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July 2011 - present
January 2002 - present
Education
October 1994 - June 1999
July 1994 - September 1994
October 1991 - June 1992
Publications
Publications (274)
Efficient communication in brain networks is foundational for cognitive function and behavior. However, how communication efficiency is defined depends on the assumed model of signaling dynamics, e.g., shortest path signaling, random walker navigation, broadcasting, and diffusive processes. Thus, a general and model-agnostic framework for character...
Communication in brain networks is the foundation of cognitive function and behavior. A multitude of evolutionary pressures, including the minimization of metabolic costs while maximizing communication efficiency, contribute to shaping the structure and dynamics of these networks. However, how communication efficiency is characterized depends on th...
Cortical network undergoes rewiring everyday due to learning and memory events. To investigate the trends of population adaptation in neocortex overtime, we record cellular activity of large-scale cortical populations in response to neutral environments and conditioned contexts and identify a general intrinsic cortical adaptation mechanism, naming...
Communication in brain networks is the foundation of cognitive function and behavior. A multitude of evolutionary pressures, including the minimization of metabolic costs while maximizing communication efficiency, contribute to shaping the structure and dynamics of these networks. However, how communication efficiency is characterized depends on th...
Communication in brain networks is the foundation of cognitive function and behavior. A multitude of evolutionary pressures, including the minimization of metabolic costs while maximizing communication efficiency, contribute to shaping the structure and dynamics of these networks. However, how communication efficiency is characterized depends on th...
We investigate the influence of the network topology on the asymptotic dynamical patterns, attractors, in a general model of excitable dynamics on signed directed graphs. In this framework, network topology manifests itself as an interplay of positive and negative feedback loops. A small change in a feedback loop, by addition or removal of edges in...
Current treatments of Parkinson’s disease (PD) have limited efficacy in alleviating freezing of gait (FoG). In this context, concomitant deep brain stimulation (DBS) of the subthalamic nucleus (STN) and the substantia nigra pars reticulata (SNr) has been suggested as a potential therapeutic approach. However, the mechanisms underlying this approach...
Lesion analysis aims to reveal the causal contributions of brain regions to brain functions. Various strategies have been used for such lesion inferences. These approaches can be broadly categorized as univariate or multivariate methods. Here we analysed data from 581 patients with acute ischaemic injury, parcellated into 41 Brodmann areas, and sys...
Communication in brain networks is the foundation of cognitive function and behavior. A multitude of evolutionary pressures, including the minimization of metabolic costs while maximizing communication efficiency, contribute to shaping the structure and dynamics of these networks. However, how communication efficiency is characterized depends on th...
Neuroscientists rely on distributed spatio-temporal patterns of neural activity to understand how neural units contribute to cognitive functions and behavior. However, the extent to which neural activity reliably indicates a unit's causal contribution to the behavior is not well understood. To address this issue, we provide a systematic multi-site...
The aim of this work was to enhance the biological feasibility of a deep convolutional neural network-based in-silico model of neurodegeneration of the visual system by equipping it with a mechanism to simulate neuroplasticity. Therefore, deep convolutional networks of multiple sizes were trained for object recognition tasks and progressively lesio...
Neuroscientists rely on distributed spatio-temporal patterns of neural activity to understand how neural units contribute to cognitive functions and behavior. However, the extent to which neural activity reliably indicates a unit's causal contribution to the behavior is not well understood. To address this issue, we provide a systematic multi-site...
Intrinsic coupling modes (ICMs) can be observed in ongoing brain activity at multiple spatial and temporal scales. Two families of ICMs can be distinguished: phase and envelope ICMs. The principles that shape these ICMs remain partly elusive, in particular their relation to the underlying brain structure. Here we explored structure-function relatio...
Nerve fiber networks connecting different brain regions are the structural foundation of brain dynamics and function. Neural connectomes have been frequently described as binary networks, in basic terms of present or absent connections. By contrast, recent approaches have provided more detailed characterizations of connectomes with weighted-strengt...
Lesion analysis reveals causal contributions of brain regions to brain functions. Various strategies have been used for inferring brain functions from brain lesions. These approaches can be broadly categorized as univariate or multivariate methods. Here we analysed data from 581 patients with acute ischemic injury, parcellated into 41 Brodmann area...
Current treatments of Parkinson’s disease (PD) have limited efficacy in alleviating freezing of gait (FoG). In this context, concomitant deep brain stimulation (DBS) of the subthalamic nucleus (STN) and the substantia nigra pars reticulata (SNr) has been suggested as a potential therapeutic approach. However, the mechanisms underlying this approach...
The connectivity of Artificial Neural Networks (ANNs) is different from the one observed in Biological Neural Networks (BNNs). Can the wiring of actual brains help improve ANNs architectures? Can we learn from ANNs about what network features support computation in the brain when solving a task? At a meso/macro-scale level of the connectivity, ANNs...
What structural and connectivity features of the human brain help to explain the extraordinary human cognitive abilities? We recently proposed a set of relevant connectomic fundamentals, some of which arise from the size scaling of the human brain relative to other primate brains, while others of these fundamentals may be uniquely human. In particu...
Lesion inference analysis is a fundamental approach for characterizing the causal contributions of neural elements to brain function. This approach has gained new prominence through the arrival of modern perturbation techniques with unprecedented levels of spatiotemporal precision. While inferences drawn from brain perturbations are conceptually po...
High-resolution functional 2-photon microscopy of neural activity is a cornerstone technique in current neuroscience, enabling, for instance, the image-based analysis of relations of the organization of local neuron populations and their temporal neural activity patterns. Interpreting local image intensity as a direct quantitative measure of neural...
For constructing neuronal network models computational neuroscientists have access to wide-ranging anatomical data that nevertheless tend to cover only a fraction of the parameters to be determined. Finding and interpreting the most relevant data, estimating missing values, and combining the data and estimates from various sources into a coherent w...
Motivation: Lesion inference approaches characterize the causal contributions of neural elements to brain functions. They have helped localizing specialized units in the brain and they have gained new prominence through the arrival of optogenetic perturbation techniques that allow probing the causal role of neural elements at an unprecedented level...
Biological neuronal networks (BNNs) are a source of inspiration and analogy making for researchers that focus on artificial neuronal networks (ANNs). Moreover, neuroscientists increasingly use ANNs as a model for the brain. Despite certain similarities between these two types of networks, important differences can be discerned. First, biological ne...
Lesion analysis is a fundamental and classical approach for inferring the causal contributions of brain regions to brain function. However, many studies have been limited by the shortcomings of methodology or clinical data. Aiming to overcome these limitations, we here use an objective multivariate approach based on game theory, Multi-perturbation...
High-resolution functional 2-photon microscopy of neural activity is a cornerstone technique in current neuroscience, enabling, for instance, the image-based analysis of relations of the organization of local neuron populations and their temporal neural activity patterns. Interpreting local image intensity as a direct quantitative measure of neural...
Structural connections between cortical areas form an intricate network with a high degree of specificity. Many aspects of this complex network organization in the adult mammalian cortex are captured by an architectonic type principle, which relates structural connections to the architectonic differentiation of brain regions. In particular, the lam...
Biological neuronal networks (BNNs) constitute a niche for inspiration and analogy making for researchers that focus on artificial neuronal networks (ANNs). Moreover, neuroscientists increasingly use ANNs as a model for the brain. However, apart from certain similarities and analogies that can be drawn between ANNs and BNNs, such networks exhibit m...
The connectivity of Artificial Neural Networks (ANNs) is different from the one observed in Biological Neural Networks (BNNs). Can the wiring of actual brains help improve ANNs architectures? Can we learn from ANNs about what network features support computation in the brain when solving a task?
ANNs’ architectures are carefully engineered and have...
Significance
Communication between cells in the brain relies on different types of transmitter receptors. Can we uncover organizational principles that harness the diversity of such signatures across the brain? We focus on the human cerebral cortex and demonstrate that the distribution of receptors forms a natural axis that stretches from associati...
The architectonic type principle conceptualizes structural connections between brain areas in terms of the relative architectonic differentiation of connected areas. It has previously been shown that spatio-temporal interactions between the time and place of neurogenesis could underlie multiple features of empirical mammalian connectomes, such as p...
Transmitter receptors constitute a key component of the molecular machinery for inter-cellular communication in the brain. Recent efforts have mapped the density of diverse transmitter receptors across the human cerebral cortex with an unprecedented level of detail. Here, we distil these observations into key organizational principles. We demonstra...
Elucidating causal relations between the brain and its produced behaviour is a fundamental neuroscientific goal. Traditional approaches for revealing such relations have relied on univariate single-site lesion experiments in which an individual brain region is perturbed and consequent behavioural effects are quantified. More recent studies, however...
For constructing neuronal network models computational neuroscientists have access to a wealth of anatomical data that nevertheless tend to cover only a fraction of the parameters to be determined. Finding and interpreting the most relevant data, estimating missing values, and combining the data and estimates from various sources into a coherent wh...
Behavioral effects of transcranial magnetic stimulation (TMS) often show substantial differences between subjects. One factor that might contribute to these inter-individual differences is the interaction of current brain states with the effects of local brain network perturbation. The aim of the current study was to identify brain regions whose co...
White matter bundles linking gray matter nodes are key anatomical players to fully characterize associations between brain systems and cognitive functions. Here we used a multivariate lesion inference approach grounded in coalitional game theory (multiperturbation Shapley value analysis, MSA) to infer causal contributions of white matter bundles to...
Unfortunately, some errors slipped into the manuscript, which we correct here.
Structural connections between cortical areas form an intricate network with a high degree of specificity. Many aspects of this complex network organization in the adult mammalian cortex are captured by an architectonic type principle, which relates structural connections to the architectonic differentiation of brain regions. In particular, the lam...
The study of brain-function relationships is undergoing a conceptual and methodological transformation due to the emergence of network neuroscience and the development of multivariate methods for lesion-deficit inferences. Anticipating this process, in 1998 Godefroy and co-workers conceptualized the potential of four elementary typologies of brain-...
Beyond disruption of neuronal pathways, focal stroke lesions induce structural disintegration of distant, yet connected brain regions via retrograde neuronal degeneration. Stroke lesions alter functional brain connectivity and topology in large-scale brain networks. These changes are associated with the degree of clinical impairment and recovery. I...
Activity patterns of cerebral cortical regions represent the current environment in which animals receive multi-modal inputs. These patterns are also shaped by the history of activity that reflects learned information on past multimodal exposures. We studied the long-term dynamics of cortical activity patterns during the formation of multimodal mem...
The anatomical wiring of the brain is a central focus in network neuroscience. Diffusion MRI tractography offers the unique opportunity to investigate the brain fiber architecture in vivo and noninvasively. However, its reliability is still highly debated. Here, we explored the ability of diffusion MRI tractography to match invasive anatomical trac...
The connections linking neurons within and between cerebral cortical areas form a multiscale network for communication. We review recent work relating essential features of cortico-cortical connections, such as their existence and laminar origins and terminations, to fundamental structural parameters of cortical areas, such as their distance, simil...
Activity patterns of cerebral cortical regions represent the present environment in which animals receive multi-modal inputs. They are also shaped by the history of previous activity that reflects learned information on past multimodal exposures. We studied the long-term dynamics of cortical activity patterns during the formation of multimodal memo...
The wiring of vertebrate and invertebrate brains provides the anatomical skeleton for cognition and behavior. Connections among brain regions are characterized by heterogeneous strength that is parsimoniously described by the wiring cost and homophily principles. Moreover, brains exhibit a characteristic global network topology, including modules a...
The laminar organization of the cerebral cortex is a fundamental characteristic of the brain, with essential implications for cortical function. Due to the rapidly growing amount of high-resolution brain imaging data, a great demand arises for automated and flexible methods for discriminating the laminar texture of the cortex. Here, we propose a co...
Modularity is a ubiquitous topological feature of structural brain networks at various scales. Although a variety of potential mechanisms have been proposed, the fundamental principles by which modularity emerges in neural networks remain elusive. We tackle this question with a plasticity model of neural networks derived from a purely topological p...
The ‘Sprague Effect’ described in the seminal paper of James Sprague (Science 153:1544–1547, 1966a) is an unexpected paradoxical effect in which a second brain lesion reversed functional deficits induced by an earlier lesion. It was observed initially in the cat where severe and permanent contralateral visually guided attentional deficits generated...
The present study describes the ipsilateral and contralateral cortico‐cortical and cortico‐thalamic connectivity of the parietal visual areas PPc and PPr in the ferret using standard anatomical tract‐tracing methods. The two divisions of posterior parietal cortex of the ferret are strongly interconnected, however area PPc shows stronger connectivit...
The present study describes the ipsilateral and contralateral cortico‐cortical and cortico‐thalamic connectivity of the occipital visual areas 17,18, 19 and 21 in the ferret using standard anatomical tract‐tracing methods. In line with previous studies of mammalian visual cortex connectivity, substantially more anterograde and retrograde label was...
The present study describes the ipsilateral and contralateral cortico‐cortical and cortico‐thalamic connectivity of the temporal visual areas 20a and 20b in the ferret using standard anatomical tract‐tracing methods. The two temporal visual areas are strongly interconnected, but area 20a is primarily connected to the occipital visual areas, whereas...
The anatomical wiring of the brain is a central focus in network neuroscience. Diffusion MRI tractography offers the unique opportunity to investigate the brain fiber architecture in vivo and non invasively. However, its reliability is still highly debated. Here, we explored the ability of diffusion MRI tractography to match invasive anatomical tra...
Intrinsic coupling modes (ICMs) reflect the patterns of functional connectivity or synchronization between neuronal ensembles during spontaneous brain activity. These coupling modes represent a widely used concept in modern cognitive neuroscience for probing the connectional organization of intact or damaged brains. However, the principles that sha...
The architectonic type principle relates patterns of cortico-cortical connectivity to the relative architectonic differentiation of cortical regions. One mechanism through which the observed close relation between cortical architecture and connectivity may be established is the joint development of cortical areas and their connections in developmen...
Correlation of relative connection frequency with distance and absolute density difference for all growth layouts.
Distribution of absent and present connections across distance (left panels) and absolute density difference (right panels) for all growth layouts. Absolute numbers of absent and present projections (bars) are depicted alongside the co...
Developmental trajectories of all 21 growth layouts.
Illustration of the spatiotemporal growth trajectory for each growth layout. The successive population of the cortical sheet with neurons is shown for the first three growth events. For static growth, all neurons grow simultaneously, hence only one growth event is shown. Abbreviations and backgro...
Correlation area degree with neuron density for all growth layouts.
Variation of area degree (number of connections) across areas’ neuron density is shown. Simulation instances were chosen to be representative of the median values shown in Fig 7. Spearman rank correlation results for each particular instance are shown on top of each plot. A.u.: arb...
Data underlying the presented findings.
(XLSX)
Studies of structural brain connectivity have revealed many intriguing features of complex cortical networks. To advance integrative theories of cortical organization, an understanding is required of how connectivity interrelates with other aspects of brain structure. Recent studies have suggested that interareal connectivity may be related to a va...
The laminar organization of the cerebral cortex is a fundamental characteristic of the brain, with essential implications for cortical function. Due to the rapidly growing amount of high-resolution brain imaging data, a great demand arises for automated and flexible methods for discriminating the laminar texture of the cortex. Here, we propose a co...
The architectonic type principle attributes patterns of cortico-cortical connectivity to the relative architectonic differentiation of cortical regions. One mechanism through which the observed close relation between cortical architecture and connectivity may be established is the joint development of cortical areas and their connections in develop...
Modularity is a ubiquitous topological feature of structural brain networks at various scales. While a varietyof potential mechanisms have been proposed, the fundamental principles by which modularity emerges in neural networks remain elusive. We tackle this question with a plasticity model of neural networks derived from a purely topological persp...
The relationship between the structural connectivity (SC) and functional connectivity (FC) of neural systems is of central importance in brain network science. It is an open question, however, how the SC-FC relationship depends on specific topological features of brain networks or the models used for describing neural dynamics. Using a basic but ge...
Cortical network structure has been extensively characterized at the level of local circuits and in terms of long-range connectivity, but seldom in a manner that integrates both of these scales. Furthermore, while the connectivity of cortex is known to be related to its architecture, this knowledge has not been used to derive a comprehensive cortic...
The primate connectome, possessing a characteristic global topology and specific regional connectivity profiles, is well organized to support both segregated and integrated brain function. However, the organization mechanisms shaping the characteristic connectivity and its relationship to functional requirements remain unclear. The primate brain co...
The adjacent matrix of the macaque cortical network.
The element of this matrix Aij = 1 represents the connectivity from region j to region i.
(TXT)
List of 12 generative models.
(XLSX)
Recovery of degree sequence and degree distribution by the original generative model [14] without fixing the degrees (left panel, A and C) and by the cost-efficiency trade-off model without fixing the degrees [27] (right panel, B and D).
(A, B) The (total) degrees of each node in the model vs. that in the real macaque cortical network with 95% conf...
(A) The mean distance (black bar) and (B) the mean connectivity density (white bar) for areas within the same sub-tree and between different sub-trees in the real networks.
The error-bars in (A) represent the standard deviations of the physical distance in the ensemble of all links within sub-trees.
(EPS)
The list of the 3-D coordinates of 103 cortical areas in macaque.
(TXT)
The recovery for the regional connectivity profile by the optimal generative model with fixed degrees.
(A) Recovery rate Rrecov for each area. (B) The Z-score of the recovery rate ZR(i) of the synthetic network from the generative model when compared to the random benchmark networks. (C) The Z-score of the areas sorted by the rank of total degree i...
Recovery rate of the trade-off model in short and long distance ranges.
(A) Recovery rate r0 for the unconnected pairs with short distance (x < 30 mm) in the reconstructed networks as a function of α. (B) Recovery rate r1 for the connections with long distance (x > 30 mm) as a function of α.
(TIF)
Recovered and unrecovered links, complementary to Fig 3A and 3B in the main text.
(A) The adjacent matrix A¯ of the reconstructed network at α = 0.006. The red color represents the recovered links and the green color denotes links that are unrecovered but redistributed in the reconstructed network at α = 0.006. (B) Schematics of the re-distribution...
The number of special cortical areas whose connections cannot be well recovered by the trade-off model at different α.
(A) The number of areas with Z-score Z(i) < − 1.65. (B) The number of areas with ZR(i) < 1.65.
(EPS)
Objective
To investigate whether the structural connectivity of the brain's rich-club organization is altered in patients with primary progressive MS and whether such changes to this fundamental network feature are associated with disability measures.
Methods
We recruited 37 patients with primary progressive MS and 21 healthy controls for an obser...
Traffic signs are important visual guiding signals for the safe navigation through complex road traffic. Interestingly, there is little variation in the traffic signs for cars around the world. However, remarkable variation exists for pedestrian traffic signs. Following up from an earlier study, we investigated the visual efficacy of female vs. mal...
Topological features play a major role in the emergence of complex brain network dynamics underlying brain function. Specific topological properties of brain networks, such as their modular organization, have been widely studied in recent years and shown to be ubiquitous across spatial scales and species. However, the mechanisms underlying the gene...
Structural connectivity among cortical areas provides the substrate for information exchange in the cerebral cortex and is characterized by systematic patterns of presence or absence of connections. What principles govern this cortical wiring diagram? Here, we investigate the relation of physical distance and cytoarchitecture with the connectional...
Anatomical studies conducted in neurological conditions have developed our understanding of the causal relationships between brain lesions and their clinical consequences. The analysis of lesion patterns extended across brain networks has been particularly useful in offering new insights on brain–behavior relationships. Here we applied multiperturb...
We investigated if single and double conflicts are processed separately in different brain regions and if they are differentially vulnerable to TMS perturbation. Fifteen human volunteers performed a single (Flanker or Simon) conflict task or a double (Flanker and Simon) conflict task in a combined functional Magnetic Resonance Imaging (fMRI) and Tr...
Brain regions of the cerebral cortex differ in their cytoarchitecture as well as in the intrinsic connectivity within an area and the organization of macroscopic connections between different cortical areas. Nonetheless, it is not clear which rules underlie the relationship of cellular and fiber architecture, and how the characteristic cortical mic...
Zusammenfassung
Die zelluläre Architektur (Zytoarchitektur) der kortikalen Areale der Großhirnrinde unterscheidet sich regional, ebenso wie die Verschaltungen innerhalb eines Areals und die Verbindungen zwischen den Arealen. Weitgehend unbekannt sind jedoch die genauen Regeln, nach denen die zellulare und Faserbahnarchitektur zueinander in Beziehun...
Brain regions of the cerebral cortex differ in their cytoarchitecture as well as in the intrinsic connectivity within an area and the organization of macroscopic connections between different cortical areas. Nonetheless, it is not clear which rules underlie the relationship of cellular and fiber architecture, and how the characteristic cortical mic...
Cortical activity patterns change in different depths of general anesthesia. Here we investigate the associated network level changes of functional connectivity. We recorded ongoing electrocorticographic (ECoG) activity from the ferret temporo-parieto-occipital cortex under various levels of isoflurane and determined the functional connectivity by...
Here we use computational modeling of fast neural dynamics to explore the relationship between structural and functional coupling in a population of healthy subjects. We use DTI data to estimate structural connectivity and subsequently model phase couplings from band-limited oscillatory signals derived from multichannel EEG data. Our results show t...
Empirical data.
Detailed description of empirical data recording procedures.
(PDF)
Evaluation of different EEG frequencies.
A: The mean coherence values (±SEM, shaded area) between all ROIs (n = 2145) is calculated for the frequency range of 3–30 Hz. Overall coherence at lower frequencies is higher with a peak around 8 Hz and a smaller peak around 24 Hz. B: The model performance at different bandpass filters of the EEG source tim...
Dependence between connection strength and euclidean distance.
The euclidean distance is measured between the center coordinates of individual ROIs. The strength between ROIs are the number of tracked DTI fibers divided by the product of both ROI sizes. The logarithm of the structural connection strength is inversely correlated with the euclidean d...
Understanding the wiring diagram of the human cerebral cortex is a fundamental challenge in neuroscience. Elemental aspects of its organization remain elusive. Here we examine which structural traits of cortical regions, particularly their cytoarchitecture and thickness, relate to the existence and strength of inter-regional connections. We use the...
![Figure 2: N100 m predictions in comparison with available data [1, 2]...](profile/Geir-Halnes/publication/306311805/figure/fig84/AS:396950076706822@1471651681620/N100-m-predictions-in-comparison-with-available-data-1-2-for-a-range-of-pure-tones-A_Q320.jpg)
Presentation on "25th Annual Computational Neuroscience Meeting: CNS-2016 "
BMC Neuroscience 17, 112-113 (2016).
