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Search Results: 1 - 10 of 182256 matches for " Marc de Lussanet "
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How the flow and processing of information shapes the cerebrum
Marc HE de Lussanet
PeerJ , 2015, DOI: 10.7287/peerj.preprints.239v1
Abstract: The cerebrum of mammals spans a vast range of sizes and yet has a very regular structure. The amount of folding of the cortical surface and the proportion of white matter gradually increase with size, but the underlying mechanisms remain elusive. Here, two laws are derived to fully explain these cerebral scaling relations. The two general laws are derived from the notion that total processing power of the cortex is determined by the total cortical surface (i.e., the number of neurons), whereas the most efficient over-all flow of information is governed by the size of local networks (cortical columns). Since information is transferred by axonal connections which have a definite volume, a trade-off can be formulated from theoretical considerations between local, inter-gyral information transfer and long-range information transfer. It can be shown that this trade-off is governed by a single parameter describing the size of local networks, \(t_{local}\). Despite having just one free parameter, the first law fits the mammalian cerebrum better than any existing function, both across species and within humans. According to the second law, the scaling of white matter volume is also determined by the information principles. It follows that large cerebrums have much local processing and little global information flow. Moreover, paradoxically, a further increase in long-range connections would decrease the efficiency of information flow. These theoretical scaling principles help to compare the cerebrums across mammals regardless their size.
The human and mammalian cerebrum scale by computational power and information resistance
Marc H. E. de Lussanet
Quantitative Biology , 2013,
Abstract: The cerebrum of mammals spans a vast range of sizes and yet has a very regular structure. The amount of folding of the cortical surface and the proportion of white matter gradually increase with size, but the underlying mechanisms remain elusive. Here, two laws are derived to fully explain these cerebral scaling relations. The first law holds that the long-range information flow in the cerebrum is determined by the total cortical surface (i.e., the number of neurons) and the increasing information resistance of long-range connections. Despite having just one free parameter, the first law fits the mammalian cerebrum better than any existing function, both across species and within humans. According to the second law, the white matter volume scales, with a few minor corrections, to the cortical surface area. It follows from the first law that large cerebrums have much local processing and little global information flow. Moreover, paradoxically, a further increase in long-range connections would decrease the efficiency of information flow.
A hexamer origin of the echinoderms' five rays
Marc H. E. de Lussanet
Quantitative Biology , 2011, DOI: 10.1111/j.1525-142x.2011.00472.x
Abstract: Of the major deuterostome groups, the echinoderms with their multiple forms and complex development are arguably the most mysterious. Although larval echinoderms are bilaterally symmetric, the adult body seems to abandon the larval body plan and to develop independently a new structure with different symmetries. The prevalent pentamer structure, the asymmetry of Loven's rule and the variable location of the periproct and madrepore present enormous difficulties in homologizing structures across the major clades, despite the excellent fossil record. This irregularity in body forms seems to place echinoderms outside the other deuterostomes. Here I propose that the predominant five-ray structure is derived from a hexamer structure that is grounded directly in the structure of the bilaterally symmetric larva. This hypothesis implies that the adult echinoderm body can be derived directly from the larval bilateral symmetry and thus firmly ranks even the adult echinoderms among the bilaterians. In order to test the hypothesis rigorously, a model is developed in which one ray is missing between rays IV-V (Loven's schema) or rays C-D (Carpenter's schema). The model is used to make predictions, which are tested and verified for the process of metamorphosis and for the morphology of recent and fossil forms. The theory provides fundamental insight into the M-plane and the Ubisch', Loven's and Carpenter's planes and generalizes them for all echinoderms. The theory also makes robust predictions about the evolution of the pentamer structure and its developmental basis. *** including corrections (see footnotes) ***
Time-Delayed Mutual Information of the Phase as a Measure of Functional Connectivity
Andreas Wilmer, Marc de Lussanet, Markus Lappe
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0044633
Abstract: We propose a time-delayed mutual information of the phase for detecting nonlinear synchronization in electrophysiological data such as MEG. Palus already introduced the mutual information as a measure of synchronization [1]. To obtain estimates on small data-sets as reliably as possible, we adopt the numerical implementation as proposed by Kraskov and colleagues [2]. An embedding with a parametric time-delay allows a reconstruction of arbitrary nonstationary connective structures – so-called connectivity patterns – in a wide class of systems such as coupled oscillatory or even purely stochastic driven processes [3]. By using this method we do not need to make any assumptions about coupling directions, delay times, temporal dynamics, nonlinearities or underlying mechanisms. For verifying and refining the methods we generate synthetic data-sets by a mutual amplitude coupled network of R?ssler oscillators with an a-priori known connective structure. This network is modified in such a way, that the power-spectrum forms a power law, which is also observed in electrophysiological recordings. The functional connectivity measure is tested on robustness to additive uncorrelated noise and in discrimination of linear mixed input data. For the latter issue a suitable de-correlation technique is applied. Furthermore, the compatibility to inverse methods for a source reconstruction in MEG such as beamforming techniques is controlled by dedicated dipole simulations. Finally, the method is applied on an experimental MEG recording.
Decussation as an axial twist: A Comment on Kinsbourne (2013)
Marc HE de Lussanet,Jan W.M. Osse
PeerJ , 2015, DOI: 10.7287/peerj.preprints.432v2
Abstract: One of the great mysteries of the brain, which has puzzled all-time students of brain form and function is the contralateral organization of the forebrain, and the crossings of its major afferent and efferent connections. As a novel explanation, two recent studies have proposed that the rostral part of the head, including the forebrain, is rotated by 180 degrees with respect to the rest of the body (de Lussanet and Osse, 2012, Animal Biology 62, 193–216; Kinsbourne, 2013, Neuropsychology 27, 511–515). Kinsbourne proposes one 180-degree turn while we consider the 180 degrees being the result of two 90-degree turns in opposite directions. We discuss the similarities and differences between the two hypotheses.
An ancestral axial twist explains the contralateral forebrain and the optic chiasm in vertebrates
Marc H. E. de Lussanet,Jan W. M. Osse
Quantitative Biology , 2010, DOI: 10.1163/157075611X617102
Abstract: Among the best-known facts of the brain are the contralateral visual, auditory, sensational, and motor mappings in the forebrain. How and why did these evolve? The few theories to this question provide functional answers, such as better networks for visuomotor control. However, these theories contradict the data, as discussed here. Instead we propose that a 90-deg left-turn around the body-axis evolved in a common ancestor of all vertebrates. Compensatory migrations of the tissues during development restore body symmetry. Eyes, nostrils and forebrain compensate in the direction of the turn, whereas more caudal structures migrate in the opposite direction. As a result of these opposite migrations the forebrain becomes crossed and inverted with respect to the rest of the nervous system. We show that these compensatory migratory movements can indeed be observed in the zebrafish (Danio rerio) and the chick (Gallus gallus). With a model we show how the axial twist hypothesis predicts that an optic chiasm should develop on the ventral side of the brain, whereas the olfactory tract should be uncrossed. In addition, the hypothesis explains the decussation of the trochlear nerve, why olfaction is non-crossed, why the cerebellar hemispheres represent the ipsilateral bodyside, why in sharks the forebrain halves each represent the ipsilateral eye, why the heart and other inner organs are asymmetric in the body. Due to the poor fossil record, the possible evolutionary scenarios remain speculative. Molecular evidence does support the hypothesis. The findings may throw new insight on the problematic structure of the forebrain.
Impairments of Biological Motion Perception in Congenital Prosopagnosia
Joachim Lange,Marc de Lussanet,Simone Kuhlmann,Anja Zimmermann,Markus Lappe,Pienie Zwitserlood,Christian Dobel
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0007414
Abstract: Prosopagnosia is a deficit in recognizing people from their faces. Acquired prosopagnosia results after brain damage, developmental or congenital prosopagnosia (CP) is not caused by brain lesion, but has presumably been present from early childhood onwards. Since other sensory, perceptual, and cognitive abilities are largely spared, CP is considered to be a stimulus-specific deficit, limited to face processing. Given that recent behavioral and imaging studies indicate a close relationship of face and biological-motion perception in healthy adults, we hypothesized that biological motion processing should be impaired in CP. Five individuals with CP and ten matched healthy controls were tested with diverse biological-motion stimuli and tasks. Four of the CP individuals showed severe deficits in biological-motion processing, while one performed within the lower range of the controls. A discriminant analysis classified all participants correctly with a very high probability for each participant. These findings demonstrate that in CP, impaired perception of faces can be accompanied by impaired biological-motion perception. We discuss implications for dedicated and shared mechanisms involved in the perception of faces and biological motion.
Spinal lordosis optimizes the requirements for a stable erect posture
Heiko Wagner, Anne Liebetrau, David Schinowski, Thomas Wulf, Marc HE de Lussanet
Theoretical Biology and Medical Modelling , 2012, DOI: 10.1186/1742-4682-9-13
Abstract: We developed a musculoskeletal model of the lumbar spine, that includes an asymmetric, dorsally shifted location of the spinal column in the body, realistic moment arms, and physiological cross-sectional areas (PCSA) of the muscles as well as realistic force-length and force-velocity relationships. The model was used to analyze the stability of an upright body posture. According to our results, lordosis reduces the local joint torques necessary for an equilibrium of the vertebral column during an erect posture. At the same time lordosis increases the demands on the global muscles to provide stability.We conclude that the development of a spinal lordosis is a compromise between the stability requirements of an erect posture and the necessity of torque equilibria at each spinal segment.Lordosis is the typical convex bending of the human lumbar spine, and is thought to be an adaptation to bipedalism [1-3]. The upright body posture distinguishes humans from most mammals. Despite lordosis and the substantial evolutionary modifications of the human lower spine and hip, the topography of back muscles in humans is remarkably similar to that found in other primates [3]. The development of a lumbar lordosis in humans is apparently not genetically determined. Children develop a lordosis as they adopt bipedal standing and walking. Even Japanese macaques gradually acquire a pronounced lordosis of the lumbar spine when they are trained to walk bipedally [1]. In women, lordosis proliferates substantially during pregnancy [4]. Thus, why do humans and some animals develop a lumbar lordosis while learning to walk bipedally? Why is this apparently a solution that is spontaneously arrived at by the motor system? When regarding the coronal plane, the spine is medial in the body, so the spinal-muscular system is symmetric (Figure 1A,B). Normally the spine does not develop a curvature in the coronal plane (known as scoliosis). On the other hand, the spine does have an eccentric, dorsal po
A educa??o na pris?o n?o é uma mera atividade
Maeyer, Marc De;
Educa??o & Realidade , 2013, DOI: 10.1590/S2175-62362013000100004
Abstract: education and prison have always formed an incoherent pair: the first, finding its universal reasons in the particular context of the second, which, by its nature, offers only a contradictory frame for the free expression of the first one. how can prison, being anti-educative by itself, offer people an opportunity to explore useful knowledge from now until the day they are released? we will try to demonstrate that, amidst these contradictions, education is possible with the proviso that it is effectively an education for life, and not only instruction or reeducation.
Reflections on outcome analyses: Introducing the concept of near misses
Marc R. de Leval
Global Cardiology Science & Practice , 2011, DOI: 10.5339/ahcsps.2011.12
Abstract:
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