Improving unbiased left/right training of rats and use of physostigmine to counteract scopolamine-induced short-term memory impairment

Rationale: The DNMTP task measures short-term / working memory uncontaminated by learning capacity,  spatial abilities, motor performance or general motivational and arousal factors. However, DNMTP training  of rats can take two months, and we aimed to reduce this. Methods: Two experiments were conducted on rats  in an operant DNMTP task. Improvements were made on the training procedure. The method was validated  by replicating the effect of scopolamine on working memory. The experiments also explored the influence  of physostigmine in reversing impairment induced by scopolamine. Thus in experiment 1, ten Lewis rats  were trained in an operant DNMTP task (1, 2, 4 and 8 s delay intervals) before 9 of them received vehicle,  scopolamine, saline or combinations of scopolamine and physostigmine. In experiment 2, ten Lewis rats (5  old and 5 young) were trained in the same task (1, 2, 4, 8 and 16 s delay intervals). There were six treatments:  0.05 mg/kg scopolamine, 0.1 mg/kg physostigmine or 0.15 mg/kg physostigmine, control involving  saline or involving no injection and no handling, and finally a combined treatment of 0.05mg/kg scopolamine  and 0.15 mg/kg physostigmine. In both experiments scopolamine significantly reduced correct  responses, nose-pokes and lever presses compaired to control conditions. Furthermore, in experiment 2,  there was insignificant difference between saline and combined scopolamine/physostigmine for correct  responses and for delay prior to pressing the sample lever. As expected, there was significant difference  between scopolamine and combined scopolamine/physostigmine for correct responses, for delay prior to  pressing the sample lever and for delay prior to pressing the non-matching lever. As a result, the animals  were ready for drug injection after 17 days from habituation and the method ensured that there were no dropouts  due to left or right lever preference. This is a shorter training period than previously thought necessary.  The brief training method was validated by replicating the effect of scopolamine on working memory.

Evolution of deformation and stress changes during the caldera collapse and dyking at Bárdarbunga, 2014–2015: Implication for triggering of seismicity at nearby Tungnafellsjökull volcano

Stress transfer associated with an earthquake, which may result in the seismic triggering of aftershocks (earthquake–earthquake interactions) and/or increased volcanic activity (earthquake–volcano interactions), is a well-documented phenomenon. However limited studies have been undertaken concerning volcanic triggering of activity at neighbouring volcanoes (volcano–volcano interactions). Here we present new deformation and stress modelling results utilising a wealth of diverse geodetic observations acquired during the 2014–2015 unrest and eruption within the Bárdarbunga volcanic system. These comprise a combination of InSAR, GPS, LiDAR, radar profiling and optical satellite measurements. We find a strong correlation between the locations of increased seismicity at nearby Tungnafellsjökull volcano and regions of increased tensile and Coulomb stress changes. Our results suggest that stress transfer during this major event has resulted in earthquake triggering at the neighbouring Tungnafellsjökull volcano by unclamping faults within the associated fissure swarm. This work has immediate application to volcano monitoring; to distinguish the difference between stress transfer and new intrusive activity

Gradual caldera collapse at Bárdarbunga volcano, Iceland, regulated by lateral magma outflow

Large volcanic eruptions on Earth commonly occur with a collapse of the roof of a crustal magma reservoir, forming a caldera. Only a few such collapses occur per century, and the lack of detailed observations has obscured insight into the mechanical interplay between collapse and eruption.We usemultiparameter geophysical and geochemical data to show that the 110-squarekilometer and 65-meter-deep collapse of Bárdarbunga caldera in 2014-2015 was initiated through withdrawal of magma, and lateral migration through a 48-kilometers-long dike, from a 12-kilometers deep reservoir. Interaction between the pressure exerted by the subsiding reservoir roof and the physical properties of the subsurface flow path explain the gradual, nearexponential decline of both collapse rate and the intensity of the 180-day-long eruption.</p

New mass increase beneath Askja volcano, Iceland – a precursor to renewed activity?

Askja is an active central volcano located on the NS trending en echelon rift zone marking the mid-Atlantic plate boundary in North Iceland. Between 2007 and 2009, we observed a gravity increase at the centre of the caldera. This contrasts with net gravity decreases recorded between 1988 and 2007 interpreted previously in terms of magma drainage. The recent gravity increase is rapid, but similar in terms of lateral extent to the preceding decrease. This gravity increase corresponds to a sub-surface mass increase of 0.68×1011kg at about 3km depth. It is possible that the new gravity increases observed at Askja reflect accumulation of magma beneath the caldera and thus may herald a new phase in the activity of this volcano, which last erupted in 1961

Pressure sources versus surface loads: Analyzing volcano deformation signal composition with an application to Hekla volcano, Iceland

The load of lava emplaced over periods of decades to centuries induces a gradual viscous response of the Earth resulting in measurable deformation. This effect should be considered in source model inversions for volcanic areas with large lava production and flow emplacement in small centralized regions. If deformation data remain uncorrected, constructive load and pressure source interference may result in an overestimate of depth and volume of a magma reservoir whereas destructive signal interference may cause these values to be underestimated. In both cases the source geometry preference could be biased. The ratio of horizontal and vertical displacements aids the identification of composite signals. We provide a method to quantify and remove the lava load deformation signals, using deformation at Hekla volcano, Iceland as an example.Remote SensingAerospace Engineerin

Interplay of surface loading and glacial isostatic adjustment in Iceland

Iceland is a laboratory for studying the solid Earth response to changes in surface loading because of the underlying hot mantle and thin uppermost elastic layer (relating to mantle plume – oceanic ridge interaction), and rapid major ice mass and magma load changes. Glacial isostatic adjustment (GIA) following the end of the last glaciation in Iceland is inferred to have been complete in coastal areas about 9000 years ago. Nevertheless, GPS-measurements show the area around Vatnajökull, in SE Iceland, is uplifting at present at a rate of over 30 mm/yr, interpreted as the GIA response to present retreat of ice caps since 1890. These deformation trends have also been mapped by interferometric analysis of synthetic aperture radar images (InSAR). Influence from annual load changes are superimposed on the general trends, and can be used to constrain the annual mass balance variations of Icelandic ice caps. The elastic structure has furthermore been constrained from response to redistribution of ice mass during a glacial surge. We demonstrate that InSAR studies using data from the Sentinel-1 satellites, provide constraints on load induced deformation of high spatial resolution and can be integrated into future modeling efforts. Additional constraints on the visco-elastic structure under Iceland are provided by: i) Post-seismic response, observed following the 2000 and 2008 South Iceland earthquakes, ii) Post-rifting adjustment in central Iceland following major dyking event and caldera collapse in Bárðarbunga in 2014-2015, which at present is responsible for ongoing transient deformation near Bárðarbunga, iii) Measurements of sea-level changes, that have, however, been limited in Iceland. Predictions of sea level change in Iceland using global GIA models, which do not take into account the specific Earth structure and low viscosity under Iceland, provide unrealistic predictions and limit the usefulness of such models for Iceland. Well constrained models of Earth structure and load changes help to understand the various effects of the present unloading on magmatism in Iceland, including increased mantle melting in response to unloading, variation in magma transfer and storage in the crust, and instability of magma bodies at shallow depths beneath Iceland

Geodetic data shed light on ongoing caldera subsidence at Askja, Iceland

Subsidence within the main caldera of Askja volcano in the North of Iceland has been in progress since 1983. Here, we present new ground and satellite based deformation data, which we interpret together with new and existing micro-gravity data, to help understand which processes may be responsible for the unrest. From 2003-2007 we observe a net micro-gravity decrease combined with subsidence and from 2007-2009 we observe a net micro-gravity increase while the subsidence continues. We infer subsidence is caused by a combination of a cooling and contracting magma chamber at a divergent plate boundary. Mass movements at active volcanoes can be caused by several processes, including water table/lake level movements, hydrothermal activity and magma movements. We suggest that here, magma movement and/or a steam cap in the geothermal system of Askja at depth, are responsible for the observed microgravity variations. In this respect, we rule out the possibility of a shallow intrusion as an explanation for the observed micro-gravity increase but suggest magma may have flowed into the residing shallow magma chamber at Askja despite continued subsidence. In particular variable compressibility of magma residing in the magma chamber, but also compressibility of the surrounding rock may be the reason why this additional magma did not create any detectable surface deformation

Increased capture of magma in the crust promoted by ice-cap retreat in Iceland

Climate warming at the end of the last glaciation caused ice caps on Icelandic volcanoes to retreat. Removal of surface ice load is thought to have decreased pressures in the underlying mantle, triggering decompression melting, enhanced magma generation and increased volcanic activity1–3. Present-day climate change could have the same effect, although there may be a time lag of hundreds of years between magma generation and eruption4,5. However, in addition to increased magma generation, pressure changes associated with ice retreat should also alter the capacity for storing magma within the crust. Here we use a numerical model to evaluate the effect of the current decrease in ice load on magma storage in the crust at the Kverkfjöll volcanic system, located partially beneath Iceland’s largest ice cap. We compare the model results with radar and global positioning system measurements of surface displacement and changes in crustal stress between 2007 and 2008, during the intrusion of a deep dyke at Upptyppingar. We find that although the main component of stress recorded during dyke intrusion relates to plate extension, another component of stress is consistent with the stress field caused by the retreating ice cap. We conclude that the retreating ice cap led to enhanced capture of magma within the crust. We suggest that ice-cap retreat can promote magma storage, rather than eruption, at least in the short term