold line of either contrast polarity. Furthermore, the subthreshold line is found to enhance the visibility of the illusory contour. Stimuli which do not induce illusory contours, but reduce uncertainty about the spatial position of the line, give rise to a slight detection facilitation, but the threshold of 75% correct responses is not attained. The data indicate that superimposing illusory contours and subthreshold lines produces interactions which are similar to classic subthreshold summation. They thus provide psychophysical evidence for the functional equivalence of illusory contours and real lines suggested by recent neurophysiological findings.

Contrast Sensitivity↗
PubMed1995

Lipoxygenase products and expression of 5-lipoxygenase and 5-lipoxygenase-activating protein in human cultured synovial cells.

5-Lipoxygenase products are pro-inflammatory mediators. Their roles and cellular origin in chronic inflammatory rheumatisms such as rheumatoid arthritis (RA) are poorly understood. The expression of arachidonate 5-lipoxygenase (5-LOX, arachidonate: oxygen 5-oxydoreductase; EC 1.13.11.34) and the 5-lipoxygenase activating protein (FLAP) genes in osteoarthritis and RA synoviocytes was studied at the transcriptional level by reverse transcription-polymerase chain reaction (RT-PCR) methodology. Arachidonic acid metabolism was analyzed by reverse-phase high pressure liquid chromatography. 5-LOX and FLAP mRNA were detectable using RT-PCR in all sources of synoviocytes tested. The expression of 5-LOX and FLAP mRNA led to the synthesis of 5-LOX metabolites. 12- and 15-LOX activities were also present. These LOX products can participate in inflammatory processes leading to joint destruction in RA.

5-Lipoxygenase-Activating Proteins↗
PubMed1995

Evidence for a sleep-promoting influence of stress.

In the present review the data supporting the existence at the central level of a stress-sleep relation are reported and discussed. An immobilization stress of 1 or 2 hour(s) is accompanied by a marked polygraphic waking and followed by a significant sleep rebound concerning mainly paradoxical sleep (PS). During the restraint, an important release of 5-hydroxyindoles [5-OHles, a good index of serotonin (5-HT) release] occurs in the basal hypothalamus (BH). This release, produced by the nerve endings originating from the nucleus raphe dorsalis (nRD), might secondarily influence the release and/or the synthesis of hypnogenic substances directly involved in the sleep rebound production. Corticotropin-like intermediate lobe peptide (CLIP, or ACTH18-39) is a peptide possessing hypnogenic properties and derived from proopiomelanocortin (POMC) whose perikarya are contained within the BH (arcuate nucleus). The POMC nerve endings impinge on the nucleus raphe dorsalis, a structure containing sleep permissive components upon which CLIP acts to trigger sleep. It remains to be defined how the activity of the neuronal loop described above is impaired under chronic stress conditions.

Acute-Phase Reaction↗
PubMed1995

Influence of unattended features on the processing of a single line segment.

This work investigates the interference of unattended line segments (distractors) of different orientations on a single line segment (target) when observer attention is focused on it in order to determine its orientation. It appears that the presence of line segments of different orientations in the visual field strongly influences the observer's decision on the judgement of the target orientation, whereas sensitivity is not affected. Two experiments were carried out to investigate distractor influence as a function of their number (Experiment I) and as a function of their proximity to the target, that is, to the point on which attention is focused (Experiment II). It appeared that distractors close to the target interfered more intensely than distractors at greater distances from the target, even if the latter were far more numerous. The results suggest that the output of the decision system is a function of all the information transmitted by feature detectors which act separately and in parallel.

Adult↗
PubMed1995

Spatiotemporal boundaries of linear vection.

Thresholds for the perception of linear vection were measured. These thresholds allowed us to define the spatiotemporal contrast surface sensitivity and the spatiotemporal domain of the perception of rectilinear vection (a visually induced self-motion in a straight line). Moreover, a Weber's law was found, such that a mean relative differential threshold in angular velocity of about 41% is necessary to perceive curvilinear vection. This visually induced self-motion corresponds to the sensation of moving in a curved path. It is proposed that curvilinear vection is induced when the apparent velocity difference is detectable. The spatiotemporal domain of perception of rectilinear vection and its spatiotemporal contrast surface sensitivity are centered on low spatial frequencies. Concurrently, the values which correspond to the relative differential thresholds of curvilinear vection are low spatial frequencies. Accordingly, the peripheral ambient visual system seems to be involved in perceiving linear vection. It is argued further that the central ambient system might also be involved in the processing of linear vection.

Contrast Sensitivity↗
PubMed1995

Deficits of cognitive executive functions in patients with sleep apnea syndrome.

Impairment of cognitive executive functions previously has been suspected to occur in association with sleep apnea syndrome (SAS), as suggested by some neuropsychological studies. However, such functions have not been assessed directly. In the present study, 17 patients with SAS were evaluated with various focused frontal lobe-related tests in comparison with 17 normal controls. Such tasks explored attention, short-term memory spans, learning abilities, planning and programming capacities, categorizing activities and verbal fluency. Patients were found to have a significantly decreased ability to initiate new mental processes and to inhibit automatic ones, in conjunction with a tendency for preservative errors. They were also affected with deficits of verbal and visual learning abilities and had reduced memory spans. Such defects were further evaluated via logistic regression against two criteria of the severity of the disease: the number of apneas and hypopneas per hour of sleep and the level of nocturnal hypoxemia. Memory deficits were rather related to the former, whereas typical frontal lobe-related abnormalities seemed rather consistent with the latter. These findings are discussed in light of data from the literature concerning cognitive impairments described for patients with isolated daytime sleepiness versus hypoxemia, as illustrated in other pathological or physiological circumstances.

Adult↗
PubMed1994

Immunocytochemical study of the CLIP/ACTH-immunoreactive nerve fibres in the dorsal raphe nucleus of the rat.

The injection of corticotrophin-like intermediate lobe peptide (CLIP) in the lateral ventricle or the dorsal raphe nucleus (DRN) of the rat is followed by a significant increase in the amount of paradoxical sleep. In the DRN, CLIP would act through a somatic and/or dendritic release of serotonin. To establish the anatomical basis of these effects, the nerve fibres immunoreactive for CLIP/ACTH were labelled and their fine anatomical relationships with the neuronal elements of the DRN were studied at the ultrastructural level. Half of the profiles of labelled varicosities were 'free' in the neuropile, the other half was in close contact with dendrites, either shafts or spines. It was interesting to note that few contacts with dendritic shafts were under the form of a synapse, whereas a large number of the contacts with spines were synaptic. The chemical nature of these dendritic targets remains to be determined but preliminary results indicate that they are partly serotoninergic.

Adrenocorticotropic Hormone↗
PubMed1994

Circadian changes of left ventricular ejection fraction in normal subjects.

Sleep has a specific physiology with related cardiovascular changes. We have previously found in respiratory patients [chronic obstructive pulmonary disease (COPD) and sleep apnea syndrome (OSAS)] an unexpected decrease in left ventricular ejection fraction (LVEF) at waking in the morning when compared with the rest period during the day. Whether this observation was linked to the consequences of the respiratory abnormalities or reflected physiological fluctuations related to the changes in autonomic nervous system tone remained unknown. Thus, we have set out to analyze the changes in LVEF with sleep in normal individuals. Eight healthy young men had LVEF measured before and after submaximal exercise, at rest before bedtime, and on waking in the morning. Technetium-99m with in vivo red cell labelling was used. Sleep parameters were assessed using classical polysomnography. In order to detect any influence of autonomic nervous system stimulation on LVEF, sympathovagal tone (SVT) was also assessed during night-time LVEF measurements using spectral analysis of RR intervals. LVEF at rest was within the normal limits for all the subjects (range 51-62%). On submaximal exercise, the LVEF increased in four subjects, was unchanged in two, and decreased in two. The main result concerns the changes in LVEF overnight. In the morning, LVEF decreased dramatically in three subjects and reached a level of < 30% in four. These decreases in LVEF were not related to changes in SVT or sleep structure. LVEF values returned to normal in 30 min. The LVEF changes during exercise are in accordance with previous data in the literature. The dramatic decrease in LVEF observed in the morning could be related either to vascular resistance changes or to nocturnal variations in cardiac contractility, which both need further studies to be established.

Adult↗
PubMed1994

Idiopathic retroperitoneal fibrosis with systemic manifestations.

We describe a previously unreported association of idiopathic retroperitoneal fibrosis with mesenteric, pulmonary and perhaps periarticular fibrotic involvement, and panniculitis resembling Weber-Christian panniculitis. The onset of the disease was uncommon with arthritis. Then, several episodes of migratory panniculitis appeared; biopsy showed septal panniculitis without necrosis of adipose tissue. Considering the patient's anamnesis, it is tempting to speculate that these manifestations all originate from the same mechanism.

Adult↗