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H. Benali

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21 papers
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21

YNICL Journal 2015 Journal Article

Increased cortico-striatal connectivity during motor practice contributes to the consolidation of motor memory in writer's cramp patients

  • C. Gallea
  • M. Balas
  • E. Bertasi
  • R. Valabregue
  • D. García-Lorenzo
  • D. Coynel
  • C. Bonnet
  • D. Grabli

Sensorimotor representations of movements are created in the sensorimotor network through repeated practice to support successful and effortless performance. Writer's cramp (WC) is a disorder acquired through extensive practice of finger movements, and it is likely associated with the abnormal acquisition of sensorimotor representations. We investigated (i) the activation and connectivity changes in the brain network supporting the acquisition of sensorimotor representations of finger sequences in patients with WC and (ii) the link between these changes and consolidation of motor performance 24 h after the initial practice. Twenty-two patients with WC and 22 age-matched healthy volunteers practiced a complex sequence with the right (pathological) hand during functional MRI recording. Speed and accuracy were measured immediately before and after practice (day 1) and 24 h after practice (day 2). The two groups reached equivalent motor performance on day 1 and day 2. During motor practice, patients with WC had (i) reduced hippocampal activation and hippocampal-striatal functional connectivity; and (ii) overactivation of premotor-striatal areas, whose connectivity correlated with motor performance after consolidation. These results suggest that patients with WC use alternative networks to reach equiperformance in the acquisition of new motor memories.

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YNIMG Journal 2014 Journal Article

Framework for integrated MRI average of the spinal cord white and gray matter: The MNI–Poly–AMU template

  • V.S. Fonov
  • A. Le Troter
  • M. Taso
  • B. De Leener
  • G. Lévêque
  • M. Benhamou
  • M. Sdika
  • H. Benali

The field of spinal cord MRI is lacking a common template, as existing for the brain, which would allow extraction of multi-parametric data (diffusion-weighted, magnetization transfer, etc.) without user bias, thereby facilitating group analysis and multi-center studies. This paper describes a framework to produce an unbiased average anatomical template of the human spinal cord. The template was created by co-registering T2-weighted images (N=16 healthy volunteers) using a series of pre-processing steps followed by non-linear registration. A white and gray matter probabilistic template was then merged to the average anatomical template, yielding the MNI–Poly–AMU template, which currently covers vertebral levels C1 to T6. New subjects can be registered to the template using a dedicated image processing pipeline. Validation was conducted on 16 additional subjects by comparing an automatic template-based segmentation and manual segmentation, yielding a median Dice coefficient of 0. 89. The registration pipeline is rapid (~15min), automatic after one C2/C3 landmark manual identification, and robust, thereby reducing subjective variability and bias associated with manual segmentation. The template can notably be used for measurements of spinal cord cross-sectional area, voxel-based morphometry, identification of anatomical features (e. g. , vertebral levels, white and gray matter location) and unbiased extraction of multi-parametric data.

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YNIMG Journal 2012 Journal Article

Reduction of physiological noise with independent component analysis improves the detection of nociceptive responses with fMRI of the human spinal cord

  • G. Xie
  • M. Piché
  • M. Khoshnejad
  • V. Perlbarg
  • J.-I. Chen
  • R.D. Hoge
  • H. Benali
  • S. Rossignol

The evaluation of spinal cord neuronal activity in humans with functional magnetic resonance imaging (fMRI) is technically challenging. Major difficulties arise from cardiac and respiratory movement artifacts that constitute significant sources of noise. In this paper we assessed the Correction of Structured noise using spatial Independent Component Analysis (CORSICA). FMRI data of the cervical spinal cord were acquired in 14 healthy subjects using gradient-echo EPI. Nociceptive electrical stimuli were applied to the thumb. Additional data with short TR (250ms, to prevent aliasing) were acquired to generate a spatial map of physiological noise derived from Independent Component Analysis (ICA). Physiological noise was subsequently removed from the long-TR data after selecting independent components based on the generated noise map. Stimulus-evoked responses were analyzed using the general linear model, with and without CORSICA and with a regressor generated from the cerebrospinal fluid region. Results showed higher sensitivity to detect stimulus-related activation in the targeted dorsal segment of the cord after CORSICA. Furthermore, fewer voxels showed stimulus-related signal changes in the CSF and outside the spinal region, suggesting an increase in specificity. ICA can be used to effectively reduce physiological noise in spinal cord fMRI time series.

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YNIMG Journal 2011 Journal Article

Demyelination and degeneration in the injured human spinal cord detected with diffusion and magnetization transfer MRI

  • J. Cohen-Adad
  • M-M. El Mendili
  • S. Lehéricy
  • P-F. Pradat
  • S. Blancho
  • S. Rossignol
  • H. Benali

Characterizing demyelination/degeneration of spinal pathways in traumatic spinal cord injured (SCI) patients is crucial for assessing the prognosis of functional rehabilitation. Novel techniques based on diffusion-weighted (DW) magnetic resonance imaging (MRI) and magnetization transfer (MT) imaging provide sensitive and specific markers of white matter pathology. In this paper we combined for the first time high angular resolution diffusion-weighted imaging (HARDI), MT imaging and atrophy measurements to evaluate the cervical spinal cord of fourteen SCI patients and age-matched controls. We used high in-plane resolution to delineate dorsal and ventrolateral pathways. Significant differences were detected between patients and controls in the normal-appearing white matter for fractional anisotropy (FA, p<0. 0001), axial diffusivity (p<0. 05), radial diffusivity (p<0. 05), generalized fractional anisotropy (GFA, p<0. 0001), magnetization transfer ratio (MTR, p<0. 0001) and cord area (p<0. 05). No significant difference was detected in mean diffusivity (p=0. 41), T1-weighted (p=0. 76) and T2-weighted (p=0. 09) signals. MRI metrics were remarkably well correlated with clinical disability (Pearson's correlations, FA: p<0. 01, GFA: p<0. 01, radial diffusivity: p=0. 01, MTR: p=0. 04 and atrophy: p<0. 01). Stepwise linear regressions showed that measures of MTR in the dorsal spinal cord predicted the sensory disability whereas measures of MTR in the ventro-lateral spinal cord predicted the motor disability (ASIA score). However, diffusion metrics were not specific to the sensorimotor scores. Due to the specificity of axial and radial diffusivity and MT measurements, results suggest the detection of demyelination and degeneration in SCI patients. Combining HARDI with MT imaging is a promising approach to gain specificity in characterizing spinal cord pathways in traumatic injury.

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YNIMG Journal 2011 Journal Article

Wallerian degeneration after spinal cord lesions in cats detected with diffusion tensor imaging

  • J. Cohen-Adad
  • H. Leblond
  • H. Delivet-Mongrain
  • M. Martinez
  • H. Benali
  • S. Rossignol

One goal of in vivo neuroimaging is the detection of neurodegenerative processes and anatomical reorganizations after spinal cord (SC) injury. Non-invasive examination of white matter fibers in the living SC can be conducted using magnetic resonance diffusion-weighted imaging. However, this technique is challenging at the spinal level due to the small cross-sectional size of the cord and the presence of physiological motion and susceptibility artifacts. In this study, we acquired in vivo high angular resolution diffusion imaging (HARDI) data at 3T in cats submitted to partial SC injury. Cats were imaged before, 3 and 21days after injury. Spatial resolution was enhanced to 1. 5×1. 5×1mm3 using super-resolution technique and distortions were corrected using the reversed gradient method. Tractography-derived regions of interest were generated in the dorsal, ventral, right and left quadrants, to evaluate diffusion tensor imaging (DTI) and Q-Ball imaging metrics with regards to their sensitivity in detecting primary and secondary lesions. A three-way ANOVA tested the effect of session (intact, D3, D21), cross-sectional region (left, right, dorsal and ventral) and rostrocaudal location. Significant effect of session was found for FA (P<0. 001), GFA (P<0. 05) and radial diffusivity (P<0. 001). Post-hoc paired T-test corrected for multiple comparisons showed significant changes at the lesion epicenter (P<0. 005). More interestingly, significant changes were also found several centimeters from the lesion epicenter at both 3 and 21days. This decrease was specific to the type of fibers, i. e. , rostrally to the lesion on the dorsal aspect of the cord and caudally to the lesion ipsilaterally, suggesting the detection of Wallerian degeneration.

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YNIMG Journal 2008 Journal Article

Detection of multiple pathways in the spinal cord using q-ball imaging

  • J. Cohen-Adad
  • M. Descoteaux
  • S. Rossignol
  • R.D. Hoge
  • R. Deriche
  • H. Benali

Magnetic resonance diffusion tensor imaging (DTI) has been extensively applied to the spinal cord for depicting its architecture and for assessing its integrity following spinal lesions. However, DTI is limited in representing complex white matter architecture, notably in the presence of crossing fibres. Recently, q-ball imaging (QBI) has been proposed as a new method for recovering complex white matter architecture. We applied this technique to both ex vivo and in vivo spinal cords of cats using a 3T scanner. For the purpose of comparison, gradients have been applied in 55 and 100 encoding directions and b-values varied from 800 to 3000 s/mm2. As a result, QBI was able to retrieve crossing fibre information, where the DTI approach was constrained in a unique diffusion direction. To our knowledge, this is the first study demonstrating the benefits of QBI for detecting the presence of longitudinal, commissural and dorso-ventral fibres in the spinal cord. It is a first step towards in vivo characterization of the healthy and injured human spinal cord using high angular resolution diffusion imaging and QBI.

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YNIMG Journal 2008 Journal Article

In vivo DTI of the healthy and injured cat spinal cord at high spatial and angular resolution

  • J. Cohen-Adad
  • H. Benali
  • R.D. Hoge
  • S. Rossignol

Spinal cord diffusion tensor imaging (DTI) is challenging in many ways: the small size of the cord, physiological motion and susceptibility artifacts pose daunting obstacles to the acquisition of high-quality data. Here, we present DTI results computed from in vivo studies of the healthy and injured spinal cord of five cats. Both high spatial (1. 1 mm3) and angular (55 directions) resolutions were used to optimise modelling of the diffusion process. Also, particular effort was directed towards a strategy that limits susceptibility artifacts. For validation purposes, acquisitions were repeated in two cats before and after making a spinal lesion. As a result, various axonal trajectories were identified by tractography including dorsal and ventral columns as well as lateral tracts. Also, fibre bundles showed robust disruption at the site of spinal cord injuries (partial and complete) via tractography, accompanied with significantly lower fractional anisotropy values at the site of lesions. Important outcomes of this work are (i) tractography-based localisation of anatomical tracts in the thoraco-lumbar spinal cord and (ii) in vivo assessment of axonal integrity following experimental spinal cord injury.

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YNIMG Journal 2006 Journal Article

Evaluation of EEG localization methods using realistic simulations of interictal spikes

  • C. Grova
  • J. Daunizeau
  • J.-M. Lina
  • C.G. Bénar
  • H. Benali
  • J. Gotman

Performing an accurate localization of sources of interictal spikes from EEG scalp measurements is of particular interest during the presurgical investigation of epilepsy. The purpose of this paper is to study the ability of six distributed source localization methods to recover extended sources of activated cortex. Due to the frequent lack of a gold standard to evaluate source localization methods, our evaluation was performed in a controlled environment using realistic simulations of EEG interictal spikes, involving several anatomical locations with several spatial extents. Simulated data were corrupted by physiological EEG noise. Simulations involving pairs of sources with the same amplitude were also studied. In addition to standard validation criteria (e. g. , geodesic distance or mean square error), we proposed an original criterion dedicated to assess detection accuracy, based on receiver operating characteristic (ROC) analysis. Six source localization methods were evaluated: the minimum norm, the minimum norm weighted by multivariate source prelocalization (MSP), cortical LORETA with or without additional minimum norm regularization, and two derivations of the maximum entropy on the mean (MEM) approach. Results showed that LORETA-based and MEM-based methods were able to accurately recover sources of different spatial extents, with the exception of sources in temporo-mesial and fronto-mesial regions. Several spurious sources were generated by those methods, however, whereas methods using the MSP always located very accurately the maximum of activity but not its spatial extent. These findings suggest that one should always take into account the results from different localization methods when analyzing real interictal spikes.

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YNIMG Journal 2005 Journal Article

Investigations of dipole localization accuracy in MEG using the bootstrap

  • F. Darvas
  • M. Rautiainen
  • D. Pantazis
  • S. Baillet
  • H. Benali
  • J.C. Mosher
  • L. Garnero
  • R.M. Leahy

We describe the use of the nonparametric bootstrap to investigate the accuracy of current dipole localization from magnetoencephalography (MEG) studies of event-related neural activity. The bootstrap is well suited to the analysis of event-related MEG data since the experiments are repeated tens or even hundreds of times and averaged to achieve acceptable signal-to-noise ratios (SNRs). The set of repetitions or epochs can be viewed as a set of independent realizations of the brain's response to the experiment. Bootstrap resamples can be generated by sampling with replacement from these epochs and averaging. In this study, we applied the bootstrap resampling technique to MEG data from somatotopic experimental and simulated data. Four fingers of the right and left hand of a healthy subject were electrically stimulated, and about 400 trials per stimulation were recorded and averaged in order to measure the somatotopic mapping of the fingers in the S1 area of the brain. Based on single-trial recordings for each finger we performed 5000 bootstrap resamples. We reconstructed dipoles from these resampled averages using the Recursively Applied and Projected (RAP)-MUSIC source localization algorithm. We also performed a simulation for two dipolar sources with overlapping time courses embedded in realistic background brain activity generated using the prestimulus segments of the somatotopic data. To find correspondences between multiple sources in each bootstrap, sample dipoles with similar time series and forward fields were assumed to represent the same source. These dipoles were then clustered by a Gaussian Mixture Model (GMM) clustering algorithm using their combined normalized time series and topographies as feature vectors. The mean and standard deviation of the dipole position and the dipole time series in each cluster were computed to provide estimates of the accuracy of the reconstructed source locations and time series.

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YNIMG Journal 2004 Journal Article

Dynamics of parietofrontal networks underlying visuospatial short-term memory encoding

  • A.C. Croizé
  • R. Ragot
  • L. Garnero
  • A. Ducorps
  • M. Pélégrini-Issac
  • K. Dauchot
  • H. Benali
  • Y. Burnod

Brain imaging studies in TEP, functional magnetic resonance imaging (fMRI) and electroencephalography (EEG) have shown that visuospatial short-term memory tasks depend on dorsal parietofrontal networks. Knowing the spatiotemporal dynamics of this network would provide further understanding of the neural bases of the encoding process. We combined magnetoencephalography (MEG) with EEG and fMRI techniques to study this network in a task, in which participants had to judge the symmetry in position of two dots, presented either simultaneously (“immediate comparison”) or successively (“memorization” of a first dot and “delayed comparison”, after 3 s, with a second dot). With EEG, larger amplitude was observed in the parietocentral P3b component (350–500 ms) in the immediate and “delayed comparisons” than in “memorization” condition, where topography at this time was more anterior and right lateralized. MEG provided a more accurate localization and temporal variations of sources, revealing a strong M4 component at 450 ms in the “memorization” condition, with two sources localized in parietal and right premotor regions. These localizations are consistent with both fMRI foci and EEG cortical current source densities (CSD), but only MEG revealed the strong increase in premotor region at 450 ms related to “memorization”. These combined results suggest that EEG P3B and MEG M4 components reflect two different dynamics in parietofrontal networks: the parietocentral P3b indexes a decision mechanism during the immediate and “delayed comparisons”, whereas the MEG M4 component, with a larger right premotor source, reflects the encoding process in visuospatial short-term memory.

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