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Results for “functional connectivity”

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At least 253 records · Page 14Linked to original sources
PubMed1978

[Structural foundation for the functional connections of the endocrine apparatus and nervous system of the kidneys].

Data from the current literature are used to demonstrate the structural-functional relationship of endocrine and nervous apparatuses of the kidneys which must be taken into consideration in the analysis of clinical manifestations and pathogenesis of many diseases, first of all those of the kidneys. Therefore it is recommended that in examinations of kidney biopsies the state of the endocrine apparatuses and nervous system be evaluated which requires deep kidney biopsy and special methods of morphological analysis.

Aldosterone↗
PubMed2005

Functional connectivity in elderly controls and AD patients using resting state fMRI: a pilot study.

Conventionally, Alzheimer's disease (AD) and other dementias are diagnosed using clinical assessment, neuropsychology and also structural neuroimaging, showing neuronal degeneration starting in the hippocampal regions. However, there is an increasing need for a new method that is more sensitive to early AD identification than currently possible. A new promising technique that may be used for this is to measure local brain activation using functional magnetic resonance imaging (fMRI), since functional loss predates structural loss of brain tissue. A new method to apply fMRI is to study connectivity between brain regions during a resting state without application of a task. Recent data suggest that connectivity within memory systems during such a resting state is associated with the level of memory function. Here we explain how we will study healthy elderly controls, patients with a mild cognitive impairment (MCI, considered to be a transitional stage between normal condition and AD), and AD patients using resting state connectivity fMRI. If resting state connectivity is sensitive to cognitive decline, this will be of great importance for noninvasive dementia research, offering a tool to easily study functional networks in the brain without the requirement of a memory task, and perhaps offering a tool sensitive for early diagnostics.

Aged↗
PubMed1998

Identification of functional connections between calmodulin and the yeast actin cytoskeleton.

One of four intragenic complementing groups of temperature-sensitive yeast calmodulin mutations, cmd1A, results in a characteristic functional defect in actin organization. We report here that among the complementing mutations, a representative cmd1A mutation (cmd1-226: F92A) is synthetically lethal with a mutation in MYO2 that encodes a class V unconventional myosin with calmodulin-binding domains. Gel overlay assay shows that a mutant calmodulin with the F92A alteration has severely reduced binding affinity to a GST-Myo2p fusion protein. Random replacement and site-directed mutagenesis at position 92 of calmodulin indicate that hydrophobic and aromatic residues are allowed at this position, suggesting an importance of hydrophobic interaction between calmodulin and Myo2p. To analyze other components involved in actin organization through calmodulin, we isolated and characterized mutations that show synthetic lethal interaction with cmd1-226; these "cax" mutants fell into five complementation groups. Interestingly, all the mutations themselves affect actin organization. Unlike cax2, cax3, cax4, and cax5 mutations, cax1 shows allele-specific synthetic lethality with the cmd1A allele. CAX1 is identical to ANP1/GEM3/MCD2, which is involved in protein glycosylation. CAX4 is identical to the ORF YGR036c, and CAX5 is identical to MNN10/SLC2/BED1. We discuss possible roles for Cax proteins in the regulation of the actin cytoskeleton.

Actins↗
PubMed2004

Synchronization of gamma oscillations increases functional connectivity of human hippocampus and inferior-middle temporal cortex during repetitive visuomotor events.

Do recency processes associated with repetitive sensorimotor events modulate the magnitude and functional coupling of brain rhythmicity in human temporal cortex? Intracranial stereo electroencephalographic activity (SEEG; 256 Hz sampling rate) was recorded from hippocampus, and inferior (BA20) and middle (BA21) temporal cortex in four epilepsy patients. The repetitive events were represented by predicted imperative somatosensory stimuli (CNV paradigm) triggering hand movements ("repetitive visuomotor") or counting ("repetitive counting"). The non-repetitive events were "rare" (P3 paradigm) somatosensory stimuli triggering hand movements ("non-repetitive visuomotor") or counting ("non-repetitive counting"). Brain rhythmicity was indexed by event-related desynchronization/synchronization (ERD/ERS) of SEEG data, whereas the functional coupling was evaluated by spectral SEEG coherence between pairs of the mentioned areas. The frequency bands of interest were theta (4-8 Hz), alpha (8-12 Hz), beta (14-30 Hz), and gamma (32-46 Hz). Compared to the non-repetitive events, the "repetitive visuomotor" events showed a significant beta and gamma ERS in the hippocampus and a significant theta ERD in the inferior temporal cortex. Furthermore, the "repetitive visuomotor" events induced a task-specific significant gamma coherence among the examined areas. These results suggest that recency processes do modulate the magnitude and functional coupling of brain rhythmicity (especially gamma) in the human temporal cortex.

Adult↗
PubMed2005

Functional connection between the Clb5 cyclin, the protein kinase C pathway and the Swi4 transcription factor in Saccharomyces cerevisiae.

The rsf12 mutation was isolated in a synthetic lethal screen for genes functionally interacting with Swi4. RSF12 is CLB5. The clb5 swi4 mutant cells arrest at G(2)/M due to the activation of the DNA-damage checkpoint. Defects in DNA integrity was confirmed by the increased rates of chromosome loss and mitotic recombination. Other results suggest the presence of additional defects related to morphogenesis. Interestingly, genes of the PKC pathway rescue the growth defect of clb5 swi4, and pkc1 and slt2 mutations are synthetic lethal with clb5, pointing to a connection between Clb5, the PKC pathway, and Swi4. Different observations suggest that like Clb5, the PKC pathway and Swi4 are involved in the control of DNA integrity: there is a synthetic interaction between pkc1 and slt2 with rad9; the pkc1, slt2, and swi4 mutants are hypersensitive to hydroxyurea; and the Slt2 kinase is activated by hydroxyurea. Reciprocally, we found that clb5 mutant is hypersensitive to SDS, CFW, latrunculin B, or zymolyase, which suggests that, like the PKC pathway and Swi4, Clb5 is related to cell integrity. In summary, we report numerous genetic interactions and phenotypic descriptions supporting a close functional relationship between the Clb5 cyclin, the PKC pathway, and the Swi4 transcription factor.

Blotting, Western↗
PubMed2002

Dopamine-dependent changes in the functional connectivity between basal ganglia and cerebral cortex in humans.

We test the hypothesis that interaction between the human basal ganglia and cerebral cortex involves activity in multiple functional circuits characterized by their frequency of oscillation, phase characteristics, dopamine dependency and topography. To this end we took recordings from macroelectrodes (MEs) inserted into the subthalamic nucleus (STN) in eight awake patients following functional neurosurgery for Parkinson's disease. An EEG was also recorded, as were the signals from MEs in the globus pallidus interna (GPi) in two of the cases. Coherence between EEG and ME potentials was apparent in three major frequency bands, 2-10 Hz, 10-30 Hz and 70-85 Hz. These rhythmic activities differed in their cortical topography, although coherence was always strongest over the midline. Coherence between EEG and ME potentials in the 70-85 Hz band was only recorded in patients treated with levodopa. Cortical activity phase led that in the basal ganglia in those oscillatory activities with frequencies <30 Hz. In contrast, STN and GPi phase led cortex in the 70-85 Hz band. The temporal differences in the way in which cortical activity led or lagged behind that in STN/GPi were similar, around 20 ms, regardless of the overall direction of information flow and frequency band. We conclude that the basal ganglia may receive multiple cortical inputs at frequencies <30 Hz and, in the presence of dopaminergic activity, produce a high frequency drive back to the cerebral cortex, in particular the supplementary motor area (SMA).

Adult↗
PubMed1981

[Convergence and divergence of interneuronal functional connections].

Multiunit activity was recorded in the auditory and motor cortex of cats with implanted electrodes, impulses with highest and lowest amplitudes being isolated by means of an amplitude discriminator. Crossinterval histograms were obtained for two simultaneous records. Functional relationships between neurons under different electrodes were evaluated by statistical interdependence of isolated trains. In the auditory cortex, neurons with high amplitude spikes mainly produced connections of excitatory type whereas neurons with low amplitude spikes produced connections of inhibitory type. In the motor cortex neurons producing heterogenous effect were predominant.

Animals↗
PubMed1994

Effect of white matter disease on functional connections in the aging brain.

Periventricular white matter hyperintensities (PVHs) seen on T2 weighted MRI studies are common in elderly people and often represent demyelination of fibres. Damage to these fibres could lead to functional disconnection between brain regions. Electroencephalographic coherence, a measure of shared electrical activity between regions, was examined to determine if there was evidence for such disconnection. Twenty two subjects with clinically diagnosed dementia of the Alzheimer's type, 16 with multi-infarct dementia, and 18 normal controls were studied. It was hypothesised that coherence between areas presumably linked by fibres that traverse the periventricular region would be decreased in subjects with PVHs, and that PVHs would have a stronger association with decreased coherence than clinical diagnosis. It was also hypothesised that coherence between areas presumably connected by long corticocortical tracts that are neuroanatomically separated from the ventricles would be low in patients with Alzheimer's disease because of pyramidal cell death in this group, but would not be affected by the presence of PVHs. Patients with PVHs in fact had lower coherence than those without PVHs in the pre-Rolandic and post-Rolandic areas, where connecting fibres traverse the periventricular region. There was no effect of PVHs, however, on coherence between areas separated by the Rolandic fissure that were connected by long corticocortical tracts; this coherence was lowest among the patients with Alzheimer's disease. These patterns of association suggest that coherence may detect different types of neurophysiological "disconnection," and may be sensitive to selective damage to different fibre pathways.

Aged↗
PubMed1992

A functional connection between the pores of distantly related ion channels as revealed by mutant K+ channels.

The overall sequence similarity between the voltage-activated K+ channels and cyclic nucleotide-gated ion channels from retinal and olfactory neurons suggests that they arose from a common ancestor. On the basis of sequence comparisons, mutations were introduced into the pore of a voltage-activated K+ channel. These mutations confer the essential features of ion conduction in the cyclic nucleotide-gated ion channels; the mutant K+ channels display little selectivity among monovalent cations and are blocked by divalent cations. The property of K+ selectivity is related to the presence of two amino acids that are absent from the pore-forming region of the cyclic nucleotide-gated channels. These data demonstrate that very small differences in the primary structure of an ion channel can account for extreme functional diversity, and they suggest a possible connection between the pore-forming regions of K+, Ca2+, and cyclic nucleotide-gated ion channels.

Amino Acid Sequence↗
PubMed1986

Intraocular colchicine inhibits competition between resident and foreign optic axons for functional connections in the doubly innervated goldfish optic tectum.

After unilateral optic tectum ablation in the goldfish, regenerating optic axons grow into the optic layers of the remaining ipsilateral tectal lobe and regain visual function. The terminal arbors of the foreign fibers are initially diffusely distributed among the resident optic axons, but within two months the axon terminals from each retina are seen to segregate into irregular ocular dominance patches. Visual recovery is delayed until after segregation. This suggests that the foreign fibers compete with the residents for tectal targets and that the segregation of axon terminations is an anatomical characteristic of the process. Here we investigate whether inhibiting axonal transport in the resident fibers inhibits competition with foreign fibers. The eye contralateral to the intact tectal lobe received a single injection of 0.1 microgram colchicine, which does not block vision with the intact eye. We measured visual function using a classical conditioning technique. Segregation of axon terminations was examined shortly following visual recovery by autoradiography. The no-drug control fish showed reappearance of vision with the experimental eye at 9 weeks postoperatively and ocular dominance patches were well developed. Colchicine administered to the intact eye (resident fibers) several weeks postsurgery decreased the time to reappearance of vision with the experimental eye by several weeks. Autoradiography revealed some signs of axonal segregation but the labeled foreign axons were mainly continuously distributed. Administration of colchicine at the time of tectum ablation, or of lumicolchicine at two weeks postoperatively produced normal visual recovery times. Fast axonal transport of 3H-labeled protein was inhibited by 1.0 and 0.5 microgram but not by 0.1 microgram of colchicine or by 1.0 microgram of lumicolchicine.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2006

Functional connections between auditory cortical fields in humans revealed by Granger causality analysis of intra-cranial evoked potentials to sounds: comparison of two methods.

Knowledge of neural interactions amongst cortical sites is important for understanding higher brain function. We studied such interactions using Granger causality (GC) to analyze auditory event-related potentials (ERPs) recorded directly and simultaneously from two physiologically identified and functionally interconnected auditory areas of cerebral cortex in human neurosurgical patients. Two methods of GC analysis were used and the results compared. Both approaches involved adaptive autoregressive modeling but differed from each other in other ways. Results obtained by using the two methods also differed. Fewer false-positive results were obtained using the method that suppressed the ERP non-stationarity and that expressed the GC as the sum of model coefficients, which suggests that this is the more appropriate approach for analyzing ERPs recorded directly from the human cortex.

Auditory Cortex↗
PubMed2006

Physical and functional connection between auxilin and dynamin during endocytosis.

During clathrin-mediated endocytosis, the GTPase dynamin promotes formation of clathrin-coated vesicles, but its mode of action is unresolved. We provide evidence that a switch in three functional states of dynamin (dimers, tetramers, rings/spirals) coordinates its GTPase cycle. Dimers exhibit negative cooperativity whereas tetramers exhibit positive cooperativity with respect to GTP. Our study identifies tetramers as the kinetically most stable GTP-bound conformation of dynamin, which is required to promote further assembly into higher order structures such as rings or spirals. In addition, using fluorescence lifetime imaging microscopy, we show that interactions between dynamin and auxilin in cells are GTP-, endocytosis- and tetramer-dependent. Furthermore, we show that the cochaperone activity of auxilin is required for constriction of clathrin-coated pits, the same early step in endocytosis known to be regulated by the lifetime of dynamin:GTP. Together, our findings support the model that the GTP-bound conformation of dynamin tetramers stimulates formation of constricted coated pits at the plasma membrane by regulating the chaperone activity of hsc70/auxilin.

Animals↗
PubMedDate not supplied

[Dynamics of interhemispheric functional relations during formation of a functional connection between a visual signal and an unrecognized word].

The study was made on adult humans in a conflict situation. A combination of a non-verbal visual stimulus with an unrecognized emotional word substantially changes interhemispheric functional relations. The latency of the P300 potential in response to the first stimulus becomes reduced in the left occipital area. The potential amplitude considerably diminishes in all the recorded cortical areas (occipital, associative and central), but the reductions more pronounced in the left hemisphere. The nature of the P300 wave changes in response to the conditional stimulus is determined by psychophysiological properties of the "reinforcing" stimulus, in particular by its being non-recognized. Conditioned changes of the P300 wave in tests, where the "reinforcing" stimulus is not recognized, are very stable, and are not extinguished, despite repetitive presentation of the signal without combining it with the emotional word.

Adolescent↗
PubMed1996

Studies of functional connectivity in the developing and mature visual cortex.

We have investigated several aspects of cortical organization in adult cats and in young kittens. First, we determined receptive field (RF) maps of correlated discharge between pairs of cortical cells. Unique bicellular RFs appear to convey high resolution information. Second, we studied the dynamics of neural interaction between pairs of cells. Using cross-correlation analysis, we studied monosynaptic and polysynaptic interactions in both kittens and cats. A somewhat surprising finding is that there were no cases of monosynaptic excitation from simple to complex cells as would be predicted by a simple hierarchical processing theory. Third, we studied length and side tuning characteristics of cortical cells and worked out the relationships between them. Fourth we carried out an investigation of binocular processing in which we compared monocular and binocular sensitivity of cortical cells with respect to contrast. Our results are comparable to those found in psychophysical work. Fifth, we examined how stereoscopic depth information is encoded by simple cells in the visual cortex. We show that structural differences in RFs of left and right eyes may be expressed in terms of phase. Phase-based encoding appears to be a very plausible alternative to the standard position-based notion. Sixth, we attempted to induce plastic changes in connections between cell pairs by long-term activation (up to 2 h) in kittens and cats. Although connection strength between some cell pairs was increased during long-term activation, there was no consistent pattern of this effect. Seventh, we attempted to study the functional basis of reported claims of RF expansion following use of an artificial scotoma. However, we found no receptive field size change from this procedure. For some cells, there is an apparent change of gain in the form of base (spontaneous) rates and absolute response levels. Finally, we have examined RF dynamics in the central visual pathways. The standard treatment of RFs in to consider only spatial aspects. But the RF is inherently both temporal and spatial in nature and we have examined the dynamics of spatiotemporal organization of RFs in central visual pathways.

Animals↗
PubMed1990

Functional connections in the human temporal lobe. I. Analysis of limbic system pathways using neuronal responses evoked by electrical stimulation.

Connections in the human mesial temporal lobe were investigated using brief, single pulses of electrical stimulation to evoke field potential responses in limbic structures of 74 epileptic patients. Eight specific areas within these structures were stereotactically targeted for study, including amygdala, entorhinal cortex, presubiculum, the anterior, middle and posterior levels of hippocampus and the middle and posterior levels of parahippocampal gyrus. These sites were studied systematically in order to quantitatively assess the response characteristics and reliability of responses evoked during stimulation of pathways connecting the areas. Specific measures included response probability, amplitude, latency and conduction velocities. The results are assumed to be representative of typical human limbic pathways since all recordings were made interictally and response probabilities across sites were not found to differ significantly between non-epileptogenic vs. identified epileptogenic regions. Field potentials ranging in amplitude from less than 0.1 to greater than 6.0 mV were evoked ipsilaterally, with mean onset latencies and conduction velocities ranging from 4.4 ms and 3.64 m/s in the perforant pathway connecting entorhinal cortex to anterior hippocampus to 24.8 ms and 0.88 m/s in the pathway connecting the amygdala and middle hippocampus. Stimulation of presubiculum and entorhinal cortex were most effective in evoking widespread responses in adjacent limbic recording sites, whereas posterior parahippocampal gyrus appeared functionally separated from other limbic sites since its probability of influencing ipsilateral sites was significantly lower than any other area. It was particularly noteworthy that stimulation did not evoke responses in any sites in contralateral hippocampal formation; even though a large number of sites were tested with bilateral implantation of homotopic electrodes.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMed2005

Differentiation and functional connection of vascular elements in compatible and incompatible pear/quince internode micrografts.

Micrografts of internodes excised from in vitro grown pear plants (Pyrus communis L. cv. 'Bosc' (B) and cv. 'Butirra Hardy' (BH)) and quince (Cydonia oblonga Mill. East Malling clone C (EMC)), were cultured aseptically to test the effectiveness of their functional vascular reconnection in relation to incompatibility-compatibility relationships that these genotypes exhibit in the field. The incompatible heterograft (B/EMC) showed a marked delay in internode cohesion compared with the autografts (both B/B and BH/BH) and the compatible heterograft (BH/EMC). Even when fused, the translocation of [14C]-sorbitol from upper to lower internode was lower in B/EMC micrografts than in the other combinations. Epifluorescence studies performed with carboxyfluorescin, a specific phloem probe, indicated that the limited translocation was caused by a delay in the establishment of functional phloem continuity between the two internodes. In the B/EMC combination, new differentiated tracheary elements (TE) in the parenchyma tissue at the graft interface between the two internodes were not detected until 30 days after grafting, whereas in the BH/EMC heterograft and both autografts, new xylem connections appeared to cross the interface 20 days after grafting. Immunohistochemical detection (terminal nick-end labeling assay) of the number of cells undergoing nuclear DNA fragmentation at the graft interface confirmed that the limited and delayed TE differentiation in B/EMC heterografts was associated with a decrease in the activity of programmed cell death processes involved in the differentiation of TE.

Apoptosis↗