Optical pumping via incoherent Raman transitions

A new optical pumping scheme is presented that uses incoherent Raman transitions to prepare a trapped Cesium atom in a specific Zeeman state within the 6S_{1/2}, F=3 hyperfine manifold. An important advantage of this scheme over existing optical pumping schemes is that the atom can be prepared in any of the F=3 Zeeman states. We demonstrate the scheme in the context of cavity quantum electrodynamics, but the technique is equally applicable to a wide variety of atomic systems with hyperfine ground-state structure.Comment: 8 pages, 4 figure

Cortical topography of intracortical inhibition influences the speed of decision making

The neocortex contains orderly topographic maps; however, their functional role remains controversial. Theoretical studies have suggested a role in minimizing computational costs, whereas empirical studies have focused on spatial localization. Using a tactile multiple-choice reaction time (RT) task before and after the induction of perceptual learning through repetitive sensory stimulation, we extend the framework of cortical topographies by demonstrating that the topographic arrangement of intracortical inhibition contributes to the speed of human perceptual decision-making processes. RTs differ among fingers, displaying an inverted U-shaped function. Simulations using neural fields show the inverted U-shaped RT distribution as an emergent consequence of lateral inhibition. Weakening inhibition through learning shortens RTs, which is modeled through topographically reorganized inhibition. Whereas changes in decision making are often regarded as an outcome of higher cortical areas, our data show that the spatial layout of interaction processes within representational maps contributes to selection and decision-making processes

Occupational lead neurotoxicity: Improvement in behavioural effects after reduction of exposure.

To evaluate critical exposure levels and the reversibility of lead neurotoxicity a group of lead exposed foundry workers and an unexposed reference population were followed up for three years. During this period, tests designed to monitor neurobehavioural function and lead dose were administered. Evaluations of 160 workers during the first year showed dose dependent decrements in mood, visual/motor performance, memory, and verbal concept formation. Subsequently, an improvement in the hygienic conditions at the plant resulted in striking reductions in blood lead concentrations over the following two years. Attendant improvement in indices of tension (20% reduction), anger (18%), depression (26%), fatigue (27%), and confusion (13%) was observed. Performance on neurobehavioural testing generally correlated best with integrated dose estimates derived from blood lead concentrations measured periodically over the study period; zinc protoporphyrin levels were less well correlated with function. This investigation confirms the importance of compliance with workplace standards designed to lower exposures to ensure that individual blood lead concentrations remain below 50 micrograms/dl

Li/MgO with spin sensors as catalyst for the oxidative coupling of methane

Co-doping of Li/MgO, a well-known catalyst for the oxidative coupling of methane, was investigated. It is demonstrated that Gd3+ and Fe3+ can be used as spin sensors in these solids to investigate the structure via EPR spectroscopy. These aliovalent ions occupy Mg2+ sites in the lattice; the expected coupling with charge-compensating neighboring Li+ was detected. A strong increase of the activity was observed. However, all samples suffered from deactivation. The solubility of Gd3+ in MgO turned out to be inhibited. No such restriction was observed for Fe3+

Transcutaneous electrical nerve stimulation using an LTP-like repetitive stimulation protocol for patients with upper limb complex regional pain syndrome: A feasibility study

Introduction This feasibility study aimed to (i) develop a clinical protocol using a long-term potentiation-like repetitive stimulation protocol for transcutaneous electrical nerve stimulation in patients with upper limb complex regional pain syndrome and (ii) develop a research protocol for a single-blind randomised controlled trial investigating the efficacy of transcutaneous electrical nerve stimulation for complex regional pain syndrome. Methods This small-scale single-blind feasibility randomised-controlled trial planned to randomise 30 patients with upper limb complex regional pain syndrome to either a variant of transcutaneous electrical nerve stimulation or placebo transcutaneous electrical nerve stimulation for three weeks. Stimulation comprised 20 pulses over 1 s with a non-stimulation interval of 5 s, a so-called repetitive electrical stimulation protocol following the timing of long-term potentiation. Pain, function and body image were measured at baseline, post-treatment and at three months follow-up. At three months, participants were invited to one-to-one interviews, which were analysed thematically. Results A transcutaneous electrical nerve stimulation protocol with electrodes applied proximal to the area of allodynia in the region of the upper arm was developed. Participant concordance with the protocol was high. Recruitment was below target (transcutaneous electrical nerve stimulation (n = 6), placebo (n = 2)). Mean (SD) pain intensity for the transcutaneous electrical nerve stimulation group on a 0 to 10 scale was 7.2 (2.4), 6.6 (2.8) and 7.8 (1.9), at baseline, post-treatment and at three-month follow-up, respectively. Qualitative data suggested that some patients found transcutaneous electrical nerve stimulation beneficial, easy to use and were still using it at three months. Conclusion Patients tolerated transcutaneous electrical nerve stimulation well, and important methodological information to facilitate the design of a large-scale trial was obtained (ISRCTN48768534). </jats:sec

The nature of iron-oxygen vacancy defect centers in PbTiO3

The iron(III) center in ferroelectric PbTiO3 together with an oxygen vacancy forms a charged defect associate, oriented along the crystallographic c-axis. Its microscopic structure has been analyzed in detail comparing results from a semi-empirical Newman superposition model analysis based on finestructure data and from calculations using density functional theory. Both methods give evidence for a substitution of Fe3+ for Ti4+ as an acceptor center. The position of the iron ion in the ferroelectric phase is found to be similar to the B-site in the paraelectric phase. Partial charge compensation is locally provided by a directly coordinated oxygen vacancy. Using high-resolution synchrotron powder diffraction, it was verified that lead titanate remains tetragonal down to 12 K, exhibiting a c/a-ratio of 1.0721.Comment: 11 pages, 5 figures, accepted in Phys. Rev.

The radical cation of bacteriochlorophyll b. A liquid-phase endor and triple resonance study

The previous termradical cationnext term of bacterioehlorophyll b (BChl b) is investigated by ENDOR and TRIPLE resonance in liquid solution. The experimental hyperfine coupling constants, ten proton and three nitrogen couplings, are compared with the predictions from advanced molecular-orbital calculations (RHF INDO/SP). The detailed picture obtained of the spin density distribution is a prerequisite for the investigation of the primary electron donor previous termradical cationnext term in BChl b containing photosynthetic bacteria

Depth-dependent intracortical myelin organization in the living human brain determined by in vivo ultra-high field magnetic resonance imaging

Background: Intracortical myelin is a key determinant of neuronal synchrony and plasticity that underpin optimal brain function. Magnetic resonance imaging (MRI) facilitates the examination of intracortical myelin but presents with methodological challenges. Here we describe a whole-brain approach for the in vivo investigation of intracortical myelin in the human brain using ultra-high field MRI. Methods: Twenty-five healthy adults were imaged in a 7 Tesla MRI scanner using diffusion-weighted imaging and a T 1 -weighted sequence optimized for intracortical myelin contrast. Using an automated pipeline, T 1 values were extracted at 20 depth-levels from each of 148 cortical regions. In each cortical region, T 1 values were used to infer myelin concentration and to construct a non-linearity index as a measure the spatial distribution of myelin across the cortical ribbon. The relationship of myelin concentration and the non-linearity index with other neuroanatomical properties were investigated. Five patients with multiple sclerosis were also assessed using the same protocol as positive controls. Results: Intracortical T 1 values decreased between the outer brain surface and the gray-white matter boundary following a slope that showed a slight leveling between 50% and 75% of cortical depth. Higher-order regions in the prefrontal, cingulate and insular cortices, displayed higher non-linearity indices than sensorimotor regions. Across all regions, there was a positive association between T 1 values and non-linearity indices (P &lt; 10 125 ). Both T 1 values (P &lt; 10 125 ) and non-linearity indices (P &lt; 10 1215 ) were associated with cortical thickness. Higher myelin concentration but only in the deepest cortical levels was associated with increased subcortical fractional anisotropy (P = 0.05). Conclusions: We demonstrate the usefulness of an automatic, whole-brain method to perform depth-dependent examination of intracortical myelin organization. The extracted metrics, T 1 values and the non-linearity index, have characteristic patterns across cortical regions, and are associated with thickness and underlying white matter microstructure

Effects of Aging on Paired-Pulse Behavior of Rat Somatosensory Cortical Neurons

Aging affects all levels of neural processing including changes of intracortical inhibition and cortical excitability. The paired-pulse stimulation protocol, the application of 2 stimuli in close succession, is used to investigate cortical excitability. The paired-pulse behavior is characterized by the fact that the second response is significantly suppressed at short interstimulus intervals (ISIs) but approaches the first response with increasing ISIs. However, there are controversial reports about the influence of age on paired-pulse behavior. We therefore used pairs of tactile stimuli (ISIs from tens to hundreds of milliseconds) to record extracellular responses of somatosensory cortical neurons of young and aged rats. Paired-pulse behavior was quantified as the ratio of the amplitude of the second response divided by the first. For all ISIs, we found significantly higher ratios in the old animals indicating reduced paired-pulse suppression (PPS). Evaluation of the single response components revealed a significant reduction of the response to the first stimulus for old animals but no age-dependent decrement to the second. Changes in PPS are usually mediated by modulating the second response characteristics. Thus, our data demonstrate reduced PPS due to an overall reduction of the first response as a form of modified PPS developing at old age

Differential Effects of Aging on Fore– and Hindpaw Maps of Rat Somatosensory Cortex

Getting older is associated with a decline of cognitive and sensorimotor abilities, but it remains elusive whether age-related changes are due to accumulating degenerational processes, rendering them largely irreversible, or whether they reflect plastic, adaptational and presumably compensatory changes. Using aged rats as a model we studied how aging affects neural processing in somatosensory cortex. By multi-unit recordings in the fore- and hindpaw cortical maps we compared the effects of aging on receptive field size and response latencies. While in aged animals response latencies of neurons of both cortical representations were lengthened by approximately the same amount, only RFs of hindpaw neurons showed severe expansion with only little changes of forepaw RFs. To obtain insight into parallel changes of walking behavior, we recorded footprints in young and old animals which revealed a general age-related impairment of walking. In addition we found evidence for a limb-specific deterioration of the hindlimbs that was not observed in the forelimbs. Our results show that age-related changes of somatosensory cortical neurons display a complex pattern of regional specificity and parameter-dependence indicating that aging acts rather selectively on cortical processing of sensory information. The fact that RFs of the fore- and hindpaws do not co-vary in aged animals argues against degenerational processes on a global scale. We therefore conclude that age-related alterations are composed of plastic-adaptive alterations in response to modified use and degenerational changes developing with age. As a consequence, age-related changes need not be irreversible but can be subject to amelioration through training and stimulation