18,196 research outputs found
Dynamic BOLD functional connectivity in humans and its electrophysiological correlates
No full textNeural oscillations subserve many human perceptual and cognitive operations. Accordingly, brain functional connectivity is not static in time, but fluctuates dynamically following the synchronization and desynchronization of neural populations. This dynamic functional connectivity has recently been demonstrated in spontaneous fluctuations of the Blood Oxygen Level-Dependent (BOLD) signal, measured with functional Magnetic Resonance Imaging (fMRI). We analyzed temporal fluctuations in BOLD connectivity and their electrophysiological correlates, by means of long (≈50 min) joint electroencephalographic (EEG) and fMRI recordings obtained from two populations: 15 awake subjects and 13 subjects undergoing vigilance transitions. We identified positive and negative correlations between EEG spectral power (extracted from electrodes covering different scalp regions) and fMRI BOLD connectivity in a network of 90 cortical and subcortical regions (with millimeter spatial resolution). In particular, increased alpha (8-12 Hz) and beta (15-30 Hz) power were related to decreased functional connectivity, whereas gamma (30-60 Hz) power correlated positively with BOLD connectivity between specific brain regions. These patterns were altered for subjects undergoing vigilance changes, with slower oscillations being correlated with functional connectivity increases. Dynamic BOLD functional connectivity was reflected in the fluctuations of graph theoretical indices of network structure, with changes in frontal and central alpha power correlating with average path length. Our results strongly suggest that fluctuations of BOLD functional connectivity have a neurophysiological origin. Positive correlations with gamma can be interpreted as facilitating increased BOLD connectivity needed to integrate brain regions for cognitive performance. Negative correlations with alpha suggest a temporary functional weakening of local and long-range connectivity, associated with an idling state
The BOLD MRI response of the brain to alterations in arterial blood pressure
No full textThe impact of blood pressure changes on cerebral blood flow is an important area of investigation. The cerebral autoregulation mechanism acts to maintain blood supply to the brain, despite changes in blood pressure. Blood flow alterations are closely linked to neuronal activation, and this activity can be visualised using blood oxygenation level dependent magnetic resonance imaging (BOLD MRI) – functional MRI. The aim of this project is to investigate the effect of dynamic blood pressure stimuli on the BOLD MRI signal in the brain. Two blood pressure stimuli were employed; thigh cuff deflation and the Valsalva manoeuvre. BOLD MRI signal changes were measured throughout both challenges. Arterial and venous blood pressure and tympanic membrane displacement (TMD) measurements were also made during these challenges. Blood pressure data was used to drive two linked models. The first model represented cerebral vascular physiology (Ursino) and this fed into a second model (Buxton), which predicted the resulting BOLD signal changes. This allowed comparison with experimental BOLD data. TMD data was also compared to intracranial pressure changes predicted by the Ursino model. The experimental BOLD data was found to agree reasonably well with the BOLD signal changes predicted by the modelling. BOLD signal changes are most influenced by deoxyhaemoglobin changes, predominantly as a result of blood flow alterations during the blood pressure challenges, which are not immediately compensated for by the autoregulation mechanism. TMD changes did not reflect intracranial pressure changes predicted by the modelling. In conclusion, if such blood pressure changes do occur during a functional MRI experiment, they may cause changes in the BOLD signal that are not due to neuronal activation. These signal changes may be employed to investigate the cerebral autoregulation mechanism across the brain, or to correct for inaccuracies in functional MRI data in patients with impaired cerebral autoregulatio
From Blood Oxygenation Level Dependent (BOLD) signals to brain temperature maps
No full textA theoretical framework is presented for converting Blood Oxygenation Level Dependent (BOLD) images to temperature maps, based on the idea that disproportional local changes in cerebral blood flow (CBF) as compared with cerebral metabolic rate of oxygen consumption (CMRO2) during functional brain activity, lead to both brain temperature changes and the BOLD effect. Using an oxygen limitation model and a BOLD signal model we obtain a transcendental equation relating CBF and CMRO2 changes with the corresponding BOLD signal, which is solved in terms of the Lambert W function. Inserting this result in the dynamic bio-heat equation describing the rate of temperature changes in the brain, we obtain a non autonomous ordinary differential equation that depends on the BOLD response, which is solved numerically for each brain voxel. In order to test the method, temperature maps obtained from a real BOLD dataset are calculated showing temperature variations in the range: (-0.15, 0.1) which is consistent with experimental results. The method could find potential clinical uses as it is an improvement over conventional methods which require invasive probes and can record only few locations simultaneously. Interestingly, the statistical analysis revealed that significant temperature variations are more localized than BOLD activations. This seems to exclude the use of temperature maps for mapping neuronal activity as areas where it is well known that electrical activity occurs (such as V5 bilaterally) are not activated in the obtained maps. But it also opens questions about the nature of the information processing and the underlying vascular network in visual areas that give rise to this result
Noncanonical spike-related BOLD responses in focal epilepsy
No full textTill now, most studies of the Blood Oxygen Level-Dependent (BOLD) response to interictal epileptic discharges (IED) have assumed that its time course matches closely to that of brief physiological stimuli, commonly called the canonical event-related haemodynamic response function (canonical HRF). Analyses based on that assumption have produced significant response patterns that are generally concordant with prior electroclinical data. In this work, we used a more flexible model of the event-related response, a Fourier basis set, to investigate the presence of other responses in relation to individual IED in 30 experiments in patients with focal epilepsy. We found significant responses that had a noncanonical time course in 37% of cases, compared with 40% for the conventional, canonical HRF-based approach. In two cases, the Fourier analysis suggested activations where the conventional model did not. The noncanonical activations were almost always remote from the presumed generator of epileptiform activity. In the majority of cases with noncanonical responses, the noncanonical responses in single-voxel clusters were suggestive of artifacts. We did not find evidence for IED-related noncanonical HRFs arising from areas of pathology, suggesting that the BOLD response to IED is primarily canonical. Noncanonical responses may represent a number of phenomena, including artefacts and propagated epileptiform activity
A speciality theorem for curves in .
No full textLet be an integral projective
curve. One defines the speciality index of as the
maximal integer such that , where
denotes the dualizing sheaf of . Extending a
classical result of Halphen concerning the speciality of a space
curve, in the present paper we prove that if
is an integral degree curve not contained in any surface of
degree , in any threefold of degree , and in any fourfold
of degree , and if , then Moreover equality
holds if and only if is a complete intersection of
hypersurfaces of degrees , , and
. We give also some partial results in the general
case ,
Boosting BOLD fMRI by K-Space density weighted echo planar imaging
No full textFunctional magnetic resonance imaging (fMRI) has become a powerful and influential method to non-invasively study neuronal brain activity. For this purpose, the blood oxygenation level-dependent (BOLD) effect is most widely used. T2* weighted echo planar imaging (EPI) is BOLD sensitive and the prevailing fMRI acquisition technique. Here, we present an alternative to its standard Cartesian recordings, i.e. k-space density weighted EPI, which is expected to increase the signal-to-noise ratio in fMRI data. Based on in vitro and in vivo pilot measurements, we show that fMRI by k-space density weighted EPI is feasible and that this new acquisition technique in fact boosted spatial and temporal SNR as well as the detection of local fMRI activations. Spatial resolution, spatial response function and echo time were identical for density weighted and conventional Cartesian EPI. The signal-to-noise ratio gain of density weighting can improve activation detection and has the potential to further increase the sensitivity of fMRI investigations
The long and short of it. Being the recollections and reminiscences of Edna Bold
No full textThe Burnett Archive of Working Class Autobiographies was gathered together by John Burnett, David Vincent and David Mayall whilst compiling their three volumes annotated bibliography, "The Autobiography of the Working Class" (Harvester Press, 1984-1989). This book includes descriptions of unpublished autobiographies and indicates their locations. Excerpts from some of the autobiographies have been published in "Destiny obscure: autobiographies of childhood, education, and family from the1820s to the 1920s", edited by John Burnett (Routledge 1994 and A. Lane, 1982). The authors "sought to identify not only the large numbers of printed works scattered in various local history libraries and record offices, but also extant private memoirs, many of which remain hidden in family attics, known only to the author and a handful of relatives" (Introduction to vol.1, p. xxix). The criteria for inclusion were: the writers were working class for at least part of their lives; they wrote in English; and they lived for some time in England, Scotland or Wales between 1790 and 1945. John Burnett was professor of social history at Brunel University from 1972 to 1990.The memoirs of Edna Bold, born in Manchester (1904). Bold supplies a detailed account of childhood games, leisure and schooling. Bold also comments on family and ancestry, sex education, Ancoats Brotherhood and L.S. Lowry. The memoir contains additional reflections on 1960s youth culture and popular music
The spatio-temporal mapping of epileptic networks: Combination of EEG–fMRI and EEG source imaging
No full textSimultaneous EEG–fMRI acquisitions in patients with epilepsy often reveal distributed patterns of Blood Oxygen Level Dependant (BOLD) change correlated with epileptiform discharges. We investigated if electrical source imaging (ESI) performed on the interictal epileptiform discharges (IED) acquired during fMRI acquisition could be used to study the dynamics of the networks identified by the BOLD effect, thereby avoiding the limitations of combining results from separate recordings.
Nine selected patients (13 IED types identified) with focal epilepsy underwent EEG–fMRI. Statistical analysis was performed using SPM5 to create BOLD maps. ESI was performed on the IED recorded during fMRI acquisition using a realistic head model (SMAC) and a distributed linear inverse solution (LAURA).
ESI could not be performed in one case. In 10/12 remaining studies, ESI at IED onset (ESIo) was anatomically close to one BOLD cluster. Interestingly, ESIo was closest to the positive BOLD cluster with maximal statistical significance in only 4/12 cases and closest to negative BOLD responses in 4/12 cases. Very small BOLD clusters could also have clinical relevance in some cases. ESI at later time frame (ESIp) showed propagation to remote sources co-localised with other BOLD clusters in half of cases. In concordant cases, the distance between maxima of ESI and the closest EEG–fMRI cluster was less than 33 mm, in agreement with previous studies.
We conclude that simultaneous ESI and EEG–fMRI analysis may be able to distinguish areas of BOLD response related to initiation of IED from propagation areas. This combination provides new opportunities for investigating epileptic networks
Continuous EEG source imaging enhances analysis of EEG-fMRI in focal epilepsy
No full textIntroduction: EEG-correlated fMRI (EEG-fMRI) studies can reveal haemodynamic changes associated with Interictal Epileptic Discharges (IED). Methodological improvements are needed to increase sensitivity and specificity for localising the epileptogenic zone. We investigated whether the estimated EEG source activity improved models of the BOLD changes in EEG-fMRI data, compared to conventional « event-related » designs based solely on the visual identification of IED.
Methods: Ten patients with pharmaco-resistant focal epilepsy underwent EEG-fMRI. EEG Source Imaging (ESI) was performed on intra-fMRI averaged IED to identify the irritative zone. The continuous activity of this estimated IED source (cESI) over the entire recording was used for fMRI analysis (cESI model). The maps of BOLD signal changes explained by cESI were compared to results of the conventional IED-related model.
Results: ESI was concordant with non-invasive data in 13/15 different types of IED. The cESI model explained significant additional BOLD variance in regions concordant with video-EEG, structural MRI or, when available, intracranial EEG in 10/15 IED. The cESI model allowed better detection of the BOLD cluster, concordant with intracranial EEG in 4/7 IED, compared to the IED model. In 4 IED types, cESI-related BOLD signal changes were diffuse with a pattern suggestive of contamination of the source signal by artefacts, notably incompletely corrected motion and pulse artefact. In one IED type, there was no significant BOLD change with either model.
Conclusion: Continuous EEG source imaging can improve the modelling of BOLD changes related to interictal epileptic activity and this may enhance the localisation of the irritative zone
Bold | Número 05
No full text- Hacia una historia visual de la fruticultura | Julio Bariani
- Edgardo Antonio Vigo y la Comunicación a Distancia | Natalia Aguerre
- La persistencia de la razón en la locura. Recuperación de la antigua imprenta del Borda | Fabio Ares
- Didáctica y desafíos en Comunicación Visual | María Branda
- Ideología del presente | Jorge Mallo
- Taller 5. Cátedra D: Complejo Bibliotecario Municipal de La Plata.: Reposicionamiento como centro cultural | María Martina Erreca Jaureguiberry
- Taller 5. Cátedra D: Rediseño de plan de comunicación visual integral. Secretaría de Cultura y Educación | Facundo Tubío
- Taller 5. Cátedra B: La Casita de Colores, asociación civil | Lucía Del Giovannino
- Taller 5. Cátedra C: Mayores cuidados frente al VIH/SIDA. Infecciones de transmisión sexual a los 50 | Ignacio Elbio Marconi PorcelFacultad de Bellas Arte
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