Biomedical subjects

F Liégeois

Publications and source records attributed to F Liégeois.

6 recordsLinked to original sources

PubMed2004

Language reorganization in children with early-onset lesions of the left hemisphere: an fMRI study.

It is widely assumed that following extensive damage to the left hemisphere sustained in early childhood, language functions are likely to reorganize and develop in the right hemisphere, especially if the lesion affects the classical Broca's or Wernicke's language areas. In the present study, functional MRI (fMRI) was used to examine language lateralization in 10 children and adolescents with intractable epilepsy who sustained an early lesion in the left hemisphere. Lesions were adjacent to or within anterior language cortex in five patients, while they were remote from both Broca's and Wernicke's areas in the remainder. A lateralization index was calculated on the basis of the number of voxels activated in the left and right inferior frontal gyri when performing a covert verb generation task. Only two patients were right-handed, suggesting a high incidence of functional reorganization for motor control in the remaining patients. Five out of 10 showed bilateral or right language lateralization, but lateralization could not be inferred from the proximity of lesions to classical language areas on an individual basis. Lesions in or near Broca's area were not associated with inter-hemispheric language reorganization in four out of five cases, but with perilesional activation within the damaged left hemisphere. Paradoxically, lesions remote from the classical language areas were associated with non-left language lateralization in four out of five cases. Finally, handedness, age at onset of chronic seizures, and site of EEG abnormality also showed no obvious association with language lateralization. In conclusion, it is difficult to infer intra- versus inter-hemispheric language reorganization on the basis of clinical observations in the presence of early pathology to the left hemisphere.

Adolescent↗

PubMed2002

A direct test for lateralization of language activation using fMRI: comparison with invasive assessments in children with epilepsy.

This study introduces a direct method of assessing cerebral lateralization for language based on fMRI activation. The method, derived from a voxel-based morphometry study by C. H. Salmond et al. (2000, Hum. Brain Mapping 11, 223-232), bases lateralization on the direct statistical comparison of the magnitude of task-induced activation in homotopic regions of the two hemispheres. Lateralization results obtained with this direct method were compared to those obtained with a widely used method which involves the calculation of a laterality index (LI) based on the number of significantly activated voxels in the inferior frontal gyrus of each hemisphere. In order to compare the validity of the two methods, a covert verb-generation task was performed by eight children with epilepsy whose language lateralization was examined using invasive techniques. Lateralization results derived from fMRI activation showed that the calculation of a LI presented some limitations. Importantly, the LI value was dependent on the activation threshold chosen to calculate that LI. As a consequence, the correlation between the LI and the invasive methods could vary with the chosen threshold. By contrast, the proposed direct method gave some indication of the reliability of the lateralization and provided results that, in all eight children, were consistent with those obtained using invasive techniques. It is suggested that the direct method could be used in future fMRI studies to establish hemispheric lateralization for cognitive functions.

Adolescent↗

PubMed2000

When does inter-hemispheric integration of visual events emerge in infancy? A developmental study on 19- to 28-month-old infants.

Simultaneous attention in the two visual fields and interhemispheric integration of visual information was studied in 19-23 and 24-28-month-old infants. The stimuli were schematic faces within which the pair of eyes was made of either two identical (two circles or two triangles) or two different eyes (triangle-circle, circle-triangle). The faces were presented either in one visual hemifield, on the right or left side of a central fixation point (unilateral presentation), or across the two visual hemifields (bilateral presentation), with one eye of the stimulus on each side of the fixation point. The task was an operant conditioning task where the children had to decide whether the shapes of the two eyes were identical or not. The results show that even the younger subjects were able to perform the task when presented in the unilateral presentation condition, whereas only children aged 24 months and older could learn the task when presented in the bilateral condition. It is concluded that simultaneous attention to the two visual fields and inter-hemispheric co-ordination of visual information emerge very late in development at about the age of 24 months.

Age Factors↗

PubMed1998

[Spontaneous rupture of the bladder. Apropos of 2 cases with an unusual presentation].

Spontaneous bladder ruptures is the accepted term of bladder rupture not associated with trauma. This rare condition occurs when an obstacle to urinary outflow is associated with a diseased bladder wall. The diagnosis is usually made on the retrograde cystogram. We report two cases of atypical spontaneous bladder rupture with intravesical herniation of the small bowel. The diagnosis was not suspected clinically but was made on CT and MRI.

Ascites↗

PubMed1997

What does the haptic modality do during cognitive activities on letter shapes? A study with left- and right-handers.

This study was undertaken to analyze intermanual (interhemispheric) transfer in left and right handed subject and to assess how information was extracted during finger scanning of letter shape at the different levels of letter processing: shape recognition during a physical matching task, letter recognition in a verbal "meaning" matching task and letter naming. The dichhaptic procedure was used to study interhemispheric relations. It was hypothesized that cognitive activities have a feed-forward effect on the exploration of shapes, and that the performance is related to the nature of the task and to handedness. The exploratory strategies of the two types of handedness were also analyzed. The results showed that response latencies were generally similar for left- and right-handed subjects, but accuracy was better for left than right handers in "verbal" matching with the same overall exploratory strategies. In physical matching, left- and right-handed subjects performed equally but used different exploratory strategies. The naming task was very difficult for both groups but failed to discriminate their on accuracy, response latency, and exploratory strategy. The results are discussed with reference to the different exploratory strategies used and the interhemispheric interaction at work in different cognitive processes.

Adult↗

PubMed1997

Simultaneous attention in the two visual hemifields and interhemispheric integration: a developmental study on 20- to 26-month-old infants.

Simultaneous attention in the two visual fields was studied in 20-, 24- and 26-month-old infants. The stimuli were pairs of simple geometrical elements. The two elements were presented simultaneously either to one visual hemifield (unilateral presentation), on the right or left side of a central fixation point, or across the two visual fields (bilateral presentation), with one component on each side of the fixation point. The task was an operant conditioning task with two conditions. In the Position condition, subjects had to decide whether the two components were horizontally aligned or not. In the Shape condition, they had to decide whether the shapes of the two components were identical or not. The results show that even the youngest group of subjects was able to reach the learning criterion in the unilateral presentation condition, whereas reaching the learning criterion in the bilateral condition becomes possible only at the age of about 24 months. No differences in the subjects' performances were found to exist between the Position and Shape conditions. It is concluded that simultaneous attention to the two visual fields and the production of a unified response emerge very late in development at about the age of 24 months.

Attention↗