104 research outputs found
Computational modelling in disorders of consciousness: Closing the gap towards personalised models for restoring consciousness
Disorders of consciousness are complex conditions characterised by persistent loss of responsiveness due to brain injury. They present diagnostic challenges and limited options for treatment, and highlight the urgent need for a more thorough understanding of how human consciousness arises from coordinated neural activity. The increasing availability of multimodal neuroimaging data has given rise to a wide range of clinically- and scientifically-motivated modelling efforts, seeking to improve data-driven stratification of patients, to identify causal mechanisms for patient pathophysiology and loss of consciousness more broadly, and to develop simulations as a means of testing in silico potential treatment avenues to restore consciousness. As a dedicated Working Group of clinicians and neuroscientists of the international Curing Coma Campaign, here we provide our framework and vision to understand the diverse statistical and generative computational modelling approaches that are being employed in this fast-growing field. We identify the gaps that exist between the current state-of-the-art in statistical and biophysical computational modelling in human neuroscience, and the aspirational goal of a mature field of modelling disorders of consciousness; which might drive improved treatments and outcomes in the clinic. Finally, we make several recommendations for how the field as a whole can work together to address these challenges
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Ten simple rules for aspiring graduate students.
Several supervillains have higher degreesâwhy donât you? There can be a variety of reasons
for wanting to go to grad school and for applying to a particular school and program. But
often, one can only tell apart good and bad reasons from hindsight. Failing at something is perhaps
the best way to know what can go wrong and what advice would have been useful when
considering graduate school applications.We should know: one of us started graduate school 4 separate times, and another learned what a PhD was only after having started one; lost 2 supervisors before even starting to write her thesis, and yet another accepted a PhD offer
from the lab where she was working, without considering any alternatives; finally, one of us
had applied to graduate schools for 5 years (with 19 rejections) before finally landing a PhD
offer from their dream school. We hope that our hard-earned lessons will help you to avoid
some of the pitfalls that we ourselves fell prey to. In this article, we address how to choose a
graduate program, how to apply strategically, and some of the key challenges that may arise
along the way toward graduate school. Conveniently, our advice can be summarized as 10 simple
rules . . . so here they are.The authors acknowledge the support of
the Gates Cambridge Trust [AIL], Cancer Research
UK [RRG], Alzheimerâs Society [CCN], Merck
[CCN], and the Isaac Newton Trust [EG]
Synergistic information supports modality integration and flexible learning in neural networks solving multiple tasks
Striking progress has been made in understanding cognition by analyzing how the brain is engaged in different modes of information processing. For instance, so-called synergistic information (information encoded by a set of neurons but not by any subset) plays a key role in areas of the human brain linked with complex cognition. However, two questions remain unanswered: (a) how and why a cognitive system can become highly synergistic; and (b) how informational states map onto artificial neural networks in various learning modes. Here we employ an information-decomposition framework to investigate neural networks performing cognitive tasks. Our results show that synergy increases as networks learn multiple diverse tasks, and that in tasks requiring integration of multiple sources, performance critically relies on synergistic neurons. Overall, our results suggest that synergy is used to combine information from multiple modalitiesâand more generally for flexible and efficient learning. These findings reveal new ways of investigating how and why learning systems employ specific information-processing strategies, and support the principle that the capacity for general-purpose learning critically relies on the systemâs information dynamics
Quantifying synergy and redundancy in multiplex networks
Understanding how different networks relate to each other is key for
obtaining a greater insight into complex systems. Here, we introduce an
intuitive yet powerful framework to characterise the relationship between two
networks, comprising the same nodes. We showcase our framework by decomposing
the shortest paths between nodes as being contributed uniquely by one or the
other source network, or redundantly by either, or synergistically by the two
together. Our approach takes into account the networks' full topology, but it
also provides insights at multiple levels of resolution: from global
statistics, to individual paths of different length. We show that this approach
is widely applicable, from brains to the London transport system. In humans and
across other species, we demonstrate that reliance on unique
contributions by long-range white matter fibers is a conserved feature of
mammalian structural connectomes. Across species, we also find that efficient
communication relies on significantly greater synergy between long-range and
short-range fibers than expected by chance, and significantly less redundancy.
Our framework may find applications to help decide how to trade-off different
desiderata when designing network systems, or to evaluate their relative
presence in existing systems, whether biological or artificial
Acute thalamic connectivity precedes chronic post-concussive symptoms in mild traumatic brain injury
Chronic post-concussive symptoms are common after mild traumatic brain injury (mTBI) and are difficult to predict or treat. Thalamic functional integrity is particularly vulnerable in mTBI and may be related to long-term outcomes but requires further investigation. We compared structural MRI and resting state functional MRI in 108 patients with a Glasgow Coma Scale (GCS) of 13-15 and normal CT, and 76 controls. We examined whether acute changes in thalamic functional connectivity were early markers for persistent symptoms and explored neurochemical associations of our findings using PET data. Of the mTBI cohort, 47% showed incomplete recovery 6 months post-injury. Despite the absence of structural changes, we found acute thalamic hyperconnectivity in mTBI, with specific vulnerabilities of individual thalamic nuclei. Acute fMRI markers differentiated those with chronic post-concussive symptoms, with time- and outcome-dependent relationships in a sub-cohort followed longitudinally. Moreover, emotional and cognitive symptoms were associated with changes in thalamic functional connectivity to known serotonergic and noradrenergic targets, respectively. Our findings suggest that chronic symptoms can have a basis in early thalamic pathophysiology. This may aid identification of patients at risk of chronic post-concussive symptoms following mTBI, provide a basis for development of new therapies and facilitate precision medicine application of these therapies.</p
Consciousness-specific dynamic interactions of brain integration and functional diversity
Abstract: Prominent theories of consciousness emphasise different aspects of neurobiology, such as the integration and diversity of information processing within the brain. Here, we combine graph theory and dynamic functional connectivity to compare resting-state functional MRI data from awake volunteers, propofol-anaesthetised volunteers, and patients with disorders of consciousness, in order to identify consciousness-specific patterns of brain function. We demonstrate that cortical networks are especially affected by loss of consciousness during temporal states of high integration, exhibiting reduced functional diversity and compromised informational capacity, whereas thalamo-cortical functional disconnections emerge during states of higher segregation. Spatially, posterior regions of the brainâs default mode network exhibit reductions in both functional diversity and integration with the rest of the brain during unconsciousness. These results show that human consciousness relies on spatio-temporal interactions between brain integration and functional diversity, whose breakdown may represent a generalisable biomarker of loss of consciousness, with potential relevance for clinical practice
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Brain network integration dynamics are associated with loss and recovery of consciousness induced by sevoflurane
Funder: Canadian Institute for Advanced Research; Id: http://dx.doi.org/10.13039/100007631Funder: Gates Cambridge Trust; Id: http://dx.doi.org/10.13039/501100005370Funder: Queens College CambridgeFunder: Stephen Erskine FellowshipFunder: Royal College Of Anaesthetists; Id: http://dx.doi.org/10.13039/501100001297Funder: British Oxygen ProfessorshipFunder: Technische UniversitĂ€t MĂŒnchen; Id: http://dx.doi.org/10.13039/501100005713Abstract: The dynamic interplay of integration and segregation in the brain is at the core of leading theoretical accounts of consciousness. The human brain dynamically alternates between a subâstate where integration predominates, and a predominantly segregated subâstate, with different roles in supporting cognition and behaviour. Here, we combine graph theory and dynamic functional connectivity to compare restingâstate functional MRI data from healthy volunteers before, during, and after loss of responsiveness induced with different concentrations of the inhalational anaesthetic, sevoflurane. We show that dynamic states characterised by high brain integration are especially vulnerable to general anaesthesia, exhibiting attenuated complexity and diminished smallâworld character. Crucially, these effects are reversed upon recovery, demonstrating their association with consciousness. Higher doses of sevoflurane (3% vol and burstâsuppression) also compromise the temporal balance of integration and segregation in the human brain. Additionally, we demonstrate that reduced anticorrelations between the brain's default mode and executive control networks dynamically reconfigure depending on the brain's state of integration or segregation. Taken together, our results demonstrate that the integrated subâstate of brain connectivity is especially vulnerable to anaesthesia, in terms of both its complexity and information capacity, whose breakdown represents a generalisable biomarker of loss of consciousness and its recovery
Consciousness & Brain Functional Complexity in Propofol Anaesthesia
Funder: Oon Khye Beng ChâHia Tsio Studentship for Research in Preventive Medicine, administered via Downing CollegeFunder: LâOrĂ©al-Unesco for Women in Science Excellence Research FellowshipFunder: Canadian Institute for Advanced research (CIFAR)Funder: Cambridge Biomedical Research Centre NIHR Senior Investigator AwardsFunder: Stephen Erskine Fellowship at Queensâ College, CambridgeAbstract: The brain is possibly the most complex system known to mankind, and its complexity has been called upon to explain the emergence of consciousness. However, complexity has been defined in many ways by multiple different fields: here, we investigate measures of algorithmic and process complexity in both the temporal and topological domains, testing them on functional MRI BOLD signal data obtained from individuals undergoing various levels of sedation with the anaesthetic agent propofol, replicating our results in two separate datasets. We demonstrate that the various measures are differently able to discriminate between levels of sedation, with temporal measures showing higher sensitivity. Further, we show that all measures are strongly related to a single underlying construct explaining most of the variance, as assessed by Principal Component Analysis, which we interpret as a measure of âoverall complexityâ of our data. This overall complexity was also able to discriminate between levels of sedation and serum concentrations of propofol, supporting the hypothesis that consciousness is related to complexity - independent of how the latter is measured
Mechanisms underlying disorders of consciousness: Bridging gaps to move toward an integrated translational science
AIM: In order to successfully detect, classify, prognosticate, and develop targeted therapies for patients with disorders of consciousness (DOC), it is crucial to improve our mechanistic understanding of how severe brain injuries result in these disorders.
METHODS: To address this need, the Curing Coma Campaign convened a Mechanisms Sub-Group of the Coma Science Work Group (CSWG), aiming to identify the most pressing knowledge gaps and the most promising approaches to bridge them.
RESULTS: We identified a key conceptual gap in the need to differentiate the neural mechanisms of consciousness per se, from those underpinning connectedness to the environment and behavioral responsiveness. Further, we characterised three fundamental gaps in DOC research: (1) a lack of mechanistic integration between structural brain damage and abnormal brain function in DOC; (2) a lack of translational bridges between micro- and macro-scale neural phenomena; and (3) an incomplete exploration of possible synergies between data-driven and theory-driven approaches.
CONCLUSION: In this white paper, we discuss research priorities that would enable us to begin to close these knowledge gaps. We propose that a fundamental step towards this goal will be to combine translational, multi-scale, and multimodal data, with new biomarkers, theory-driven approaches, and computational models, to produce an integrated account of neural mechanisms in DOC. Importantly, we envision that reciprocal interaction between domains will establish a virtuous cycle, leading towards a critical vantage point of integrated knowledge that will enable the advancement of the scientific understanding of DOC and consequently, an improvement of clinical practice
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