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Search Results: 1 - 10 of 144750 matches for " Lotfi B. Merabet "
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Teaching the Blind to Find Their Way by Playing Video Games
Lotfi B. Merabet, Erin C. Connors, Mark A. Halko, Jaime Sánchez
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0044958
Abstract: Computer based video games are receiving great interest as a means to learn and acquire new skills. As a novel approach to teaching navigation skills in the blind, we have developed Audio-based Environment Simulator (AbES); a virtual reality environment set within the context of a video game metaphor. Despite the fact that participants were na?ve to the overall purpose of the software, we found that early blind users were able to acquire relevant information regarding the spatial layout of a previously unfamiliar building using audio based cues alone. This was confirmed by a series of behavioral performance tests designed to assess the transfer of acquired spatial information to a large-scale, real-world indoor navigation task. Furthermore, learning the spatial layout through a goal directed gaming strategy allowed for the mental manipulation of spatial information as evidenced by enhanced navigation performance when compared to an explicit route learning strategy. We conclude that the immersive and highly interactive nature of the software greatly engages the blind user to actively explore the virtual environment. This in turn generates an accurate sense of a large-scale three-dimensional space and facilitates the learning and transfer of navigation skills to the physical world.
Effects of Sensory Behavioral Tasks on Pain Threshold and Cortical Excitability
Magdalena Sarah Volz, Vanessa Suarez-Contreras, Mariana E. Mendonca, Fernando Santos Pinheiro, Lotfi B. Merabet, Felipe Fregni
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0052968
Abstract: Background/Objective Transcutaneous electrical stimulation has been proven to modulate nervous system activity, leading to changes in pain perception, via the peripheral sensory system, in a bottom up approach. We tested whether different sensory behavioral tasks induce significant effects in pain processing and whether these changes correlate with cortical plasticity. Methodology/Principal Findings This randomized parallel designed experiment included forty healthy right-handed males. Three different somatosensory tasks, including learning tasks with and without visual feedback and simple somatosensory input, were tested on pressure pain threshold and motor cortex excitability using transcranial magnetic stimulation (TMS). Sensory tasks induced hand-specific pain modulation effects. They increased pain thresholds of the left hand (which was the target to the sensory tasks) and decreased them in the right hand. TMS showed that somatosensory input decreased cortical excitability, as indexed by reduced MEP amplitudes and increased SICI. Although somatosensory tasks similarly altered pain thresholds and cortical excitability, there was no significant correlation between these variables and only the visual feedback task showed significant somatosensory learning. Conclusions/Significance Lack of correlation between cortical excitability and pain thresholds and lack of differential effects across tasks, but significant changes in pain thresholds suggest that analgesic effects of somatosensory tasks are not primarily associated with motor cortical neural mechanisms, thus, suggesting that subcortical neural circuits and/or spinal cord are involved with the observed effects. Identifying the neural mechanisms of somatosensory stimulation on pain may open novel possibilities for combining different targeted therapies for pain control.
Rapid and Reversible Recruitment of Early Visual Cortex for Touch
Lotfi B. Merabet, Roy Hamilton, Gottfried Schlaug, Jascha D. Swisher, Elaine T. Kiriakopoulos, Naomi B. Pitskel, Thomas Kauffman, Alvaro Pascual-Leone
PLOS ONE , 2008, DOI: 10.1371/journal.pone.0003046
Abstract: Background The loss of vision has been associated with enhanced performance in non-visual tasks such as tactile discrimination and sound localization. Current evidence suggests that these functional gains are linked to the recruitment of the occipital visual cortex for non-visual processing, but the neurophysiological mechanisms underlying these crossmodal changes remain uncertain. One possible explanation is that visual deprivation is associated with an unmasking of non-visual input into visual cortex. Methodology/Principal Findings We investigated the effect of sudden, complete and prolonged visual deprivation (five days) in normally sighted adult individuals while they were immersed in an intensive tactile training program. Following the five-day period, blindfolded subjects performed better on a Braille character discrimination task. In the blindfold group, serial fMRI scans revealed an increase in BOLD signal within the occipital cortex in response to tactile stimulation after five days of complete visual deprivation. This increase in signal was no longer present 24 hours after blindfold removal. Finally, reversible disruption of occipital cortex function on the fifth day (by repetitive transcranial magnetic stimulation; rTMS) impaired Braille character recognition ability in the blindfold group but not in non-blindfolded controls. This disruptive effect was no longer evident once the blindfold had been removed for 24 hours. Conclusions/Significance Overall, our findings suggest that sudden and complete visual deprivation in normally sighted individuals can lead to profound, but rapidly reversible, neuroplastic changes by which the occipital cortex becomes engaged in processing of non-visual information. The speed and dynamic nature of the observed changes suggests that normally inhibited or masked functions in the sighted are revealed by visual loss. The unmasking of pre-existing connections and shifts in connectivity represent rapid, early plastic changes, which presumably can lead, if sustained and reinforced, to slower developing, but more permanent structural changes, such as the establishment of new neural connections in the blind.
Modulation of inhibitory systems to enhance motor rehabilitation: insights for the use of noninvasive brain stimulation
Reidler, Jay S.;Nascimento, Bruno C.;Wu, Daniel S.K.;Carvas, Marcelo;Massuyama, Breno K.;Oliveira, Bruno M.R. de;Zaghi, Soroush;Rezende, Daniel T. de;El-Nazer, Rasheda;Gon?alves, Walyson N.;Merabet, Lotfi B.;Fregni, Felipe;
Psychology & Neuroscience , 2010, DOI: 10.3922/j.psns.2010.2.004
Abstract: motor impairment following stroke is a leading cause of disability in adults. despite advances in motor rehabilitation techniques, many adult stroke survivors never approach full functional recovery. intriguingly, children exhibit better rehabilitation outcomes when compared to adults suffering from comparable brain injuries, yet the reasons for this remain unclear. a common explanation is that neuroplasticity in adults is substantially limited following stroke, thus constraining the brain's ability to reorganize in response to neurological insult. this explanation, however, does not suffice for there is much evidence suggesting that neuroplasticity in adults is not limited following stroke. we hypothesize that diminished functional recovery in adults is in part due to inhibitory neuronal interactions, such as transcallosal inhibition, that serve to optimize motor performance as the brain matures. following stroke, these inhibitory interactions pose rigid barriers to recovery by inhibiting activity in the affected regions and hindering recruitment of compensatory pathways. in contrast, children exhibit better rehabilitation outcomes in part because they have not fully developed the inhibitory interactions that impede functional recovery in adults. we suggest that noninvasive brain stimulation can be used in the context of motor rehabilitation following stroke to reduce the effects of existing inhibitory connections, effectively returning the brain to a state that is more amenable to rehabilitation. we conclude by discussing further research to explore this hypothesis and its implications.
Paleomagnetism of the Liassic member of the Zarza tine Formation (stable Saharan craton, Illizi basin, Algeria)
M. E. M. Derder,B. Henry,N. Merabet,B. Bayou
Annals of Geophysics , 2001, DOI: 10.4401/ag-3551
Abstract: A paleomagnetic study was carried out in the carbonates and marls of the Liassic member of the Zarza tine Formation of the Illizi basin (SE Algeria) deposited in a continental environment. Two magnetization components were identified. The first, defined at relatively low blocking temperature, was isolated in five sites, and yields the following paleomagnetic pole (80.8°N, 20.1°E, K = 811 and A 95 = 2.2°). This magnetization is considered an overprint acquired during Cenozoic times. The second component was defined by both normal and reversed polarity. The normal polarity was identified in fourteen sites using both linear regression and great circles. The reversed one was inferred in four sites from the remagnetization circle and demagnetization path analyses. This component is mainly (it could be in part the primary magnetization) a late diagenesis magnetic overprint. It yields a new Liassic pole (71.8°S, 54.9°E, K = 91 and A 95 = 3.9°) for Africa.
Two-Component Reduction of Nahm's Equations and Hyper-elliptic Solution
Houari Merabet
Physics , 1997, DOI: 10.1016/S0370-2693(97)01351-8
Abstract: We find the general hyper-elliptic solutions to the two-component reduced Nahm equations proposed by Hitchin et al. Elliptic solutions are a special case and can appear only for specific values of the monopole charges.
Nutritional and Metabolic Profile in Diabetic Patients and Relationship with Metabolic Syndrome  [PDF]
Djahida Hadj Merabet, Karima Bereksi Reguig
Food and Nutrition Sciences (FNS) , 2016, DOI: 10.4236/fns.2016.73017
Abstract: Background & Objectives: Diabetes and metabolic syndrome spread alarmingly throughout the whole world including Algeria, so our study makes the links closer between these two entities and that through studying nutritional, metabolic and physical profiles. Study Design: 204 patients were recruited and interviewed (anthropometric measurements, blood pressure, age, sex, personal and family history, the practice of physical activity and evaluation of food consumption). Patients and Methods: A cross-sectional survey was conducted in the western Algerian region (Sidi Bel Abbes). Patients with MetS are defined according to the criteria of the National Cholesterol Education Program Adult Treatment Panel III (NCEP ATP III). Results: The results show that the frequency of the metabolic syndrome is 86.27% with predominance of women (92.15% women vs 80.39% men). The age group most affected by the MetS among women and men is [54 - 79] years. We also note that 51.28% of men present three criteria of MetS, while 65.21% of women have four and five criteria. The results show that the criteria most dominant in men are hypertension and type 2 diabetes, whereas in women, the high waist is the most abundant criterion. Moreover, the whole is underlined by a low physical activity with only 21.56% who practice it regularly (15.95% women vs 28.04% men). The estimate of food intake shows a qualitative imbalance: protein intake is 19.65% in women vs. 19.43% in men represented mainly by vegetable protein (83.72% for women vs. 72.85% for men); lipids intake is characterized by a lower consumption than the recommendation of the Mediterranean diet concerning the mono-unsaturated fatty acids (MUFA) (39.44% among women vs 40.24% at the men), as in poly unsaturated fatty-acids including (PUFA) (23.30% among women vs 23.64% at the men) whereas an increase in the consumption of the saturated fatty-acids (SFA) is observed in the whole population including (37.24% among women vs 36.10% at the men); lower concentration in calcium, magnesium and en fibers; important concentration of sodium and an insufficient contribution of water. Conclusion: We should be aware of the importance of the modulation of these risk factors through harmonization of “lifestyle” to prevent the occurrence of metabolic syndrome.
Interdiffusion and Compound Formation in the Mo/Si Thin Film Metallization System
Houria Benkherbache,Abdelali Merabet
Journal of Engineering and Applied Sciences , 2012,
Abstract: In this study, we have used the silicon wafers. Before the deposit of film, the oxide layer has been removed by chemical cleaning. After, the thickness of 80 nm molybdenum layer has been deposited by electronic bombardment. The samples were heat treated at temperatures ranging from 500 to 700 C for different time duration under vacuum. We report here on the electrical characterization of the interdiffused and reacted Molybdenum-Silicon bilayered system by means of sheet resistivity measurements using four point probes. X-ray diffractometry were taken, in order to observe the formation of phases that occur at annealing conditions which cause drastic modifications in the sheet resistivity values.
Nahm's equations and root systems
Tomasz Brzezinski,Houari Merabet
Physics , 1997, DOI: 10.1023/A:1021649915250
Abstract: A method of deriving solutions to Nahm's equations based on root structure of simple Lie algebras is given. As an illustration of this method the recently found solutions to Nahm's equations with tetrahedral and octahedral symmetries are shown to correspond to $A_2$ and $A_3$ root systems.
The Breathing Mode in Extended Skyrme Model
Abdellatif Abada,Houari Merabet
Physics , 1993, DOI: 10.1103/PhysRevD.48.2337
Abstract: We study an extended Skyrme model which includes fourth and sixth-order terms. We explore some static properties like the $\Delta$-nucleon mass splitting and investigate the Skyrmion breathing mode in the framework of the linear response theory. We find that the monopole response function has a pronounced peak located at $\sim$ 400 MeV, which we identify to the Roper resonance $N(1440)$. As compared to the standard one, the extended Skyrme model provides a more accurate description of baryon properties.
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