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Results for “functional connectivity”

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At least 451 records · Page 25Linked to original sources
PubMedDate not supplied

[The spatial-temporal organization of cortical neuronal functions in a conditioned reflex to time].

Multiunit activity in the motor cortex of cats was analysed during food-procuring conditioning to time (2-minute interval). Comparison of behavioural and neurophysiological correlates at the initial stage of conditioning showed that it was accompanied by very complicated system transformations which were different for neuronal micro- and macrostructures. Systemic processes in the micro- and macroareas were distinguished by a specificity of space distribution, quantity, strength, and stability of manifestations of functional connections. Capability of neurons for functional orientation, increase of percentage of incidence of functional connections in the second half of the conditioned interval, considerable destabilization of all neuronal associations at the last and highest stage of conditioning were the common features for micro- and macroareas during formation of the food-procuring conditioned response.

Animals↗
PubMed1993

Dependence of functional synaptic connections of hippocampal and neocortical neurons on types of memory.

Different types of memory are thought to be processed by different neuronal networks. The present study evaluated the functional synaptic connections among neurons by means of cross-correlation analysis when two types of memory, working and reference memory, were being processed in behaving rats. Some of the synaptic connections of neurons in the hippocampal CA1, CA3, dentate gyrus and auditory cortex functioned when the rat was performing only one of the memory tasks. Working memory needed more of these memory-type dependent synapses in the hippocampal regions than reference memory.

Animals↗
PubMed1979

Cross-correlation analysis of the lateral pulvinar and scalp EEG in man.

Cross-correlation analysis of the EEG between the lateral pulvinar and various cortical regions was made after EEG was recorded during stereotactic pulvinectomy. Cross-correlation analysis of the alpha-waves between the lateral pulvinar and the scalp EEG showed that the lateral pulvinar has the highest degree of functional connection with the pre-central area, diminishing in degree with the parietal and frontal areas, and has poor functional connections with the occipital area. From these results, it might be concluded that the lateral pulvinar may be related to motor function by functional connections with the pre-central area rather than the parietal area.

Alpha Rhythm↗
PubMedDate not supplied

Connectivity and complexity: the relationship between neuroanatomy and brain dynamics.

Nervous systems facing complex environments have to balance two seemingly opposing requirements. First, there is a need quickly and reliably to extract important features from sensory inputs. This is accomplished by functionally segregated (specialized) sets of neurons, e.g. those found in different cortical areas. Second, there is a need to generate coherent perceptual and cognitive states allowing an organism to respond to objects and events, which represent conjunctions of numerous individual features. This need is accomplished by functional integration of the activity of specialized neurons through their dynamic interactions. These interactions produce patterns of temporal correlations or functional connectivity involving distributed neuronal populations, both within and across cortical areas. Empirical and computational studies suggest that changes in functional connectivity may underlie specific perceptual and cognitive states and involve the integration of information across specialized areas of the brain. The interplay between functional segregation and integration can be quantitatively captured using concepts from statistical information theory, in particular by defining a measure of neural complexity. Complexity measures the extent to which a pattern of functional connectivity produced by units or areas within a neural system combines the dual requirements of functional segregation and integration. We find that specific neuroanatomical motifs are uniquely associated with high levels of complexity and that such motifs are embedded in the pattern of long-range cortico-cortical pathways linking segregated areas of the mammalian cerebral cortex. Our theoretical findings offer new insight into the intricate relationship between connectivity and complexity in the nervous system.

Animals↗
PubMed2001

In vivo assessment of human visual system connectivity with transcranial electrical stimulation during functional magnetic resonance imaging.

Functional magnetic resonance imaging (fMRI) was used to investigate local and distant cerebral activation induced by transcranial electrical stimulation in order to noninvasively map functional connectivity in the human visual system. Stimulation with lateromedially directed currents and the anode 4.5 cm dorsally to the inion over the right visual cortex induced phosphenes extending into the contralateral lower quadrant of the visual field. fMRI showed a focal hemodynamic response underneath the anode in extrastriate cortex and distant coactivation in subcortical (lateral geniculate nucleus), cortical visual (striate and extrastriate), and visuomotor areas (frontal and supplementary eye fields). This pattern of activation resembles a network of presumably interconnected visual and visuomotor areas. Analysis of activation sites supplies new information about cerebral correlates of phosphenes and shows that the cortical region underneath the cranial stimulation site is not necessarily the origin of behavioral and/or perceptual effects of transcranial stimulation. We conclude that combining transcranial electrical stimulation of neural tissue with simultaneous fMRI offers the possibility to study noninvasively cerebral connectivity in the human brain.

Adult↗
PubMed2001

Functional interactions of the inferior frontal cortex during the processing of words and word-like stimuli.

The hypothesis that ventral/anterior left inferior frontal gyrus (LIFG) subserves semantic processing and dorsal/posterior LIFG subserves phonological processing was tested by determining the pattern of functional connectivity of these regions with regions in left occipital and temporal cortex during the processing of words and word-like stimuli. In accordance with the hypothesis, we found strong functional connectivity between activity in ventral LIFG and activity in occipital and temporal cortex only for words, and strong functional connectivity between activity in dorsal LIFG and activity in occipital and temporal cortex for words, pseudowords, and letter strings, but not for false font strings. These results demonstrate a task-dependent functional fractionation of the LIFG in terms of its functional links with posterior brain areas.

Adult↗
PubMed2001

Coherence between cortical and muscular activities after subcortical stroke.

BACKGROUND AND PURPOSE: Functional connection between the motor cortex and muscle can be measured by electroencephalogram-electromyogram (EEG-EMG) coherence. To evaluate the functional connection to muscle between contralateral and ipsilateral motor cortices after pyramidal tract lesions, we investigated 6 patients with chronic subcortical stroke. METHODS: High-resolution EEG and EMG of the hand, forearm, and biceps muscles were recorded during 3 tonic contraction tasks: (1) elbow flexion, (2) wrist extension, and (3) power grip. To evaluate the cortical control of EMG, EEG-EMG coherence was computed. RESULTS: EEG-EMG coherence was localized over the contralateral sensorimotor area in all circumstances, and there was no significant coherence at the ipsilateral side. EEG-EMG coherence was significantly smaller on the affected side for the hand and forearm muscles but not for the biceps muscle. CONCLUSIONS: All direct functional connections to muscle after recovered subcortical stroke come from the contralateral motor cortex. The different effects of the lesion on the proximal and distal muscles appear to be associated with the strength of the corticospinal pathway.

Aged↗
PubMed2002

An investigation of functional and anatomical connectivity using magnetic resonance imaging.

This article examines functional and anatomical connectivity in healthy human subjects measured with magnetic resonance imaging methods. Anatomical connectivity in white matter is obtained from measurements of the diffusion tensor. A Monte-Carlo simulation determines the probability that a particle diffuses between two points, with the probability of a jump in a particular direction from a given voxel being based on the local value of the diffusion tensor components. Functional connectivity between grey matter pixels is assessed without recourse to a specific activation paradigm, by calculating the correlation coefficient between random fluctuations in the blood oxygenation level-dependent signal time course in different pixels. The methods are used to examine the anatomical and functional connectivities between crowns of adjacent gyri. A high functional connectivity was found between grey matter pixels, with white matter displaying only very low correlation. A comparison of the measurements of anatomical and functional connectivity found that there is no simple correlation between these measures, except that low values of functional connectivity were not found together with high values of anatomical connectivity. Furthermore pairs of regions situated around the central sulcus indicated a dependence of the two connectivity measures on each other. These results are in accordance with an interpretation that regions which are clearly directly linked by white matter fiber tracts should show high functional connectivity, but that the inverse need not be true as functional connectivity may also be indirectly mediated via more distant grey matter regions.

Algorithms↗
PubMed2004

Scale-free network with Boolean dynamics as a function of connectivity.

In this work we analyze scale-free networks with different power-law spectra N (k) approximately k(-gamma) under a Boolean dynamic, where the Boolean rule that each node obeys is a function of its connectivity k. This is done by using only two logical functions (AND and XOR) which are controlled by a parameter q. Using a damage spreading technique we show that the Hamming distance and the number of 1's exhibit power-law behavior as a function of q. The exponents appearing in the power laws depend on the value of gamma.

Journal Article↗
PubMed2000

Termino-lateral neurorrhaphy: the functional axonal anatomy.

The goal of this study was to determine the functional axonal anatomy of a termino-lateral neurorrhaphy (TLN). We hypothesize that axons populating a TLN must relinquish functional connections with their original targets prior to establishing new connections via the TLN. Two-month-old F344 rats underwent a TLN between the left peroneal nerve and a nerve graft tunneled to the contralateral hindlimb. Three months postoperatively, an end-to-end neurorrhaphy was performed between the nerve graft and the right peroneal nerve. Four months after the second operation, contractile properties and electromyographic (EMG) signals were measured in the bilateral hindlimbs. Left peroneal nerve stimulation proximal to the TLN site resulted in bilateral extensor digitorum longus (EDL) and tibialis anterior (TA) muscle contractions, with significantly lower forces on the side reinnervated by TLN. Evoked EMGs demonstrated that the right and left hindlimb musculature were electrically discontinuous following TLN. These data support our hypothesis that axons can form functional connections via a TLN, but they must first relinquish functional connections with their original targets.

Anastomosis, Surgical↗
PubMed2000

Delivery of a GDNF gene into the substantia nigra after a progressive 6-OHDA lesion maintains functional nigrostriatal connections.

The effects of delivering GDNF via an adenoviral vector (AdGDNF) 1 week after lesioning dopaminergic neurons in the rat substantia nigra (SN) with 6-hydroxydopamine (6-OHDA) were examined. Rats were unilaterally lesioned by injection of 6-OHDA into the striatum, resulting in progressive degeneration of dopaminergic neurons in the SN. One week later, when substantial damage had already occurred, AdGDNF or a control vector harboring beta-galactosidase (AdLacZ) was injected into either the striatum or SN (3.2 x 10(7) PFU/microl in 2 microl). Rats were examined behaviorally with the amphetamine-induced rotation test and for forelimb use for weight-bearing movements. On day 30 postlesion, the extent of nigrostriatal tract degeneration was determined by injecting a retrograde tracer (FluoroGold) bilaterally into the lesioned striatum. Five days later, rats were sacrificed within 2 h of amphetamine injection to examine amphetamine-induced Fos expression in the striatum, a measure of dopaminergic-dependent function in target neurons. AdGDNF injection in the SN rescued dopaminergic neurons in the SN and increased the number of dopaminergic neurons that maintained a connection to the striatum, compared to rats injected with AdLacZ. Further support that these spared SN cells maintained functional connections to the striatum was evidenced by increased Fos expression in striatal target neurons and a decrease in amphetamine-induced rotation. In contrast to the effects observed in rats injected with AdGDNF in the SN, rats injected with AdGDNF in the striatum did not exhibit significant ameliorative effects. This study demonstrates that experimentally increasing levels of GDNF biosynthesis near the dopaminergic neuronal soma is effective in protecting the survival of these neurons and their function even when therapy is begun after 6-OHDA-induced degeneration has commenced. Thus, GDNF gene therapy may ameliorate the consequences of Parkinson's disease through rescuing compromised dopaminergic neurons.

Animals↗
PubMed2026

Electroencephalographic evidence of cortical network disruption preceding overt cardioinhibition during tilt-induced reflex syncope.

OBJECTIVE: Reflex syncope is a common cause of transient loss of consciousness. However, the early cerebral mechanisms underlying cardiovascular changes remain poorly understood. Our objective was to investigate early cerebral changes by quantitatively analyzing EEG activity preceding overt cardioinhibition during tilt-induced reflex syncope. METHODS: EEG recordings from patients undergoing tilt testing were retrospectively analyzed. Patients who experienced reflex syncope were compared to those who did not. Spectral and functional connectivity analyses were performed across baseline, pre-cardioinhibition, and syncopal phases. RESULTS: Prior to the onset of cardioinhibitory pathological reflex, a significant increase in theta-band spectral power was observed in the right temporal region, accompanied by a widespread increase in functional connectivity within the same frequency band. These findings suggest the involvement of brain networks before cardioinhibition. CONCLUSIONS: EEG changes in the theta band (power and functional connectivity) were observed before overt cardioinhibition during tilt-induced reflex syncope. SIGNIFICANCE: Our findings support the hypothesis of cortical processing preceding cardioinhibition in reflex syncope. EEG may represent a valuable complementary tool for improving the understanding and diagnosis of these events.

Humans↗
PubMedDate not supplied

Spatial-temporal organization of the functions of cortical neurons in a conditioned reflex to time.

The impulse activity of neurons in the motor cortex of cats during the development of a conditioned food-procuring reflex in relation to a time interval of 2 min (CRT) was analyzed. It was demonstrated, by comparing the behavioral and neurophysiological correlates of the formation of the conditioned food-procuring reaction, that its formation is accompanied by extremely complex systemic transformations which are different for neuronal micro- and macrostructures. The systemic processes in the micro- and macrostructures differed with respect to the specific characteristics of spatial distribution, and with respect to the number, strength, and stability of the manifestation of the functional connections. The capacity of the neurons for functional orientation even at the initial levels of the formation of the reaction, an increase in the per cent of incidence of functional connections in the second half of the conditioned reflex interval, and the substantial destabilization of all neuronal units at the last, highest level of formation of the conditioned reflex food-procuring reaction were common to the micro- and macrostructures in this form of learning.

Animals↗
PubMedDate not supplied

[Vitamins K and E and the functional state of connective tissue].

The function of the connective tissue in the skin of albino rats with the vitamin K deficiency was studied. Changes both in the cellular elements and in the fibrous structures (deranged differentiation of cellular elements, changes in the collagenformation, accumulation of acid mucopolysaccarides, etc.) were revealed. All of the mentioned changes are eliminated not only by introduction of vicasol, but also by that of alpha-tocopherol.

Animals↗
PubMed1993

Relationship between intrinsic connections and functional architecture revealed by optical imaging and in vivo targeted biocytin injections in primate striate cortex.

In primate primary visual cortex, neurons sharing similar response properties are clustered together forming functional domains that appear as a mosaic of patches or bands, often traversing the entire cortical depth from the pia to the white matter. Similarly, each cortical site connects laterally through an extensive network of intrinsic projections that are organized in multiple clusters (patches) and reach distances of up to a few millimeters. The relationship between the functional domains and these laterally connected patches has remained a controversial issue despite intensive research efforts. To investigate this relationship, we obtained high-resolution functional maps of the cortical architecture by in vivo optical imaging. Subsequently, extracellular injections of the sensitive anterograde tracer biocytin were targeted into selected functional domains. Within the ocular dominance system, we found that long-range intrinsic connections tended to link the monocular regions of same-eye ocular dominance columns. Furthermore, we discovered that binocular domains formed a separate set of connections in area V1; binocular regions were selectively connected among themselves but were not connected to strictly monocular regions, suggesting that they constitute a distinct columnar system. In the other subsystem subserving orientation preference, patches of intrinsic connections tended to link domains sharing similar orientation preferences. Analyses of the precision of these connections indicated that in both functional subsystems, < 15% of the connections were between domains having orthogonal response properties. However, their selectivity was limited; approximately 30% +/- 10% of the interconnected patches contained neurons exhibiting orientation tuning that differed from those found at the injection sites by at least 45 degrees. At short range (up to 400 microns from the injection site), this casual trend seemed markedly accentuated; the local, synaptic-rich axonal and dendritic arbors crossed freely through columns of diverse functional properties. These complex sets of connections can endow cortical neurons with a rich diversity of response properties and broad tuning.

Animals↗
PubMed2006

Development of functional synaptic connections in the auditory system visualized with optical recording: afferent-evoked activity is present from early stages.

A comprehensive survey of auditory network formation was performed in the brain stem of the chicken embryo using voltage-sensitive dye recording. Intact medulla/brain stem preparations with the auditory branch of the eighth nerve attached were dissected from 5.5- to 8-day chicken embryos, and responses evoked by nerve stimulation were recorded optically. In the medulla of 7- and 8-day embryos, we identified four response areas, corresponding to ipsilateral Nucleus magnocellularis (NM) and Nucleus angularis (NA), which receive the auditory afferents, and ipsi- and contralateral Nucleus laminaris (NL), which receive projections from NM. The optical responses consisted of a fast spikelike signal followed by a long-lasting slow signal, which reflected the sodium-dependent action potential and glutamatergic excitatory postsynaptic potential (EPSP), respectively. In NM, NA, and NL, the EPSP-related slow optical signals were detected from some 6-day and all 7- and 8-day preparations, indicating that functional synaptic connectivity in these nuclei arises by the 7-day stage. In the pons of 7- and 8-day embryos, we identified two additional response areas, which evidently correspond to ipsi- and contralateral Nucleus lemnisci lateralis (NLL), the higher-order nuclei of the auditory pathway. Furthermore, we detected optical responses from the contralateral cerebellum, which possibly correspond to transient projections observed only during embryogenesis. The present study demonstrates that functional auditory circuits are established in the chicken embryo at stages earlier than previously reported. We discuss the possible role of afferent-evoked activity with reference to auditory neural network formation.

Action Potentials↗
PubMed1983

Schizophrenia, abnormal connection, and brain evolution.

Abnormalities of functional connection between specialized areas in the human brain may underlie the symptoms which constitute the schizophrenia syndrome. Callosal and intrahemispheric fibres may be equally involved. The clinical emergence of symptoms in the later stages of brain maturation may be dependent on myelination of these fibre groups, both of which have extended myelination cycles. Ontogenetically earlier variants of the same mechanism could theoretically result in dyslexia and the syndromes of Kanner and Gilles de la Tourette. As new and unique extensions of specialized function emerge within the evolving brain, biological trial and error of connection both within and between them may produce individuals possessing phylogenetically advanced abilities, or equally, others possessing a wide range of abnormalities including those which comprise the schizophrenia syndrome. A dormant phenotypic potential for schizophrenia may exist in individuals who never develop symptoms during the course of a lifetime though some of these may become clinically apparent under the influence of various precipitating factors. It is concluded that abnormal functional connection and its normal and "supernormal" counterparts may be natural, essential, and inevitable consequences of brain evolution, and that this may have been so throughout the history of vertebrate brain evolution.

Agenesis of Corpus Callosum↗