Short timescale modulation of cortical and cerebellar activity in the early phase of motor sequence learning: an fMRI study.

Motor learning is a multi-stage process, in which the involvement of different brain regions is related to the specific stage. We aimed at characterising short timescale changes of brain activity induced by motor sequence learning. Twenty healthy volunteers performed a serial reaction time task during an MRI session in a 3 T scanner. The task consisted of two conditions: repeated and random, that were compared over the whole fMRI run, as well as within sections, to investigate brain activity modulating related to the learning stage. The whole fMRI run analysis showed a stronger response for the repeated condition in fronto-parietal regions, cerebellum and thalamus. The analysis on sections showed initially increased right cerebellar activity. In the subsequent phase, bilateral cerebellar activity was observed, while no increased activity was seen in the last phase, when the learning was established. At the neocortical level, the repeated condition showed stronger activity at first in fronto-parietal regions bilaterally, then lateralized to the right hemisphere in the last learning phase. This study showed short time scale brain activity modulation in cortical and cerebellar regions with involvement of different brain regions over the learning process not restricted to the motor circuit.

Surgical Impact of the Montgomery Implant System on Arytenoid Cartilage and the Paralyzed Vocal Fold.

OBJECTIVES/HYPOTHESIS: Medialization thyroplasty (MT) has become a prominent method for treating glottal insufficiency. This study aimed to visualize the biomechanical influence of a medialization implant on arytenoid cartilage, particularly on the length and level of paralyzation in the vocal fold, in patients with unilateral vocal fold paralysis. STUDY DESIGN: Prospective study. METHODS: We recruited 15 patients (10 men, 5 women) with unilateral vocal fold paralysis that underwent MT with a Montgomery® thyroplasty implant. We performed high-resolution computed tomography of the arytenoid cartilage before and after MT and analyzed the three-dimensional images. To visualize the movement of the arytenoid and to measure the lengthening of the vocal fold, we superimposed pre- and postoperative 3D images with MIMICS software. RESULTS: On the affected side, the implant pushed the arytenoid backwards. In addition, the vocal process of the arytenoid was inwardly rotated. These movements resulted in an elongated, augmented vocal fold on the affected side. CONCLUSION: MT led to an elongated, medialized vocal fold on the treated side. After the intervention, the vocal folds on both sides were the same length in the phonatory position.

Greenland subglacial drainage evolution regulated by weakly connected regions of the bed.

Penetration of surface meltwater to the bed of the Greenland Ice Sheet each summer causes an initial increase in ice speed due to elevated basal water pressure, followed by slowdown in late summer that continues into fall and winter. While this seasonal pattern is commonly explained by an evolution of the subglacial drainage system from an inefficient distributed to efficient channelized configuration, mounting evidence indicates that subglacial channels are unable to explain important aspects of hydrodynamic coupling in late summer and fall. Here we use numerical models of subglacial drainage and ice flow to show that limited, gradual leakage of water and lowering of water pressure in weakly connected regions of the bed can explain the dominant features in late and post melt season ice dynamics. These results suggest that a third weakly connected drainage component should be included in the conceptual model of subglacial hydrology.

A Temperate Alpine Glacier as a Reservoir of Polychlorinated Biphenyls: Model Results of Incorporation, Transport, and Release.

In previous studies, the incorporation of polychlorinated biphenyls (PCBs) has been quantified in the accumulation areas of Alpine glaciers. Here, we introduce a model framework that quantifies mass fluxes of PCBs in glaciers and apply it to the Silvretta glacier (Switzerland). The models include PCB incorporation into the entire surface of the glacier, downhill transport with the flow of the glacier ice, and chemical fate in the glacial lake. The models are run for the years 1900-2100 and validated by comparing modeled and measured PCB concentrations in an ice core, a lake sediment core, and the glacial streamwater. The incorporation and release fluxes, as well as the storage of PCBs in the glacier increase until the 1980s and decrease thereafter. After a temporary increase in the 2000s, the future PCB release and the PCB concentrations in the glacial stream are estimated to be small but persistent throughout the 21st century. This study quantifies all relevant PCB fluxes in and from a temperate Alpine glacier over two centuries, and concludes that Alpine glaciers are a small secondary source of PCBs, but that the aftermath of environmental pollution by persistent and toxic chemicals can endure for decades.

Polychlorinated Biphenyls in a Temperate Alpine Glacier: 2. Model Results of Chemical Fate Processes.

We present results from a chemical fate model quantifying incorporation of polychlorinated biphenyls (PCBs) into the Silvretta glacier, a temperate Alpine glacier located in Switzerland. Temperate glaciers, in contrast to cold glaciers, are glaciers where melt processes are prevalent. Incorporation of PCBs into cold glaciers has been quantified in previous studies. However, the fate of PCBs in temperate glaciers has never been investigated. In the model, we include melt processes, inducing elution of water-soluble substances and, conversely, enrichment of particles and particle-bound chemicals. The model is validated by comparing modeled and measured PCB concentrations in an ice core collected in the Silvretta accumulation area. We quantify PCB incorporation between 1900 and 2010, and discuss the fate of six PCB congeners. PCB concentrations in the ice core peak in the period of high PCB emissions, as well as in years with strong melt. While for lower-chlorinated PCB congeners revolatilization is important, for higher-chlorinated congeners, the main processes are storage in glacier ice and removal by particle runoff. This study gives insight into PCB fate and dynamics and reveals the effect of snow accumulation and melt processes on the fate of semivolatile organic chemicals in a temperate Alpine glacier.

Direct observations of evolving subglacial drainage beneath the Greenland Ice Sheet.

Seasonal acceleration of the Greenland Ice Sheet is influenced by the dynamic response of the subglacial hydrologic system to variability in meltwater delivery to the bed via crevasses and moulins (vertical conduits connecting supraglacial water to the bed of the ice sheet). As the melt season progresses, the subglacial hydrologic system drains supraglacial meltwater more efficiently, decreasing basal water pressure and moderating the ice velocity response to surface melting. However, limited direct observations of subglacial water pressure mean that the spatiotemporal evolution of the subglacial hydrologic system remains poorly understood. Here we show that ice velocity is well correlated with moulin hydraulic head but is out of phase with that of nearby (0.3-2 kilometres away) boreholes, indicating that moulins connect to an efficient, channelized component of the subglacial hydrologic system, which exerts the primary control on diurnal and multi-day changes in ice velocity. Our simultaneous measurements of moulin and borehole hydraulic head and ice velocity in the Paakitsoq region of western Greenland show that decreasing trends in ice velocity during the latter part of the melt season cannot be explained by changes in the ability of moulin-connected channels to convey supraglacial melt. Instead, these observations suggest that decreasing late-season ice velocity may be caused by changes in connectivity in unchannelized regions of the subglacial hydrologic system. Understanding this spatiotemporal variability in subglacial pressures is increasingly important because melt-season dynamics affect ice velocity beyond the conclusion of the melt season.

Release of legacy pollutants from melting glaciers: model evidence and conceptual understanding.

Recently, increasing concentrations of persistent organic pollutants (POPs) have been observed in the sediment of glacier-fed Lake Oberaar, Switzerland. Melting glaciers have been suggested as a secondary source of POPs released to Alpine lakes. Here we further investigate whether climate warming may accelerate the release of POPs previously deposited to Alpine glaciers ("glacier hypothesis"). To test this hypothesis, a dynamic multimedia mass balance model is developed for the catchment area of Lake Oberaar and is applied to polychlorinated biphenyls (PCBs), polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), and dichlorodiphenyl trichloroethane (DDT). This lake model is combined with two other models. The first is a dynamic multimedia mass balance model parametrized for the Swiss lowlands that is used to calculate (on the basis of historical emission data) the atmospheric concentrations that are an advective input into the model of the lake catchment. The second is a flow model of Oberaar Glacier that determines the residence time of persistent chemicals in the glacier after their deposition to the glacier surface. According to results from these three models in combination, the release of POPs by the glacier is currently increasing and accounts for the observed increase in concentrations in the lake sediment. The models indicate that approximately half of the amount of PCBs, PCDD/Fs, and DDT initially incorporated into the glacier ice is still stored in the glacier. Under the assumption that the climate is warming, accelerated release of POPs is to be expected for the future; in a model run where no climate warming is assumed, the period of time required for release of the same amount of chemicals is longer by several decades than in the scenario with a changing climate.