Biomedical subjects

P Denise

Publications and source records attributed to P Denise.

At least 19 recordsLinked to original sources

PubMed2006

Total sleep deprivation can increase vestibulo-ocular responses.

The effect of sleep deprivation on the vestibular function is largely unknown. Some studies have found that postural balance or vestibular reflexes are decreased in sleep-deprived subjects while others found no change. The aim of this study was to evaluate the effect of sleep deprivation on the vestibulo-ocular reflex (VOR). Horizontal eye movements were recorded in healthy subjects during earth vertical axis rotation in darkness once after an ordinary night sleep and once after 26-29 h of sleep deprivation. In the first experiment (n = 8), for which rotation was a 60 degrees s(-1) velocity step, sleep deprivation induced a significant increase in VOR gain. In the second experiment (n = 12), for which rotation was sinusoidal (0.2 Hz +/- 25 degrees s(-1)), sleep deprivation induced no significant modification in VOR gain. The difference between the two studies was the abrupt onset of the step stimulation in comparison with the sinusoidal rotation. Because of its unexpected onset and the potential threat to postural balance, the step stimulation may activate the system specialized in reorienting attention towards salient or behaviourally relevant events. This system includes the right temporoparietal cortex, an area also involved in VOR control. A number of studies have found that sleep deprivation alters the activity of this cortical area during attentional tasks. It is therefore our hypothesis that the difference between the effects of these two vestibular stimulations results from a sleep deprivation-induced modulation of the right temporoparietal cortex.

Adult↗

PubMed2005

Are eye movement abnormalities indicators of genetic vulnerability to schizophrenia?

UNLABELLED: Fifty to eighty-five percent of schizophrenic patients are impaired on ocular pursuit paradigms. However, results regarding the relatives are more discordant. The aim of this study was to investigate whether eye movement disorders could be a vulnerability marker of schizophrenia. METHOD: Twenty-one schizophrenic patients (DSM-IV), 31 first-degree relatives of those patients without schizophrenic spectrum disorders, and two groups of healthy controls matched by age and sex were included. Three oculomotor tasks (smooth pursuit, reflexive saccades and antisaccades) were used. RESULTS: Patients had a lower averaged gain (P= 0.035) during smooth pursuit than controls, made less correct visually guided saccades (P< 0.001) and more antisaccades errors (P= 0.002) than controls. In contrast, none of the comparison between the relatives and their controls was significant. CONCLUSION: Schizophrenic patients were impaired on smooth pursuit and antisaccade paradigms. None of these impairments was, however, observed in their first-degree relatives. Our results suggest that the eye movement parameters tested could not be considered as vulnerability markers for schizophrenia.

Adult↗

PubMed2005

Interaction between cortical control of vestibular function and spatial representation in man.

An asymmetry of the vestibulo-ocular reflex is observed after unilateral posterior cortical lesions in human. The co-occurrence of vestibular deficits and visuo-spatial disorders suggests a functional link between the representation and update of space and the integration of vestibular information in the occipito-parieto-temporal cortex of the right hemisphere.

Cerebral Cortex↗

PubMed2003

Evidence for interacting cortical control of vestibular function and spatial representation in man.

The objective of this research was to determine the possible relation between deficits in spatial representation capability and vestibular function following cortical lesions. We thus investigated vestibulo-ocular behaviour in a group of 14 patients with unilateral cortical damage involving the occipito-temporo-parietal junction. Patients were divided in three sub-groups: (1) Group R+: five patients with right sided cortical lesions associated with a left hemi-neglect, (2) Group R-: four patients with right sided cortical lesions with no hemi-neglect and (3) Group L: five patients with left-sided cortical lesions. The patient groups were compared to a group of eight healthy age-matched subjects. The vestibulo-ocular reflex (VOR) was tested in complete darkness by rotating the subject around the vertical axis by sinusoidal rotation at different frequencies, and by steps of acceleration or deceleration. The nystagmus slow phase velocity was measured and plotted as a function of the head velocity and the VOR parameters including gain, bias, time constant and phase were calculated. The cortical lesions induced a significant VOR asymmetry in terms of: a directional preponderance of the VOR gain to the contralesion side, only during sinusoidal rotation, and, in contrast, a VOR bias and a directional preponderance of the VOR time constant and of the nystagmus frequency to the side of the cortical lesion. These latter VOR deficits were the most significant in the R+ group, i.e. in right cortical lesions with hemi-neglect syndrome. These results demonstrate in man, the existence of a cortical influence on vestibular function related to the mechanisms of spatial representation.

Adult↗

PubMed2003

Effects of zolpidem 10 mg, zopiclone 7.5 mg and flunitrazepam 1 mg on night-time motor activity.

The effects of a single dose of zolpidem (10 mg), zopiclone (7.5 mg) and flunitrazepam (1 mg) on motor activity the following 3 nights were compared to those of a placebo in a double-blind, crossover study. Thirty-three healthy subjects received medication between 10.30 and 11.30 p.m. and were asked to rise between 7.30 and 8.30 a.m. During the night under treatment, flunitrazepam, zopiclone and zolpidem significantly reduced motor activity. Changes in motor activity are quantitatively compatible with the hypothesis of reduced light sleep and wakefulness after sleep onset. During the first or second post-drug night, for zolpidem and zopiclone the opposite effect was observed, i.e. increased activity compared with placebo. These modifications cannot be explained by modified sleep structure. This last result underlines our inadequate understanding of the underlying mechanisms of motor activity during sleep. However, being sensitive and easy to use, actigraphy is an ideal technique to assess the effect of hypnotics on large populations and for long duration studies.

Adult↗

PubMed2003

Do zopiclone, zolpidem and flunitrazepam have residual effects on simulated task of collision anticipation?

Few studies have addressed the modifications in visual information processing brought about by taking hypnotic substances. The present experiment with healthy subjects investigated the residual effects of taking a single night-time dose of hypnotics on collision anticipation capacities the next morning. Visual sequences simulated the movement of a driver approaching an intersection where another vehicle was arriving. Ten participants had to estimate, as quickly as possible, whether the other vehicle would arrive before or after them at the intersection. They were tested after having taken a capsule of zolpidem (10 mg), zopiclone (7.5 mg), flunitrazepam (1 mg) or a placebo. The results show no residual effects of the molecules. Only flunitrazepam, a benzodiazepine with a long half-life, appears to cause subjects to focus their attention on an element which, while relevant for the task (a road sign playing the role of a spatial reference), is not used correctly.

Accidents, Traffic↗

PubMed2002

Effect of human head flexion on the control of peripheral blood flow in microgravity and in 1 g.

This study evaluated, in six healthy subjects, whether head flexion, which stimulates the vestibular system and the tonic neck receptors, interferes with cardiovascular regulation. Arterial parameters were measured continuously using a pulsed Doppler ultrasound probe during parabolic flights with subjects either in the supine craned-head position (control) or in the supine anterior neck flexion bent-neck position. Exposure to 0 g induced a fluid shift towards the head (stroke volume +8%, P<0.05). Compared to the control situation the mean (SD) blood flow in the femoral artery decreased [ -10 (9)% vs +1 (10)%; P<0.05], and the ratio cerebral artery:femoral artery blood flow ( : ) increased [+8 (14)% vs -4 (7)%; P<0.05], in the bent-neck position. Thus, neck flexion without otolith loading (subject in 0 g) favoured cerebral perfusion during the exposure to 0 g. The return to 1 g, even in the supine position, induced a fluid shift towards the lower limbs. From 0 to 1 g, reduced less [ +6 (8)% vs -1 (8)%; P<0.05], and the : decreased more [-11 (9)% vs 0 (10)%; P<0.05], in the bent-neck position than in the control position. Thus the redistribution of peripheral blood flow in response to the fluid shift towards the legs was less efficient in the bent-neck position. In 0 g environment the passive flexion of the neck (neck receptor stimulation only) increased resistance in the femoral artery [ R(fa) +20 (21)%; P<0.05] and reduced the [-15(10)%; P<0.07] which increased the redistribution of flow towards the brain [; +12 (7)%; P<0.07]. This response was of lower amplitude when both otoliths and neck muscle were stimulated (neck flexion in 1 g) [ R(fa)+9 (7)%, P<0.05; -9 (12), NS; : 0 (12), NS]. We suggest that otolith and neck muscle stimulation (by neck flexion) trigger opposite vascular effects in response to a fluid shift towards the legs.

Adaptation, Physiological↗

PubMed2002

Influence of otoliths and neck muscle receptors on peripheral hemodynamic regulation.

To evaluate the cardiovascular changes induced by otoliths and neck mechanoreceptors stimulation during head movements, nine subjects in supine prone position performed passive head-down neck flexion (P.Ext) and head up P.Extension (P.Flex) As the lower limbs vasoconstricted from P.Ext to P.Flex, it is suggested that the otoliths stimulation towards the base of the head (like in standing position) contribute to reduce the vasoconstriction whereas when stimulated towards the top of the head (head flexion) they increase it.

Journal Article↗

PubMed2001

Poor performance in smooth pursuit and antisaccadic eye-movement tasks in healthy siblings of patients with schizophrenia.

This study examines the area of eye movement dysfunctions as an indicator of vulnerability to schizophrenia. Eye movement performance was investigated with three different paradigms: Smooth Pursuit Eye Movements (SPEM); Visually Guided Saccades (VGS); and Antisaccades (AS) in 21 clinically stable patients with schizophrenia, 21 of their healthy, biological full siblings and 21 healthy control subjects. The three groups did not differ on VGS performance, whereas both patients and their siblings showed lower SPEM gain, an increased catch-up Saccades (CUS) rate, reduced AS accuracy and an increased number of AS errors in comparison to control subjects. In addition, patients with schizophrenia exhibited increased AS latency. Among the patients with schizophrenia, eye movement abnormalities did not correlate with age, gender, clinical state or duration of illness. These data suggest that abnormalities of SPEM and AS may represent neurobiological markers of the vulnerability to schizophrenia in individuals at high genetic risk for the disease.

Adult↗

PubMed2001

Saccadic and smooth-pursuit eye movements in deficit and non-deficit schizophrenia.

We have analyzed eye movement performances in schizophrenics showing primary negative or deficit symptoms (n=16) and non-deficit schizophrenics (n=55), and compared them with those of controls (n=34) in order to study the relationships between negative symptoms and eye movement abnormalities. Patients were subtyped into deficit and non-deficit subgroups using the Schedule for the Deficit Syndrome. Three oculomotor paradigms were used: smooth pursuit, a reflexive saccade paradigm and an antisaccadic task. The smooth pursuit gain was significantly decreased (and the rate of catch-up saccades increased) in schizophrenics as compared with controls, but no difference was observed between patient groups. In the reflexive saccade paradigm, no difference was found between controls and patients, except for latency in deficit patients. In the antisaccade paradigm, the number of errors and the latency of successful antisaccades were significantly increased in schizophrenics as compared with controls. The latency of successful antisaccades in both directions was significantly increased in deficit patients as compared with non-deficit patients. The latency of rightward successful antisaccades was significantly increased as compared with the latency of leftward antisaccades in deficit patients only. However, when patients were classified into negative and non-negative groups using the PANSS, no difference was found in the antisaccade paradigm. Smooth pursuit impairment does not seem to depend on the primary enduring negative symptoms.In deficit schizophrenics, the abnormalities observed in the antisaccadic task are consistent with prefrontal dysfunction, and may suggest parietal lobe dysfunction as well.

Adult↗

PubMed2001

New questions on the hemispheric encoding/retrieval asymmetry (HERA) model assessed by divided visual-field tachistoscopy in normal subjects.

According to the hemispheric encoding/retrieval asymmetry (HERA) model, based on data obtained through functional neuroimaging, the left and right prefrontal cortices are preferentially, and, respectively, involved in long-term episodic memory encoding and retrieval. In this study, the HERA model was tested from a behavioral perspective using divided visual-field tachistoscopy. A recognition paradigm with both verbal and visuospatial materials was devised to differentiate memory-related effects (encoding vs. retrieval) from effects linked to the materials. The paradigm used lists of 12 and four items to assess long-term episodic memory and short-term memory, respectively. The aim of the latter condition was to test whether the HERA model is applicable in short-term memory. For long-term episodic memory, the data obtained validated the HERA model; the direction of the hemispheric asymmetry was found to depend on the type of materials used, whereas its magnitude was determined by the type of memory process. For verbal short-term memory, the HERA model seems to be confirmed. The pre-existing representations of the material could take into account the similarity of the hemispheric asymmetry pattern between short-term memory and long-term memory. In contrast, for visuospatial short-term memory, Baddeley's working memory model seems to better explain our results insofar as the asymmetries were essentially linked to the material in encoding but not in retrieval. This latter difference between short-term memory and long-term indicates that processes involved in LTM depend on episodic processes per se, hence, lending more support for the HERA model. Accordingly, these two memory systems seem to bring into play two different modes of hemisphere specialization.

Adult↗

PubMed2000

Motion sickness occurrence does not correlate with nystagmus characteristics.

The purpose of this study was to test the hypothesis whereby eye movements as such may be an important factor in the development of motion sickness (MS). The horizontal eye movements of 27 subjects were measured during earth vertical axis rotation (EVAR) and during off vertical axis rotation (OVAR). Two groups were set up, one including subjects who suffered severe MS during the test, and the other including subjects with no MS symptoms. We found no differences in nystagmus parameters (EVAR: gain and time constant; OVAR: eye velocity modulation and eye position modulation) between the MS and the non-MS groups. We can conclude that eye movements are not involved in the development of MS.

Adolescent↗

PubMed2000

Nonconvulsive status epilepticus: the role of morphine and its antagonist.

A 77-year-old woman with no history of epilepsy presented a probable nonconvulsive status epilepticus while receiving continuous intravenous morphine for back pain relating to vertebral metastasis of a malignant lymphoma. A generalized tonic-clonic seizure occurred a few minutes after injection of the morphine antagonist naloxone. No cerebral lesion was detected. This observation supports the notion of a possible pro-epileptogenic effect of opioid substances in association with metabolic and other toxic factors. Various hypotheses as to the complex actions of morphine and its antagonist in epileptogenesis are discussed.

Aged↗

PubMed2000

Residual effects of hypnotics on disengagement of spatial attention.

In an earlier study, we postulated that the residual effects of hypnotics could induce a spatial attention disengagement deficit independent of any decrease in alertness. To test this hypothesis, we compared the residual effects of zolpidem, zopiclone and flunitrazepam in two ocular saccade tests, gap and overlap. In the gap paradigm, the lateral target is illuminated 200 ms after the extinguishing of the central target. In the overlap paradigm, the central target stayed on when the lateral target was illuminated. Zopiclone increases latency in the overlap, but not in the gap test, which appears to be specific to a deficit of disengagement of spatial attention. Zopiclone impairs the saccadic precision in gap, but not in overlap, which may be interpreted as an impairment of visuospatial memory. The effects of zolpidem are limited to visuospatial impairment. The effects of flunitrazepam are massive and probably the results of a decrease in alertness.

Adult↗

PubMed2000

Otolith dysfunction in skew deviation after brain stem lesions. Abnormalities of eye movements induced by off-vertical-axis rotation (OVAR).

We investigated the horizontal and the vertical otolith-ocular reflex induced by off-vertical-axis rotation and subjective visual vertical in 14 patients with skew deviation due to brain stem lesion. Patients were divided into two groups: the group C (N = 7) with caudal brain stem lesions and the group R (N = 7) with rostral brain stem lesions as defined by the midpons level. The patient group was compared to a control group of 20 healthy subjects. The otolith-ocular reflex was evoked by constant velocity rotation in yaw plane around an axis tilted at 15 deg with respect to gravity. In group C, the horizontal off-vertical-axis nystagmus bias was negative i.e. anticompensatory to chair rotation, when directed toward the lesioned side. Furthermore, patients of group C were presenting with a significant tilt of subjective visual vertical. In group R, a vertical downward offset was induced predominantly in the hypotropic eye and in the direction of rotation away from the lesion. Finally, in patients of group R, horizontal and vertical modulation was increased for rotation away from the lesion. These results are discussed in terms of 1) asymmetrical horizontal and vertical dynamic otolith signals feeding the velocity storage network after brain stem lesion, 2) possible involvement of cerebellar function in OVAN modulation.

Adult↗

PubMed1999

Vestibular information contributes to update retinotopic maps.

In order to investigate the contribution of the vestibular system to spatial orientation, we studied memory-guided saccades in three conditions: visual-memory guided saccades (ViC), saccades to the remembered spatiotopic position of a visual target, after whole-body rotation (SVeC) and saccades to the remembered retinotopic position of a visual target, after whole-body rotation (RVeC). Visual feedback presented after each trial allowed eye position correction. The error was larger in SVeC, but the performance improved throughout the experiment (learning) in that condition only. As learning occurred over the first four trials, we omitted these trials from the average computation, and the significant difference between the conditions disappeared. It is concluded that vestibular information does contribute to update the internal spatial representation of visual information when a visual feedback is provided.

Feedback↗

PubMed1999

Hyper- and hypogravity alter posture in rats compensated on Earth for a vestibular asymmetry.

Head posture and neck muscle activity (EMGs) were examined in unilateral (UL) and bilateral (BL) vestibularly lesioned rats in hypergravity (1.7 g) and hypogravity (0 g) during parabolic flights. Compared with BL rats taken as control, the head and the body of UL deviated toward the lesion side at 0 g and toward the intact side at 1.7 g. Recorded in head fixed condition, left and right EMGs remained symmetrical in BL while UL rats displayed an asymmetry between left and right muscles at 1.7 g, but not at 0 g. These results demonstrate that an experimental otolithic asymmetry, compensated on Earth, can become unbalanced in altered gravity. Paradoxically, the utricular system appears to play a major role in that process.

Animals↗

PubMed1999

Vestibular function in children with the CHARGE association.

BACKGROUND: Histopathological examinations and computed tomographic scans of the temporal bone in patients with the CHARGE association (a malformative syndrome that includes coloboma, heart disease, choanal atresia, retarded development, genital hypoplasia, and ear anomalies, including hypoplasia of the external ear and hearing loss) have shown an absence of semicircular canals and a Mondini form of cochlear dysplasia. Until recently, no information was available concerning a possible loss of vestibular function, which could be a factor in retarded posturomotor development. To our knowledge, this is the first report of otolith tests done on patients with the CHARGE association. OBJECTIVE: To test residual vestibular function in patients with the CHARGE association. STUDY DESIGN: In 7 patients with the CHARGE association, we made electro-oculographic recordings of vestibulo-ocular responses to earth-vertical and off-vertical axis rotations to evaluate the function of the canal and the otolith-vestibular systems. RESULTS: None of the 7 patients had semicircular canals in the computed tomographic scan, and none had canal vestibulo-ocular responses to earth-vertical axis rotation, but all had normal otolith vestibulo-ocular responses to the off-vertical axis rotation test. CONCLUSIONS: These results support the hypothesis of a residual functional otolith organ in the hypoplastic posterior labyrinth of children with the CHARGE association. The severe delays in psychomotor development presented by these children are more likely a consequence of multiple factors: canal vestibular deficit, visual impairment, and environmental conditions (long hospital stays and breathing and feeding problems). The remaining sensitivity of the otolith system to gravity and linear acceleration forces in these children could be exploited in early education programs to improve their posturomotor development.

Abnormalities, Multiple↗