[show abstract][hide abstract] ABSTRACT: Post-concussion syndrome has been related to axonal damage in patients with mild traumatic brain injury, but little is known about the consequences of injury on brain networks. In the present study, our aim was to characterize changes in functional brain networks following mild traumatic brain injury in patients with post-concussion syndrome using resting-state functional magnetic resonance imaging data. We investigated 17 injured patients with persistent post-concussion syndrome (under the DSM-IV criteria) at 6 months post-injury compared with 38 mild traumatic brain injury patients with no post-concussion syndrome and 34 healthy controls. All patients underwent magnetic resonance imaging examinations at the subacute (1-3 weeks) and late (6 months) phases after injury. Group-wise differences in functional brain networks were analyzed using graph theory measures. Patterns of long-range functional networks alterations were found in all mild traumatic brain injury patients. Mild traumatic brain injury patients with post-concussion syndrome had greater alterations than patients without post-concussion syndrome. In patients with post-concussion syndrome, changes specifically affected temporal and thalamic regions predominantly at the subacute stage and frontal regions at the late phase. Our results suggest that the post-concussion syndrome is associated with specific abnormalities in functional brain network that may contribute to explain deficits typically observed in PCS patients.
PLoS ONE 01/2013; 8(6):e65470. · 3.73 Impact Factor
[show abstract][hide abstract] ABSTRACT: The presence of a postconcussion syndrome (PCS) induces substantial socio-professional troubles in mild traumatic brain injury (mTBI) patients. Although the exact origin of these disorders is not known, they may be the consequence of diffuse axonal injury (DAI) impacting structural integrity. In the present study, we compared structural integrity at the subacute and late stages after mTBI and in case of PCS, using diffusion-weighted imaging (DWI). Fifty-three mTBI patients were investigated and compared with 40 healthy controls. All patients underwent a DWI examination at the subacute (8-21 days) and late (6 months) phases after injury. MTBI patients with PCS were detected at the subacute phase using the ICD-10 classification. Groupwise differences in structural integrity were investigated using Tract-Based Spatial Statistics (TBSS). A loss of structural integrity was found in mTBI patients at the subacute phase but partially resolved over time. Moreover, we observed that mTBI patients with PCS had greater and wider structural impairment than patients without PCS. These damages persisted over time for PCS patients, while mTBI patients without PCS partly recovered. In conclusion, our results strengthen the relationship between structural integrity and PCS.
Brain Imaging and Behavior 04/2012; 6(2):283-92. · 2.67 Impact Factor
[show abstract][hide abstract] ABSTRACT: Consciousness is reduced during nonrapid eye movement (NREM) sleep due to changes in brain function that are still poorly understood. Here, we tested the hypothesis that impaired consciousness during NREM sleep is associated with an increased modularity of brain activity. Cerebral connectivity was quantified in resting-state functional magnetic resonance imaging times series acquired in 13 healthy volunteers during wakefulness and NREM sleep. The analysis revealed a modification of the hierarchical organization of large-scale networks into smaller independent modules during NREM sleep, independently from EEG markers of the slow oscillation. Such modifications in brain connectivity, possibly driven by sleep ultraslow oscillations, could hinder the brain's ability to integrate information and account for decreased consciousness during NREM sleep.
Proceedings of the National Academy of Sciences 03/2012; 109(15):5856-61. · 9.74 Impact Factor
[show abstract][hide abstract] ABSTRACT: Gilles de la Tourette syndrome is a clinically heterogeneous disorder with poor known pathophysiology. Recent neuropathological and structural neuroimaging data pointed to the dysfunction of cortico-basal ganglia networks. Nonetheless, it is not clear how these structural changes alter the functional activity of the brain and lead to heterogeneous clinical expressions of the syndrome. The objective of this study was to evaluate global integrative state and organization of functional connections of sensori-motor, associative and limbic cortico-basal ganglia networks, which are likely involved in tics and behavioural expressions of Gilles de la Tourette syndrome. We also tested the hypothesis that specific regions and networks contribute to different symptoms. Data were acquired on 59 adult patients and 27 gender- and age-matched controls using a 3T magnetic resonance imaging scanner. Cortico-basal ganglia networks were constructed from 91 regions of interest. Functional connectivity was quantified using global integration and graph theory measures. We found a stronger functional integration (more interactions among anatomical regions) and a global functional disorganization of cortico-basal ganglia networks in patients with Gilles de la Tourette syndrome compared with controls. All networks were characterized by a shorter path length, a higher number of and stronger functional connections among the regions and by a loss of pivotal regions of information transfer (hubs). The functional abnormalities correlated to tic severity in all cortico-basal ganglia networks, namely in premotor, sensori-motor, parietal and cingulate cortices and medial thalamus. Tic complexity was correlated to functional abnormalities in sensori-motor and associative networks, namely in insula and putamen. Severity of obsessive-compulsive disorder was correlated with functional abnormalities in associative and limbic networks, namely in orbito-frontal and prefrontal dorsolateral cortices. The results suggest that the pattern of functional changes in cortico-basal ganglia networks in patients could reflect a defect in brain maturation. They also support the hypothesis that distinct regions of cortico-basal ganglia networks contribute to the clinical heterogeneity of this syndrome.
[show abstract][hide abstract] ABSTRACT: Consciousness has been related to the amount of integrated information that the brain is able to generate. In this paper, we tested the hypothesis that the loss of consciousness caused by propofol anesthesia is associated with a significant reduction in the capacity of the brain to integrate information. To assess the functional structure of the whole brain, functional integration and partial correlations were computed from fMRI data acquired from 18 healthy volunteers during resting wakefulness and propofol-induced deep sedation. Total integration was significantly reduced from wakefulness to deep sedation in the whole brain as well as within and between its constituent networks (or systems). Integration was systematically reduced within each system (i.e., brain or networks), as well as between networks. However, the ventral attentional network maintained interactions with most other networks during deep sedation. Partial correlations further suggested that functional connectivity was particularly affected between parietal areas and frontal or temporal regions during deep sedation. Our findings suggest that the breakdown in brain integration is the neural correlate of the loss of consciousness induced by propofol. They stress the important role played by parietal and frontal areas in the generation of consciousness.
[show abstract][hide abstract] ABSTRACT: Mild traumatic brain injury (mTBI) can induce long-term behavioral and cognitive disorders. Although the exact origin of these mTBI-related disorders is not known, they may be the consequence of diffuse axonal injury (DAI). Here, we investigated whether MRI at the subacute stage can detect lesions that are associated with poor functional outcome in mTBI by using anatomical images (T(1) ) and diffusion tensor imaging (DTI). Twenty-three patients with mTBI were investigated and compared with 23 healthy volunteers. All patients underwent an MRI investigation and clinical tests between 7 and 28 days (D15) and between 3 and 4 months (M3) after injury. Patients were divided in two groups of poor outcome (PO) and good outcome (GO), based on their complaints at M3. Groupwise differences in gray matter partial volume between PO patients, GO patients and controls were analyzed using Voxel-Based Morphometry (VBM) from T(1) data at D15. Differences in microstructural architecture were investigated using Tract-Based Spatial Statistics (TBSS) and the diffusion images obtained from DTI data at D15. Permutation-based non-parametric testing was used to assess cluster significance at p < 0.05, corrected for multiple comparisons. Twelve GO patients and 11 PO patients were identified on the basis of their complaints. In PO patients, gray matter partial volume was significantly lower in several cortical and subcortical regions compared with controls, but did not differ from that of GO patients. No difference in diffusion variables was found between GO and controls. PO patients showed significantly higher mean diffusivity values than both controls and GO patients in the corpus callosum, the right anterior thalamic radiations and the superior longitudinal fasciculus, the inferior longitudinal fasciculus and the fronto-occipital fasciculus bilaterally. In conclusion, PO patients differed from GO patients by the presence of diffusion changes in long association white matter fiber tracts but not by gray matter partial volume. These results suggest that DTI at the subacute stage may be a predictive marker of poor outcome in mTBI.
Human Brain Mapping 06/2011; 32(6):999-1011. · 6.88 Impact Factor
[show abstract][hide abstract] ABSTRACT: Gonadotropin-releasing hormone (GnRH) agonists, such as leuprorelin, are recommended in the patients with pedophilia at highest risk of offending. However, the cerebral mechanisms of the effects of these testosterone-decreasing drugs are poorly known. This study aimed to identify changes caused by leuprorelin in a pedophilic patient's brain responses to pictures representing children. Clinical, endocrine, and fMRI investigations were done of a man with pedophilia before leuprorelin therapy and 5 months into leuprorelin therapy. Patient was compared with an age-matched healthy control also assessed 5 months apart. Before therapy, pictures of boys elicited activation in the left calcarine fissure, left insula, anterior cingulate cortex, and left cerebellar vermis. Five months into therapy, all the above-mentioned activations had disappeared. No such activations and, consequently, no such decreases occurred in the healthy control. The results of this pilot study suggest that leuprorelin decreased activity in regions known to mediate the perceptual, motivational, and affective responses to visual sexual stimuli.
International Journal of Offender Therapy and Comparative Criminology 04/2011; 56(1):50-60. · 0.84 Impact Factor
[show abstract][hide abstract] ABSTRACT: Diffuse optical imaging (DOI) is a non invasive technique allowing the recovery of hemodynamic changes in the brain. Due to the diffusive nature of photon propagation in turbid media and the fact that cerebral tissues are located around 1.5 cm under the adult human scalp, DOI measurements are subject to partial volume errors. DOI measurements are also sensitive to large pial vessels because oxygenated and deoxygenated hemoglobin are the dominant chromophores in the near infrared window. In this study, the effect of the extra-cerebral vasculature in proximity of the sagittal sinus was investigated for its impact on DOI measurements simulated over the human adult visual cortex. Numerical Monte Carlo simulations were performed on two specific models of the human head derived from magnetic resonance imaging (MRI) scans. The first model included the extra-cerebral vasculature in which constant hemoglobin concentrations were assumed while the second did not. The screening effect of the vasculature was quantified by comparing recovered hemoglobin changes from each model for different optical arrays and regions of activation. A correction factor accounting for the difference between the recovered and the simulated hemoglobin changes was computed in each case. The results show that changes in hemoglobin concentration are better estimated when the extra-cerebral vasculature is modeled and the correction factors obtained in this case were at least 1.4-fold lower. The effect of the vasculature was also examined in a high-density diffuse optical tomography configuration. In this case, the difference between changes in hemoglobin concentration recovered with each model was reduced down to 10%.
[show abstract][hide abstract] ABSTRACT: A low-cost device using diffuse optical imaging (DOI) for measuring in vivo hemodynamic changes in the spinal cord has been developed. The proposed system is aimed at monitoring for the first time real-time hemodynamic changes associated with intraspinal rhythmic motor activity monitored by electroneurogram (ENG) evoked in paralyzed cats (fictive locomotion). The device contains the emitting and collecting probes within a saddle that fits over a vertebra and has been developed with discrete component circuits. Experiments performed in two acutely decerebrate and paralyzed cats confirm a noticeable and reproducible hemodynamic response during episodes of fictive locomotion. The device is designed so that it could be implanted chronically. In the future, a multi-implant imaging platform could measure long-term hemodynamic changes in the spinal cord.
IEEE Transactions on Biomedical Circuits and Systems 11/2010; · 2.74 Impact Factor
[show abstract][hide abstract] ABSTRACT: During smooth pursuit, the image of the target is stabilized on the fovea, implying that speed judgments made during pursuit must rely on an extraretinal signal providing precise eye speed information. To characterize the introduction of such extraretinal signal into the human visual system, we performed a factorial, functional magnetic resonance imaging experiment, in which we manipulated the factor eye movement, with "fixation" and "pursuit" as levels, and the factor task, with "speed" and "form" judgments as levels. We hypothesized that the extraretinal speed signal is reflected as an interaction between speed judgments and pursuit. Random effects analysis yielded an interaction only in dorsal early visual cortex. Retinotopic mapping localized this interaction on the horizontal meridian (HM) between dorsal areas visual 2 and 3 (V2/V3) at 1-2 degrees azimuth. This corresponded to the position the pursuit target would have reached, if moving retinotopically, at the time of the subject's speed judgment. Because the 2 V2/V3 HMs are redundant, both may be involved in speed judgments, the ventral one involving judgments based on retinal motion and the dorsal one judgments requiring an internal signal. These results indicate that an extraretinal speed signal is injected into early visual cortex during pursuit.
[show abstract][hide abstract] ABSTRACT: While the cortical components of functional networks detected by spatial independent component analysis (sICA) in functional magnetic resonance imaging (fMRI) have been reproducibly described in various While the cortical components of functional networks detected by spatial independent component analysis (sICA) in functional magnetic resonance imaging (fMRI) have been reproducibly described in various studies, little is known about their subcortical components. In this study, we propose a method that extracts cortico-subcortical networks from fMRI data by first detecting cortical networks with sICA and then by complementing them with subcortical components using multiple regression, at both the individual and the group levels.studies, little is known about their subcortical components. In this study, we propose a method that extracts cortico-subcortical networks from fMRI data by first detecting cortical networks with sICA and then by complementing them with subcortical components using multiple regression, at both the individual and the group levels.
Biomedical Imaging: From Nano to Macro, 2010 IEEE International Symposium on; 05/2010
[show abstract][hide abstract] ABSTRACT: We use Monte Carlo simulations to investigate the influence of the sagittal sinus vein on diffuse optical imaging measurements. Effects are characterized by quantitative additional partial volume errors computed with respect to a cerebral activation.
[show abstract][hide abstract] ABSTRACT: Grid technologies are appealing to deal with the challenges raised by computational neurosciences and support multi-centric brain studies. However, core grids middleware hardly cope with the complex neuroimaging data representation and multi-layer data federation needs. Moreover, legacy neuroscience environments need to be preserved and cannot be simply superseded by grid services. This paper describes the NeuroLOG platform design and implementation, shedding light on its Data Management Layer. It addresses the integration of brain image files, associated relational metadata and neuroscience semantic data in a heterogeneous distributed environment, integrating legacy data managers through a mediation layer.
Studies in health technology and informatics 01/2010; 159:112-23.
[show abstract][hide abstract] ABSTRACT: When characterizing regional cerebral gray matter differences in structural magnetic resonance images (sMRI) by voxel-based morphometry (VBM), one faces a known drawback of VBM, namely that histogram unequalization in the intensity images introduces false-positive results.
To overcome this limitation, we propose to improve VBM by a new approach (called eVBM for enhanced VBM) that takes the histogram distribution of the sMRI into account by adding a histogram equalization step within the VBM procedure. Combining this technique with two most widely used VBM software packages (FSL and SPM), we studied GM variability in a group of 62 patients with Alzheimer's disease compared to 73 age-matched elderly controls.
The results show that eVBM can reduce the number of false-positive differences in gray matter concentration.
Because it takes advantage of the properties of VBM while improving sMRI histogram distribution at the same time, the proposed method is a powerful approach for analyzing gray matter differences in sMRI and may be of value in the investigation of sMRI gray and white matter abnormalities in a variety of brain diseases.
[show abstract][hide abstract] ABSTRACT: Motor skill learning is associated with profound changes in brain activation patterns over time. Associative and rostral premotor cortical and subcortical regions are mostly recruited during the early phase of explicit motor learning, while sensorimotor regions may increase their activity during the late learning phases. Distinct brain networks are therefore engaged during the early and late phases of motor skill learning. How these regions interact with one another and how information is transferred from one circuit to the other has been less extensively studied. In this study, we used functional MRI (fMRI) at 3T to follow the changes in functional connectivity in the associative/premotor and the sensorimotor networks, during extended practice (4 weeks) of an explicitly known sequence of finger movements. Evolution of functional connectivity was assessed using integration, a measure that quantifies the total amount of interaction within a network. When comparing the integration associated with a complex finger movement sequence to that associated with a simple sequence, we observed two patterns of decrease during the 4 weeks of practice. One was not specific as it was observed for all sequences, whereas a specific decrease was observed only for the execution of the learned sequence. This second decrease was a consequence of a relative decrease in associative/premotor network integration, together with a relative increase in between-network integration. These findings are in line with the hypothesis that information is transferred from the associative/premotor circuit to the sensorimotor circuit during the course of motor learning.