Search results for " neurological"
showing 10 items of 166 documents
Synaptic Scaling Enables Dynamically Distinct Short- and Long-Term Memory Formation
2013
Memory storage in the brain relies on mechanisms acting on time scales from minutes, for long-term synaptic potentiation, to days, for memory consolidation. During such processes, neural circuits distinguish synapses relevant for forming a long-term storage, which are consolidated, from synapses of short-term storage, which fade. How time scale integration and synaptic differentiation is simultaneously achieved remains unclear. Here we show that synaptic scaling – a slow process usually associated with the maintenance of activity homeostasis – combined with synaptic plasticity may simultaneously achieve both, thereby providing a natural separation of short- from long-term storage. The inter…
The cost of an action potential.
2000
Neuronal modules, or 'cell-assemblies', comprising millions of mutually interconnected cells have been postulated to form the basis of many functions of the brain, such as mood, sleep, hunger, vigilance, and more. Depending on the extent of the module, neurocommunication in cell-assemblies might exceed metabolic resources. A medium-size (10000 neurons) module would require at least 10 J per l of brain, based on a calculated cost of an isolated action potential (AP) of 10(11)-10(12) molecules of ATP per cm(2) of cell membrane, with an absolute minimum of 10(6) ATP at a node of Ranvier. The figure matches the cost of depolarizing the unmyelinated axon of the large monopolar cell in the blowfl…
Gyrification from constrained cortical expansion
2014
The exterior of the mammalian brain - the cerebral cortex - has a conserved layered structure whose thickness varies little across species. However, selection pressures over evolutionary time scales have led to cortices that have a large surface area to volume ratio in some organisms, with the result that the brain is strongly convoluted into sulci and gyri. Here we show that the gyrification can arise as a nonlinear consequence of a simple mechanical instability driven by tangential expansion of the gray matter constrained by the white matter. A physical mimic of the process using a layered swelling gel captures the essence of the mechanism, and numerical simulations of the brain treated a…
Spatiotemporal receptive fields: A dynamical model derived from cortical architectonics
1986
We assume that the mammalian neocortex is built up out of some six layers which differ in their morphology and their external connections. Intrinsic connectivity is largely excitatory, leading to a considerable amount of positive feedback. The majority of cortical neurons can be divided into two main classes: the pyramidal cells, which are said to be excitatory, and local cells (most notably the non-spiny stellate cells), which are said to be inhibitory. The form of the dendritic and axonal arborizations of both groups is discussed in detail. This results in a simplified model of the cortex as a stack of six layers with mutual connections determined by the principles of fibre anatomy. This …
A human post-mortem brain model for the standardization of multi-centre MRI studies
2015
Multi-centre MRI studies of the brain are essential for enrolling large and diverse patient cohorts, as required for the investigation of heterogeneous neurological and psychiatric diseases. However, the multi-site comparison of standard MRI data sets that are weighted with respect to tissue parameters such as the relaxation times (T1, T2) and proton density (PD) may be problematic, as signal intensities and image contrasts depend on site-specific details such as the sequences used, imaging parameters, and sensitivity profiles of the radiofrequency (RF) coils. Water or gel phantoms are frequently used for long-term and/or inter-site quality assessment. However, these phantoms hardly mimic t…
Redistribution of aquaporin-4 in human glioblastoma correlates with loss of agrin immunoreactivity from brain capillary basal laminae
2003
Vasogenic edema is one of the most serious clinical problems in brain tumors and tightly connected to water shifts between the different fluid compartments in the brain. Aquaporin water channels have been recognized to have an important impact on the development of edematous swelling in the brain. Astrocytes, which are believed to induce or at least maintain the blood-brain barrier in the brain capillary endothelial cells, express the aquaporin isoform AQP4. Normally, AQP4 is highly concentrated in the glial membrane where astrocytes contact mesenchymal space, such as perivascular or brain superficial regions. Parenchymal membranes do not show any immunocytochemical AQP4-specific signal. We…
Death in the substantia nigra: a motor tragedy
2007
It is well known that the death of dopaminergic neurons of the substantia nigra pars compacta (SNc) is the pathological hallmark of Parkinson's disease (PD), the second most common and disabling condition in the expanding elderly population. Nevertheless, the intracellular cascade of events leading to dopamine cell death is still unknown and, consequently, treatment is largely symptomatic rather than preventive. Moreover, the mechanisms whereby nigral dopaminergic neurons may degenerate still remain controversial. Hitherto, several data have shown that the earlier cellular disturbances occurring in dopaminergic neurons include oxidative stress, excitotoxicity, inflammation, mitochondrial dy…
Extended causal modeling to assess Partial Directed Coherence in multiple time series with significant instantaneous interactions.
2010
The Partial Directed Coherence (PDC) and its generalized formulation (gPDC) are popular tools for investigating, in the frequency domain, the concept of Granger causality among multivariate (MV) time series. PDC and gPDC are formalized in terms of the coefficients of an MV autoregressive (MVAR) model which describes only the lagged effects among the time series and forsakes instantaneous effects. However, instantaneous effects are known to affect linear parametric modeling, and are likely to occur in experimental time series. In this study, we investigate the impact on the assessment of frequency domain causality of excluding instantaneous effects from the model underlying PDC evaluation. M…
Adaptive independent vector analysis for multi-subject complex-valued fMRI data.
2017
Abstract Background Complex-valued fMRI data can provide additional insights beyond magnitude-only data. However, independent vector analysis (IVA), which has exhibited great potential for group analysis of magnitude-only fMRI data, has rarely been applied to complex-valued fMRI data. The main challenges in this application include the extremely noisy nature and large variability of the source component vector (SCV) distribution. New method To address these challenges, we propose an adaptive fixed-point IVA algorithm for analyzing multiple-subject complex-valued fMRI data. We exploited a multivariate generalized Gaussian distribution (MGGD)- based nonlinear function to match varying SCV dis…
MDMA Administration and Heat Shock Proteins Response: Foreseeing a Molecular Link
2010
Molecular and cellular mechanisms of MDMA-induced toxicity have been extensively studied in a number of experimental models. Nevertheless, only few studies investigated the involvement of HSPs ("molecular chaperones") in MDMA organs toxicity. In the present minireview we highlight this subject analysing the results of these studies conducted especially on brain tissue. Despite of it seems obvious that HSPs overexpression is a protective reaction against MDMA treatment, the molecular mechanisms for exerting their action are far to be undiscovered. At the same time, we need of comprehensive studies concerning the whole range of Hsps/chaperones expressions in all organs after acute and chronic…