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Biomedical subjects

B Dan

Publications and source records attributed to B Dan.

At least 19 recordsLinked to original sources
PubMed2006

Effect of gravity on human spontaneous 10-Hz electroencephalographic oscillations during the arrest reaction.

Electroencephalographic oscillations at 10 Hz (alpha and mu rhythms) are the most prominent rhythms observed in awake, relaxed (eye-closed) subjects. These oscillations may be considered as a marker of cortical inactivity or an index of the active inhibition of the sensory information. Different cortical sources may participate in the 10-Hz oscillation and appear to be modulated by the sensory context and functional demands. In microgravity, the marked reduction in multimodal graviceptive inputs to cortical networks participating in the representation of space could be expected to affect the 10-Hz activity. The effect of microgravity on this basic oscillation has heretofore not been studied quantitatively. Because the alpha rhythm has a functional role in the regulation of network properties of the visual areas, we hypothesised that the absence of gravity would affect its strength. Here, we report the results of an experiment conducted over the course of 3 space flights, in which we quantified the power of the 10-Hz activity in relation to the arrest reaction (i.e., in 2 distinct physiological states: eyes open and eyes closed). We observed that the power of the spontaneous 10-Hz oscillation recorded in the eyes-closed state in the parieto-occipital (alpha rhythm) and sensorimotor areas (mu rhythm) increased in the absence of gravity. The suppression coefficient during the arrest reaction and the related spectral perturbations produced by eye-opening/closure state transition also increased in on orbit. These results are discussed in terms of current theories on the source and the importance of the alpha rhythm for cognitive function.

Adult↗
PubMed2005

Strongly accelerated and humidity-independent drying of nanochannels induced by sharp corners.

Measurements are shown indicating that the drying rate of nanochannels can be enhanced by up to 3 orders of magnitude relative to drying by vapor diffusion, and that the drying rate is independent of the relative humidity of the environment up to a relative humidity of more than 90%. Micromachined Pyrex glass nanochannels of 72 nm height and with sharp corners (corner angles 7 degrees) were used. Available theory shows that the sharp corners function as a low-resistance pathway for liquid water, siphoning (wicking) the water to a location close to the channel exit before it evaporates. The described phenomena are of importance for the understanding of drying processes in industry and agriculture. The introduction of sharp corners or grooves can furthermore be beneficial for the functioning of microheat pipes and capillary-pumped loops.

Journal Article↗
PubMed2005

[Imaging in paediatric epilepsy].

Epilepsy is a chronic disease, often with an onset during childhood and characterized by spontaneous and recurrent seizures. It concerns 0.5-1% of children under 16 years of age. A classification proposed by the International League Against Epilepsy (ILEA) in 2001 takes into account recent genetic factors involved in epilepsy and attenuates the sharp demarcation between generalized and partial seizures. This classification tends to define whether imaging is indicated or not. Imaging is useless in simple cases of fits associated with hyperthermia and in benign idiopathic epilepsy. It is debated if it is a first episode of epilepsy without a particular context and no neurological signs. In all other cases of epilepsy in children, imaging is indicated. In descending order of frequency the possible causes include malformations (as abnormal gyral development and phakomatoses), hypoxic-ischemic lesions, non-accidental injuries, infections, metabolic diseases and tumors. Being much more sensitive than computed tomography (CT), magnetic resonance imaging (MRI) is the technique of choice to identify an underlying cause in symptomatic epilepsy. Clinical data are mandatory in order to direct a proper MRI investigation. The recently developed diffusion-weighted sequence is particularly useful in the acute phase of certain events such as hypoxia-ischemia, trauma and metabolic disease. CT scan is used in emergency situations and also as a complement to MRI for example to identify calcified lesions. In this way, imaging contributes to establish the nature and define the extension of epileptogenic lesions, thereby guiding therapeutic management. MRI also allows follow-up of the consequences of repeated seizures (such as mesial temporal sclerosis and selective neuronal necrosis) on the cerebral parenchyma and plays a role in the establishment of a prognosis.

Adolescent↗
PubMed2005

Fast cerebellar oscillation associated with ataxia in a mouse model of Angelman syndrome.

Ataxia may result from various cerebellar cortex dysfunctions. It is included in the diagnostic criteria of Angelman syndrome, a human neurogenetic condition. In order to better understand the cerebellar dysfunction in this condition, we recorded in vivo cerebellar activity in a mouse model of Angelman syndrome produced by null mutation of the maternal Ube3a gene. We found fast oscillation (approximately 160 Hz) in the cerebellar cortex sustained by abnormally increased Purkinje cell firing rate and rhythmicity. This oscillation is inhibited by sensory stimulation and gap junction or GABA(A) receptor blockers. A physiologically similar oscillation was previously found in mice lacking calcium-binding proteins that also present ataxia, but never in wild-type mice. We propose that fast oscillation in the cerebellar cortex is implicated in the cerebellar symptomatology of Angelman syndrome.

Angelman Syndrome↗
PubMed2005

Mono- and dual-frequency fast cerebellar oscillation in mice lacking parvalbumin and/or calbindin D-28k.

Calbindin is a fast Ca2+-binding protein expressed by Purkinje cells and involved in their firing regulation. Its deletion produced approximately 160-Hz oscillation sustained by synchronous, rhythmic Purkinje cells in the cerebellar cortex of mice. Parvalbumin is a slow-onset Ca2+-binding protein expressed in Purkinje cells and interneurons. In order to assess its function in Purkinje cell firing regulation, we studied the firing behavior of Purkinje cells in alert mice lacking parvalbumin (PV-/-), calbindin (CB-/-) or both (PV-/- CB-/-) and in wild-type controls. The absence of either protein resulted in Purkinje cell firing alterations (decreased complex spike duration and pause, increased simple spike firing rate) that were more pronounced in CB-/- than in PV-/- mice. Cumulative effects were found in complex spike alterations in PV-/- CB-/- mice. PV-/- and CB-/- mice manifested approximately 160-Hz oscillation that was sustained by Purkinje cells firing rhythmically and synchronously along the parallel fiber axis. This oscillation was dependent on GABA(A), N-methyl-D-aspartate and gap junction transmission. PV-/- CB-/- mice exhibited a dual-frequency (110 and 240 Hz) oscillation. The instantaneous spectral densities of both components were inversely correlated. Simple and complex spikes of Purkinje cells were phase-locked to one of the two oscillation frequencies. Mono- and dual-frequency oscillations presented similar pharmacological properties. These results demonstrate that the absence of the Ca2+ buffers parvalbumin and calbindin disrupts the regulation of Purkinje cell firing rate and rhythmicity in vivo and suggest that precise Ca2+ transient control is required to maintain the normal spontaneous arrhythmic and asynchronous firing pattern of the Purkinje cells.

2-Amino-5-phosphonovalerate↗
PubMed2004

Meningitis following basal skull fracture in two in-line skaters.

INTRODUCTION: In-line skating has been reported to cause severe head injury. Basilar skull fracture (BSF) is associated with a high risk of complication. CASE REPORT: We report two children who had bacterial meningitis following seemingly trivial in-line skating injuries. In both, anterior BSF was diagnosed retrospectively following occurrence of Streptococcus pneumoniae meningitis. DISCUSSION: The clinical signs indicating BSF depend on the fracture location. Plain skull radiography and computed tomography (CT) are not sensitive enough to detect thin fractures in the anterior cranial fossa. We argue that high resolution multiple-plane CT and coronal T2-weighted magnetic resonance imaging are indicated to diagnose BSF.

Child↗
PubMed2004

[Headache in childhood: which diagnostic imaging strategies?].

There are various causes of headaches in children. The majority of cases are considered as primary and include migraine and tension headaches. Headaches secondary to an underlying pathology are much less frequent. The aim of imaging will be to depict lesions that can benefit from specific therapy and hence improve life quality and expectancy of the affected child. In case of secondary headaches, imaging will have to precise the diagnosis, which is based mainly upon history of the disease and clinical findings. These findings are important to the radiologist as they will help to choose the more adequate technique between CT scan and MRI. This choice is based upon the presumed diagnoses, degree of emergency and availability of the technique. Knowledge of the differential diagnoses influences the way to perform the examination itself (choice of slice thickness, plane of imaging, MR sequences, need for an MR angiogram or injection of contrast medium...). In our opinion, dedicated MR imaging is the technique of choice to investigate secondary headaches in children given its superior sensitivity in depicting certain tumors (glioma of the pons, posterior fossa tumors...), intracranial hypotension, Chiari I malformation, lesions of the hypothalamo-hypophyseal axis etc...

Adolescent↗
PubMed2003

A dynamic recurrent neural network for multiple muscles electromyographic mapping to elevation angles of the lower limb in human locomotion.

This paper describes the use of a dynamic recurrent neural network (DRNN) for simulating lower limb coordination in human locomotion. The method is based on mapping between the electromyographic signals (EMG) from six muscles and the elevation angles of the three main lower limb segments (thigh, shank and foot). The DRNN is a fully connected network of 35 hidden units taking into account the temporal relationships history between EMG and lower limb kinematics. Each EMG signal is sent to all 35 units, which converge to three outputs. Each output neurone provides the kinematics of one lower limb segment. The training is supervised, involving learning rule adaptations of synaptic weights and time constant of each unit. Kinematics of the locomotor movements were recorded and analysed using the opto-electronic ELITE system. Comparative analysis of the learning performance with different types of output (position, velocity and acceleration) showed that for common gait mapping velocity data should be used as output, as it is the best compromise between asymptotic error curve, rapid convergence and avoidance of bifurcation. Reproducibility of the identification process and biological plausibility were high, indicating that the DRNN may be used for understanding functional relationships between multiple EMG and locomotion. The DRNN might also be of benefit for prosthetic control.

Adult↗
PubMed2003

Sudden infant deaths: stress, arousal and SIDS.

The prevalence of the Sudden Infant Death Syndrome (SIDS) has dropped in most countries following the development of education campaigns on the avoidance of preventable risk factors for SIDS. These include factors in the infant's micro environment, such as prenatal passive smoking, administration of sedative drugs, prone sleep, high ambient temperature or sleeping with the face covered. Sleep laboratory studies have shown that these risk conditions contribute to the development of respiratory and autonomic disorders and reduce the child's arousability. The opposite effects were seen when studying factors protective from SIDS, such as breastfeeding or the use of a pacifier. In victims of SIDS, similar breathing, autonomic and arousal characteristics were recorded days or weeks before their death. It is concluded that in some infants, already immature control mechanisms can be aggravated by environmental factors.

Arousal↗
PubMed2003

Oral ketamine in paediatric non-convulsive status epilepticus.

In children, non-convulsive status epilepticus (NCSE) is rare and difficult to treat. Response to steroids and GABAergic medication is variable and often decreases with increasing duration of NCSE. We present our experience with oral ketamine, an NMDA-receptor antagonist, administered to five children with severe epilepsy (Lennox-Gastaut Syndrome, myoclonic-astatic epilepsy, progressive myoclonic epilepsy and Pseudo-Lennox Syndrome) during an episode of NCSE. Resolution of NCSE was documented in all cases clinically and electroencephalographically within 24-48 hours of starting ketamine. No significant side effects were noted.

Administration, Oral↗
PubMed2003

Facilitation of motor evoked potentials in ischemic stroke patients: prognostic value and neurophysiologic correlations.

OBJECTIVE: To investigate the predictive value of paired transcranial magnetic stimulation (TMS) at rest in stroke patients in comparison with the predictive value derived from data obtained by single TMS during facilitation. METHODS: Fifty-six patients with a single ischemic lesion and no electromyographic responses from single TMS in the resting affected hand muscles participated in the study. TMS assessment was performed 32 days post-stroke. It consisted of a single stimulation at maximal output during facilitation (controlateral hand grip and elbow flexion) and a paired-pulse stimulation at rest with two stimuli at maximal output at interstimulus intervals ranging from 15 to 100 ms. Two blind clinical assessments using the 'motricity index' were carried out 26 and 76 days post-stroke. RESULTS: Thirty-seven percent of patients were responsive to single TMS during facilitation, had better clinical scores at both evaluations and better clinical recovery. Fifty-four percent of patients responded to paired TMS, had better clinical scores at the second evaluation and better clinical recovery. All patients who responded to the single stimulation paradigm also responded to the paired one. CONCLUSIONS: A positive correlation was found between the responsiveness to both the TMS paradigms (facilitation procedure and paired stimulation) and clinical recovery. This underlines the importance of facilitation during single TMS in stroke patients and suggests that paired TMS at rest might supplement this procedure in stroke studies.

Adult↗
PubMed2003

Angelman syndrome reviewed from a neurophysiological perspective. The UBE3A-GABRB3 hypothesis.

Angelman syndrome is characterised by neurodevelopmental impairment (with or without epileptic seizures) associated with functional deficit of the UBE3A gene. Different mechanisms of UBE3A inactivation correlate with clinical phenotypes of varying severity. However, three distinctive, highly consistent electroencephalographic rhythmic patterns can be observed in almost all patients irrespective of genotype, clinical severity and the presence or severity of a seizure disorder. Pattern I consists of runs of high amplitude 2 - 3/s rhythmic activity predominating over the frontal regions. Pattern II consists of more diffuse runs of 4 - 6/s rhythmic activity. Pattern III consists of bursts or runs of high amplitude 3 - 5/s rhythmic activity, maximal over the occipital region, sometimes containing small spikes and facilitated by eye closure. We review the available neurophysiological evidence from human and animal studies in the light of recent molecular advances. Electroencephalographic features in both patients and various mouse models point to two separable categories: characteristic rhythmic patterns, which are not related to epilepsy, and less specific epilepsy-related discharge activity. These features are consistent with a model of cortical and thalamo-cortical dysfunction resulting from dysregulation of synaptic GABAergic neurotransmission by (1) deficient recruitment of functional GABA (A) receptors related to reduced UBE3A gene expression in all cases and (2) decreased amount of beta3 sub-unit in these receptors related to reduced GABRB3 gene expression in deletion cases.

Angelman Syndrome↗
PubMed2003

[Chronic subdural hematoma and extramedullary erythropoiesis in an infant].

We report the case of a six-month old child with bilateral chronic subdural hematoma of unknown origin containing erythroblasts, metamyelocytes and blast-like cells. No such cells were found in venous blood. No primary neoplastic disorder was found. Throughout a 19-month follow-up period, general and neurodevelopmental examination remained normal with complete resolution of the subdural haematoma in the presence of macrocephaly. We discuss the origin and role of these cells.

Brain↗
PubMed2003

[Angelman syndrome: clinical and genetic model].

Angelman syndrome is a neurogenetic disorder characterized by developmental delay, absence of speech, motor impairment, epilepsy and a peculiar behavioural phenotype associated with abnormalities of chromosome 15q11-13. Precise diagnosis carries clinical and genetic counseling implications. However, many clinicians still seem unfamiliar with it despite the severity and typical aspects of presentation. Beyond individual situations, Angelman syndrome can serve as a model opening broad questioning of genetic and epigenetic influences in neurology, as well as of several concepts such as psychomotor development, cerebral palsy, behavioural phenotypes and epileptic syndromes. Recent advances in molecular biology and animal models of the syndrome provide new data which must be included in our interpretation of Angelman syndrome.

Angelman Syndrome↗
PubMed2002

Sudden infant deaths: from epidemiology to physiology.

The incidence of sudden infant death syndrome (SIDS) has dropped significantly in most countries following the development of education campaigns on the avoidance of risk factors for SIDS. However, questions have been raised about the physiological mechanism responsible for the effects of these environmental risk factors. Since 1985, a series of prospective, multicentric studies have been developed to address these questions; over 20,000 infants were recorded during one night in a sleep laboratory and among these, 40 infants eventually died of SIDS. In this review, the following methods were employed: sleep recordings and analysis, monitoring procedure, data analysis of sleep stages, cardiorespiratory and oxygen saturation, scoring of arousals, spectral analysis of the heart rate and the determination of arousal thresholds, and statistical analysis and the results including sleep apneas, arousals and heart rate and autonomic controls in both future SIDS victims and normal infants were introduced separately. In addition, the physiological effect of prenatal risk factors (maternal smoking during gestation) and postnatal risk factors (administration of sedative drugs, prone sleeping position, ambient temperature, sleeping with the face covered by a bed sheet, pacifiers and breastfeeding) in normal infants were analyzed. In conclusion, the physiological studies undertaken on the basis of epidemiological findings provide some clues about the physiological mechanisms linked with SIDS. Although the description of the mechanisms responsible for SIDS is still far from complete, it appears to involve both arousal responses and cardiac autonomic controls during sleep-wake processes.

Autonomic Nervous System↗