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Search Results: 1 - 10 of 6827 matches for " Leonardo;Rorden "
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Asymmetry of the structural brain connectome in healthy older adults.
Leonardo Bonilha,Travis Nesland,Chris Rorden,Julius Fridriksson
Frontiers in Psychiatry , 2013, DOI: 10.3389/fpsyt.2013.00186
Abstract: Background: It is now possible to map neural connections in vivo across the whole brain (i.e., the brain connectome). This is a promising development in neuroscience since many health and disease processes are believed to arise from the architecture of neural networks. Objective: To describe the normal range of hemispheric asymmetry in structural connectivity in healthy older adults. Methods: We obtained high-resolution structural magnetic resonance images (MRI) from 17 healthy older adults. For each subject, the brain connectome was reconstructed by parcelating the probabilistic map of gray matter into anatomically defined regions of interested (ROIs). White matter fiber tractography was reconstructed from diffusion tensor imaging and streamlines connecting gray matter ROIs were computed. Asymmetry indices were calculated regarding ROI connectivity (representing the sum of connectivity weight of each cortical ROI) and for regional white matter links. All asymmetry measures were compared to a normal distribution with mean=0 through one sample t-tests. Results: Leftward cortical ROI asymmetry was observed in medial temporal, dorsolateral frontal and occipital regions. Rightward cortical ROI asymmetry was observed in middle temporal and orbito-frontal regions. Link-wise asymmetry revealed stronger connections in the left hemisphere between the medial temporal, anterior and posterior peri-Sylvian and occipito-temporal regions. Rightward link asymmetry was observed in lateral temporal, parietal and dorsolateral frontal connections. Conclusions: We postulate that asymmetry of specific connections may be related to functional hemispheric organization. This study may provide reference for future studies evaluating the architecture of the connectome in health and disease processes in senior individuals.
Global versus local processing: seeing the left side of the forest and the right side of the trees
John Christie,Jay P. Ginsberg,Julius Fridriksson,Leonardo Bonilha,Christopher Rorden
Frontiers in Human Neuroscience , 2012, DOI: 10.3389/fnhum.2012.00028
Abstract: Previous studies using hierarchical figures (where a large global shape is composed of a series of smaller local shapes) suggest that performance is better for local features presented in the right relative to left visual field, whereas the opposite pattern is observed for global features. However, these previous studies have focused on effects between hemifields. Recent data from patients with neurological damage suggest that local deficits can be allocentric (e.g., following left hemisphere injury, individuals are relatively slow to detect features on the right side of an object, regardless of visual field). Therefore, we decided to extend previous global versus local research by also observing local performance within hemifields. Specifically, on each trial we presented two hierarchical figures (one in each hemifield), but crucially the left and right side of each item were composed of different local features. In this task, the participant simply reports if a circle is present, regardless of location or whether this is a local or global feature. We observed that both neurologically healthy individuals, as well as an individual with brain injury, were relatively better detecting local information on the right side of objects, regardless of spatial location, while both showed better performance for global stimuli in the left visual field. This work is consistent with recent work in patients with neurological damage, and provides a new paradigm for exploring hemispheric specialization.
Conceptualising Regulatory Change - Explaining Shifts in Telecommunications Governance
Seamus Simpson,Rorden Wilkinson
Computer Science , 2001,
Abstract: Drawing on perspectives from telecommunications policy and neo-Gramscian understandings of international political economy, this paper offers an explanation and analysis of the shifting patterns of regulation which have been evident in the telecommunications sector in recent years. It aims to illustrate explain and explore the implications of the movement of regulatory sovereignty away from the nation-state, through regional conduits, to global organisations in the crystallisation of a world system of telecommunications governance. Our central argument is that telecommunications governance has evolved from a regulatory arena characterised, in large part, by national diversity, to one wherein a more convergent global multilayered system is emerging. We suggest that the epicentre of this regulatory system is the relatively new World Trade Organisation (WTO). Working in concert with the WTO are existing well-established nodes regulation. In further complement, we see regional regulatory projects, notably the European Union (EU), as important conduits and nodes of regulation in the consolidation of a global regulatory regime. By way of procedure, we first explore the utility of a neo-Gramscian approach for understanding the development of global regulatory frameworks. Second, we survey something of the recent history - and, in extension, conventional wisdom - of telecommunications regulation at national and regional levels. Third, we demonstrate how a multilayered system of global telecommunications regulation has emerged centred around the regulatory authority of the WTO. Finally, we offer our concluding comments.
Statistical voxel-wise analysis of ictal SPECT reveals pattern of abnormal perfusion in patients with temporal lobe epilepsy
Amorim, Bárbara Juarez;Etchebehere, Elba Cristina Sá de Camargo;Camargo, Edwaldo Eduardo;Rio, Pablo Augusto;Bonilha, Leonardo;Rorden, Chris;Li, Li Min;Cendes, Fernando;
Arquivos de Neuro-Psiquiatria , 2005, DOI: 10.1590/S0004-282X2005000600014
Abstract: objective: to investigate the pattern of perfusion abnormalities in ictal and interictal brain perfusion spect images (bsi) from patients with temporal lobe epilepsy (tle). method: it was acquired interictal and ictal bsi from 24 patients with refractory tle. bsis were analyzed by visual inspection and statistical parametric mapping (spm2). statistical analysis compared the patients group to a control group of 50 volunteers. the images from patients with left-tle were left-right flipped. results: it was not observed significant perfusional differences in interictal scans with spm. ictal bsi in spm analysis revealed hyperperfusion within ipsilateral temporal lobe (epileptogenic focus) and also contralateral parieto-occipital region, ipsilateral posterior cingulate gyrus, occipital lobes and ipsilateral basal ganglia. ictal bsi also showed areas of hypoperfusion. conclusion: in a group analysis of ictal bsi of patients with tle, voxel-wise analysis detects a network of distant regions of perfusional alteration which may play active role in seizure genesis and propagation.
Neural Correlates of Inter-Trial Priming and Role-Reversal in Visual Search
Christopher Rorden,Arni Kristjansson,Kathleen Pirog Revill,Styrmir Saevarsson
Frontiers in Human Neuroscience , 2011, DOI: 10.3389/fnhum.2011.00151
Abstract: Studies of priming of visual perception demonstrate that observers respond more quickly to targets in a field of distractors when relevant features are repeated versus novel or role-reversed. In a recent brain imaging study by Kristjánsson et al. (2007), participants were presented with two items of one color and a single item in a different color with the task of reporting the orientation of the uniquely colored item. Consistent with previous behavioral reports, they found that observers were faster to respond when the target and distractor colors were identical to the previous trial than when they were reversed. They found reduced BOLD activity in brain areas linked with attentional control on trials where the target and distractor colors were repeated relative to reversed, which they interpreted as reflecting response suppression (decreased BOLD signal for repeated stimuli). However, since their design only compared repeated versus reversed task demands, it is logically possible that this pattern reflects increased BOLD signal for role-reversed stimuli: activity required to inhibit previously facilitated information and select previously inhibited information. We explored this possibility with a task where we contrasted the signal generated by repeated, reversed, and novel features. Our data suggest that the majority of the change in neural signal elicited by priming of pop-out reflects increased activation when selection criteria are reversed.
Thermal Soliton Correlation Functions in Theories with a Z(N) Symmetry  [PDF]
Leonardo Mondaini
Journal of Modern Physics (JMP) , 2012, DOI: 10.4236/jmp.2012.311221
Abstract: We show that the quantum solitons occurring in theories describing a complex scalar field in (1 + 1)-dimensions with a Z(N) symmetry may be identified with sine-Gordon quantum solitons in the phase of this field. Then using both the Euclidean thermal Green function of the two-dimensional free massless scalar field in coordinate space and its dual, we obtain an explicit series expression for the corresponding solitonic correlation function at finite temperature.
The Rise of Solitons in Sine-Gordon Field Theory: From Jacobi Amplitude to Gudermannian Function  [PDF]
Leonardo Mondaini
Journal of Applied Mathematics and Physics (JAMP) , 2014, DOI: 10.4236/jamp.2014.213141
Abstract: We show how the famous soliton solution of the classical sine-Gordon field theory in (1 + 1)-dimensions may be obtained as a particular case of a solution expressed in terms of the Jacobi amplitude, which is the inverse function of the incomplete elliptic integral of the first kind.
Obtaining a New Representation for the Golden Ratio by Solving a Biquadratic Equation  [PDF]
Leonardo Mondaini
Journal of Applied Mathematics and Physics (JAMP) , 2014, DOI: 10.4236/jamp.2014.213134
Abstract: In the present work we show how different ways to solve biquadratic equations can lead us to different representations of its solutions. A particular equation which has the golden ratio and its reciprocal as solutions is shown as an example.
Towards a Field Theoretical Stochastic Model for Description of Tumour Growth  [PDF]
Leonardo Mondaini
Journal of Applied Mathematics and Physics (JAMP) , 2017, DOI: 10.4236/jamp.2017.55095
Abstract: We develop a field theory-inspired stochastic model for description of tumour growth based on an analogy with an SI epidemic model, where the susceptible individuals (S) would represent the healthy cells and the infected ones (I), the cancer cells. From this model, we obtain a curve describing the tumour volume as a function of time, which can be compared to available experimental data.
The P300 as a Marker of Waning Attention and Error Propensity
Avijit Datta,Rhodri Cusack,Kari Hawkins,Joost Heutink,Chris Rorden,Ian H. Robertson,Tom Manly
Computational Intelligence and Neuroscience , 2007, DOI: 10.1155/2007/93968
Abstract: Action errors can occur when routine responses are triggered inappropriately by familiar cues. Here, EEG was recorded as volunteers performed a “go/no-go” task of long duration that occasionally and unexpectedly required them to withhold a frequent, routine response. EEG components locked to the onset of relevant go trials were sorted according to whether participants erroneously responded to immediately subsequent no-go trials or correctly withheld their responses. Errors were associated with a significant relative reduction in the amplitude of the preceding P300, that is, a judgement could be made bout whether a response-inhibition error was likely before it had actually occurred. Furthermore, fluctuations in P300 amplitude across the task formed a reliable associate of individual error propensity, supporting its use as a marker of sustained control over action.
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