Biomedical subjects

E Paulesu

Publications and source records attributed to E Paulesu.

43 records · Page 3Linked to original sources

PubMed1993

Left and right hemisphere contribution to recovery from neglect after right hemisphere damage--an [18F]FDG pet study of two cases.

A 2-[18F]-Fluoro-2-Deoxy-D-Glucose ([18F]FDG) and positron emission tomography (PET) study was performed in the acute and chronic phase of stroke in one patient with unilateral neglect due to a right hemispheric lesion. In the acute phase, severe neglect, as well as hypometabolism in both the right and in the left unaffected cerebral hemisphere, was demonstrated. At follow-up evaluation the patient showed an almost complete recovery from unilateral neglect. This was associated with a return of left hemisphere metabolism to normal values and partial metabolic recovery in the right hemisphere, where frontal and parietal areas remained functionally impaired. Another patient with an extensive right cerebral ischaemic lesion on CT and severe unilateral neglect was studied by PET in chronic phase. A severe metabolic depression in the left unaffected hemisphere and in the right cerebral areas spared by the lesion, was found. These data suggest that the remission of unilateral neglect might be associated to a functional metabolic recovery in both the undamaged left hemisphere and the unaffected regions of the right hemisphere.

Aged↗

PubMed1993

Investigations of the functional anatomy of attention using the Stroop test.

In two separate experiments positron emission tomography (PET) was used to measure changes in regional cerebral blood flow while normal subjects performed the Stroop colour word interference test, a test of selective attention. In the first experiment performance of the Stroop task was associated with activation of right orbito-frontal and bilateral parietal structures, an unexpected result in view of previously reported findings. In addition, there were highly significant time related focal changes in rCBF. A second experiment was therefore carried out which altered the experimental parameters to replicate an earlier study. In this second experiment focal activation of the right anterior cingulate and right frontal polar cortex occurred during the Stroop task. As in the first experiment significant time effects were again apparent. To determine the functionally related brain systems during the performance of the Stroop task a correlation analysis was carried out in relation to blood flow changes induced by experimental manipulation in the right anterior cingulate. This analysis indicated the engagement of a widespread network of anterior brain regions and reciprocal inhibition of posterior brain regions during the performance of the task. The results provide evidence for the involvement of anterior right hemisphere and medial frontal structures in attentional tasks but also indicate that time effects can confound task specific activations. Furthermore subtle experimental treatment parameters, such as stimulus presentation rate, influence the degree and distribution of observed activations.

Adult↗

PubMed1993

Crossed aphasia: a PET follow up study of two cases.

Two cases of aphasia after right hemispheric stroke in right handed patients are described. The first patient had a severe mixed transcortical aphasia, apraxia and neglect after a lesion involving the right lenticular nucleus and periventricular white matter; aphasia was still present after three months. The second patient had a mild, transient fluent aphasia after a small right hemispheric periventricular lesion. Studies with [18F]FDG and positron emission tomography (PET) showed functional depression extending to the structurally unaffected left hemisphere in both patients in the acute stage. After three months, in the patient with persistent aphasia, metabolism was still reduced in the right hemisphere, with some recovery of hypometabolism on the left, while metabolic values had returned to normal in the patient with full language recovery. A close parallelism between glucose metabolism and clinical course in crossed aphasia is shown, as well as the presence of a functional involvement of the structurally unaffected left hemisphere in the acute stage.

Aged↗

PubMed1992

Relationship between corpus callosum atrophy and cerebral metabolic asymmetries in multiple sclerosis.

Corpus callosum (CC) atrophy by magnetic resonance imaging (MRI) is a common finding in multiple sclerosis (MS). In order to examine the relationship between CC atrophy and cortical brain metabolism, we compared the cerebral metabolic rates for glucose (CMRglc), measured by positron emission tomography (PET), of 8 MS patients with evidence of CC atrophy on midsagittal MRI, 8 MS patients without CC atrophy and 10 healthy controls. Results showed no significant differences in supratentorial CMRglc absolute values between the three groups, although a slight metabolic reduction was observed in both MS groups compared with normal controls. By contrast, only patients with CC atrophy showed greater directional metabolic asymmetry than normals, the left frontal, temporal and parietal association cortices being significantly lower than the right. Predominant left hemispheric metabolic reductions were not accompanied by a corresponding left-sided predominance in the extent of MRI-detected demyelinating lesions. Therefore our data suggest that CC atrophy interfers more with left than with right metabolic function.

Adult↗

PubMed1992

Metabolic impairment in human amnesia: a PET study of memory networks.

Human amnesia is a clinical syndrome exhibiting the failure to recall past events and to learn new information. Its "pure" form, characterized by a selective impairment of long-term memory without any disorder of general intelligence or other cognitive functions, has been associated with lesions localized within Papez's circuit and some connected areas. Thus, amnesia could be due to a functional disconnection between components of this or other neural structures involved in long-term learning and retention. To test this hypothesis, we measured regional cerebral metabolism with 2-[18F]fluoro-2-deoxy-D-glucose ([18F]FDG) and positron emission tomography (PET) in 11 patients with "pure" amnesia. A significant bilateral reduction in metabolism in a number of interconnected cerebral regions (hippocampal formation, thalamus, cingulate gyrus, and frontal basal cortex) was found in the amnesic patients in comparison with normal controls. The metabolic impairment did not correspond to alterations in structural anatomy as assessed by magnetic resonance imaging (MRI). These results are the first in vivo evidence for the role of a functional network as a basis of human memory.

Adult↗

PubMed1992

The effect of apomorphine and buspirone on regional cerebral blood flow during the performance of a cognitive task-measuring neuromodulatory effects of psychotropic drugs in man.

Psychopharmacological activation, in conjunction with positron emission tomographic measurements of regional cerebral blood flow (rCBF), was used to investigate the neurotransmitter basis of a specific cognitive function in man. Monoaminergic neurotransmission was pharmacologically manipulated during performance of auditory - verbal memory tasks. Statistical parametric mapping was used to identify the brain sites of interaction between memory-induced increases in rCBF and active drugs. Memory task-induced increases in rCBF in the left prefrontal cortex were attenuated by apomorphine, a non-selective dopamine agonist, whilst buspirone, a serotonin1A partial agonist, augmented rCBF increases in this area. In addition, apomorphine and buspirone augmented memory-induced increases in rCBF centred in the posterior cingulate cortex, whilst buspirone alone attenuated rCBF increases in the retrosplenial cortex and posterior parahippocampal gyrus. These regionally selective interactions may represent neuromodulatory effects of monoaminergic neurotransmission on a specific cognitive function in man.

Journal Article↗

PubMedDate not supplied

Head holder for PET, CT, and MR studies.

A new head holder for the fixation and repositioning of the patient head in PET, CT, and MR scanners has been designed and tested. With this device, a bidimensional correlation between functional and anatomical brain images can also be obtained. Head fixation and repositioning are achieved using the patient's dental morphology as an anatomical reference. With a dentistic material, a mold of the patient's teeth is obtained in a few minutes. The molding substance rests on a plastic support, fixed to the head holder. Each time the patient undergoes a new study, his/her personal mold is used, ensuring accurate head repositioning. External markers fixed on the head holder (made visible in lateral PET and CT projection images, midsaggital MR images, and also on the axial images) make it possible to record and recognize the angular orientation and the position of the brain in the three-dimensional space, to correlate images of the same patient obtained with different neuroimaging modalities, and to accurately reposition patients for follow-up studies. The head holder was tested on several subjects. Fixation and repositioning accuracy of within 2.5 mm were achieved in the three-dimensional space. Orientation accuracy was 1 degree.

Equipment Design↗