Transcranial focused ultrasound enables precise and non-invasive manipulations of deep brain circuits in humans, promising to provide safe and effective treatments of various neurological and mental health conditions. Ultrasound focused to deep brain targets can be used to modulate neural activity directly or localize the release of psychoactive drugs. However, these applications have been impeded by a key barrier-the human skull, which attenuates ultrasound strongly and unpredictably. To address this issue, we have developed an ultrasound-based approach that directly measures and compensates for the ultrasound attenuation by the skull. No additional skull imaging, simulations, assumptions, or free parameters are necessary; the method measures the attenuation directly by emitting a pulse of ultrasound from an array on one side of the head and measuring with an array on the opposite side. Here, we apply this emerging method to two primary future uses-neuromodulation and local drug release. Specifically, we show that the correction enables effective stimulation of peripheral nerves and effective release of propofol from nanoparticle carriers through an ex vivo human skull. Neither application was effective without the correction. Moreover, the effects show the expected dose-response relationship and targeting specificity. This article highlights the need for precise control of ultrasound intensity within the skull and provides a direct and practical approach for addressing this lingering barrier.

Riverine islands are widespread alluvium wetlands developed in large rivers, and bacterial communities are crucial to their ecological function, yet their assembly processes are rarely addressed. The ecosystem services provided by the middle and the lower Yangtze are primarily threatened by pollution discharge from agricultural land use, and resource overutilization (e.g., embankments), respectively. Here, we assessed bacterial community assembly processes and their drivers within riverine islands in the middle Yangtze River (MR islands) and those in the lower reach (LR islands). A significant distance-decay relationship was observed, although the turnover rate was lower than that of the terrestrial ecosystem with less connectivity. Deterministic and stochastic processes jointly shaped community patterns, and the influence of stochastic increased from 26% in MR islands to 59% for those in LR islands. Meanwhile, the bacterial community in MR islands was controlled more by inorganic nitrogen availability, whereas those in LR islands were governed by pH and EC, although those factors explained a limited fraction of variation in the bacterial community. Potential indicator taxa (affiliated with Nocardioides and Lysobacter) characterized the waterway transport pollution. Overall, our study demonstrated that bacterial community dissimilarity and the importance of dispersal limitation increased concurrently along the flow direction, while distinct local factors further determined bacterial community compositions by selecting habitat-specificity taxa and particularly metabolism function. These findings enhanced our understanding of the mechanisms driving changes in bacterial communities of riverine islands subject to increased anthropogenic impacts.IMPORTANCERivers are among the most threatened ecosystems globally and face multiple stressors related to human activity. However, linkages between microbial diversity patterns and assembly processes in rivers remain unclear, especially in riverine islands developed in large rivers. Our findings reveal that distinct factors result in divergent bacterial community compositions and functional profiles in the riverine islands in the middle Yangtze and those in the lower Yangtze, with substantial differentiation in deterministic and stochastic processes that jointly contribute to bacterial community assemblages. Additionally, keystone species may play important metabolic roles in coping with human-related disturbances. This study provides an improved understanding of relationships between microbial diversity patterns and ecosystem functions under environmental changes in large river ecosystems.

Brown algae are multicellular organisms that have evolved independently from plants and animals. Knowledge of the mechanisms involved in their embryogenesis is available only for the Fucus, Dictyota, and Ectocarpus, which are brown algae belonging to three different orders. Here, we address the control of cell growth and cell division orientation in the embryo of Saccharina latissima, a brown alga belonging to the order Laminariales, which grows as a stack of cells through transverse cell divisions until growth is initiated along the perpendicular axis. Using laser ablation, we show that apical and basal cells have different functions in the embryogenesis of this alga, with the apical cell being involved mainly in growth and basal cells controlling the orientation of cell division by inhibiting longitudinal cell division and thereby the widening of the embryo. These functions were observed in the very early development before the embryo reached the 8-cell stage. In addition, the growth of the apical and basal regions appears to be cell-autonomous, because there was no compensation for the loss of a significant part of the embryo upon laser ablation, resulting in smaller and less elongated embryos compared with intact embryos. In contrast, the orientation of cell division in the apical region of the embryo appears to be controlled by the basal cell only, which suggests a polarised, non-cell-autonomous mechanism. Altogether, our results shed light on the early mechanisms of growth rate and growth orientation at the onset of the embryogenesis of Saccharina, in which non-cell-specific cell-autonomous and cell-specific non-cell-autonomous processes are involved. This complex control differs from the mechanisms described in the other brown algal embryos, in which the establishment of embryo polarity depends on environmental cues.

This paper presents a comparative study of entropy estimation in a large-alphabet regime. A variety of entropy estimators have been proposed over the years, where each estimator is designed for a different setup with its own strengths and caveats. As a consequence, no estimator is known to be universally better than the others. This work addresses this gap by comparing twenty-one entropy estimators in the studied regime, starting with the simplest plug-in estimator and leading up to the most recent neural network-based and polynomial approximate estimators. Our findings show that the estimators\' performance highly depends on the underlying distribution. Specifically, we distinguish between three types of distributions, ranging from uniform to degenerate distributions. For each class of distribution, we recommend the most suitable estimator. Further, we propose a sample-dependent approach, which again considers three classes of distribution, and report the top-performing estimators in each class. This approach provides a data-dependent framework for choosing the desired estimator in practical setups.

OBJECTIVE: Deep brain stimulation (DBS) studies have shown that stimulation of the motor segment of the thalamus based on probabilistic tractography is predictive of improvement in essential tremor (ET). However, probabilistic methods are computationally demanding, requiring the need for alternative tractography methods for use in the clinical setting. The purpose of this study was to compare probabilistic vs deterministic tractography methods for connectivity-based targeting in patients with ET.
METHODS: Probabilistic and deterministic tractography methods were retrospectively applied to diffusion-weighted data sets in 36 patients with refractory ET. The thalamus and precentral gyrus were selected as regions of interest and fiber tracking was performed between these regions to produce connectivity-based thalamic segmentations, per prior methods. The resultant deterministic target maps were compared with those of thresholded probabilistic maps. The center of gravity (CG) of each connectivity map was determined and the differences in spatial distribution between the tractography methods were characterized. Furthermore, the intersection between the connectivity maps and CGs with the therapeutic volume of tissue activated (VTA) was calculated. A mixed linear model was then used to assess clinical improvement in tremor with volume of overlap.
RESULTS: Both tractography methods delineated the region of the thalamus with connectivity to the precentral gyrus to be within the posterolateral aspect of the thalamus. The average CG of deterministic maps was more medial-posterior in both the left (3.7 ± 1.3 mm3) and the right (3.5 ± 2.2 mm3) hemispheres when compared to 30 %-thresholded probabilistic maps. Mixed linear model showed that the volume of overlap between CGs of deterministic and probabilistic targeting maps and therapeutic VTAs were significant predictors of clinical improvement.
CONCLUSIONS: Deterministic tractography can reconstruct DBS thalamic target maps in approximately 5 min comparable to those produced by probabilistic methods that require > 12 h to generate. Despite differences in CG between the methods, both deterministic-based and probabilistic targeting were predictive of clinical improvement in ET.

Reversal learning measures the ability to form flexible associations between choice outcomes with stimuli and actions that precede them. This type of learning is thought to rely on several cortical and subcortical areas, including the highly interconnected orbitofrontal cortex (OFC) and basolateral amygdala (BLA), and is often impaired in various neuropsychiatric and substance use disorders. However, the unique contributions of these regions to stimulus- and action-based reversal learning have not been systematically compared using a chemogenetic approach particularly before and after the first reversal that introduces new uncertainty. Here, we examined the roles of ventrolateral OFC (vlOFC) and BLA during reversal learning. Male and female rats were prepared with inhibitory designer receptors exclusively activated by designer drugs targeting projection neurons in these regions and tested on a series of deterministic and probabilistic reversals during which they learned about stimulus identity or side (left or right) associated with different reward probabilities. Using a counterbalanced within-subject design, we inhibited these regions prior to reversal sessions. We assessed initial and pre-/post-reversal changes in performance to measure learning and adjustments to reversals, respectively. We found that inhibition of the ventrolateral orbitofrontal cortex (vlOFC), but not BLA, eliminated adjustments to stimulus-based reversals. Inhibition of BLA, but not vlOFC, selectively impaired action-based probabilistic reversal learning, leaving deterministic reversal learning intact. vlOFC exhibited a sex-dependent role in early adjustment to action-based reversals, but not in overall learning. These results reveal dissociable roles for BLA and vlOFC in flexible learning and highlight a more crucial role for BLA in learning meaningful changes in the reward environment.

OBJECTIVE: To determine the sensitivity profiles of probabilistic and deterministic DTI tractography methods in estimating geometric properties in arm muscle anatomy.
METHODS: Spin-echo diffusion-weighted MR images were acquired in the dominant arm of 10 participants. Both deterministic and probabilistic tractography were performed in two different muscle architectures of the parallel-structured biceps brachii (and the pennate-structured flexor carpi ulnaris. Muscle fascicle geometry estimates and number of fascicles were evaluated with respect to tractography turning angle, polynomial fitting order, and SNR. The DTI tractography estimated fascicle lengths were compared with measurements obtained from conventional cadaveric dissection and ultrasound modalities.
RESULTS: The probabilistic method generally estimated fascicle lengths closer to ranges reported by conventional methods than the deterministic method, most evident in the biceps brachii (p > 0.05), consisting of longer, arc-like fascicles. For both methods, a wide turning angle (50º-90°) generated fascicle lengths that were in close agreement with conventional methods, most evident in the flexor carpi ulnaris (p > 0.05), consisting of shorter, feather-like fascicles. The probabilistic approach produced at least two times more fascicles than the deterministic approach. For both approaches, second-order fitting yielded about double the complete tracts as third-order fitting. In both muscles, as SNR decreased, deterministic tractography produced less fascicles but consistent geometry (p > 0.05), whereas probabilistic tractography produced a consistent number but altered geometry of fascicles (p < 0.001).
CONCLUSIONS: Findings from this study provide best practice recommendations for implementing DTI tractography in skeletal muscle and will inform future in vivo studies of healthy and pathological muscle structure.

Various attempts have been made to develop models for predicting the development of damage in metals and alloys due to pitting corrosion. These models may be divided into two classes: the empirical approach which employs extreme value statistics, and the deterministic approach based on perceived mechanisms for nucleation and growth of damage. More recently, Artificial Neural Networks (ANNs), a nondeterministic type of model, has been developed to describe the progression of damage due to pitting corrosion. We compare the three approaches above-statistical, deterministic, and neural networks. Our goal is to illustrate the advantages and disadvantages of each approach, in order that the most reliable methods may be employed in future algorithms for predicting pitting damage functions for engineering structures. To illustrale the difficulty that we face in predicting cumulative pitting damage, we selected a set of data that was collected in the laboratory. We compare and contrast the three approaches by reference to this data set.

Research Highlight: Seibold, S., Weisser, W., Ambarli, D., Gossner, M. M., Mori, A., Cadotte, M., Hagge, J., Bässler, C. & Thorn, S. (2022). Drivers of community assembly change during succession in wood-decomposing beetle communities. Journal of Animal Ecology, https://doi.org/10.1111/1365-2656.13843. Paradigms of succession and its drivers have largely developed from systems relying on living plants. A substantial portion of terrestrial biodiversity and biomass exists in detrital systems that rely on dead organic matter, yet successional patterns in detrital systems have received far less attention. In particular, deadwood significantly contributes to forest ecosystem nutrient cycling and storage and represents a relatively long-lived detrital system in which to study patterns of succession. Seibold et al. examined successional patterns of deadwood beetle communities over 8 years in a large-scale experiment that included 379 logs from 13 different tree species in 30 forest stands in three regions of Germany. They predicted that deadwood beetle communities would initially differ among deadwood tree species, across space, and with climatic differences but would become more similar over time as deadwood decomposed and characteristics of remaining habitat become more homogeneous. However, Seibold et al. predicted that beetle communities would become increasingly different across space along deadwood succession if late successional species were weaker dispersers than early successional species. Surprisingly, beetle communities became more dissimilar over time contrary to predictions. But, as predicted, increasing phylogenetic distance among tree species led to increasingly dissimilar deadwood beetle communities. Lastly, differences across space, forest structure and climate led to different deadwood beetle communities, but these effects remained constant over time. These results suggest that deadwood succession is influenced by both deterministic and stochastic processes and that stochastic processes may be increasingly important in late successional stages. Seibold et al. reveal important drivers of detrital successional patterns in deadwood that indicate that deadwood beetle biodiversity can be promoted via maintaining a diversity of deadwood decay stages across a large phylogenetic diversity of trees species and structurally diverse forests. Future studies that test the mechanisms driving these patterns and whether these results hold for other saproxylic organisms will help inform forest conservation and management strategies.

Eukaryotic plankton are pivotal members of marine ecosystems playing crucial roles in marine food webs and biogeochemical cycles. However, understanding the patterns and drivers of their community assembly remains a grand challenge. A study was conducted in the northern South China Sea (SCS) to address this issue. Here, 49 samples were collected and size-fractionated from discrete depths at continental shelf and continental slope in the northern SCS over a diel cycle. From high throughput sequencing of the 18S rDNA gene V4 region, 2463 operational taxonomic units (OTUs) were retrieved. Alveolata and Opisthokonta overwhelmingly dominated the assemblages in the abundance (44.76%, 31.08%) and species richness (59%, 12%). Biodiversity was higher in the slope than the shelf and increased with depth. Temperature and salinity appeared to be the most important deterministic drivers of taxon composition. Community structure was influenced by multiple factors in the importance order of: environmental factors (temperature + salinity) > spatial factor > water depth > sampling time. Furthermore, the neutral model explained more variations in the smaller-sized (0.22-3 μm) community (24%) than larger-sized (3-200 μm) community (16%) but generally explained less variations than did deterministic processes. Additionally, our data indicated that the larger plankton might be more environmentally filtered and less plastic whereas the smaller plankton had stronger dispersal ability. This study sheds light on the differential contributions of the deterministic process and stochastic process and complexities of assembly mechanisms in shaping the community assembly of micro-nano and pico-eukaryotic biospheres in a subtropical ocean.