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At least 145 records · Page 8Linked to original sources
PubMed1998

Topology of EEG coherence changes may reflect differential neural network activation in cold and pain perception.

Pain perception in the brain can be analyzed by neuroimaging (PET, fMRI) and electrophysiological parameter mapping (EEG, ERP/MEG, MEF). These studies have generally been focused on the localization of cerebral activation. Whether pain can be conceptualized as localized function or best be understood by distributed function is important to the theory of human pain processing in the brain. Here, we report that cold and pain perception in the brain is characterized by webs of EEG coherence changes which may reflect coupling or de-coupling of different cortical areas during cold and pain processing. EEG was recorded during cold and pain perception (right hand immersion in 15 degrees C cool-water vs. 0.3 degrees C ice-water for 3 min.) with eyes opened. Subjects rated the cold perception at 2.3 (cool to cold, but no pain) and the pain perception at 6.7 (moderate-strong pain) in a 1-10 scale. The obtained EEG spectral parameters were compared with the corresponding parameters of the resting baseline using paired Wilcoxon tests in the sense of statistical filters to depict those differences which differ clearly from changes by chance. The results were presented in probability maps. The EEG results indicated highly differential coherence networks between cold and pain perception. The cold perception was characterized as decreased coherence in the theta band mainly between frontal electrodes and increased interhemispheric coherence in the alpha range mainly between central and frontal positions. During pain perception almost no coherence changes in the theta band were observed, but great coherence increase in the delta band between central, parietal and frontal electrodes. The network of coherence changes in the alpha band showed strong involvement of electrode C3 concerning coherence increases with frontal positions. In the beta-1 band coherence increase within the left hemisphere was much more pronounced during pain than during cold. The differential characteristics of EEG coherence changes based on neural networks and their spatial organization in the neocortex indicate the distributed brain processing between cold and pain perception in man. This study may contribute to our understanding of the large scale neural networks in cognition based on neurophysiological binding hypothesis and network connections of neural ensembles.

Adult↗
PubMed2000

Directed spatial potassium redistribution in rat neocortex.

The functional role of the glial network as a draining system for extracellular potassium (spatial buffer) was investigated in rat neocortical brain slices. After electrical stimulation, extracellular space volume decreased in the middle cortical layers and increased in the upper cortical layers, confirming predictions for a spatial buffer. The widening of extracellular space was associated with an increase in extracellular potassium. The data suggested a delayed redistribution of potassium from middle to superficial cortical layers. Interruption of gap junctions abolished the widening of extracellular space. The data show that a multicellular directed network connected by gap junctions participates in maintaining potassium homeostasis in brain.

Animals↗
PubMed2001

The immunoglobulin-like genetic predetermination of the brain: the protocadherins, blueprint of the neuronal network.

The morphogenesis of the brain is governed by synaptogenesis. Synaptogenesis in turn is determined by cell adhesion molecules, which bridge the synaptic cleft and, by homophilic contact, decide which neurons are connected and which are not. Because of their enormous diversification in specificities, protocadherins (pcdh alpha, pcdh beta, pcdh gamma), a new class of cadherins, play a decisive role. Surprisingly, the genetic control of the protocadherins is very similar to that of the immunoglobulins. There are three sets of variable (V) genes followed by a corresponding constant (C) gene. Applying the rules of the immunoglobulin genes to the protocadherin genes leads, despite of this similarity, to quite different results in the central nervous system. The lymphocyte expresses one single receptor molecule specifically directed against an outside stimulus. In contrast, there are three specific recognition sites in each neuron, each expressing a different protocadherin. In this way, 4,950 different neurons arising from one stem cell form a neuronal network, in which homophilic contacts can be formed in 52 layers, permitting an enormous number of different connections and restraints between neurons. This network is one module of the central computer of the brain. Since the V-genes are generated during evolution and V-gene translocation during embryogenesis, outside stimuli have no influence on this network. The network is an inborn property of the protocadherin genes. Every circuit produced, as well as learning and memory, has to be based on this genetically predetermined network. This network is so universal that it can cope with everything, even the unexpected. In this respect the neuronal network resembles the recognition sites of the immunoglobulins.

Animals↗
PubMed1995

Cognitive deficits and the neurobiology of schizophrenia.

Recent research in schizophrenia has demonstrated widespread abnormalities in patients' brain structure, cognitive function, and physiology. These abnormalities are most probably developmental in origin and involve a network of connected frontal-temporal-limbic structures.

Brain↗
PubMed2003

Statistical mechanics beyond the Hopfield model: solvable problems in neural network theory.

We present four 'case study' examples of solvable problems in the theory of recurrent neural networks, which are relevant to our understanding of information processing in the brain, but which are also interesting from a purely statistical mechanical point of view, even at the level of simple models (which helps in stimulating interdisciplinary work). The examples concern issues in network dynamics, network connectivity, spike timing and synaptic plasticity.

Action Potentials↗
PubMed1989

Serotonin-immunoreactive neurons in the brain of Manduca sexta during larval development and larval-pupal metamorphosis.

The developing serotonergic system of the tobacco hornworm, Manduca sexta, has been studied immunocytochemically in whole mount preparations of brain-retrocerebral complexes. The distribution of serotonin-immunoreactive cell bodies, fibers and terminal fields has been analysed during larval and larval-pupal development using a specific rabbit antiserum against serotonin-hemocyanin conjugates. The serotonergic system was conserved from the fourth to the fifth larval stadium, with minimal changes occurring until the onset of pupal development. At this time, alterations in the distribution of serotonin-immunoreactive cells and processes were observed, including the apparent disappearance of some cell bodies and terminals. Nevertheless, the overall appearance of this system in the pupal brain was not significantly different from that in the larva. The larval pattern was characterized by eight bilateral groups of cell bodies which sent thick bridges of fibers across the midline, a feature strikingly similar to the serotonergic system in vertebrate embryos. In addition, three bilateral immunoreactive fields of arborization were observed around and ventral to these cell groups, together with regions of serotonin immunoreactivity in the medial and lateral protocerebral lobes. The central body, larval antennal centers, larval accessory lobes, and the tritocerebrum were also immunoreactive. Fibrous networks of serotonergic processes were usually observed around nerves emanating from the brain, including the connectives from the brain to the corpus cardiacum and corpus allatum. Smaller varicosities were observed in the interior of these neurohemal and glandular organs, and a network of 5-HT fibers was occasionally found around the corpus cardiacum and corpus allatum. The possible relationship of serotonin to cerebral neuroendocrine functions during the postembryonic development of M. sexta is discussed.

Animals↗
PubMed2026

Dual Transcranial Direct Current Stimulation Modulates Hierarchical Functional Network Organization in Post-Stroke Cognitive Impairment: A Randomized Controlled Trial.

OBJECTIVE: To evaluate the clinical efficacy of dual transcranial direct current stimulation (tDCS) in patients with post-stroke cognitive impairment (PSCI) and to explore the effects on the hierarchical organization of functional brain networks, ranging from regional synchronization to inter-regional connectivity and global network topology. METHODS: In this randomized, double-blind, sham-controlled trial, 74 PSCI patients received conventional therapy alongside either active dual-tDCS (n&#x2009;=&#x2009;38) or sham stimulation (n&#x2009;=&#x2009;36). Active tDCS targeted the dorsolateral prefrontal cortex (DLPFC) via anodal-left/cathodal-right nodes (2.0&#x2009;mA, 20&#x2009;min/day, 20 sessions). The primary outcome was the Montreal Cognitive Assessment (MoCA). Secondary outcomes included the Mini-Mental Status Examination (MMSE), Stroop Test (ST), Trail Making Test (TMT), Wechsler Memory Scale (WMS), and Barthel Index (BI). A subgroup of 36 participants (18 per group) underwent resting-state functional magnetic resonance imaging (rs-fMRI) to analyze regional homogeneity (ReHo), functional connectivity (FC), and network topology. Partial correlations assessed the association between neuroimaging alterations and clinical improvements. RESULTS: The tDCS group showed significantly greater improvements in MoCA scores (tDCS: 5.74&#x2009;&#xb1;&#x2009;2.76 vs. sham: 2.69&#x2009;&#xb1;&#x2009;2.69; t&#x2009;=&#x2009;4.799, p&#x2009;<&#x2009;0.001) as well as in attention and memory domains compared to the sham group. The rs-fMRI changes included increased ReHo in the right middle temporal gyrus (MTG) and the left inferior frontal gyrus (IFG), and reduced FC between the right MTG-left superior frontal gyrus and left IFG-cerebellum (p&#x2009;<&#x2009;0.05, FWE-corrected). Additionally, small-worldness and global efficiency increased (p&#x2009;<&#x2009;0.05) with these alterations correlating with clinical recovery. Adverse events were rare and self-limiting. CONCLUSION: Dual-tDCS over bilateral DLPFC safely improves cognitive recovery in PSCI. These clinical gains are associated with rs-fMRI alterations, specifically in regional synchronization, inter-regional connectivity, and global topology, which suggest a potential biomarker for monitoring tDCS efficacy, offering a rationale for precision neuromodulation in stroke rehabilitation.

Humans↗
PubMed1999

Synaptic cell adhesion proteins and synaptogenesis in the mammalian central nervous system.

Synapses are asymmetric cell-cell contacts, typically formed between the presynaptic axon terminal of a "sending" nerve cell and the postsynaptic dendrite, the soma or - in some cases - the axon of a "receiving" one. The presynaptic axon terminal is specialized for the complex membrane trafficking mechanisms that underlie regulated secretion of neurotransmitter, while the postsynapse is uniquely specialized for signal transduction. Synaptogenesis, the formation of functional synapses, is the final step in the development of the central nervous system. In the mammalian brain it results in the establishment of a neural network, connecting some 10(12) nerve cells with up to 10(15) synapses. In principle, synaptogenesis takes place in two consecutive steps that are most likely mediated by cell adhesion molecules. First, an arriving axonal growth cone identifies its appropriate partner cell, creating an initial contact, and, second, specific axonal and dendritic protein components are recruited to this initial contact site, forming a functional synapse. Three cell adhesion systems have recently been shown to be specifically enriched at synaptic contacts: the cadherin/catenin system, the cadherinlike neuronal receptors, and the beta-neurexin/neuroligin system. Components of all three cell adhesion systems have been localized to synaptic contacts using immunogold electron microscopy but are also present outside of synapses. The present short review discusses the possible role of these synaptic cell adhesion molecules in synaptogenesis.

Animals↗
PubMed2004

Laser microdissection of immunolabeled astrocytes allows quantification of astrocytic gene expression.

Astrocytes represent the major glial cell population within the central nervous system. In order to elucidate the function of astrocytes under physiological conditions and during the course of neurological disease, astrocytic gene expression profiling is necessary. However, since astrocytes form an intimately connected network with neurons and other cell types in the brain, gene expression analysis of astrocytes with a sufficient degree of cellular specificity is difficult. Here we are presenting a rapid and, thus, RNA preserving immunostaining protocol for the detection of astrocytes in rodent brain. This protocol can readily be combined with laser microdissection (Leica AS LMD platform) and quantitative RT-PCR (qPCR). Employing this method, we studied changes in glial fibrillary acidic protein (GFAP) expression in astrocytes of mouse entorhinal cortex following entorhinal cortex lesion. Using laser microdissection, astrocytes (n = 60) were collected in the tissue surrounding the lesion, the entorhinal cortex contralateral to the lesion, and in unlesioned control animals. Changes in GFAP mRNA were quantified using qPCR. GFAP mRNA levels were 82-fold higher in astrocytes of lesioned animals at the site of the lesion compared to GFAP mRNA levels in entorhinal cortex astrocytes of control mice. GFAP mRNA levels were only slightly elevated at the contralateral side (lesioned animals). This optimized protocol for immunolabeling and laser microdissection of astrocytes followed by qPCR allows quantification of astrocytic gene expression levels with a high degree of cellular specificity. It may similarly be employed in different settings where other cell types need to be identified and microdissected for gene expression profiling.

Animals↗
PubMed2004

The cerebral oscillatory network associated with auditorily paced finger movements.

Motor tasks involve neural activity in a spatially distributed network. It is assumed that coherent activity between these brain structures reflects functional connectivity. The aim of the present study was to investigate brain areas associated with a unimanual auditorily paced finger-tapping task and to characterize their dynamic interplay. We examined cerebromuscular and cerebrocerebral coupling in 10 right-handed subjects using recordings of continuous brain activity with a 122-channel whole-head neuromagnetometer while subjects performed the task with both hands consecutively. Additionally, surface EMG of the first dorsal interosseus was measured. Our data demonstrate that an oscillatory network composed of primary sensorimotor cortex, lateral as well as mesial premotor areas, the posterior parietal cortex and thalamus contralateral, and cerebellum and primary auditory cortex ipsilateral to the tapping hand subserves task execution. Connectivity between these areas and direction of coupling agree well with anatomical findings. During the right-hand condition, additional oscillatory activity in the primary sensorimotor cortex ipsilateral to the tapping hand was evident. This result suggests an asymmetric motor control in right-handers. Cerebrocerebral coupling predominantly occurs at 8-12 Hz. Therefore, our data support the hypothesis that coupling at 8-12 Hz in a cerebello-thalamic-cortical network represents a fundamental characteristic of the motor system and provides evidence for the significance of 8-12 Hz oscillations in a large scale network during the execution of simple motor tasks.

Acoustic Stimulation↗
PubMed2003

Plasticity of cortical projections after stroke.

Ischemic stroke produces cell death and disability, and a process of repair and partial recovery. Plasticity within cortical connections after stroke leads to partial recovery of function after the initial injury. Physiologically, cortical connections after stroke become hyperexcitable and more susceptible to the induction of LTP Stroke produces changes in the distribution and laterality of sensory, motor, and language representations within the brain that correlate with functional recovery. Anatomically, ischemic lesions induce axonal sprouting within local, intracortical projections and long distance, interhemispheric projections. This postischemic axonal sprouting establishes substantially new patterns of cortical connections with de-afferented or partially damaged brain areas. Axonal sprouting after ischemic lesions is induced by a transient pattern of synchronous, low-frequency neuronal activity in a network of cortical areas connected to the infarct. This pattern of neuronal activity that induces axonal sprouting in the adult after ischemic lesions resembles that seen in the developing brain during axonal elongation and synaptogenesis. Thus, stroke induces a process of remapping and reconnection within the adult brain through changes in neuronal activity that may involve a reactivation of developmental programs in areas connected to the infarct.

Animals↗
PubMed2006

Sugar antennae for guidance signals: syndecans and glypicans integrate directional cues for navigating neurons.

Attractive and repulsive signals guide migrating nerve cells in all directions when the nervous system starts to form. The neurons extend thin processes, axons, that connect over wide distances with other brain cells to form a complicated neuronal network. One of the most fascinating questions in neuroscience is how the correct wiring of billions of nerve cells in our brain is controlled. Several protein families are known to serve as guidance cues for navigating neurons and axons. Nevertheless, the combinatorial potential of these proteins seems to be insufficient to sculpt the entire neuronal network and the appropriate formation of connections. Recently, heparan sulfate proteoglycans (HSPGs), which are present on the cell surface of neurons and in the extracellular matrix through which neurons and axons migrate, have been found to play a role in regulating cell migration and axon guidance. Intriguingly, the large number of distinct modifications that can be put onto the sugar side chains of these PGs would in principle allow for an enormous diversity of HSPGs, which could help in regulating the vast number of guidance choices taken by individual neurons. In this review, we will focus on the role of the cell surface HSPGs syndecan and glypican and specific HS modifications in promoting neuronal migration, axon guidance, and synapse formation.

Animals↗
PubMed2004

Integrating databases and expert systems for the analysis of brain structures: connections, similarities, and homologies.

The NeuroHomology Database system (NHDB) combines databases related to brain structures from different species with different knowledge management systems (KMSs) for systematization, evaluation and processing neurobiological data. Special attention is assessment of similarity of data from different species as a basis for exploring neural homologies. NHDB includes modules that handle brain structure and connectivity data, as well as inference engines for evaluation of the stored neurobiological information. The spatial inference engine evaluates the possible topological relations between cortical structures in different neuroanatomical atlases. The connectivity inference engine evaluates the reliability of information pertaining to fiber tracts as those are reflected in the literature. The inference engine for translation of neuroanatomical connections in different atlases evaluates the probability of existence of connections of interest in different parcellation schemes. Finally, the similarity inference engine calculates the overall degree of similarity of pairs of brain structures from different species by taking into account a set of eight criteria. We present examples of search for information in NHDB system, inferences of relations between cortical structures from equivalent neuroanatomical atlases, reconstruction of functional networks of brain structures from data collated from the literature, translation of connectivity matrices in equivalent parcellation schemes, and evaluations of similarities of brain structures from humans, macaques and rats.

Algorithms↗
PubMed2006

Effective connectivity within the distributed cortical network for face perception.

Face perception elicits activation within a distributed cortical network in the human brain. The network includes visual ("core") regions, as well as limbic and prefrontal ("extended") regions, which process invariant facial features and changeable aspects of faces, respectively. We used functional Magnetic Resonance Imaging and Dynamic Causal Modeling to investigate effective connectivity and functional organization between and within the core and the extended systems. We predicted a ventral rather than dorsal connection between the core and the extended systems during face viewing and tested whether valence and fame would alter functional coupling within the network. We found that the core system is hierarchically organized in a predominantly feed-forward fashion, and that the fusiform gyrus (FG) exerts the dominant influence on the extended system. Moreover, emotional faces increased the coupling between the FG and the amygdala, whereas famous faces increased the coupling between the FG and the orbitofrontal cortex. Our results demonstrate content-specific dynamic alterations in the functional coupling between visual-limbic and visual-prefrontal face-responsive pathways.

Adult↗
PubMed2005

[Localisation of brain function, 125 years after the thesis of Aletta Jacobs, the first Dutch female physician].

Aletta H. Jacobs was the first female physician in the Netherlands. In 1879, she defended her thesis which addressed the subject of localising brain functions. In it she described three neurological patients using systematic conventions highly resembling those in use today. Moreover, she discussed whether or not functions were regionally represented. Her discussion concluded in favour of localisation. These days, the concept of distributed networks goes beyond simple topographical representation. This is illustrated in the cerebral organisation of vision. It is possible to discern visual centres that are specialised in processing specific qualities such as colour or visual motion. An additional feature of such segregated processing streams is the presence of underlying connections to specific brain areas at a distance. Functioning as a node in multiple networks, one single brain region may potentially be involved in multiple functions. This depends on the interactions with other regions and on the actual dominance of information processing within such networks.

Brain↗
PubMed2006

Adaptive reconfiguration of fractal small-world human brain functional networks.

Brain function depends on adaptive self-organization of large-scale neural assemblies, but little is known about quantitative network parameters governing these processes in humans. Here, we describe the topology and synchronizability of frequency-specific brain functional networks using wavelet decomposition of magnetoencephalographic time series, followed by construction and analysis of undirected graphs. Magnetoencephalographic data were acquired from 22 subjects, half of whom performed a finger-tapping task, whereas the other half were studied at rest. We found that brain functional networks were characterized by small-world properties at all six wavelet scales considered, corresponding approximately to classical delta (low and high), , alpha, beta, and gamma frequency bands. Global topological parameters (path length, clustering) were conserved across scales, most consistently in the frequency range 2-37 Hz, implying a scale-invariant or fractal small-world organization. Dynamical analysis showed that networks were located close to the threshold of order/disorder transition in all frequency bands. The highest-frequency gamma network had greater synchronizability, greater clustering of connections, and shorter path length than networks in the scaling regime of (lower) frequencies. Behavioral state did not strongly influence global topology or synchronizability; however, motor task performance was associated with emergence of long-range connections in both beta and gamma networks. Long-range connectivity, e.g., between frontal and parietal cortex, at high frequencies during a motor task may facilitate sensorimotor binding. Human brain functional networks demonstrate a fractal small-world architecture that supports critical dynamics and task-related spatial reconfiguration while preserving global topological parameters.

Brain↗
PubMed1979

Innervation of hippocampal explants by central catecholaminergic neurons in co-cultured fetal mouse brain stem explants.

The ability of central catecholaminergic neurons to grow into and establish functional connections with the hippocampus in vitro was studied using organotypic tissue culture. Brain stem explanted from the region of the locus coeruleus and hippocampal explants, from 18-day fetal mice, were maintained as co-cultures and were also grown separately. After 1-4 weeks these tissues were analyzed by glyoxylic acid-induced histofluorescence, by light and electron microscopic radioautography after incubation with [3H]norepinephrine, and by electrophysiology. Brain stem explants exhibited specifically fluorescent catecholaminergic cell bodies and varicose fibers after 2-4 weeks in culture. In contrast, no fluorescent cells or neurites could be seen in isolated hippocampal cultures grown for 2-3 weeks in vitro. When hippocampal explants were grown near brain stem explants, catecholaminergic fibers grew out of the brain stem and entered the hippocampus. In additional experiments, co-cultures of brain stem and hippocampus were incubated with [3H]norepinephrine (0.5 micron) and the monoamine oxidase inhibitor nialamide (100 micron). Radioautographic analyses revealed that brain stem neurites which entered the hippocampus took up norepinephrine, whereas neurites in the isolated hippocampal explants did not. Electron microscopic studies of the hippocampus showed varicose axon terminals within the hippocampus to be preferentially labeled. Although close relationships could be seen between labeled axons and dendrites, junctions exhibiting the membranous modifications associated with synapses were never seen. Electrophysiological studies suggested that the catecholaminergic neurites within the hippocampus were functional. Complex synaptically mediated slow wave discharges could be evoked by electrical stimuli in isolated hippocampal explants. Introduction of the beta adrenergic antagonist propranolol (0.4-4.3 micron) did not alter, or slightly depressed, these hippocampal discharges. On the other hand, in hippocampus-brain stem co-cultures, these concentrations of propranolol enhanced the complex hippocampal responses to brain stem or hippocampal stimuli. Similar enhancement of hippocampal responses by propranolol also occurred in these cocultures after acute surgical extirpation of the brain stem explant. The data suggest, therefore, that the action of propranol was probably to block adrenergic inhibitory connections with hippocampal synaptic networks. These experiments provide morphological and electrophysiological evidence that catecholaminergic neurons from fetal mouse brain stem maintained in organotypic tissue culture can grow into and functionally innervate the hippocampus.

Animals↗