170 research outputs found

    Neurophysiology underlying neuroimaging of cortical function

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    The aim of this study was to shed light on some of the neurophysiological mechanisms behind visual perception and specifically look into feedback processes that may be taking place during visual processing and also inhibition processes of the visual cortex. The oblique effect is a preference of the visual system for cardinal orientations rather than oblique ones. A recent MEG study (Koelewijn, et al. 2011) finds in V1 an initial inverse oblique effect (80 msec from stim onset) which however later (120msec from stimulus onset) showed a trend towards the classical oblique effect and feedback processes here are suggested taking place from the extrastriate cortex. We look into this using fMRI and interestingly we do manage to find an inverse oblique effect, which indicates that the initial MEG “inverse” effect in V1 is detectable with fMRI even though fMRI does not have the temporal resolution of MEG. Unfortunately in this fMRI study the extrastiate region was not localized. In the 3rd experimental chapter (following up on a study by Edden et al.) we look into the relation of behavioural thresholds and gamma activity in the visual cortex. Here we found in the SAM analysis) for the oblique condition, a positive correlation of the oblique main effect in a cortical location in the medial visual cortex (at a frequency range of 30--‐70 Hz) to behavioural thresholds. However here we did not detected an oblique effect when we compared oblique to cardinal condition. In the final experimental chapter we look into the relation between GABA and training effects using however two GABA scanning protocols (with and without macromolecule suppression). Here we find that training effects depend on GABA concentration (as found in unpublished findings by Edden et al.). Additionally here we find negative correlations with behavioural thresholds and GABA however these are strongest for the untrained sessions

    Early brain activity : Translations between bedside and laboratory

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    Neural activity is both a driver of brain development and a readout of developmental processes. Changes in neuronal activity are therefore both the cause and consequence of neurodevelopmental compromises. Here, we review the assessment of neuronal activities in both preclinical models and clinical situations. We focus on issues that require urgent translational research, the challenges and bottlenecks preventing translation of biomedical research into new clinical diagnostics or treatments, and possibilities to overcome these barriers. The key questions are (i) what can be measured in clinical settings versus animal experiments, (ii) how do measurements relate to particular stages of development, and (iii) how can we balance practical and ethical realities with methodological compromises in measurements and treatments.Peer reviewe

    Visual Cortex

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    The neurosciences have experienced tremendous and wonderful progress in many areas, and the spectrum encompassing the neurosciences is expansive. Suffice it to mention a few classical fields: electrophysiology, genetics, physics, computer sciences, and more recently, social and marketing neurosciences. Of course, this large growth resulted in the production of many books. Perhaps the visual system and the visual cortex were in the vanguard because most animals do not produce their own light and offer thus the invaluable advantage of allowing investigators to conduct experiments in full control of the stimulus. In addition, the fascinating evolution of scientific techniques, the immense productivity of recent research, and the ensuing literature make it virtually impossible to publish in a single volume all worthwhile work accomplished throughout the scientific world. The days when a single individual, as Diderot, could undertake the production of an encyclopedia are gone forever. Indeed most approaches to studying the nervous system are valid and neuroscientists produce an almost astronomical number of interesting data accompanied by extremely worthy hypotheses which in turn generate new ventures in search of brain functions. Yet, it is fully justified to make an encore and to publish a book dedicated to visual cortex and beyond. Many reasons validate a book assembling chapters written by active researchers. Each has the opportunity to bind together data and explore original ideas whose fate will not fall into the hands of uncompromising reviewers of traditional journals. This book focuses on the cerebral cortex with a large emphasis on vision. Yet it offers the reader diverse approaches employed to investigate the brain, for instance, computer simulation, cellular responses, or rivalry between various targets and goal directed actions. This volume thus covers a large spectrum of research even though it is impossible to include all topics in the extremely diverse field of neurosciences

    Precision grasping in people : a detailed analysis of the central and external properties of precision grasping from the young to the elderly

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    ix, 116 leaves : ill. ; 29 cm.To understand the grasping abnormalities in Parkinson's or stroke patients, normal grasping must be examined, and whether that normality is determined by biological factors or experiential influence must also be considered. The purpose of this thesis is to determine what normal variations of precision grasping exist in healthy, normal adults, children and elderly people. Using Eshkol-Wachmann Movement Notation, five types of contact strategies were interpolated, based on the digit that contacts the object first, and whether that digit dragged or stabilized the object for grasping. Each contact strategy was associated with an ideal graphical representation of the thumb and index finger velocities. There were seven variations of purchase patterns, based on the digits used to contact the objects, and four variations of postures of the non-grasping digits on top of the five contact strategies. Object size affected purchase pattern preference: smaller objects elicited the pincer grasp more than the larger objects. The purchase pattern distribution of variation is similar in adults and children, although children exhibit an extra purchase pattern, and older adults exhibit less variation purchase patterns. The findings from this thesis suggest that central factors, such as gender and handedness, as well as external factors, such as size of the object, determine individual preference of grasping. The loss of variation with age can be attributed to the developing corticospinal tract in children as well as the deterioration of normal hand function in the elderly

    Early postnatal development of neocortex-wide activity patterns in GABAergic and pyramidal neurons

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    Before the onset of sensory experience, developing circuits generate synchronised activity that will not only influence its wiring, but ultimately contribute to behaviour. These complex functions rely on widely distributed cortical that simultaneously operate at multiple spatiotemporal scales. The timing of GABAergic maturation appears to align with the developmental trajectories of cortical regions, playing a crucial role in the functional development of individual brain areas. While local connectivity in cortical microcircuits has been extensively studied, the dynamics of brain-wide functional maturation, especially for GABAergic populations, remain underexplored. In this project, a dual-colour widefield calcium imaging approach was developed to examine the neocortex-wide dynamics of cortical GABAergic and excitatory neurons simultaneously across early postnatal development. This study provides the first broad description of neocortex-wide GABAergic developmental trajectories and their cross-talk with excitatory dynamics during the second and third postnatal weeks. The observed spontaneous activity revealed discrete activity domains, reflecting the modular organisation of the cortex. Both excitatory and GABAergic population exhibited an increase in the size and frequency of activity motifs, as well as changes in motif variability. However, as they matured, the distribution of these spatiotemporal properties displayed divergent trajectories across populations and regions. These findings suggest fundamental differences in the spatial organisation of both populations, indicating potential distinct roles in cortical network function development. Moreover, while excitatory and GABAergic dynamics exhibited high correlations, brief deviations from perfect timing were observed. This correlation patterns changed significantly during development and across regions, with the two populations gradually becoming more correlated as they matured. Manipulating inhibition in vivo disrupted these fluctuations, impacting both local activity and the wider functional network.These findings provide valuable insights into the developmental trajectories of spontaneous activity patterns in excitatory and GABAergic cell populations during early postnatal development. The interplay between both neuronal populations plays a critical role in shaping activity patterns, and understanding the underlying mechanisms of their development can provide valuable insights into neurodevelopmental disorders

    PlasticitĂ© intermodale chez le hamster Ă©nuclĂ©Ă© Ă  la naissance : Études de la distribution des interneurones CaBPir dans les cortex visuel et auditif primaires

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    La pĂ©riode postnatale et l’expĂ©rience sensorielle sont critiques pour le dĂ©veloppement du systĂšme visuel. Les interneurones inhibiteurs exprimant l’acide Îł-aminobutyrique (GABA) jouent un rĂŽle important dans le contrĂŽle de l’activitĂ© neuronale, le raffinement et le traitement de l’information sensorielle qui parvient au cortex cĂ©rĂ©bral. Durant le dĂ©veloppement, lorsque le cortex cĂ©rĂ©bral est trĂšs susceptible aux influences extrinsĂšques, le GABA agit dans la formation des pĂ©riodes critiques de sensibilitĂ© ainsi que dans la plasticitĂ© dĂ©pendante de l’expĂ©rience. Ainsi, ce systĂšme inhibiteur servirait Ă  ajuster le fonctionnement des aires sensorielles primaires selon les conditions spĂ©cifiques d’activitĂ© en provenance du milieu, des affĂ©rences corticales (thalamiques et autres) et de l’expĂ©rience sensorielle. Certaines Ă©tudes montrent que des diffĂ©rences dans la densitĂ© et la distribution de ces neurones inhibiteurs corticaux reflĂštent les caractĂ©ristiques fonctionnelles distinctes entre les diffĂ©rentes aires corticales. La Parvalbumine (PV), la Calretinine (CR) et la Calbindine (CB) sont des protĂ©ines chĂ©latrices du calcium (calcium binding proteins ou CaBPs) localisĂ©es dans diffĂ©rentes sous-populations d’interneurones GABAergiques corticaux. Ces protĂ©ines tamponnent le calcium intracellulaire de sorte qu’elles peuvent moduler diffĂ©remment plusieurs fonctions neuronales, notamment l’aspect temporel des potentiels d’action, la transmission synaptique et la potentialisation Ă  long terme. Plusieurs Ă©tudes rĂ©centes montrent que les interneurones immunorĂ©actifs (ir) aux CaBPs sont Ă©galement trĂšs sensibles Ă  l’expĂ©rience et Ă  l’activitĂ© sensorielle durant le dĂ©veloppement et chez l’adulte. Ainsi, ces neurones pourraient avoir un rĂŽle crucial Ă  jouer dans le phĂ©nomĂšne de compensation ou de plasticitĂ© intermodale entre les cortex sensoriels primaires. Chez le hamster (Mesocricetus auratus), l’énuclĂ©ation Ă  la naissance fait en sorte que le cortex visuel primaire peut ĂȘtre recrutĂ© par les autres modalitĂ©s sensorielles, telles que le toucher et l’audition. Suite Ă  cette privation oculaire, il y a Ă©tablissement de projections ectopiques permanentes entre les collicules infĂ©rieurs (CI) et le corps genouillĂ© latĂ©ral (CGL). Ceci a pour effet d’acheminer l’information auditive vers le cortex visuel primaire (V1) durant le dĂ©veloppement postnatal. À l’aide de ce modĂšle, l’objectif gĂ©nĂ©ral de ce projet de thĂšse est d’étudier l’influence et le rĂŽle de l’activitĂ© sensorielle sur la distribution et l’organisation des interneurones corticaux immunorĂ©actifs aux CaBPs dans les aires sensorielles visuelle et auditive primaires du hamster adulte. Les changements dans l’expression des CaBPs ont Ă©tĂ© dĂ©terminĂ©s d’une maniĂšre quantitative en Ă©valuant les profils de distribution laminaire de ces neurones rĂ©vĂ©lĂ©s par immunohistochimie. Dans une premiĂšre expĂ©rience, nous avons Ă©tudiĂ© la distribution laminaire des CaBPs dans les aires visuelle (V1) et auditive (A1) primaires chez le hamster normal adulte. Les neurones immunorĂ©actifs Ă  la PV et la CB, mais non Ă  la CR, sont distribuĂ©s diffĂ©remment dans ces deux cortex primaires dĂ©diĂ©s Ă  une modalitĂ© sensorielle diffĂ©rente. Dans une deuxiĂšme Ă©tude, une comparaison a Ă©tĂ© effectuĂ©e entre des animaux contrĂŽles et des hamsters Ă©nuclĂ©Ă©s Ă  la naissance. Cette Ă©tude montre que le cortex visuel primaire de ces animaux adopte une chimioarchitecture en PV similaire Ă  celle du cortex auditif. Nos recherches montrent donc qu’une suppression de l’activitĂ© visuelle Ă  la naissance peut influencer l’expression des CaBPs dans l’aire V1 du hamster adulte. Ceci suggĂšre Ă©galement que le type d’activitĂ© des affĂ©rences en provenance d’autres modalitĂ©s sensorielles peut moduler, en partie, une circuiterie corticale en CaBPs qui lui est propre dans le cortex hĂŽte ou recrutĂ©. Ainsi, nos travaux appuient l’hypothĂšse selon laquelle il serait possible que certaines de ces sous-populations d’interneurones GABAergiques jouent un rĂŽle crucial dans le phĂ©nomĂšne de la plasticitĂ© intermodale.The postnatal period and sensory experience are critical for the development of the visual system. The inhibitory interneurons expressing the Îł-aminobutyric acid (GABA) play an important role in the control of neural activity, refinement and treatment of sensory information which reaches the cerebral cortex. During development, when the cerebral cortex is very likely to be influenced by extrinsic factors, GABA acts in the formation of critical period of receptivity as well as in experience dependent plasticity. Thus, this inhibitory system adjusts the functioning of the primary sensory areas according to the specific conditions of activity from the environment, cortical afferents (e.g. of thalamic origin), and sensory experience. Several studies show that differences in the distribution and density of these inhibitory interneurons tend to reflect functional discrepancies between the different neocortical areas. Parvalbumin (PV), Calretinin (CR) and Calbindin (CB) are calcium-binding proteins (CaBPs) found in different sub-populations of GABAergic cortical interneurons. These proteins buffer intracellular calcium levels, which can in turn modulate several neural functions, notably the temporal aspect of action potentials, synaptic transmission and long-term potentiation. Several recent studies are showing that CaBPs immunoreactive (ir) interneurons are also very sensitive to experience and sensory activity during development and adulthood. Therefore, these neurons may have a critical role in intermodal plasticity or compensatory processes between primary sensory cortices. In the hamster (Mesocricetus auratus), after enucleation at birth, the primary visual cortex can be recruited by other sensory modalities such as touch and audition. After this type of visual deprivation, there is establishment of permanent ectopic projections between the inferior colliculus (IC) and the lateral geniculate nucleus (LGN). This phenomenon leads to the rerouting of auditory information to the primary visual cortex (V1) during postnatal development. By using this animal model, the general objective of this thesis is to study the influence and the role of sensory activity on the distribution and organization of cortical interneurons that display immunoreactivity for CaBPs in the primary visual and auditory sensory areas in adult hamsters. Changes in the expression of CaBPs were quantitatively determined by assessing the laminar distribution profiles of cell bodies revealed by immunohistochemistry. In the first experiment, we studied laminar distribution of CaBPs in the primary visual (V1) and auditory (A1) cortices of normal hamsters. PVir and CBir, but not CRir neurons, are distributed in a dissimilar fashion between the two primary cortices devoted to each sensory modality. In the second study, a comparison was performed between control animals and hamsters which were enucleated at birth. The results of this study show that the primary visual cortex of these animals adopts a PVir chemoarchitecture similar to that of the auditory cortex. Our research shows that the abolition of visual activity at birth can influence the expression of CaBPs in V1 of the adult hamster. The present results also suggest that the type of activity in afferents from other sensory modalities can at least in part modulate the cortical circuitry of CaBPs in the host or recruited cortex. Thus, our work supports the hypothesis that sub-populations of GABAergic interneurons may play a critical role in the intermodal cortical plasticity

    Hippocampal gabaergic inhibitory interneurons

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    This is the author accepted manuscript. The final version is available from American Physiological Society via the DOI in this record In the hippocampus GABAergic local circuit inhibitory interneurons represent only ~10–15% of the total neuronal population; however, their remarkable anatomical and physiological diversity allows them to regulate virtually all aspects of cellular and circuit function. Here we provide an overview of the current state of the field of interneuron research, focusing largely on the hippocampus. We discuss recent advances related to the various cell types, including their development and maturation, expression of subtype-specific voltage-and ligand-gated channels, and their roles in network oscillations. We also discuss recent technological advances and approaches that have permitted high-resolution, subtype-specific examination of their roles in numerous neural circuit disorders and the emerging therapeutic strategies to ameliorate such pathophysiological conditions. The ultimate goal of this review is not only to provide a touchstone for the current state of the field, but to help pave the way for future research by highlighting where gaps in our knowledge exist and how a complete appreciation of their roles will aid in future therapeutic strategies.National Institute of Child Health and Human Developmen
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