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Biomedical subjects

C Segebarth

Publications and source records attributed to C Segebarth.

At least 19 recordsLinked to original sources
PubMed2002

Central processing of rectal pain in patients with irritable bowel syndrome: an fMRI study.

OBJECTIVES: In healthy subjects, the neural correlates of visceral pain bear much similarity with the correlates of somatic pain. In patients with irritable bowel syndrome, the central nervous system is believed to play a strong modulatory or etiological role in the pathophysiology of the disease. We hypothesize that this role must be reflected in aberrations of central functional responses to noxious visceral stimulation in these patients. To verify this hypothesis, we have induced transient rectal pain in patients and assessed the functional responses of the brain by means of functional magnetic resonance imaging. METHODS: Twelve right-handed patients (11 female) were examined. Functional imaging (1.5 T) was performed following a block paradigm, alternating epochs with and without noxious stimulation of the rectum. Rectal pain was induced by inflating a latex balloon. Whole-brain coverage was achieved by means of echo-planar magnetic resonance acquisition. RESULTS: A strong variability of the individual responses to rectal pain was found in patients with irritable bowel syndrome. Significant activations were found in only two patients, and group analysis did not reveal significant activations. In contrast, all patients exhibited significant deactivations. Group analysis revealed significant deactivations within the right insula, the right amygdala, and the right striatum. CONCLUSIONS: This study reveals aberrant functional responses to noxious rectal stimulation in patients with irritable bowel syndrome. Those results add grounds to the hypothesis that the central nervous system plays a significant role in the pathophysiology of this syndrome.

Adult↗
PubMed2001

How the brain perceives causality: an event-related fMRI study.

Detection of the causal relationships between events is fundamental for understanding the world around us. We report an event-related fMRI study designed to investigate how the human brain processes the perception of mechanical causality. Subjects were presented with mechanically causal events (in which a ball collides with and causes movement of another ball) and non-causal events (in which no contact is made between the balls). There was a significantly higher level of activation of V5/MT/MST bilaterally, the superior temporal sulcus bilaterally and the left intraparietal sulcus to causal relative to non-causal events. Directing attention to the causal nature of the stimuli had no significant effect on the neural processing of the causal events. These results support theories of causality suggesting that the perception of elementary mechanical causality events is automatically processed by the visual system.

Adult↗
PubMed2001

Does perception of biological motion rely on specific brain regions?

Perception of biological motions plays a major adaptive role in identifying, interpreting, and predicting the actions of others. It may therefore be hypothesized that the perception of biological motions is subserved by a specific neural network. Here we used fMRI to verify this hypothesis. In a group of 10 healthy volunteers, we explored the hemodynamic responses to seven types of visual motion displays: drifting random dots, random dot cube, random dot cube with masking elements, upright point-light walker, inverted point-light walker, upright point-light walker display with masking elements, and inverted point-light walker display with masking elements. A gradient in activation was observed in the occipitotemporal junction. The responses to rigid motion were localized posteriorly to those responses elicited by nonrigid motions. Our results demonstrate that in addition to the posterior portion of superior temporal sulcus, the left intraparietal cortex is involved in the perception of nonrigid biological motions.

Adult↗
PubMed2001

Functional MRI assessment of the hemispheric predominance for language in epileptic patients using a simple rhyme detection task.

This study assesses the interest of a simple fMRI rhyme detection paradigm to determine hemispheric predominance for language in epileptic patients. Nineteen patients were examined. The findings derived from the fMRI examinations were compared with those obtained on the same patients using the Wada test, stereotactic intracerebral EEG stimulations and recordings, and/or video-EEG recordings. For the seventeen patients for whom language dominance could be assessed by means of at least one of the latter procedures, the fMRI examination provided concordant results in sixteen. In two patients, the hemispheric predominance for language could only be determined by fMRI. Nine patients underwent surgery subsequent to the fMRI examination. None of them exhibited any aphasic problems following surgery. The rhyme detection task used in the fMRI examination generates robust responses in the language areas, permits easy monitoring of the patient's task performance and can be easily undertaken by the epileptic patients. Thus, this study demonstrates that the fMRI rhyme detection paradigm is particularly well-suited for determining hemispheric language predominance in epileptic candidates for surgery.

Adult↗
PubMed2000

Moving illusory contours activate primary visual cortex: an fMRI study.

Identifying the cortical areas activated by illusory contours provides valuable information on the mechanisms of object perception. We applied functional magnetic resonance imaging to identify the visual areas of the human brain involved in the perception of a moving Kanizsa-type illusory contour. Our results indicate that, in addition to other cortical regions, areas V5 and V1 are activated. Activity in area V1 was particularly prominent.

Adult↗
PubMed1999

Categorical and coordinate spatial relations: fMRI evidence for hemispheric specialization.

Functional magnetic resonance imaging (fMRI) was applied to determine the involvement of the angular gyri in the processing of categorical and coordinate spatial relations. In a categorical task, subjects were asked to judge whether a dot was presented above or below a horizontal line. In a coordinate task, they were asked to judge whether or not the distance between the dot and the bar was within a reference distance. Results showed stronger activation of the left than of the right angular gyrus in the categorical task, and stronger activation, initially, of the right than of the left angular gyrus in the coordinate task. In addition, in the latter task, the involvement of the right angular gyrus decreased with practice while that of the left angular gyrus increased. These results are interpreted in terms of the development of new categorical representations with practice in the coordinate task.

Adult↗
PubMed1999

MRI measurement of the functional blood flow changes in a large superficial vein draining the motor cortex.

In this study, phase-contrast MR techniques are applied in order to measure the blood flow changes induced by a motor task in a large superficial vein draining the motor cortex. The measurements were applied to six healthy volunteers, in motor rest conditions and during performance of a motor task. The latter consisted of sequential finger-to-thumb opposition. The task was actually executed and mentally simulated. Significant blood flow increases were found when changing from from mental simulation to actual execution of the motor task (increases ranging between 1.6 and 10.3 ml/min, i.e. 9% and 45%, respectively) and from resting conditions to actual execution of the motor task (increases ranging between 1.7 and 14.0 ml/min, i.e. 32% and 72%, respectively).

Adult↗
PubMed1999

Necrotic tumor versus brain abscess: importance of amino acids detected at 1H MR spectroscopy--initial results.

PURPOSE: To assess the usefulness of the 0.9-ppm peak from amino acids (-CH3 moieties from valine, leucine, and isoleucine) for the differentiation of brain abscesses and tumors at in vivo hydrogen 1 magnetic resonance (MR) spectroscopy. MATERIALS AND METHODS: Amino acid concentrations were determined in vitro in 13 purulent samples from brain and nonbrain tissues and in nine aseptic fluids from necrotic brain tumors at two-dimensional (2D) 1H MR spectroscopy and liquid chromatography. Thirty-four patients with cystic intracerebral mass lesions (28 tumors, six abscesses) were examined at 1H MR spectroscopy in vivo. RESULTS: Amino acids were identified in vitro in both purulent and aseptic samples. Amino acid concentrations measured in the aseptic fluids at both liquid chromatography and 2D MR spectroscopy were far below the detection threshold of in vivo 1H MR spectroscopy. Quantitative results obtained at 2D MR spectroscopy showed no overlap in the ranges of amino acid concentrations in purulent and aseptic samples. In vivo, the proton spectra obtained with a 136-msec echo time (TE) revealed amino acids (inverted peak at 0.9 ppm) in only the abscesses. CONCLUSION: The detection of amino acid resonance at 0.9 ppm at in vivo 1H MR spectroscopy (136-msec TE) is a promising tool for distinguishing bacterial abscesses and cystic brain tumors.

Adolescent↗
PubMed1996

Possible involvement of primary motor cortex in mentally simulated movement: a functional magnetic resonance imaging study.

The role of the primary motor cortex (M1) during mental simulation of movement is open to debate. In the present study, functional magnetic resonance imaging (fMRI) signals were measured in normal right-handed subjects during actual and mental execution of a finger-to-thumb opposition task with either the right or the left hand. There were no significant differences between the two hands with either execution or simulation. A significant involvement of contralateral M1 (30% of the activity found during execution) was detected in four of six subjects. Premotor cortex (PM) and the rostral part of the posterior SMA were activated bilaterally during motor imagery. These findings support the hypothesis that motor imagery involves virtually all stages of motor control.

Adult↗
PubMed1995

Intracranial gradient-echo and spin-echo functional MR angiography in humans.

PURPOSE: To investigate the predominance of venous signal intensity at 1.5-T gradient-echo (GRE) functional magnetic resonance (MR) imaging of motor activity and to demonstrate the contribution from task-induced changes in flow velocity to the functional MR imaging signal intensity. MATERIALS AND METHODS: Functional MR imaging of motor activity was performed in healthy volunteers. In a first examination, conventional two-dimensional GRE blood oxygenation level-dependent (BOLD) functional MR imaging techniques were used, and the image planes were carefully positioned with respect to the veins that responded to the motor task. In a second examination, two-dimensional spin-echo (SE) techniques were used, and the image planes were oriented axially and measured in a sequential multisection manner. The areas of hyperintensity on functional MR images were eventually processed by means of maximum intensity projection. RESULTS: Functional MR angiograms were obtained in both examinations. The possibility to generate SE functional MR angiograms demonstrates that venous inflow effects may contribute substantially to signal intensity in conventional two-dimensional GRE BOLD functional MR imaging of motor activity. CONCLUSION: Veins have a substantial role in BOLD functional MR imaging of motor activity.

Adult↗
PubMed1994

Functional MRI of the human brain: predominance of signals from extracerebral veins.

This study demonstrates the predominance of extracerebral vascular signals in gradient-echo functional magnetic resonance imaging of motor activity at 1.5 Tesla. The demonstration is based upon a novel experimental approach. Maximum intensity projection images are derived from a large set of contiguous 2D functional MR images, and compared with MR angiograms obtained from the volume covered by the set of functional MR images. The comparison shows that the hyperintensities in the functional MR images cover extensive areas, which can be superimposed with a number of veins in the MR angiograms. These results should trigger a general caution in interpretation of the observations in 1.5 Tesla functional MRI.

Brain↗
PubMed1994

Early MR detection of cortical and subcortical hypoxic-ischemic encephalopathy in full-term-infants.

Four observations illustrate the potential of MR imaging in the early depiction of multiple types of neuropathologic lesions which may coexist in the full-term newborn, upon severe hypoxic-ischemic encephalopathy (HIE). In particular, diffuse, postnatal involvement of cerebral cortex and subcortical white matter (WM) is demonstrated. Cortical hyperintensity on both proton-density- and T1-weighted images is probably related to cellular necrosis which is distributed diffusely or parasagittally. Hyperintense, frontal, subcortical WM edging on proton-density-weighted images results from the increase of water concentration, induced either by infarct or by edema. Diffuse WM areas of low intensity on T1-weighted images and of high intensity on T2-weighted images are presumably related to cytotoxic and/or vasogenic edema, proportional to the underlying damaged tissues. On follow-up MR examinations, several months later, the importance of cortical atrophy and of the myelination delay appeared related to the importance of the lesions detected during the postnatal period.

Brain Ischemia↗
PubMed1994

Three-dimensional reconstruction of the in vivo human diaphragm shape at different lung volumes.

The ability of the diaphragm to generate pressures at different lung volumes (VLs) in humans may be determined by the following factors: 1) its in vivo three-dimensional shape, radius of curvature, and tension according to Laplace law; 2) the relative degree to which it is apposed to the rib cage (i.e., zone of apposition) and lungs (i.e., diaphragm dome); and 3) its length-force properties. To gain more insight into these factors we have reconstructed from nuclear magnetic images the three-dimensional shape of the diaphragm of four normal subjects under supine relaxed conditions at four different VLs: residual volume, functional residual capacity, functional residual capacity plus one-half of the inspiratory capacity, and total lung capacity. Under our experimental conditions the shape of the diaphragm changes substantially in the anteroposterior plane but not in the coronal one. Multivariate regression analysis indicates that the zone of apposition is dependent on both diaphragm shortening and lower rib cage widening with lung inflation, although much more on the first of these two factors. Because of the changes in anteroposterior shape and expansion of the insertional origin at the costal margin with lung inflation, the data therefore suggest that the diaphragm may be more accurately modeled by a "widening piston" (Petroll's model) than a simple "piston in a cylinder" model. A significant portion of the muscular surface is lung apposed, suggesting that diaphragmatic force has radial vectors in the dome and vectors along the body axis in the zone of apposition. The muscular surface area of the diaphragm decreased linearly by approximately 41% with VL from residual volume to total lung capacity. Diaphragmatic fibers may shorten under physiological conditions more than any other skeletal muscle. The large changes in fiber length combined with limited shape changes with lung inflation suggest that the length-twitch force properties of the diaphragm may be the most important factor for the pressure-generating function of this respiratory muscle in response to bilateral phrenic shocks at different VLs.

Diaphragm↗
PubMed1993

MRI in seven cases of Rathke's cleft cyst in infants and children.

Seven MRI observations of presumed Rathke's cleft cysts in infants and children are reported. Age ranged between 6 months and 13 years. Size of the cysts ranged between 4 and 20 mm. While 3 small cysts were detected incidentally, 4 were large enough to cause symptoms secondary to compression of the pituitary gland and suprasellar components. The MRI appearance of the Rathke's cleft cysts varied according to their nature. MRI provides a major contribution to the diagnosis of these lesions; nevertheless, it often remains difficult to differentiate complex Rathke's cleft cysts from cystic craniopharyngiomas. The difficulties related to this differentiation are discussed.

Adolescent↗
PubMed1992

Mechanical implications of in vivo human diaphragm shape.

Using magnetic resonance imaging, we measured the three-dimensional form of the diaphragm in vivo in four supine relaxed subjects at functional residual capacity and calculated its total surface area, the right and left surface areas in the zone of apposition, and the principal radii of curvature as a function of height. The area of apposition comprised 45 +/- 1.5% (SE) of the total surface area of the diaphragm. Available data on the area of the central tendon indicate that a considerable part of the muscular part of the diaphragm is lung apposed. The curvature was linearly related to height over 7 cm of the posterior half of each hemidiaphragm. From the linear portion of this graph and assuming a vertical gradient of transdiaphragmatic pressure of 0.75 cmH2O/cm, we applied the Laplace law and calculated tensions of 54 and 32 g/cm for right and left sides, respectively. We conclude that the shape of at least part of the posterior half of the relaxed human diaphragm in the supine position at functional residual capacity can be explained by the Laplace law, suggesting that both the lung and abdominal contents behave sufficiently as fluids so that they do not impose their shape on the diaphragm. Because diaphragm muscle is partly lung apposed, it is unlikely that the diaphragm functions simply as a piston.

Adult↗