Biomedical subjects

François Lazeyras

Publications and source records attributed to François Lazeyras.

At least 19 recordsLinked to original sources

PubMed2006

Impact of intrauterine growth restriction and glucocorticoids on brain development: insights using advanced magnetic resonance imaging.

There are now a number of evidences showing that the developing organism adapts to the environment it finds itself. Short- and long-term adjustments, referred as "programming", take place and will initially induce intrauterine growth retardation but will also have consequences that will appear later in life. The use of magnetic resonance imaging (MRI) techniques in IUGR babies has delineated changes in the central nervous system (CNS) development that correlate with altered neurodevelopment and could be implicated in the development of neuropsychiatric disorders in adult life. Similarly, the use of corticosteroid treatment in preterm infants has also been implicated in abnormal CNS development. In this review, we will focus on the modifications of CNS development that occur after exposition to adverse environment such as undernutrition or corticosteroid treatment that can now be studied in vivo with advanced MRI technology.

Animals↗

PubMed2006

Neural systems for orienting attention to the location of threat signals: an event-related fMRI study.

Attention may reflexively shift towards the location of perceived threats, but it is still unclear how these spatial biases recruit the distributed fronto-parietal cortical networks involved in other aspects of selective attention. We used event-related fMRI to determine how brain responses to a neutral visual target are influenced by the emotional expression of faces appearing at the same location during a covert orienting task. On each trial, two faces were briefly presented, one in each upper visual field (one neutral and one emotional, fearful or happy), followed by a unilateral target (a small horizontal or vertical bar) replacing one of the faces. Participants had to discriminate the target orientation, shown on the same (valid) or opposite (invalid) side as the emotional face. Trials with faces but no subsequent target (cue-only trials) were included to disentangle activation due to emotional cues from their effects on target detection. We found increased responses in bilateral temporo-parietal areas and right occipito-parietal cortex for fearful faces relative to happy faces, unrelated to the subsequent target and cueing validity. More critically, we found a selective modulation of intraparietal and orbitofrontal cortex for targets following an invalid fearful face, as well as an increased visual response in right lateral occipital cortex for targets following a valid fearful face. No such effects were observed with happy faces. These results demonstrate that fearful faces can act as exogenous cues by increasing sensory processing in extrastriate cortex for a subsequent target presented at the same location, but also produce a cost in disengaging towards another location by altering the response of IPS to invalidly cued targets. Neural mechanisms responsible for orienting attention towards emotional vs. non-emotional stimuli are thus partly shared in parietal and visual areas, but also partly distinct.

Adult↗

PubMed2006

Abnormal patterns of cortical gyrification in velo-cardio-facial syndrome (deletion 22q11.2): an MRI study.

Velo-cardio-facial syndrome (VCFS), also known as 22q11.2 deletion syndrome, is a common genetic condition associated with increased risk for developing schizophrenia. Given that cortical malformations play an integral role in the pattern of neuroanatomical alterations associated with VCFS, the aim of the present study was to quantify and localize gyral abnormalities. Magnetic resonance images were obtained on a 1.5 T scanner. The gyrification index (GI), a measure of the degree of cortical complexity, was differentially calculated for each lobe using a semi-automated protocol. The GI was calculated for 37 patients affected by VCFS as well as for 36 comparison individuals group-matched for age, handedness, and gender. The subjects affected by VCFS showed a significant decrease in the GI in the frontal and parietal lobes compared with the control group. The pattern of decreased gyrification in the frontal and parietal lobes further defines the structural changes associated with the syndrome and suggests underlying abnormalities in neural connectivity. Aberrant connectivity may be partially responsible for the cognitive and behavioral impairments in the syndrome, as well as the high incidence of schizophrenia among affected individuals.

Adolescent↗

PubMed2005

Visual recovery after perinatal stroke evidenced by functional and diffusion MRI: case report.

BACKGROUND: After perinatal brain injury, clinico-anatomic correlations of functional deficits and brain plasticity remain difficult to evaluate clinically in the young infant. Thus, new non-invasive methods capable of early functional diagnosis are needed in young infants. CASE PRESENTATION: The visual system recovery in an infant with perinatal stroke is assessed by combining diffusion tensor imaging (DTI) and event-related functional MRI (ER-fMRI). All experiments were done at 1.5T. A first DTI experiment was performed at 12 months of age. At 20 months of age, a second DTI experiment was performed and combined with an ER-fMRI experiment with visual stimuli (2 Hz visual flash). At 20 months of age, ER-fMRI showed significant negative activation in the visual cortex of the injured left hemisphere that was not previously observed in the same infant. DTI maps suggest recovery of the optic radiation in the vicinity of the lesion. Optic radiations in the injured hemisphere are more prominent in DTI at 20 months of age than in DTI at 12 months of age. CONCLUSION: Our data indicate that functional cortical recovery is supported by structural modifications that concern major pathways of the visual system. These neuroimaging findings might contribute to elaborate a pertinent strategy in terms of diagnosis and rehabilitation.

Asphyxia Neonatorum↗

PubMed2005

Anatomical variability of the lateral frontal lobe surface: implication for intersubject variability in language neuroimaging.

The lateral surface of the frontal lobe shows functional activation in a large number of language related tasks. Group analyses, however, demonstrate remarkable intersubject variability of activation. There are different sources for functional variability, anatomical variability being considered as one of them. The aim of the present study therefore was to qualitatively and quantitatively investigate the anatomical variability of the lateral frontal lobe surface and to search for reliable and stable landmarks connected to language functions. MRIs of 23 healthy right-handed subjects were investigated using the publicly available software "Anatomist/BrainVISA". After standardization of the brains (SPM) and sulci identification, the most frequent pattern was determined and the variance of selected landmarks calculated. The variability of the lateral frontal lobe surface is remarkable, particularly in the prefrontal region. Relatively stable landmarks were selected as follows: (1) connection between the superior frontal sulcus (SFS) and the superior precentral sulcus (SPCS); (2) connection between the inferior frontal sulcus (IFS) and the inferior precentral sulcus (IPCS); (3) inferior end of the precentral sulcus (PCS); and (4) origin of the ascending ramus (AscR) of the Sylvian fissure (SYF). The variability (standard deviation) of the spatial coordinates along the 3 axis of these landmarks after normalization ranged from 2.5 to 5.7 mm. The present study demonstrates that intersubject variability of selected landmarks of the frontal lobe surface remains notable even after spatial normalization of the brains. These results support the concept that anatomical variability is a relevant source of functional variability. We therefore suggest to express functional activation in relation to landmarks obtained from individual anatomy. This approach may contribute to a better analysis of the differences between individuals.

Adult↗

PubMed2005

Cortical distinction between the neural encoding of objects that appear to glow and those that do not.

Objects that appear to glow appear very different from those that do not. However, the neural representation of glow has not been investigated. We present data from an fMRI study which suggest that an extra-striate visual area is involved in the encoding of glowing stimuli, and that this activation does not arise from luminance or contrast factors. Possible functional reasons for the existence of such an area are discussed.

Adult↗

PubMed2005

Functional magnetic resonance imaging and diffusion tensor imaging in a case of central poststroke pain.

The role of the lesion location within functional pain systems is not fully understood for central poststroke pain (CPSP) pathogenesis. In a patient with CPSP we used data from both functional magnetic resonance imaging (MRI) and diffusion tensor imaging (DTI) for anatomo-functional correlations. Structural MRI showed a small residual cavity confined to the right thalamic ventral posterolateral nucleus and the adjacent posterior arm of the internal capsule. DTI maps showed selective reduction of right sensory thalamocortical fibers. Functional MRI, performed with different thermonociceptive stimuli, showed pain-specific signal changes in the anterior cingulate gyrus (BA 24/32) and in the associative parietal regions (BA 5/7). These findings underline, for CPSP pathogenesis, the role of damage of lateral nociceptive thalamoparietal fibers together with the release of activity of anterior cingulate and posterior parietal regions. In a patient with CPSP, we combined noninvasive neuroimaging techniques (functional and diffusion MRI) to assess the anatomo-functional relationship in CPSP. Our investigations show, for CPSP pathogenesis, the role of damage of lateral nociceptive thalamoparietal fibers together with the release of activity of anterior cingulate and posterior parietal regions.

Aged↗

PubMed2005

Portraits or people? Distinct representations of face identity in the human visual cortex.

Humans can identify individual faces under different viewpoints, even after a single encounter. We determined brain regions responsible for processing face identity across view changes after variable delays with several intervening stimuli, using event-related functional magnetic resonance imaging during a long-term repetition priming paradigm. Unfamiliar faces were presented sequentially either in a frontal or three-quarter view. Each face identity was repeated once after an unpredictable lag, with either the same or another viewpoint. Behavioral data showed significant priming in response time, irrespective of view changes. Brain imaging results revealed a reduced response in the lateral occipital and fusiform cortex with face repetition. Bilateral face-selective fusiform areas showed view-sensitive repetition effects, generalizing only from three-quarter to front-views. More medial regions in the left (but not in the right) fusiform showed repetition effects across all types of viewpoint changes. These results reveal that distinct regions within the fusiform cortex hold view-sensitive or view-invariant traces of novel faces, and that face identity is represented in a view-sensitive manner in the functionally defined face-selective areas of both hemispheres. In addition, our finding of a better generalization after exposure to a 3/4-view than to a front-view demonstrates for the first time a neural substrate in the fusiform cortex for the common recognition advantage of three-quarter faces. This pattern provides new insights into the nature of face representation in the human visual system.

Adult↗

PubMed2005

Structural and functional brain development after hydrocortisone treatment for neonatal chronic lung disease.

OBJECTIVE: There is much concern about potential neurodevelopmental impairment after neonatal corticosteroid treatment for chronic lung disease. Dexamethasone is the corticosteroid most often used in this clinical setting, and it has been shown to impair cortical growth among preterm infants. This study evaluated long-term effects of prematurity itself and of neonatal hydrocortisone treatment on structural and functional brain development using three-dimensional MRI with advanced image-processing and neurocognitive assessments. METHODS: Sixty children born preterm, including 25 children treated with hydrocortisone and 35 children not treated with hydrocortisone, and 21 children born at term were evaluated, at a mean age of 8 years, with quantitative MRI and neurocognitive assessments (Wechsler Intelligence Scales for Children-Revised [WISC-R]). Automatic image segmentation was used to determine the tissue volumes of cerebral gray matter, white matter, and cerebrospinal fluid. In addition, the volume of the hippocampus was determined manually. WISC-R scores were recorded as mean intelligence scores at evaluation. Neonatal hydrocortisone treatment for chronic lung disease consisted of a starting dose of 5 mg/kg per day tapered over a minimum of 3 weeks. RESULTS: Cerebral gray matter volume was reduced among preterm children (regardless of hydrocortisone treatment), compared with children born at term (preterm: 649 +/- 4.4 mL; term: 666 +/- 7.3 mL). Birth weight was shown to correlate with gray matter volume at 8 years of age in the preterm group (r = 0.421). Cerebrospinal fluid volume was increased among children born preterm, compared with children born at term (preterm: 228 +/- 4.9 mL; term: 206 +/- 8.2 mL). Total hippocampal volume tended to be lower among children born preterm, with a more pronounced reduction of hippocampal volume among boys (preterm: 6.1 +/- 0.13 mL; term: 6.56 +/- 0.2 mL). The WISC-R score was lower for children born preterm, compared with children born at term (preterm: 99.4 +/- 12.4; term: 109.6 +/- 8.8). Children treated with neonatal hydrocortisone had very similar volumes of gray matter (preterm with hydrocortisone: 650 +/- 7.0 mL; preterm without hydrocortisone: 640 +/- 5.6 mL), white matter (preterm with hydrocortisone: 503 +/- 6.1 mL; preterm without hydrocortisone: 510 +/- 4.9 mL), and cerebrospinal fluid (preterm with hydrocortisone: 227 +/- 7.4 mL; preterm without hydrocortisone: 224 +/- 6.0 mL), compared with untreated infants. The hippocampal volumes were similar in the 2 groups (preterm with hydrocortisone: 5.92 +/- 0.15 mL; preterm without hydrocortisone: 5.81 +/- 0.12 mL). The WISC-R score assessments were within the normal range for both groups, with no difference between the groups (preterm with hydrocortisone: 100.8 +/- 13; preterm without hydrocortisone: 98.6 +/- 12.3). CONCLUSIONS: Prematurity is associated with mild brain structural differences that persist at 8 years of age, with associated lower scores in neurocognitive assessments. The data suggest that perinatal hydrocortisone given at the described dosage has no long-term effects on either neurostructural brain development or neurocognitive outcomes.

Anti-Inflammatory Agents↗

PubMed2004

View-independent coding of face identity in frontal and temporal cortices is modulated by familiarity: an event-related fMRI study.

Face recognition is a unique visual skill enabling us to recognize a large number of person identities, despite many differences in the visual image from one exposure to another due to changes in viewpoint, illumination, or simply passage of time. Previous familiarity with a face may facilitate recognition when visual changes are important. Using event-related fMRI in 13 healthy observers, we studied the brain systems involved in extracting face identity independent of modifications in visual appearance during a repetition priming paradigm in which two different photographs of the same face (either famous or unfamiliar) were repeated at varying delays. We found that functionally defined face-selective areas in the lateral fusiform cortex showed no repetition effects for faces across changes in image views, irrespective of pre-existing familiarity, suggesting that face representations formed in this region do not generalize across different visual images, even for well-known faces. Repetition of different but easily recognizable views of an unfamiliar face produced selective repetition decreases in a medial portion of the right fusiform gyrus, whereas distinct views of a famous face produced repetition decreases in left middle temporal and left inferior frontal cortex selectively, but no decreases in fusiform cortex. These findings reveal that different views of the same familiar face may not be integrated within a single representation at initial perceptual stages subserved by the fusiform face areas, but rather involve later processing stages where more abstract identity information is accessed.

Adult↗

PubMed2004

FMRI evidence for activation of multiple cortical regions in the primary auditory cortex of deaf subjects users of multichannel cochlear implants.

To investigate the activation of the auditory cortex by fMRI, three deaf subjects users of the Ineraid cochlear implant participated in our study. Possible interference between fMRI acquisition and the implanted electrodes was controlled and safe experimental conditions were obtained. For each subject, electrical stimuli were applied on different intracochlear electrodes, in monopolar mode. Stimulation of each electrode was actually producing auditory sensations of different pitches, as demonstrated by psychophysical pitch-ranking measurements in the same subjects. Because deaf subjects did not hear scanner noise, the data were collected in 'silent background' conditions, i.e. as a result of pure auditory sensations. Functional maps showed activation of the primary auditory cortex, predominantly in the left hemisphere. Stimulation of each different intracochlear electrode revealed different clusters of activation. After cluster grouping, at least three regions have been identified in the auditory cortex of each subject, and comparisons with previous architectonic and functional studies are proposed. However, a tonotopic organization could not be clearly identified within each region. These arguments, obtained without interference with unwanted scanner noise, plead in favor of a functional subdivision of the primary auditory cortex into multiple cortical regions in cochlear implant users.

Adult↗

PubMed2004

Transient crossed aphasia evidenced by functional brain imagery.

Crossed aphasia refers to language deficits induced by unilateral right hemisphere injuries in right-handed people who had no previous history of brain damage. One of the intriguing questions concerning crossed aphasia is the atypical language representation in the brain. In this respect, fMRI is a valuable tool for understanding the neural basis of crossed aphasia. Here, we used neuropsychological and fMRI language tasks in a right-handed subject who presented a crossed aphasia due to a right frontal meningioma. fMRI maps from two language tasks showed bilateral patterns of activation. In the light of previous studies reporting much frequent bilateral than exclusive right hemisphere representations, we hypothesise that some crossed aphasia cases could occur in subjects with bilateral language representation.

Aphasia↗

PubMed2004

Tactile awareness and limb position in neglect: functional magnetic resonance imaging.

We studied a patient with right parietal damage for whom tactile stimuli on the right/ipsilesional hand (projecting to the intact left hemisphere) were extinguished from awareness during double simultaneous stimulation, when his right hand was positioned in the left/contralesional space. This demonstrates the role of an egocentric spatial reference frame in attention that can determine awareness of stimuli despite intact sensory pathways. Using functional magnetic resonance imaging to elucidate the neural correlates of such perceptual extinction, we found that limb position modulated neural responses to tactile stimuli at early cortical stages (SI) in the intact hemisphere. Activity in bilateral middle frontal gyri also was modulated by limb position and may contribute to integrate sensory inputs into a supramodal, egocentric representation of space.

Aged↗

PubMed2004

Variability of fMRI activation during a phonological and semantic language task in healthy subjects.

Assessing inter-individual variability of functional activations is of practical importance in the use of functional magnetic resonance imaging (fMRI) in a clinical context. In this fMRI study we addressed this issue in 30 right-handed, healthy subjects using rhyme detection (phonologic) and semantic categorization tasks. Significant activations, found mainly in the left hemisphere, concerned the inferior frontal gyrus, the superior/middle temporal gyri, the prefrontal cortex, the inferior parietal lobe, the superior parietal lobule/superior occipital gyrus, the pre-central gyrus, and the supplementary motor area. Intensity/spatial analysis comparing activations in both tasks revealed an increased involvement of frontal regions in the semantic task and of temporo-parietal regions in the phonologic task. The frequency of activation analyzed in nine regional subdivisions revealed a high inter-subject variability but showed that the most frequently activated regions were the inferior frontal gyrus and the prefrontal cortex. Laterality indices, strongly lateralizing in both tasks, were slightly higher in the semantic (0.76 +/- 0.19) than the phonologic task (0.66 +/- 0.27). Frontal dominance indices (a measure of frontal vs. posterior left hemisphere dominance) indicated more robust frontal activations in the semantic than the phonologic task. Our study allowed the characterization of the most frequently involved foci in two language tasks and showed that the combination of these tasks constitutes a suitable tool for determining language lateralization and for mapping major language areas.

Adult↗

PubMed2004

Combination of event-related fMRI and diffusion tensor imaging in an infant with perinatal stroke.

Focal ischemic brain injury, or stroke, is an important cause of later handicap in children. Early assessment of structure-function relationships after such injury will provide insight into clinico-anatomic correlation and potentially guide early intervention strategies. We used combined functional MRI (fMRI) with diffusion tensor imaging (DTI) in a 3-month-old infant to explore the structure-function relationship after unilateral perinatal stroke that involved the visual pathways. With visual stimuli, fMRI showed a negative BOLD activation in the visual cortex of the intact right hemisphere, principally in the anterior part, and no activation in the injured hemisphere. The functional activation in the intact hemisphere correlated clearly with the fiber tract of the optic radiation visualized with DTI. DTI confirmed the absence of the optic radiation in the damaged left hemisphere. In addition, event-related fMRI (ER-fMRI) experiments were performed to define the characteristics of the BOLD response. The shape is that of an inverted gamma function (similar to a negative mirror image of the known positive adult BOLD response). The maximum decrease was reached at 5-7 s with signal changes of -1.7 +/- 0.4%.Thus, this report describes for the first time the combined use of DTI and event-related fMRI in an infant and provides insight into the localization of the fMRI visual response in the young infant and the characteristics of the BOLD response.

Asphyxia Neonatorum↗

PubMed2003

Inflow effect correction in fast gradient-echo perfusion imaging.

The purposes of this study were to assess the extent of the inflow effect on signal intensity (SI) for fast gradient-recalled-echo (GRE) sequences used to observe first-pass perfusion, and to develop and validate a correction method for this effect. A phantom experiment with a flow apparatus was performed to determine SI as a function of Gd-DTPA concentration for various velocities. Subsequently a flow-sensitive calibration method was developed, and validated on bolus injections into an open-circuit flow apparatus and in vivo. It is shown that calibration methods based on static phantoms are not appropriate for accurate signal-to-concentration conversion in images affected by high flow. The flow-corrected calibration method presented here can be used to improve the accuracy and robustness of the arterial input function (AIF) determination for tissue perfusion quantification using MRI and contrast media.

Blood Flow Velocity↗

PubMed2003

Brain activation using triggered event-related fMRI.

EEG-triggered fMRI provides a method for localizing the sources of brain electrical activity, such as epileptic discharges. Extending single-image acquisitions, following an event on the EEG, into triggered image series acquisitions may allow BOLD time courses to be obtained, such as those observed in event-related (ER) fMRI experiments. However, in contrast to the standard ER-fMRI, triggered image series are greatly affected by magnetization non-steady-state effects. The purpose of this paper is to show that the BOLD responses can be recovered using subtraction between two triggered image series having different functional contrasts. In order to evaluate this technique, a comparison with standard ER-fMRI using motor cortex activation task was made in 5 volunteers. We conclude that this can be a useful technique for studying brain activation associated with irregularly appearing stimuli.

Attention↗

PubMed2003

[New brain imaging techniques].

Neuroimaging technologies have improved neurology and neurosurgery by providing tools to look inside the brain and investigate its functions and diseases. As for any tool, the users should know the basics of each technique and be aware about their uses and limitations. Here we review these new techniques and illustrate their use with examples from studies at the University Hospital in Geneva. From all the techniques, MRI (Magnetic Resonance Imagery) has the highest spatial resolution. Taking advantage of the magnetic properties of the hydrogen nucleus, it is possible to reach a sub-millimeter resolution in 3D. When MRI images are digitized, they can be treated to perform re-slicing, segmentation and 3D reconstruction of cortical surfaces, as well as to measure anatomical structures (volumetry). Functional MRI (fMRI) is based on blood oxygenation changes when a task is performed or when epileptic activity occurred. Then it can be used to non-invasively show for example language, motor or epileptic network activation. Electromagnetic imaging techniques, based on EEG and MEG, have the power to localize in 3D the electrical activity of the brain with millisecond temporal resolution and then to follow the temporal activation of neuronal networks. These techniques use mathematical models and algorithms to compute 3D tomography from 2D recordings on the scalp. In the case of epilepsy, EEG allows epileptic foci identification among propagation sites when it is recorded with a sufficient number of electrodes (> 100) and when realistic head models are used. The functional imaging techniques from nuclear medicine (PET and SPECT) have become very useful in neuroscience to explore cerebral changes associated with neuronal pathologies as well as cognitive and sensory tasks. Many efforts have been made to develop new cameras and models to increase the range of research and clinical applications. Co-registration of structural and functional images allows us to add functional information to a structural deficit, or conversely to better interpret functional images such as PET, SPECT and EEG in terms of specific anatomy. In the case of SPECT and fMRI, substraction between ictal and interictal exams points out areas involved in epileptic processes.

Brain Diseases↗