198 research outputs found
Functional topography of the secondary somatosensory cortex for nonpainful and painful stimulation of median and tibial nerve: an fMRI study.
No full textFunctional magnetic resonance imaging (fMRI) was used to study the cortical activity of the bilateral secondary somatosensory cortex (SII) during nonpainful (motor threshold) and painful electrical stimulation of median and tibial nerves. fMRI recordings were performed in eight normal young adults. The aim was at evaluating the working hypothesis of a spatial segregation of nonpainful and painful populations not only in the bhandQ representation of SII [Ferretti, A., Babiloni, C., Del Gratta, C., Caulo, M., Tartaro, A., Bonomo, L., Rossini, P.M., Romani, G.L., 2003. Functional topography of the secondary somatosensory cortex for nonpainful and painful stimuli: an fMRI study. NeuroImage 20, 1625– 1638.] but also in its bfootQ representation. Results showed that, in both bhandQ and bfootQ representations of bilateral SII, the activity elicited by the painful stimulation was localized more posteriorly with respect to that elicited by the nonpainful stimulation. A fine spatial analysis of the SII responses revealed a clear somatotopic organization in the bilateral SII subregion especially reactive to the nonpainful stimuli (i.e., segregation of the hand and foot representations). In contrast, it was not possible to disentangle the bhandQ and bfootQ representations of SII for painful stimuli. These results extended to the SII bfootQ representation previous evidence of a spatial segregation in the SII bhandQ representation of subregions for the painful and nonpainful stimuli. Furthermore, they suggest that noxious information is not somatotopically represented in human bilateral SII, at least as inferred from fMRI data at 1.5 T
Nociceptive and non-nociceptive sub-regions in the human secondary somatosensory cortex: a MEG study using fMRI constraints
No full textPrevious evidence from functional magnetic resonance imaging (fMRI)
has shown that a painful galvanic stimulation mainly activates a
posterior sub-region in the secondary somatosensory cortex (SII),
whereas a non-painful sensory stimulation mainly activates an anterior
sub-region of SII [Ferretti, A., Babiloni, C., Del Gratta, C., Caulo, M.,
Tartaro, A., Bonomo, L., Rossini, P.M., Romani, G.L., 2003. Functional
topography of the secondary somatosensory cortex for non-painful and
painful stimuli: an fMRI study. Neuroimage 20 (3), 1625–1638.]. The
present study, combining fMRI with magnetoencephalographic (MEG)
findings, assessed the working hypothesis that the activity of such a
posterior SII sub-region is characterized by an amplitude and temporal
evolution in line with the bilateral functional organization of nociceptive
systems. Somatosensory evoked magnetic fields (SEFs) recordings
after alvanic median nerve stimulation were obtained from the same
sample of subjects previously examined with fMRI [Ferretti, A.,
Babiloni, C., Del Gratta, C., Caulo, M., Tartaro, A., Bonomo, L.,
Rossini, P.M., Romani, G.L., 2003. Functional topography of the
secondary somatosensory cortex for non-painful and painful stimuli:
an fMRI study. Neuroimage 20 (3), 1625–1638.]. Constraints for dipole
source localizations obtained from MEG recordings were applied
according to fMRI activations, namely, at the posterior and the
anterior SII sub-regions. It was shown that, after painful stimulation,
the two posterior SII sub-regions of the contralateral and ipsilateral
hemispheres were characterized by dipole sources with similar
amplitudes and latencies. In contrast, the activity of anterior SII subregions
showed statistically significant differences in amplitude and
latency during both non-painful and painful stimulation conditions. In
the contralateral hemisphere, the source activity was greater in
amplitude and shorter in latency with respect to the ipsilateral. Finally, painful stimuli evoked a response from the posterior sub-regions
peaking significantly earlier than from the anterior sub-regions. These
results suggested that both ipsi and contra posterior SII sub-regions
process painful stimuli in parallel, while the anterior SII sub-regions
might play an integrative role in the processing of somatosensory
stimuli
Empirical Markov Chain Monte Carlo Bayesian analysis of fMRI data
No full textIn this work an Empirical Markov Chain Monte Carlo Bayesian approach to analyse fMRI data is proposed. The Bayesian framework is appealing since complex models can be adopted in the analysis both for the image and noise model. Here, the noise autocorrelation is taken into account by adopting an AutoRegressive model of order one and a versatile non-linear model is assumed for the task-related activation. Model parameters include the noise variance and autocorrelation, activation amplitudes and the hemodynamic response function parameters. These are estimated at each voxel from samples of the Posterior Distribution. Prior information is included by means of a 4D spatio-temporal model for the interaction between neighbouring voxels in space and time. The results show that this model can provide smooth estimates from low SNR data while important spatial structures in the data can be preserved. A simulation study is presented in which the accuracy and bias of the estimates are addressed. Furthermore, some results on convergence diagnostic of the adopted algorithm are presented. To validate the proposed approach a comparison of the results with those from a standard GLM analysis, spatial filtering techniques and a Variational Bayes approach is provided. This comparison shows that our approach outperforms the classical analysis and is consistent with other Bayesian techniques. This is investigated further by means of the Bayes Factors and the analysis of the residuals. The proposed approach applied to Blocked Design and Event Related datasets produced reliable maps of activation. © 2008 Elsevier Inc. All rights reserved
ESMRMB 2015, 32nd Annual Scientific Meeting, Edinburgh, UK, 1-3 October: Abstracts, Saturday
No full textfMRI-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
Human cortical responses during one-bit delayed-response tasks: An fMRI study
No full textNeuroimaging study of cognition across aging requires simple tasks ensuring: (i) high rate of correct performances in neurophysiological settings; and (ii) significant modulation of cortical activity. As a preliminary step, the present functional magnetic resonance imaging (fMRI) study tested the hypothesis that very simple delayed-response tasks fit these requirements in normal young adults. The short-term memory (STM) variant included a sequence of cue stimulus (two vertical bars), delay period (blank screen for only 5 s), go stimulus, and motor response compatible with the taller vertical bar. Noteworthy, the retention (only one bit) could be based on visuo-spatial, phonological, and somatomotor coding. In the control variant (no STM, NSTM), the cue stimulus was present during the delay period. Results showed high rate of correct performances in both tasks (about 95%). Compared to the NSTM task (delay period), the STM task enhanced cortical responses in bilateral dorsolateral prefrontal (Brodmann area 8-9 (BA 8-9)), lateral premotor (13A 6L), medial premotor (BA 6M), inferior parietal (13A 40), and superior parietal (BA 7) areas. In the STM task, cortical responses were stronger in right than left BA 8-9 and BA 6L. These results indicate that, in normal young adults, a simple STM variant of delayed-response tasks (one bit to be retained) is correctly performed and enhances bilateral fronto-parietal responses. Therefore, it may be used for future cognitive neuroimaging studies on aging. (c) 2005 Elsevier Inc. All rights reserved
Sviluppo e validazione di un sistema integrato per dosimetria fotoneutronica basato su rivelatori ad emulsioni surriscaldate
No full textfMRI-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
Multimodal integration of fMRI and EEG data for high spatial and temporal resolution analysis of brain networks.
No full textTwo major non-invasive brain mapping techniques, electroencephalography (EEG) and functional magnetic resonance imaging (fMRI), have complementary advantages with regard to their spatial and temporal resolution. We propose an approach based on the integration of EEG and fMRI, enabling the EEG temporal dynamics of information processing to be characterized within spatially well-defined fMRI large-scale networks. First, the fMRI data are decomposed into networks by means of spatial independent component analysis (sICA), and those associated with intrinsic activity and/or responding to task performance are selected using information from the related time-courses. Next, the EEG data over all sensors are averaged with respect to event timing, thus calculating event-related potentials (ERPs). The ERPs are subjected to temporal ICA (tICA), and the resulting components are localized with the weighted minimum norm (WMNLS) algorithm using the task-related fMRI networks as priors. Finally, the temporal contribution of each ERP component in the areas belonging to the fMRI large-scale networks is estimated. The proposed approach has been evaluated on visual target detection data. Our results confirm that two different components, commonly observed in EEG when presenting novel and salient stimuli, respectively, are related to the neuronal activation in large-scale networks, operating at different latencies and associated with different functional processes
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