Giant thermal Hall conductivity in the pseudogap phase of cuprate superconductors.

The nature of the pseudogap phase of the copper oxides ('cuprates') remains a puzzle. Although there are indications that this phase breaks various symmetries, there is no consensus on its fundamental nature1. Fermi-surface, transport and thermodynamic signatures of the pseudogap phase are reminiscent of a transition into a phase with antiferromagnetic order, but evidence for an associated long-range magnetic order is still lacking2. Here we report measurements of the thermal Hall conductivity (in the x-y plane, κxy) in the normal state of four different cuprates-La1.6-xNd0.4SrxCuO4, La1.8-xEu0.2SrxCuO4, La2-xSrxCuO4 and Bi2Sr2-xLaxCuO6+δ. We show that a large negative κxy signal is a property of the pseudogap phase, appearing at its critical hole doping, p*. It is also a property of the Mott insulator at p ≈ 0, where κxy has the largest reported magnitude of any insulator so far3. Because this negative κxy signal grows as the system becomes increasingly insulating electrically, it cannot be attributed to conventional mobile charge carriers. Nor is it due to magnons, because it exists in the absence of magnetic order. Our observation is reminiscent of the thermal Hall conductivity of insulators with spin-liquid states4-6, pointing to neutral excitations with spin chirality7 in the pseudogap phase of cuprates.

Neural mass modeling of power-line magnetic fields effects on brain activity.

Neural mass models are an appropriate framework to study brain activity, combining a high degree of biological realism while being mathematically tractable. These models have been used, with a certain success, to simulate brain electric (electroencephalography, EEG) and metabolic (functional magnetic resonance imaging, fMRI) activity. However, concrete applications of neural mass models have remained limited to date. Motivated by experimental results obtained in humans, we propose in this paper a neural mass model designed to study the interaction between power-line magnetic fields (MFs) (60 Hz in North America) and brain activity. The model includes pyramidal cells; dendrite-projecting, slow GABAergic neurons; soma-projecting, fast GABAergic neurons; and glutamatergic interneurons. A simple phenomenological model of interaction between the induced electric field and neuron membranes is also considered, along with a model of post-synaptic calcium concentration and associated changes in synaptic weights Simulated EEG signals are produced in a simple protocol, both in the absence and presence of a 60 Hz MF. These results are discussed based on results obtained previously in humans. Notably, results highlight that (1) EEG alpha (8-12 Hz) power can be modulated by weak membrane depolarizations induced by the exposure; (2) the level of input noise has a significant impact on EEG power modulation; and (3) the threshold value in MF flux density resulting in a significant effect on the EEG depends on the type of neuronal populations modulated by the MF exposure. Results obtained from the model shed new light on the effects of power-line MFs on brain activity, and will provide guidance in future human experiments. This may represent a valuable contribution to international regulation agencies setting guidelines on MF values to which the general public and workers can be exposed.

Neurophysiological and behavioral effects of a 60 Hz, 1,800 µT magnetic field in humans.

The effects of time-varying magnetic fields (MF) on humans have been actively investigated for the past three decades. One important unanswered question is the potential for MF exposure to have acute effects on human biology. Different strategies have been used to tackle this question using various physiological, neurophysiological and behavioral indicators. For example, researchers investigating electroencephalography (EEG) have reported that extremely low frequency (ELF, <300 Hz) MF can increase resting occipital alpha rhythm (8-12 Hz). Interestingly, other studies have demonstrated that human motricity can be modulated by ELF MF: a reduction of anteroposterior standing balance or a decrease of physiological tremor intensity have been reported as consequences of exposure. However, the main limitation in this domain lies in the lack of results replication, possibly originating from the large variety of experimental approaches employed. Therefore, the present study aimed to investigate the effects of a 60 Hz, 1,800 µT MF exposure on neurophysiological (EEG) and neuromotor (standing balance, voluntary motor function, and physiological tremor) aspects in humans using a single experimental procedure. Though results from this study suggest a reduction of human standing balance with MF exposure, as well as an increase of physiological tremor amplitude within the frequency range associated with central nervous system contribution, no exposure effect appeared on other investigated parameters (e.g., EEG or voluntary motor control). These results suggest that 1 h of 60 Hz, 1,800 µT MF exposure may modulate human involuntary motor control without being detected in the cortical electrical activity.

A comparison of MR-based attenuation correction in PET versus SPECT.

Attenuation correction (AC) is a critical step in the reconstruction of quantitatively accurate positron emission tomography (PET) and single photon emission computed tomography (SPECT) images. Several groups have proposed magnetic resonance (MR)-based AC algorithms for application in hybrid PET/MR systems. However, none of these approaches have been tested on SPECT data. Since SPECT/MR systems are under active development, it is important to ascertain whether MR-based AC algorithms validated for PET can be applied to SPECT. To investigate this issue, two imaging experiments were performed: one with an anthropomorphic chest phantom and one with two groups of canines. Both groups of canines were imaged from neck to abdomen, one with PET/CT and MR (n = 4) and the other with SPECT/CT and MR (n = 4), while the phantom was imaged with all modalities. The quality of the nuclear medicine reconstructions using MR-based attenuation maps was compared between PET and SPECT on global and local scales. In addition, the sensitivity of these reconstructions to variations in the attenuation map was ascertained. On both scales, it was found that the SPECT reconstructions were of higher fidelity than the PET reconstructions. Further, they were less sensitive to changes to the MR-based attenuation map. Thus, MR-based AC algorithms that have been designed for PET/MR can be expected to demonstrate improved performance when used for SPECT/MR.

Effects of acute hypoxia on postural and kinetic tremor.

Human physiological tremor is a complex phenomenon that is modulated by numerous mechanical, neurophysiological, and environmental conditions. Researchers investigating tremor have suggested that acute hypoxia increases tremor amplitude. Based on the results of prior studies, we hypothesized that human participants exposed to a simulated altitude of 4,500 m would display an increased tremor amplitude within the 6-12 Hz frequency range. Postural and kinetic tremors were recorded with a laser system in 23 healthy male participants before, during, and after 1 h of altitude-induced hypoxia. A large panel of tremor characteristics was used to investigate the effect of hypoxia. Acute hypoxia increased tremor frequency content between 6 and 12 Hz during both postural and kinetic tremor tasks (P < 0.05, F = 6.142, Eta(2) = 0.24 and P < 0.05, F = 3.767 Eta(2) = 0.14, respectively). Although the physiological mechanisms underlying the observed changes in tremor are not completely elucidated yet, this study confirms that acute hypoxia increases tremor frequency in the 6-12 Hz range. Furthermore, this study indicates that changes in physiological tremor can be detected at lower hypoxemic levels than previously reported (blood saturation in oxygen = 80.9%). The effects of hypoxia mainly result from a cascade of events starting with the activation of the hypothalamic-pituitary-adrenal axis causing in turn an increase in catecholamine release, leading to an augmentation of tremor amplitude in the 6- to 12-Hz interval and heart rate increase.

Using wavelet analysis to detect the influence of low frequency magnetic fields on human physiological tremor.

The influence of extremely low frequency magnetic fields (ELF-MFs) on human physiological processes and, in particular, on motor activity is still not established with certainty. Using the wavelet-transform approach, changes in the characteristics of human finger micromovement are studied in the presence of a low intensity MF centred at the level of the head. Different approaches to nonstationary signal analysis involving real as well as complex wavelet functions are considered. We find evidence that ELF-MFs lead to more regular postural tremor and more homogeneous energy distribution.

Accelerometric measurement of involuntary movements during pallidal deep brain stimulation of patients with generalized dystonia.

Accelerometric activity during rest and posture was quantified in the upper dominant limb of 14 patients with primary or secondary dystonia and five healthy control subjects. Data were recorded before and after bilateral implantation of the stimulating electrodes in the Globus Pallidus internus. Clinical evaluation was based on the Burke-Marsden-Fahn's Dystonia Rating Scale (BMFDRS). For the patient group, I(t), the integral (i.e. area) of the acceleration power spectrum over the total frequency range (0.6-16 Hz) decreased as the clinical state of the patients improved following deep brain stimulation (p < 0.01) during rest and posture. Ten days after surgery, there were no I(t) differences between control subjects and patients (p > 0.05). A significant correlation was found between the global BMFDRS scores and I(t) for rest (p < 0.01) but not for posture. No significant correlation was found between I(t) and a partial BMFDRS score for the right arm for rest or posture. The integral I(t) provides a valid indicator of the motor activity generated by the arm of the patient but further analyses are needed to monitor patients' progress not only during their hospitalization but also after they are released from the hospital, and to understand why this measure does not correlate with partial BMFDRS scores.

[Kinematic evaluation of dystonic syndromes in patients treated with deep brain stimulation]. / La cinématique dans l'évaluation des syndromes dystoniques sous stimulation cérébrale profonde.

INTRODUCTION: Quantification of motor functions of patients with dystonic syndromes treated by chronic high frequency stimulation of the internal globulus pallidus is a challenge. OBJECTIVE: Through a series of clinical examples this paper shows that kinematic analysis of movements in dystonic syndromes treated by deep brain stimulation (DBS) is a complement to clinical evaluation. In addition, it provides valuable information for early detection of improvement or impairment of movements associated with modifications of stimulation parameters. METHOD: Thirteen dystonic patients and eleven reference subjects completed three tests (i.e., rest: lying supine; posture: standing with arms held in front (at shoulder height); and alternative movements: bimanual finger-to-nose test). These tests were recorded with an electromagnetic system quantifying movement kinematics (position) in three-dimensional space. RESULTS: From the recorded data, several indices were developed and provided a quantitative evaluation of movements during each test. In addition, a clinical evaluation (BMFDRS) was also completed. No correlation between clinical and kinematic evaluations was found. CONCLUSION: It is shown that kinematic analysis is a useful complement of clinical evaluation and can assist clinicians in monitoring the evolution of movements in dystonic patients treated by DBS in a simple, reliable and valid fashion.

Thrombocytopenia and Plasmodium falciparum malaria in children with different exposures.

We studied thrombocytopenia during acute Plasmodium falciparum malaria in 64 traveller children from Paris (France), 85 children from Dakar (Senegal) with an intermittent exposure (69 with severe attack or cerebral malaria), and 81 children from Libreville (Gabon) with a perennial exposure (43 with severe attack or cerebral malaria). Initial thrombocytopenia was present in 43-58% of children with P falciparum malaria but was not more frequent in severe outcome or cerebral malaria. Low parasitaemia may lead to the misdiagnosis of malaria and delayed treatment when there is associated thrombocytopenia

Toxicologic profile of iobitridol, a new nonionic low-osmolality contrast medium.

PURPOSE: The toxicologic profile of iobitridol, a new nonionic low-osomolality contrast medium, was evaluated in compliance with the current regulatory requirements in Europe, the USA and Canada. MATERIAL AND METHODS: The toxicity of iobitridol was tested following acute or repeated i.v. administration in several different species (mouse, rat, dog); single oral administration in the mouse and intracisternal injection in the rat. Furthermore, teratogenicity and mutagenicity were evaluated in the rat and rabbit. Local perivenous toxicity was assessed in the rabbit. RESULTS: The acute toxicity of iobitridol in the mouse is equivalent to that of iohexol, a reference product tested under the same conditions. Chronic administration (daily injections i.v. injection over 4 weeks) in the rat and dog did not demonstrate any particular toxicity for iobitridol. It should be noted that, unlike iohexol, iobitridol did not provoke any vacuolization of the renal tubular cells in the rat following repeated injections. Furthermore, this contrast agent did not show any teratogenic or mutagenic potential. The typical local inflammatory signs observed following perivenous injection in the rabbit were low in intensity and reversible. CONCLUSION: The toxicologic profile of iobitridol appears to be favorable and does not show any particular risk for clinical use under the usual indications of water soluble iodinated contrast agents.

[Is unilateral total lobectomy adequate treatment for a single malignant thyroid nodule? 67 patients operated upon between 5 and 18 years age (author's transl)]. / La lobectomie totale unilatérale est-elle un traitement chirurgical suffisant pour un nodule thyroïdien solitaire carcinomateux? 67 malades opérés depuis 5 à 18 ans.

In the treatment of thyroid carcinoma, there is still some discussion about the best operation for a solitary and well encapsulated nodule. 18 years ago, it was decided to treat every case of "cold" thyroid nodule by total lobectomy and isthmectomy. 56 patients were reevaluated 5 to 18 years after such limited operation for malignant nodules. 8 of them died between the 19 th month and the 14 th year after surgery, the death being possibly related to the thyroid cancer in only 4 patients, but without any clinical evidence of local recurrence. Among 50 surviving patients, only one controlateral recurrence was observed, two years after lobectomy; it was treated by surgical totalisation of thyroidectomy, without any new recurrence after 10 more years. These results (although the small number of cases, and too short follow-up exclude definitive conclusions) are comparable to those obtained by a more aggresive surgical approach, but have the great advantage of total absence of any functional sequellae. So are we encouraged to go further in the experience of a rather conservative surgery in the treatment of uninodular thyroid carcinoma.