Individual differences in white matter microstructure reflect variation in functional connectivity during action choice.

The relation between brain structure and function is of fundamental importance in neuroscience. Comparisons between behavioral and brain imaging measures suggest that variation in brain structure correlates with the presence of specific skills[1-3]. Behavioral measures, however, reflect the integrated function of multiple brain regions. Rather than behavior, a physiological index of function could be a more sensitive and informative measure with which to compare structural measures. Here, we test for a relationship between a physiological measure of functional connectivity between two brain areas during a simple decision making task and a measure of structural connectivity. Paired-pulse transcranial magnetic stimulation indexed functional connectivity between two regions important for action choices: premotor and motor cortex. Fractional anisotropy (FA), a marker of microstructural integrity, indexed structural connectivity. Individual differences in functional connectivity during action selection show highly specific correlations with FA in localised regions of white matter interconnecting regions including the premotor and motor cortex. Probabilistic tractography[4, 5], a technique for identifying fibre pathways from diffusion-weighted imaging (DWI), reconstructed the anatomical networks linking the component brain regions involved in making decisions. These findings demonstrate a relationship between individual differences in functional and structural connectivity within human brain networks central to action choice

New salt marshes for old: salt marsh creation and management

Abstract Salt marshes are vulnerable to rising sea levels, coastal developments, pollution and disturbance, and at the same time they provide economic, social and environmental benefits. Recently salt marsh re-creation has been undertaken in the interest of both sea defence and nature conservation. The vegetation pattern on these newly created marshes is very different from that found on mature marshes. This suggests that the soil conditions may be limiting normal vegetation development and implies that special techniques will be needed to enhance the processes involved. For pioneer salt marsh to develop a proportion of the sediment load in the water covering the marsh at high tide has to be trapped by salt marsh plants and subsequently incorporated into the marsh substrate. This paper presents the results of recent experimental studies in this area of research and examines various aspects of the key processes involved and the critical implications for salt marsh management and coastal defence

Coupling between gamma-band power and cerebral blood volume during recurrent acute neocortical seizures

Characterization of neural and hemodynamic biomarkers of epileptic activity that can be measured using non-invasive techniques is fundamental to the accurate identification of the epileptogenic zone (EZ) in the clinical setting. Recently, oscillations at gamma-band frequencies and above (>30 Hz) have been suggested to provide valuable localizing information of the EZ and track cortical activation associated with epileptogenic processes. Although a tight coupling between gamma-band activity and hemodynamic-based signals has been consistently demonstrated in non-pathological conditions, very little is known about whether such a relationship is maintained in epilepsy and the laminar etiology of these signals. Confirmation of this relationship may elucidate the underpinnings of perfusion-based signals in epilepsy and the potential value of localizing the EZ using hemodynamic correlates of pathological rhythms. Here, we use concurrent multi-depth electrophysiology and 2-dimensional optical imaging spectroscopy to examine the coupling between multi-band neural activity and cerebral blood volume (CBV) during recurrent acute focal neocortical seizures in the urethane-anesthetized rat. We show a powerful correlation between gamma-band power (25-90 Hz) and CBV across cortical laminae, in particular layer 5, and a close association between gamma measures and multi-unit activity (MUA). Our findings provide insights into the laminar electrophysiological basis of perfusion-based imaging signals in the epileptic state and may have implications for further research using non-invasive multi-modal techniques to localize epileptogenic tissue

A comprehensive X-ray view of the active nucleus in NGC 4258

(Abridged) We present a detailed broadband X-ray spectrum of NGC 4258, with the goal of precisely measuring the coronal luminosity and accretion flow properties of the AGN, and track any possible variation across two decades of observations. We collect archival XMM-Newton, Chandra, Swift/BAT and NuSTAR spectroscopic observations spanning 15 years, and fit them with a suite of state of the art models, including a warped disk model which is suspected to provide the well known obscuration observed in the X-rays. We complement this information with archival results from the literature. Clear spectral variability is observed among the different epochs. The obscuring column density shows possibly periodic fluctuations on a timescale of 10 years, while the intrinsic luminosity displays a long term decrease of a factor of three in a time span of 15 years (from $L_{2-10~\text{keV}} \sim 10^{41}$ erg s$^{-1}$ in the early 2000s, to $L_{2-10~\text{keV}} \sim 3 \times 10^{40}$ erg s$^{-1}$ in 2016). The average absorption-corrected X-ray luminosity $L_{2-10~\text{keV}}$, combined with archival determinations of the bolometric luminosity, implies a bolometric correction $k_{\rm bol} \sim 20$, intriguingly typical for Seyferts powered by accretion through geometrically thin, radiatively efficient disks. Moreover, the X-ray photon index $\Gamma$ is consistent with the typical value of the broader AGN population. However, the accretion rate in Eddington units is very low, well within the expected RIAF regime. Our results suggest that NGC 4258 is a genuinely low-luminosity Seyfert II, with no strong indications in its X-ray emission for a hot, RIAF-like accretion flow.Comment: Accepted for publication in A&A. 14 pages, 6 figures, 3 table

Comparison of stimulus-evoked cerebral hemodynamics in the awake mouse and under a novel anesthetic regime

Neural activity is closely followed by a localised change in cerebral blood flow, a process termed neurovascular coupling. These hemodynamic changes form the basis of contrast in functional magnetic resonance imaging (fMRI) and are used as a correlate for neural activity. Anesthesia is widely employed in animal fMRI and neurovascular studies, however anesthetics are known to profoundly affect neural and vascular physiology, particularly in mice. Therefore, we investigated the efficacy of a novel ‘modular’ anesthesia that combined injectable (fentanyl-fluanisone/midazolam) and volatile (isoflurane) anesthetics in mice. To characterize sensory-evoked cortical hemodynamic responses, we used optical imaging spectroscopy to produce functional maps of changes in tissue oxygenation and blood volume in response to mechanical whisker stimulation. Following fine-tuning of the anesthetic regime, stimulation elicited large and robust hemodynamic responses in the somatosensory cortex, characterized by fast arterial activation, increases in total and oxygenated hemoglobin, and decreases in deoxygenated hemoglobin. Overall, the magnitude and speed of evoked hemodynamic responses under anesthesia resembled those in the awake state, indicating that the novel anesthetic combination significantly minimizes the impact of anesthesia. Our findings have broad implications for both neurovascular research and longitudinal fMRI studies that increasingly require the use of genetically engineered mice

Higher education, mature students and employment goals: policies and practices in the UK

This article considers recent policies of Higher Education in the UK, which are aimed at widening participation and meeting the needs of employers. The focus is on the growing population of part-time students, and the implications of policies for this group. The article takes a critical perspective on government policies, using data from a major study of mature part-time students, conducted in two specialist institutions in the UK, a London University college and a distance learning university. Findings from this study throw doubt on the feasibility of determining a priori what kind of study pathway is most conducive for the individual in terms of employment gains and opportunities for upward social mobility. In conclusion, doubts are raised as to whether policies such as those of the present UK government are likely to achieve its aims. Such policies are not unique to the UK, and lessons from this country are relevant to most of the developed world