White Matter Information Flow Mapping from Diffusion MRI and EEG

International audienceThe human brain can be described as a network of specialized and spatially distributed regions. The activity of individual regions can be estimated using electroencephalography and the structure of the network can be measured using diffusion magnetic resonance imaging. However, the communication between the different cortical regions occurring through the white matter, coined information flow, cannot be observed by either modalities independently. Here, we present a new method to infer information flow in the white matter of the brain from joint diffusion MRI and EEG measurements. This is made possible by the millisecond resolution of EEG which makes the transfer of information from one region to another observable. A subject specific Bayesian network is built which captures the possible interactions between brain regions at different times. This network encodes the connections between brain regions detected using diffusion MRI tractography derived white matter bundles and their associated delays. By injecting the EEG measurements as evidence into this model, we are able to estimate the directed dynamical functional connectivity whose delays are supported by the diffusion MRI derived structural connectivity. We present our results in the form of information flow diagrams that trace transient communication between cortical regions over a functional data window. The performance of our algorithm under different noise levels is assessed using receiver operating characteristic curves on simulated data. In addition, using the well-characterized visual motor network as grounds to test our model, we present the information flow obtained during a reaching task following left or right visual stimuli. These promising results present the transfer of information from the eyes to the primary motor cortex. The information flow obtained using our technique can also be projected back to the anatomy and animated to produce videos of the information path through the white matter, opening a new window into multi-modal dynamic brain connectivity

The James Webb Space Telescope Mission

Twenty-six years ago a small committee report, building on earlier studies, expounded a compelling and poetic vision for the future of astronomy, calling for an infrared-optimized space telescope with an aperture of at least $4m$. With the support of their governments in the US, Europe, and Canada, 20,000 people realized that vision as the $6.5m$ James Webb Space Telescope. A generation of astronomers will celebrate their accomplishments for the life of the mission, potentially as long as 20 years, and beyond. This report and the scientific discoveries that follow are extended thank-you notes to the 20,000 team members. The telescope is working perfectly, with much better image quality than expected. In this and accompanying papers, we give a brief history, describe the observatory, outline its objectives and current observing program, and discuss the inventions and people who made it possible. We cite detailed reports on the design and the measured performance on orbit.Comment: Accepted by PASP for the special issue on The James Webb Space Telescope Overview, 29 pages, 4 figure

Large expert-curated database for benchmarking document similarity detection in biomedical literature search

Document recommendation systems for locating relevant literature have mostly relied on methods developed a decade ago. This is largely due to the lack of a large offline gold-standard benchmark of relevant documents that cover a variety of research fields such that newly developed literature search techniques can be compared, improved and translated into practice. To overcome this bottleneck, we have established the RElevant LIterature SearcH consortium consisting of more than 1500 scientists from 84 countries, who have collectively annotated the relevance of over 180 000 PubMed-listed articles with regard to their respective seed (input) article/s. The majority of annotations were contributed by highly experienced, original authors of the seed articles. The collected data cover 76% of all unique PubMed Medical Subject Headings descriptors. No systematic biases were observed across different experience levels, research fields or time spent on annotations. More importantly, annotations of the same document pairs contributed by different scientists were highly concordant. We further show that the three representative baseline methods used to generate recommended articles for evaluation (Okapi Best Matching 25, Term Frequency-Inverse Document Frequency and PubMed Related Articles) had similar overall performances. Additionally, we found that these methods each tend to produce distinct collections of recommended articles, suggesting that a hybrid method may be required to completely capture all relevant articles. The established database server located at https://relishdb.ict.griffith.edu.au is freely available for the downloading of annotation data and the blind testing of new methods. We expect that this benchmark will be useful for stimulating the development of new powerful techniques for title and title/abstract-based search engines for relevant articles in biomedical research.Peer reviewe

Calibration of proprioception

Although proprioceptive information allows accurate perception of limb movement in the absence of vision, its exact contribution to position coding when vision is also available is still debated (Gandevia et al, 1992). One view is that proprioceptive input would play a relatively minor role when vision is present (Hay et al., 1963). In fact, some have suggested that the processing and calibration of proprioceptive feedback would be masked by the processing of visual feedback (Tremblay and Proteau, 1998). The purpose of this thesis was to use a visuomotor adaptation paradigm to assess whether proprioception is concurrently calibrated with vision during visually guided movements. In Experiment 1, a full vision group (FV) was given vision of a cursor representing hand position and was asked to aim towards visible targets.' A no vision group (NV) performed the same task without vision of the cursor and was given knowledge of results (KR) after movement completion. A visual bias was introduced between the location of the cursor and the location of the hand in an adaptation phase, which resulted in participants deviating to the right of the intended target. Of interest was whether participants would still show rightward deviations in a post-test series of trials in which vision was removed (i.e. aftereffects). The NV group presented strong aftereffects. However, the FV group only showed modest aftereffects early in the post-test, which rapidly decayed over the course of the post-test. This suggests that proprioception was not calibrated when vision was concurrently available, and further analyses showed that the presence of those early aftereffects was rather due to an offline influence of vision on movement planning. A similar protocol was used in Experiment 2, but instead of inducing a visual bias, a sensory conflict was rather created through distortion of the proprioceptive sense by means of tendon vibration. Participants were asked to release two fingers at a specific target angle while the right elbow was passively extended. The vibration created a discrepancy between the proprioceptively perceived and visually perceived location of the effector. In an adaptation phase, participants performed with full vision (FV group), or with only terminal KR (NV group) while being vibrated on every trial. Any recalibration of the sensory modalities would be expressed by the presence of significant overshooting following the removal of visual feedback and vibration in a post-test phase (i.e. aftereffects). Both groups showed aftereffects early in the post-test, but these decayed very quickly, such that participants rapidly resorted to their pre-exposure levels. We propose that a sensory recalibration took place for both groups, but that the passive nature of the task prevented persistent aftereffects from occurring.Education, Faculty ofKinesiology, School ofGraduat

Intégration des informations visuelles et proprioceptives dans la planification de mouvements finalisés (approches comportementales et électrophysiologiques)

L objectif de cette thèse est d étudier i) l influence de la modalité sensorielle de la cible (visuelle vs proprioceptive) sur les processus intégratifs associés aux transformations sensorimotrices, et ii) l intégration des informations visuelles et proprioceptives de la main pendant l adaptation visuomotrice. Dans la première étude, nous avons tenté de déterminer si des transformations sensorimotrices communes sous-tendent la planification de mouvements dirigés vers des cibles visuelles et proprioceptives. Pour ce faire, nous avons utilisé un paradigme d adaptation prismatique afin de modifier la relation visuomotrice. Les post-effets observés pour les mouvements dirigés vers des cibles visuelles ne se sont pas généralisés aux mouvements dirigés vers des cibles proprioceptives. Dans la seconde étude, nous avons utilisé l électro-encéphalographie afin de caractériser la dynamique spatio-temporelle d activité cérébrale associée aux transformations sensorimotrices pour les cibles visuelles et proprioceptives. Les résultats ont mis en évidence une implication des structures pariétales, prémotrices et sensorimotrices controlatérales à l effecteur pour les deux types de mouvements. Toutefois, des différences ont été observées au niveau du décours temporel d activation de ces structures. Dans la troisième étude, nous avons montré qu une suppression temporaire de la transmission des informations somesthésiques prenait place au niveau cortical suite à l instauration d une nouvelle relation visuomotrice. Dans l ensemble, ces résultats démontrent que les processus d intégration des informations sensorielles de la main et de la cible sont spécifiques à la modalité sensorielle de la cible. Ils mettent aussi en évidence la flexibilité fonctionnelle de l intégration des informations visuelles et proprioceptives de la main permettant d optimiser la précision du geste pendant l adaptation visuomotrice.The objective of this thesis is to investigate: i) the influence of target modality (visual, proprioceptive) on the integrative processes associated with sensorimotor transformations, and ii) the integration of visual and proprioceptive hand signals during visuomotor adaptation. In the first experiment, we tested whether common sensorimotor transformations underlie the planning of reaching movements directed toward visual and proprioceptive targets. To do so, we used a prismatic adaptation paradigm to modify the visuomotor relationship. The aftereffects observed for movements directed toward visual targets did not generalize to movements directed toward proprioceptive targets. In the second experiment, we used electroencephalography to characterize the spatio-temporal dynamics of neural activity associated with the planning of reaching movements directed toward visual and proprioceptive targets. We found significant activation over parietal, premotor and sensorimotor scalp sites for both types of movements. However, notable differences were observed in the timing of these activations. In the third experiment, we provided evidence for a temporary suppression of the transmission of somatosensory afferents during exposure to a novel visuomotor relationship. Together, these results demonstrate that the integration of hand and target sensory signals is specific to the sensory modality of the target. They also highlight the functional flexibility with which visual and proprioceptive hand signals are integrated to optimise performance during visuomotor adaptation.AIX-MARSEILLE2-BU Sci.Luminy (130552106) / SudocSudocFranceF

Composition and decomposition of visuomotor maps during manual tracking

International audienceAdapting hand movements to changes in our body or the environment is essential for skilled motor behavior, as is the ability to flexibly combine experience gathered in separate contexts. However it has been shown that when adapting hand movements to two different visuomotor perturbations in succession, interference effects can occur. Here we investigate whether these interference effects compromise our ability to adapt to the superposition of the two perturbations. Participants tracked with a joystick a visual target that followed a smooth but unpredictable trajectory. Four separate groups of participants (total n = 83) completed one block of 50 trials under each of three mappings: one in which the cursor was rotated by 90° (ROTATION), one in which the cursor mimicked the behavior of a mass-spring system (SPRING), and one in which the SPRING and ROTATION mappings were superimposed (SPROT). The order of the blocks differed across groups. Although interference effects were found when switching between SPRING and ROTATION, participants who performed these blocks first performed better in SPROT than participants who had no prior experience with SPRING and ROTATION (i.e., composition). Moreover, participants who started with SPROT exhibited better performance under SPRING and ROTATION than participants who had no prior experience with each of these mappings (i.e., decomposition). Additional analyses confirmed that these effects resulted from components of learning that were specific to the rotational and spring perturbations. These results show that interference effects do not preclude the ability to compose/decompose various forms of visuomotor adaptation

Concurrent Implicit Adaptation to Multiple Opposite Perturbations

International audienceSimultaneous adaptation to opposite visuomotor perturbations is known to be difficult. It has been shown to be possible only in situations where the two tasks are associated with different contexts, being either a different colored background, a different area of workspace, or a different follow-through movement. However, many of these elements evoke explicit mechanisms that could contribute to storing separate (modular) memories. It remains to be shown whether simultaneous adaptation to multiple perturbations is possible when they are introduced in a fully implicit manner. Here, we sought to test this possibility using a visuomotor perturbation small enough to eliminate explicit awareness. Participants (N ¼ 25) performed center-out reaching movements with a joystick to five targets located 72°apart. Depending on the target, visual feedback of cursor position was either veridical (one target) or could be rotated by 15 or À5°(two targets each). After 300 trials of adaptation (60 to each target), results revealed that participants were able to fully compensate for each of the imposed rotations. Moreover, when veridical visual feedback was restored, participants exhibited after-effects that were consistent with the rotations applied at each target. Questionnaires collected immediately after the experiment confirmed that none of the participants were aware of the perturbations. These results speak for the existence of implicit processes that can smoothly handle small and opposite visual perturbations when these are associated with distinct target locations

Fatal lactic acidosis in malignant histiocytosis

info:eu-repo/semantics/publishe