524 research outputs found
fMRI-vs-MEG evaluation of post-stroke interhemispheric asymmetries in primary sensorimotor hand areas
No full textGrowing evidence emphasizes a positive role of brain ipsilesional (IL) reorganization in stroke patients with partial recovery. Ten patients affected by a monohemispheric stroke in the middle cerebral artery territory underwent functional magnetic resonance (IMRI) and magnetoencephalography (MEG) evaluation of the primary sensory (S I) activation via the same paradigm (median nerve galvanic stimulation). Four patients did not present S I fMRI activation [Rossini, P.M., Altamura, C., Ferretti, A., Vemieri, F., Zappasodi, F., Caulo, M., Pizzella, V, Del Gratta, C., Romani, G.L., Tecchio, F., 2004. Does cerebrovascular disease affect the coupling between neuronal activity and local haemodynamics? Brain 127, 99-110], although inclusion criteria required bilateral identifiable MEG responses. Mean Euclidean distance between IMRI and MEG SI activation Talairach coordinates was 10.1 +/- 2.9 mm, with a3D intra-class correlation (ICC) coefficient of 0.986. Interhemispheric asymmetries, evaluated by an MEG procedure independent of Talairach transformation, were outside or at the boundaries of reference ranges in 6 patients. In 3 of them, the IL activation presented medial or lateral shift with respect to the omega-shaped post-rolandic area while in the other 3, IL areas were outside the peri-rolandic region.In conclusion, despite dissociated intensity, the MEG and fMRI activations displayed good spatial consistency in stroke patients, thus confirming excessive interhemispheric asymmetries as a suitable indicator of unusual recruitments in the ipsilesional hemisphere, within or outside the peri-rolandic region. (c) 2006 Elsevier Inc. All rights reserved
fMRI-vs-MEG evaluation of post-stroke interhemispheric asymmetries in primary sensorimotor hand areas
No full textGrowing evidence emphasizes a positive role of brain ipsilesional (IL) reorganization in stroke patients with partial recovery. Ten patients affected by a monohemispheric stroke in the middle cerebral artery territory underwent functional magnetic resonance (fMRI) and magnetoencephalography (MEG) evaluation of the primary sensory (S1) activation via the same paradigm (median nerve galvanic stimulation). Four patients did not present S1 fMRI activation [Rossini, P.M., Altamura, C., Ferretti, A., Vernieri, F., Zappasodi, F., Caulo, M., Pizzella, V., Del Gratta, C., Romani, G.L., Tecchio, F., 2004. Does cerebrovascular disease affect the coupling between neuronal activity and local haemodynamics? Brain 127, 99-110], although inclusion criteria required bilateral identifiable MEG responses. Mean Euclidean distance between fMRI and MEG S1 activation Talairach coordinates was 10.1 ± 2.9 mm, with a 3D intra-class correlation (ICC) coefficient of 0.986. Interhemispheric asymmetries, evaluated by an MEG procedure independent of Talairach transformation, were outside or at the boundaries of reference ranges in 6 patients. In 3 of them, the IL activation presented medial or lateral shift with respect to the omega-shaped post-rolandic area while in the other 3, IL areas were outside the peri-rolandic region. In conclusion, despite dissociated intensity, the MEG and fMRI activations displayed good spatial consistency in stroke patients, thus confirming excessive interhemispheric asymmetries as a suitable indicator of unusual recruitments in the ipsilesional hemisphere, within or outside the peri-rolandic region. © 2006 Elsevier Inc. All rights reserved
Probing dark matter haloes of spiral galaxies at poorly explored distances using satellite kinematics
No full textAims: We present the results of a pilot project designed to study the distribution of dark matter haloes out to very large radii in spiral galaxies. As dynamical probe, we use their rotation curves and the motions of satellite galaxies. In this pilot stage, we observed seven late-type spiral galaxies of about the same luminosity MR ~ -22 (and approximately the same mass). We investigate the kinematics of these galaxies, and the radial and angular distribution of their satellites.
Methods: Using VIMOS at the VLT, we carried out a spectroscopic survey in seven 14' × 14' fields each around a late-type isolated spiral galaxy. We obtained radial velocities and spatial distributions for 77 candidate satellites. After removing the interlopers, we are left with 61 true satellites. In combination with the rotation curves of the primary galaxies, satellites are used to probe the gravitational potential of the primaries and derive the dark matter halo properties by means of standard mass modeling techniques.
Results: We find (a) that the dark matter haloes of luminous spirals (MR ~ -22) have virial radii of ~400 kpc and virial masses of 3.5 × 1012 Msun; (b) that the radial velocity and angular distributions of the satellites around the primaries are isotropic; and (c) that the resulting mass distribution is in good agreement with that found in the optical regions of spirals and described by the universal rotation curve of spirals once extrapolated to large radii. The results obtained in this pilot phase of the project are already interesting and limited only by small number statistics. The full project involving an order of magnitude more targets, would very likely provide us with a definitive picture of the dark matter distribution around spirals out to their virial radii and beyond
Erythroid colony formation and erythropoietin activity in mice treated with estradiol benzoate.
No full textSpectral signature of attentional reorienting in the human brain
No full textAs we move in the environment, attention shifts to novel objects of interest based on either their sensory salience or behavioral value (reorienting). This study measures with magnetoencephalography (MEG) different properties (amplitude, onset-to-peak duration) of event-related desynchronization/synchronization (ERD/ERS) of oscillatory activity during a visuospatial attention task designed to separate activity related to reorienting vs. maintaining attention to the same location, controlling for target detection and response processes. The oscillatory activity was measured both in fMRI-defined regions of the interest (ROIs) of the dorsal attention (DAN) and visual (VIS) networks, previously defined as task-relevant in the same subjects, or whole-brain in a pre-defined set of cortical ROIs encompassing the main brain networks.
Reorienting attention (shift cues) as compared to maintaining attention (stay cues) produced a temporal sequence of ERD/ERS modulations at multiple frequencies in specific anatomical regions/networks. An early (~330 ms), stronger, transient theta ERS occurred in task-relevant (DAN, VIS) and control networks (VAN, CON, FPN), possibly reflecting an alert/reset signal in response to the cue. A more sustained, behaviorally relevant, low-beta band ERD peaking ~450 ms following shift cues (~410 for stay cues) localized in frontal and parietal regions of the DAN. This modulation is consistent with a control signal re-routing information across visual hemifields. Contralateral vs. ipsilateral shift cues produced in occipital visual regions, a stronger, sustained alpha ERD (peak ~470 ms) and a longer, transient high beta/gamma ERS (peak ~490 ms) related to preparatory visual modulations in advance of target occurrence.
This is the first description of a cascade of oscillatory processes during attentional reorienting in specific anatomical regions and networks. Among these processes, a behaviorally relevant beta desynchronization in the FEF is likely associated with the control of attention shifts
Fetal auditory responses to external sounds and mother's heart beat: detection improved by Independent Component Analysis.
No full textIn this paper, we present a magnetoencephalographic study of the fetal auditory response to external stimuli and to the sound of the mother's heartbeat. We describe how an ad hoc functional selection procedure allowed us to isolate the sources in the fetal brain responding to sounds only, after the application to the recorded data of a standard Independent Component Analysis algorithm. In our experiment, acoustic stimuli were delivered to twelve healthy women with uncomplicated pregnancies at a time between 36 and 40 weeks gestational age, with their fetuses in breech presentation. Ultrasound images allowed determination of the region over the women's abdomen nearest to the fetal head, over which both the acoustic stimulator and the MEG sensors were subsequently placed. In 8 out of the 12 cases, our analysis provided consistent evidence of a fetal response both to the mother's heartbeat and to the external auditory stimulation; both were characterized by a clear prominent component at around 200 ms latency, which is widely accepted as the marker of the fetal response to auditory stimuli
- …
