Biomedical subjects

B Mazoyer

Publications and source records attributed to B Mazoyer.

At least 37 records · Page 2Linked to original sources

PubMed2000

Altered hemispheric functional dominance during word generation in negative schizophrenia.

Functional brain imaging studies have reported decreased frontal activations in schizophrenia, but hemispheric dominance for language has rarely been assessed. To investigate regional activation and lateralization during word production, we determined normalized regional cerebral blood flow (rCBF) variations with positron emission tomography (PET) and H2(15)O (water labeled with the isotope oxygen 15) in 14 negative schizophrenia patients and 14 volunteers. Subjects were scanned during two trials of three conditions: rest, vocalized verbal fluency, and spontaneous word production. Images were analyzed using an anatomical volumes of interest method, and the two groups' changes were compared, using rest as a baseline. Differences in the lateralization of changes were detected in homologous frontal and inferior parietal regions. The lateralization effects in patients arose from lower activations in the left frontal regions, abnormal right inferior frontal activations, and weaker right inferior parietal deactivation, during the word production tasks. The right hemisphere changes correlated negatively with the performance in verbal fluency. Thus in negative schizophrenia patients, while the activations were less focused on the left hemisphere regions usually engaged in word generation, rCBF changes in the right hemisphere might reflect a compensatory functional pattern.

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PubMed2000

Functional anatomy of high-resolution visual mental imagery.

This study had two purposes. First, in order to address the controversy regarding activation of the primary visual area (PVA) during visual mental imagery, regional cerebral blood flow (rCBF) was recorded while subjects performed a task that required high-resolution visual mental imagery. Second, in order to discover whether verbal descriptions can engage visual mechanisms during imagery in the same way as visual stimuli, subjects memorized 3D scenes that were visually presented or were based on a verbal description. Comparison of the results from the imagery conditions to a non-imagery baseline condition revealed no activation in PVA for imagery based on a verbal description and a significant decrease of rCBF in this region for imagery based on visual learning. The pattern of activation in other regions was very similar in the two conditions, including parietal, midbrain, cerebellar, prefrontal, left insular, and right inferior, temporal regions. These results provide strong evidence that imagery based on verbal descriptions can recruit regions known to be engaged in high-order visual processing.

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PubMed2000

Shifting from the perceptual brain to the logical brain: the neural impact of cognitive inhibition training.

What happens in the human brain when the mind has to inhibit a perceptual process in order to activate a logical reasoning process? Here, we use functional imaging to show the networks of brain areas involved in a deductive logic task performed twice by the same subjects, first with a perceptual bias and then with a logical response following bias-inhibition training. The main finding is a striking shift in the cortical anatomy of reasoning from the posterior part of the brain (the ventral and dorsal pathways) to a left-prefrontal network including the middle-frontal gyrus, Broca's area, the anterior insula, and the pre-SMA. This result indicates that such brain shifting is an essential element for human access to logical thinking.

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PubMed1999

The cortical serotonin2 receptors studied with positron-emission tomography and [18F]-setoperone during depressive illness and antidepressant treatment with clomipramine.

BACKGROUND: Changes in serotonin (5-HT)2 receptor densities were reported in depression by postmortem studies and following treatment with tricyclic antidepressants in animal studies. Here, 5-HT2 receptors were studied in vivo in depressed patients. METHODS: Cortical 5-HT2 receptors were investigated prospectively using positron-emission tomography and [18F]-setoperone in 7 depressed patients, before and after at least 3 weeks of clomipramine (CMI), 150 mg daily. They were compared to 7 age-matched controls. RESULTS: There was no significant difference between the untreated patients and the controls, except in the frontal region, where the [18F]-setoperone specific binding was slightly lower in patients. After CMI treatment, depression scores significantly improved and [18F]-setoperone specific binding decreased in cortical regions, suggesting receptor occupancy and/or receptor regulation, by CMI; however, no clinical score correlated with the 5-HT2 receptor measurements either in the untreated or in the treated conditions. CONCLUSIONS: These data substantiate the view that tricyclic antidepressants such as clomipramine significantly interact with cortical 5-HT2 serotoninergic receptors in actual therapeutic situations.

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PubMed1999

B-SPID: an object-relational database architecture to store, retrieve, and manipulate neuroimaging data.

We propose a hardware and software architecture to respond to crucial problems in the neuroimaging field: storage, retrieval, and processing of large datasets. The B-SPID project, here discussed, concerns the processing of neuroimages and attached components stored in an object-relational multimedia database management system (DBMS). Advanced bioinformation concepts are exploited in this project such as large scale data storage, high level graphical user interfaces and 3D graphical processing and display of data. Our database implementation is based on standard programming components, runs on several UNIX platforms and is written to be evolutive. Queries on this database are designed to obtain and display from neuroimaging data several types of results (pictures, text, or 3D graphical shapes) on heterogeneous systems.

Brain Mapping↗

PubMed1999

PET study of the human foveal fixation system.

Positron emission tomography (PET) was used to investigate the functional anatomy of the foveal fixation system in 10 subjects scanned under three different conditions: at rest (REST), during the fixation of a central point (FIX), and while fixating the same foveal target during the presentation of peripheral visual distractors (DIS). Compared with the REST condition, both FIX and DIS tasks activated a common set of cortical areas. First, in addition to the involvement of the occipital visual cortex, both the frontal eye field (FEF) and the intraparietal sulcus (IPS) were bilaterally activated. Right frontal activation was also found in the dorsolateral prefrontal cortex, the inferior part of the precentral gyrus, and the inferior frontal gyrus. These results suggest that both FEF and IPS may constitute the main cortical regions subserving bilaterally the foveal fixation system in humans. The remaining right frontal activations may be considered as part of the anterior attentional network, supporting a role for the right frontal lobe in the allocation of the attentional mechanisms. Compared with the FIX condition, the DIS task also revealed the perceptual and cognitive processes related to the presence of peripheral visual distractors during foveal fixation. In addition to a bilateral activation of the V5/MT motion-sensitive area, a right FEF-IPS network was activated which may correspond to the engagement of the visuospatial attention. Finally, normalized regional cerebral blood flow (NrCBF) decreases were also observed during both DIS and FIX condition performance. Such NrCBF decreases were centered in the superior and middle temporal gyri, the prefrontal cortex, and the precuneus and the posterior retrosplenial part of the cingulate gyrus.

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PubMed1999

FMRI and PET of self-paced finger movement: comparison of intersubject stereotaxic averaged data.

We compared the intersubject-averaged functional anatomy of self-paced right index finger movement as revealed by (15)O water positron emission tomography (PET) and blood oxygen level-dependent functional magnetic resonance imaging (FMRI) at 1.5 T. Image data sets were acquired with both techniques on a group of eight subjects, spatially normalized in the stereotaxic space and subsequently processed in order to get identical smoothness and degrees of freedom. Intersubject-averaged PET and FMRI activation maps were found congruent in the left primary sensorimotor area (PSM), bilateral supplementary motor area, bilateral supra marginalis gyri, left operculum, left inferior parietal lobule, right middle frontal gyrus, and right cerebellum. In those regions the mean distance between PET and FMRI local maxima was 7.4 mm. FMRI detected additional activations in the right precentral gyrus, right rolandic operculum, right inferior parietal lobule, and bilateral insula, whereas PET demonstrated a higher detection sensitivity at the deep nuclei level. PET and FMRI percentage signal variations were found linearly related by a factor around 10, both within the PSM and across a set of distributed local extrema. However, in most cases, FMRI was more sensitive than PET, as assessed by t values. Finally the pattern of deactivations was markedly dissimilar between the two techniques, possibly due to differences in the "Rest" control task.

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PubMed1999

Neuroanatomical correlates of visually evoked sexual arousal in human males.

Brain areas activated in human male sexual behavior have not been characterized precisely. For the first time, positron emission tomography (PET) was used to identify the brain areas activated in healthy males experiencing visually evoked sexual arousal. Eight male subjects underwent six measurements of regional brain activity following the administration of [15O]H2O as they viewed three categories of film clips: sexually explicit clips, emotionally neutral control clips, and humorous control clips inducing positive but nonsexual emotions. Statistical Parametric Mapping was used to identify brain regions demonstrating an increased activity associated with the sexual response to the visual stimulus. Visually evoked sexual arousal was characterized by a threefold pattern of activation: the bilateral activation of the inferior temporal cortex, a visual association area; the activation of the right insula and right inferior frontal cortex, which are two paralimbic areas relating highly processed sensory information with motivational states; and the activation of the left anterior cingulate cortex, another paralimbic area known to control autonomic and neuroendocrine functions. Activation of some of these areas was positively correlated with plasma testosterone levels. Although this study should be considered preliminary, it identified brain regions whose activation was correlated with visually evoked sexual arousal in males.

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PubMed1999

A review of database management systems suitable for neuroimaging.

This study comprises a technical assessment of Database Management Systems (DBMS), which may be of use in the analysis of data obtained from human brain mapping procedures. Due to the large expansion of the neuroimaging field, the use of specialized database software to store and process neuroimages and their attached components is inevitable. The advent of multiple software products, a wealth of technical terms and a wide variety of other applications make the choice of a suitable program sometimes difficult. Through the inclusion of some basic and pertinent criteria (e.g., performance, ease of opening, standardization and portability), we present a descriptive comparison of 12 DBMSs currently available in the commercial and public domain. We have compared and tested three main architecture models which are currently available and assessed their potential applications for imaging purposes: relational, object-oriented, and hybrid. The findings of our study demonstrated that the Illustra software was the best suited for a neuroimaging environment because of its intrinsic ability to handle complex and large objects, such as 3D volumes or geometric structures.

Brain Mapping↗

PubMed1998

Functional connectivity in depressive, obsessive-compulsive, and schizophrenic disorders: an explorative correlational analysis of regional cerebral metabolism.

In order to investigate the changes in functional relationships between brain regions in three psychiatric disorders, an exploratory statistical analysis of the regional cerebral metabolic rates for glucose (rCMRglu) obtained with positron emission tomography (PET) was performed. Correlations between various rCMRglu were computed in control, depressive, obsessive-compulsive, and schizophrenic groups to determine whether alterations of the correlation pattern were found in the psychiatric groups. The absence of correlation between left and right frontal lobes was common to the three psychiatric groups studied. Depressive patients recovered a better frontal interhemispheric coupling after successful treatment and the alterations in the depressed state also involved the relation between the right temporal cortex and the right thalamus. Obsessive-compulsive patients had not only lateral frontal dysfunction but also alterations in the functional relationships between cortex and thalami. In schizophrenic patients, the modifications of regional cerebral metabolic correlations involved both anterior and posterior cortical regions. Thus, although the relationship between left and right frontal lobes was altered in three psychiatric disorders, the pattern of functional connectivity between frontal regions, posterior cortical and subcortical regions differed depending on the diagnostic group.

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PubMed1998

Cortical anatomy of mental imagery of concrete nouns based on their dictionary definition.

The functional anatomy of the interactions between spoken language and visual mental imagery was investigated with PET in eight normal volunteers during a series of three conditions: listening to concrete word definitions and generating their mental images (CONC), listening to abstract word definitions (ABST) and silent REST. The CONC task specifically elicited activations of the bilateral inferior temporal gyri, of the left premotor and left prefrontal regions, while activations in the bilateral superior temporal gyri were smaller than during the ABST task, during which an additional activation of the anterior part of the right middle temporal gyrus was observed. No activation of the occipital areas was observed during the CONC task when compared either to the REST or to the ABST task. The present study demonstrates that a network including part of the bilateral ventral stream and the frontal working memory areas is recruited when mental imagery of concrete words is performed on the basis of continuous spoken language.

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PubMed1998

Left planum temporale surface correlates with functional dominance during story listening.

The relationship between anatomical asymmetry of the planum temporale (PT) and functional lateralization for language comprehension was studied in 14 normal volunteers, including five left-handers (LH). PT surfaces and asymmetry were measured in each subject using structural MRI, while functional lateralization was assessed on individual regional cerebral blood flow (rCBF) difference images of a PET-H2(15)O activation protocol in which a story listening condition was contrasted with a control state. Significant positive correlations were found between the left PT surface and the amount of NrCBF increase during the story listening in the left superior temporal gyrus as well as with the left-right activation index in the superior temporal and the temporal pole. Functional imaging data were correlated neither with the right PT surface nor with the right-left PT surface asymmetry index. However the latter index was correlated with handedness scores. The present results indicate that the size of the left PT is the relevant anatomical landmark for language dominance, and demonstrate that anatomical asymmetries are part of the functional variability for language.

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PubMed1998

Anatomical congruence of metabolic and electromagnetic activation signals during a self-paced motor task: a combined PET-MEG study.

We have investigated the degree of spatial correlation between the cerebral blood flow variations measured by positron emission tomography (PET) and the electromagnetic sources as measured by magnetoencephalography (MEG) in five subjects while performing a self-paced right index finger tapping task. Data were processed independently for each technique using both single-case and intersubject analysis. PET and MEG were coregistered with anatomical magnetic resonance images for each subject. Both extension and flexion motor-related fields were extracted from the MEG signal. Using the single dipole model we identified the motor evoked field 1 (MEF1) in all subjects and the motor field (MF) in three subjects. Individual and intersubject averaged PET data showed consistent contralateral primary sensorimotor (PSM) hand area and bilateral supplementary motor area activation. MEG individual and intersubject averaged results demonstrated that both MEF1 and MF dipoles were localized within the PSM PET activated area. Individual PSM mass center to dipole distance was 12 and 15.3 mm on average for the MEF1 and the MF component, respectively. For the same components, the intersubject averaged analysis shows distances between the PET Z-score maximum and the dipole locations of 6.3 and 15.0 mm, respectively. These results show that PET and MEG MEF1 activation signals spatially coincide within instrumental, registration, and modeling errors.

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PubMed1998

Functional anatomy of dominance for speech comprehension in left handers vs right handers.

In order to study the functional anatomy of hemispheric dominance for language comprehension we compared the patterns of activations and deactivations with PET and H(2)15O during a story-listening task in two groups of normal volunteers selected on the basis of their handedness. The reference task was a silent rest. The results showed asymmetrical temporal activations favoring the left hemisphere in right handers (RH) together with Broca's area and medial frontal activations. A rightward lateralization of deactivations located in the parietal and inferior temporal gyrus was also observed. In left handers (LH) the temporal activations were more symmetrical as were the parietal and inferior frontal deactivations. Broca's area and medial frontal gyrus activations were present in LH. The direct comparison of RH and LH activations revealed larger activations in the left superior temporal, in particular in the left planum temporale and temporal pole of RH, while LH activated an additional right middle temporal region. Individual analysis of LH differences images superimposed on individual MRI planes demonstrated an important variability of functional dominance, with two LH leftward lateralized, two symmetrical, and one showing a rightward lateralization of temporal activations. There was no relationship between functional dominance and handedness scores. These results are in accordance with data from aphasiology that suggest a greater participation of the right hemisphere in language processing in LH. In addition, the presence of bilateral deactivations of the dorsal route could support the assumption that LH ambilaterality concerns, in addition to language, other cognitive functions such as visuospatial processing.

Attention↗

PubMed1998

Reopening the mental imagery debate: lessons from functional anatomy.

Over the past few years, the neural bases of mental imagery have been both a topic of intense debate and a domain of extensive investigations using either PET or fMRI that have provided new insights into the cortical anatomy of this cognitive function. Several studies have in fact demonstrated that there exist types of mental imagery that do not rely on primary/early visual areas, whereas a consensus now exists on the validity of the dorsal/ventral-route model in the imagery domain. More importantly, these studies have provided evidence that, in addition to higher order visual areas, mental imagery shares common brain areas with other major cognitive functions, such as language, memory, and movement, depending on the nature of the imagery task. This body of recent results indicates that there is no unique mental imagery cortical network; rather, it reflects the high degree of interaction between mental imagery and other cognitive functions.

Brain Mapping↗

PubMed1998

Impaired cerebral glucose metabolism in myotonic dystrophy: a triplet-size dependent phenomenon.

Myotonic dystrophy (DM) is caused by an expansion of a CTG triplet repeat sequence in the 3'-noncoding region of a protein kinase gene, yet the mechanism by which the triplet repeat expansion causes disease remains unknown. Impaired glucose penetration into brain tissues has been described in DM patients and is a phenomenon that remains unexplained. The present study shows that altered brain glucose metabolism is triplet repeat dependent. We studied brain glucose metabolism (CMRGlu, mumol/100 g/min) by the use of positron emission tomography and 18F-fluoro-2-deoxy-D-glucose in 11 ambulatory non-obese DM patients and in 11 age and sex matched healthy subjects. All subjects underwent a glucose tolerance test with plasma insulin determinations. The expansion of CTG triplet repeats was analyzed in patients with the probe cDNA25 after EcoRI digestion. As compared to controls, in DM patients, the CMRGlu was significantly decreased (26.26 +/- 5.05 vs. 33.43 +/- 2.18, mumol/100 g/min, P = 0.004), and after oral glucose loading, plasma insulin levels were significantly higher and plasma glucose levels remained unchanged (respectively, F = 11.21, P = 0.004 and F = 0.20, P = 0.66). Subsequently, the glucose/insulin ratio was significantly lower in DM patients (F = 6.25, P = 0.02). The length of the expansion of the CTG repeats correlated negatively with the CMRGlu (r2 = 0.63, P = 0.003) and positively with the area under the curve for insulin changes over time after oral glucose (r2 = 0.49, P = 0.016). We conclude that, in DM patients, the brain metabolism of glucose is impaired in a repeat dependent manner.

Activities of Daily Living↗

PubMed1997

Mental navigation along memorized routes activates the hippocampus, precuneus, and insula.

Positron emission tomography was used to investigate the functional anatomy of mental simulation of routes (MSR) in five normal volunteers. Normalized regional cerebral blood flow was measured while subjects mentally navigated between landmarks of a route which had been previously learned by actual navigation. This task was contrasted with both static visual imagery of landmarks (VIL) and silent Rest. MSR appears to be subserved by two distinct networks: a non-specific memory network including the posterior and middle parts of the hippocampal regions, the dorsolateral prefrontal cortex and the posterior cingulum, and a specific mental navigation network, comprising the left precuneus, insula and medial part of the hippocampal regions.

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PubMed1997

Functional anatomy of human auditory attention studied with PET.

Positron emission tomography was used to investigate the functional anatomy of selective auditory attention in 17 right-handed male volunteers who submitted to different tasks: silent rest (REST) listening to frequent low- or rare high-pitched tones (LIS) delivered randomly to the right or the left ear, selective auditory attention where subjects had to attend to deviants in one ear, right (ATTR) or left (ATTL). Six subjects had the series REST, LIS, ATTR twice, eight subjects the series REST, LIS, ATTL, and the last three subjects the sereis REST, ATTR, ATTL. Event-related potentials were simultaneously recorded with PET and showed significant task and electrode site effects on the N100 amplitude. When compared to REST, LIS elicited bilateral temporal activations of the Heschl's gyri and the planum temporale, with a significant rightward asymmetry, and of the posterior part of the superior temporal gyrus. Significant right precentral and anterior cingulate gyri normalized regional cerebral blood flow increases were observed in the frontal lobe. Both the ATTR and the ATTL conditions, compared to LIS, activated the supplementary motor area, bilateral precentral, and left postcentral cortices without any temporal cortex activation. In addition, the ATTL condition resulted in a right prefrontal cortex activation. Pooling the 14 subjects revealed an asymmetry in the superior temporal gyrus favoring the cortex contralateral to the attended ear. Two major networks seem thus to be involved during selective auditory attention: (1) a local temporal network, on which selective attention produces a modulation of the functional lateralization, and (2) a frontal network that could mediate the temporal cortex modulation by attention.

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