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Search Results: 1 - 10 of 1267 matches for " Maurice Ptito "
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Cortical GABAergic Interneurons in Cross-Modal Plasticity following Early Blindness
Sébastien Desgent,Maurice Ptito
Neural Plasticity , 2012, DOI: 10.1155/2012/590725
Abstract: Early loss of a given sensory input in mammals causes anatomical and functional modifications in the brain via a process called cross-modal plasticity. In the past four decades, several animal models have illuminated our understanding of the biological substrates involved in cross-modal plasticity. Progressively, studies are now starting to emphasise on cell-specific mechanisms that may be responsible for this intermodal sensory plasticity. Inhibitory interneurons expressing γ-aminobutyric acid (GABA) play an important role in maintaining the appropriate dynamic range of cortical excitation, in critical periods of developmental plasticity, in receptive field refinement, and in treatment of sensory information reaching the cerebral cortex. The diverse interneuron population is very sensitive to sensory experience during development. GABAergic neurons are therefore well suited to act as a gate for mediating cross-modal plasticity. This paper attempts to highlight the links between early sensory deprivation, cortical GABAergic interneuron alterations, and cross-modal plasticity, discuss its implications, and further provide insights for future research in the field. 1. Introduction Patterns of activity from the peripheral sensory receptor arrays can dramatically influence the development of connectivity and functional organization of cortical fields in mammals. In some species, evolution in relation to specific environmental cues has nurtured the brain’s blueprint in such a way that a sensory cortex processing specific survival needs has been enlarged over time as compared to other modalities (Figure 1) [1–5]. Similarly, when a sensory function is lost during development, spared senses compensate by taking more cortical space and recruiting the deafferented areas, to maintain homeostasis of sensory function. This reorganization optimizes and secures the individual’s survival and awareness to future environmental changes. For example, the loss of sight at birth or during early life in humans leads to important anatomical and functional reorganization of the visually deprived cortex that will become activated by a wide variety of nonvisual stimuli involving touch, audition, and olfaction [6–11]. Enhanced spatiotemporal functions in the remaining sensory modalities have also been reported [12–16]. It seems therefore that the visual cortex of the blind is not lifeless and is capable of adapting in order to accommodate these nonvisual inputs through cross-modal plasticity. Figure 1: Primary cortical areas in three species of mammals (i.e., Mouse, Ghost Bat and
Adaptive Neuroplastic Responses in Early and Late Hemispherectomized Monkeys
Mark W. Burke,Ron Kupers,Maurice Ptito
Neural Plasticity , 2012, DOI: 10.1155/2012/852423
Abstract: Behavioural recovery in children who undergo medically required hemispherectomy showcase the remarkable ability of the cerebral cortex to adapt and reorganize following insult early in life. Case study data suggest that lesions sustained early in childhood lead to better recovery compared to those that occur later in life. In these children, it is possible that neural reorganization had begun prior to surgery but was masked by the dysfunctional hemisphere. The degree of neural reorganization has been difficult to study systematically in human infants. Here we present a 20-year culmination of data on our nonhuman primate model (Chlorocebus sabeus) of early-life hemispherectomy in which behavioral recovery is interpreted in light of plastic processes that lead to the anatomical reorganization of the early-damaged brain. The model presented here suggests that significant functional recovery occurs after the removal of one hemisphere in monkeys with no preexisting neurological dysfunctions. Human and primate studies suggest a critical role for subcortical and brainstem structures as well as corticospinal tracts in the neuroanatomical reorganization which result in the remarkable behavioral recovery following hemispherectomy. The non-human primate model presented here offers a unique opportunity for studying the behavioral and functional neuroanatomical reorganization that underlies developmental plasticity. 1. Introduction 1.1. Prologue Cerebral hemicorticectomy is a form of radical surgical intervention currently used in the treatment of intractable epilepsy [1] and malignant tumors [2] accompanied by infantile hemiplegia [3, 4].Neurological and behavioral functions are remarkably improved following the removal of the entire cerebral hemisphere, not only in infants but also in adults, with the recovery being greater for the early-lesioned subjects [5, 6]. Although hemispherectomized patients may go on to lead full lives, it is not complete and individuals have lingering behavioral manifestations [7]. The degree of recovery largely depends on the system being investigated. For example, motor functions are improved postoperatively, locomotion is preserved, and the hemiplegia of the contralateral limb is ameliorated with the apparition of simple voluntary movements [4]. Thresholds for touch, pain and temperature are elevated [4, 8, 9], and localization and discriminative abilities are diminished. Sensory functions are better preserved for the face and the leg and are worsened for the forearm and the hand [4, 9]. At the visual level, there is a persistent
Physiology and Plasticity of Interhemispheric Connections
Matteo Caleo,Giorgio M. Innocenti,Maurice Ptito
Neural Plasticity , 2013, DOI: 10.1155/2013/176183
Abstract:
Sensory Deprivation and Brain Plasticity
Maurice Ptito,Ron Kupers,Steve Lomber,Pietro Pietrini
Neural Plasticity , 2012, DOI: 10.1155/2012/810370
Abstract:
Sensory Deprivation and Brain Plasticity
Maurice Ptito,Ron Kupers,Steve Lomber,Pietro Pietrini
Neural Plasticity , 2012, DOI: 10.1155/2012/810370
Abstract:
Crossmodal Recruitment of the Ventral Visual Stream in Congenital Blindness
Maurice Ptito,Isabelle Matteau,Arthur Zhi Wang,Olaf B. Paulson,Hartwig R. Siebner,Ron Kupers
Neural Plasticity , 2012, DOI: 10.1155/2012/304045
Abstract: We used functional MRI (fMRI) to test the hypothesis that blind subjects recruit the ventral visual stream during nonhaptic tactile-form recognition. Congenitally blind and blindfolded sighted control subjects were scanned after they had been trained during four consecutive days to perform a tactile-form recognition task with the tongue display unit (TDU). Both groups learned the task at the same rate. In line with our hypothesis, the fMRI data showed that during nonhaptic shape recognition, blind subjects activated large portions of the ventral visual stream, including the cuneus, precuneus, inferotemporal (IT), cortex, lateral occipital tactile vision area (LOtv), and fusiform gyrus. Control subjects activated area LOtv and precuneus but not cuneus, IT and fusiform gyrus. These results indicate that congenitally blind subjects recruit key regions in the ventral visual pathway during nonhaptic tactile shape discrimination. The activation of LOtv by nonhaptic tactile shape processing in blind and sighted subjects adds further support to the notion that this area subserves an abstract or supramodal representation of shape. Together with our previous findings, our data suggest that the segregation of the efferent projections of the primary visual cortex into a dorsal and ventral visual stream is preserved in individuals blind from birth. 1. Introduction It is well established that early-onset blindness leads to widespread neuroplastic changes. For instance, studies have shown that the senses of hearing and touch are more developed in blind than sighted individuals [1–6], probably due to training-induced plasticity. The enlargement of the somatic and motor area representation of the index finger in proficient Braille readers is a clear example of this experience-dependent plastic process [7]. Brain imaging studies using 18F-fluoro-deoxyglucose-positron emission tomography (FDG-PET) have shown that, despite the absence of visual input, the occipital cortex of congenitally blind individuals shows a supranormal metabolism at rest [8, 9]. This indicates that the visually deprived cortex is still functionally active and can be recruited by other modalities such as touch, hearing, and smell. Indeed, studies using a variety of brain imaging tools such as PET, functional, magnetic resonance imaging (fMRI), event-related potentials and magnetoencephalography, all concur on a recruitment of the visual cortex of early blind individuals during various nonvisual tasks (e.g., [10–14]). Numerous brain imaging studies have consistently found activations of occipital
Rod Photoreceptors Express GPR55 in the Adult Vervet Monkey Retina
Joseph Bouskila, Pasha Javadi, Christian Casanova, Maurice Ptito, Jean-Fran?ois Bouchard
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0081080
Abstract: Cannabinoids exert their actions mainly through two receptors, the cannabinoid CB1 receptor (CB1R) and cannabinoid CB2 receptor (CB2R). In recent years, the G-protein coupled receptor 55 (GPR55) was suggested as a cannabinoid receptor based on its activation by anandamide and tetrahydrocannabinol. Yet, its formal classification is still a matter of debate. CB1R and CB2R expression patterns are well described for rodent and monkey retinas. In the monkey retina, CB1R has been localized in its neural (cone photoreceptor, horizontal, bipolar, amacrine and ganglion cells) and CB2R in glial components (Müller cells). The aim of this study was to determine the expression pattern of GPR55 in the monkey retina by using confocal microscopy. Our results show that GPR55 is strictly localized in the photoreceptor layer of the extrafoveal portion of the retina. Co-immunolabeling of GPR55 with rhodopsin, the photosensitive pigment in rods, revealed a clear overlap of expression throughout the rod structure with most prominent staining in the inner segments. Additionally, double-label of GPR55 with calbindin, a specific marker for cone photoreceptors in the primate retina, allowed us to exclude expression of GPR55 in cones. The labeling of GPR55 in rods was further assessed with a 3D visualization in the XZ and YZ planes thus confirming its exclusive expression in rods. These results provide data on the distribution of GPR55 in the monkey retina, different than CB1R and CB2R. The presence of GPR55 in rods suggests a function of this receptor in scotopic vision that needs to be demonstrated.
Cannabinoid Receptor CB2 Modulates Axon Guidance
Gabriel Duff, Anteneh Argaw, Bruno Cecyre, Hosni Cherif, Nicolas Tea, Nawal Zabouri, Christian Casanova, Maurice Ptito, Jean-Fran?ois Bouchard
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0070849
Abstract: Navigation of retinal projections towards their targets is regulated by guidance molecules and growth cone transduction mechanisms. Here, we present in vitro and in vivo evidences that the cannabinoid receptor 2 (CB2R) is expressed along the retino-thalamic pathway and exerts a modulatory action on axon guidance. These effects are specific to CB2R since no changes were observed in mice where the gene coding for this receptor was altered (cnr2?/?). The CB2R induced morphological changes observed at the growth cone are PKA dependent and require the presence of the netrin-1 receptor, Deleted in Colorectal Cancer. Interfering with endogenous CB2R signalling using pharmacological agents increased retinal axon length and induced aberrant projections. Additionally, cnr2?/? mice showed abnormal eye-specific segregation of retinal projections in the dorsal lateral geniculate nucleus (dLGN) indicating CB2R’s implication in retinothalamic development. Overall, this study demonstrates that the contribution of endocannabinoids to brain development is not solely mediated by CB1R, but also involves CB2R.
Examining the Mechanism for the Transferability of Leadership Elements to Students: The Case of the Catholic University Institute of Buea (CUIB)  [PDF]
Maurice Ayuketang Nso
Open Journal of Leadership (OJL) , 2018, DOI: 10.4236/ojl.2018.72009
Abstract: This paper recommends what could be a standard definition for the word “leadership”, as it found out that there has been no standard way for defining leadership, and that others have defined leadership based on the leadership elements a leader has but failed to rethink that one could be a bad leader and as such the leadership elements could not be transferred (passed on) to heirs for the simple reason that no one likes bad things.
The Connectivity of the Human Pulvinar: A Diffusion Tensor Imaging Tractography Study
Sandra E. Leh,M. Mallar Chakravarty,Alain Ptito
International Journal of Biomedical Imaging , 2008, DOI: 10.1155/2008/789539
Abstract: Previous studies in nonhuman primates and cats have shown that the pulvinar receives input from various cortical and subcortical areas involved in vision. Although the contribution of the pulvinar to human vision remains to be established, anatomical tracer and electrophysiological animal studies on cortico-pulvinar circuits suggest an important role of this structure in visual spatial attention, visual integration, and higher-order visual processing. Because methodological constraints limit investigations of the human pulvinar's function, its role could, up to now, only be inferred from animal studies. In the present study, we used an innovative imaging technique, Diffusion Tensor Imaging (DTI) tractography, to determine cortical and subcortical connections of the human pulvinar. We were able to reconstruct pulvinar fiber tracts and compare variability across subjects in vivo. Here we demonstrate that the human pulvinar is interconnected with subcortical structures (superior colliculus, thalamus, and caudate nucleus) as well as with cortical regions (primary visual areas (area 17), secondary visual areas (area 18, 19), visual inferotemporal areas (area 20), posterior parietal association areas (area 7), frontal eye fields and prefrontal areas). These results are consistent with the connectivity reported in animal anatomical studies.
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