Showing papers by "Eraldo Paulesu published in 1998"

The bilingual brain. Proficiency and age of acquisition of the second language.

Abstract: Functional imaging methods show differences in the pattern of cerebral activation associated with the subject's native language (L1) compared with a second language (L2). In a recent PET investigation on bilingualism we showed that auditory processing of stories in L1 (Italian) engages the temporal lobes and temporoparietal cortex more extensively than L2 (English). However, in that study the Italian subjects learned L2 late and attained a fair, but not an excellent command of this language (low proficiency, late acquisition bilinguals). Thus, the different patterns of activation could be ascribed either to age of acquisition or to proficiency level. In the current study we use a similar paradigm to evaluate the effect of early and late acquisition of L2 in highly proficient bilinguals. We studied a group of Italian-English bilinguals who acquired L2 after the age of 10 years (high proficiency, late acquisition bilinguals) and a group of Spanish-Catalan bilinguals who acquired L2 before the age of 4 years (high proficiency, early acquisition bilinguals). The differing cortical responses we had observed when low proficiency volunteers listened to stories in L1 and L2 were not found in either of the high proficiency groups in this study. Several brain areas, similar to those observed for L1 in low proficiency bilinguals, were activated by L2. These findings suggest that, at least for pairs of L1 and L2 languages that are fairly close, attained proficiency is more important than age of acquisition as a determinant of the cortical representation of L2.

Recovery of Neglect After Right Hemispheric Damage: H215O Positron Emission Tomographic Activation Study

Abstract: Background The neural correlates of recovery of unilateral neglect (ULN), as well as of other consequences of focal brain damage, are largely unknown. Functional neuroimaging methods (in particular, positron emission tomography [PET]) can be applied to the in vivo study of recovery mechanisms in neurologic patients. Objective To evaluate the functional cerebral correlates of recovery from ULN in patients with right-sided lesions, with the use of a PET activation paradigm. Methods Study of 3 patients with cerebrovascular lesions that involved corticosubcortical (patient 1) or subcortical (patients 2 and 3) areas of the right hemisphere. Unilateral neglect was tested twice, before and after completion of a 2-month rehabilitation program, after which all 3 patients showed considerable improvement. Similarly, 2 PET examinations were performed, before and after recovery, during the performance of a visuospatial task requiring the patients to detect and respond to visual targets moving on a computer screen from the right to the left visual hemifield (experimental condition). The cerebral activation was compared with a baseline task in which subjects responded to a black dot flashing in a fixed position of the right hemifield. Results The brain areas activated by the performance of the visuospatial task before and after recovery were compared. In all 3 patients, the regions notably more active after recovery were almost exclusively found in right-sided cortical areas and largely overlapped with those observed in a group of 4 normal subjects performing the same task. Other areas, which have been shown to be involved in attentional and oculomotor tasks in other PET studies, were also activated in patients with ULN. Conclusions The behavioral recovery of ULN in these patients with predominantly subcortical lesions is mainly associated with cerebral activations in cortical regions similar to those observed in normal subjects. There is some evidence of functional reorganization in individual subjects, which involves other areas related to space representation and exploration.

Differential distribution of striatal [123I]beta-CIT in Parkinson's disease and progressive supranuclear palsy, evaluated with single-photon emission tomography.

Abstract: Functional imaging of the presynaptic dopaminergic activity using single-photon emission tomography (SPET) and iodine-123 labelled 2-β-carboxymethoxy-3-β-(4-iodophenyl)tropane ([123I]β-CIT) is important for the assessment of disease severity and progression in patients with Parkinson’s disease (PD). However, its capability to discriminate between different extrapyramidal disorders has not yet been assessed. The aim of this study was to evaluate the possibility of differentiating patients with PD and with progressive supranuclear palsy (PSP) by means of this method. The distribution of [123I]β-CIT in the basal ganglia was assessed in six normal subjects, 13 petients with PD and five patients with PSP in whom the disease was mild. SPET images were obtained 24±2 h after i.v. injection of the tracer using a brain-dedicated system (CERASPECT). MR and SPET images were co-registered in four normal subjects and used to define a standard set of 16 circular regions of interest (ROIs) on the slice showing the highest striatal activity. The basal ganglia ROIs corresponded to (1) the head of caudate, (2) a region of transition between the head of caudate and the anterior putamen, (3) the anterior putamen and (4) the posterior putamen. A ratio of specific to non-displaceable striatal uptake was calculated normalising the activity of the basal ganglia ROIs to that of the occipital cortex (V3′′). ANOVA revealed a global reduction of V3′′ in all ROIs of PD and PSP patients compared with normal controls (P<0.0001). A Mann-Whitney U test showed that the difference between PD and PSP patients was statistically significant for the caudate region only (Z value: 2.6; P<0.01). By subtracting V3′′ caudate values from those of the putamen, differentiation from PSP was possible in 10/13 PD patients. In conclusion, analysis of [123I]β-CIT distribution in discrete striatal areas provides information on the relative caudate-putamen damage, with different values being obtained in patients clinically diagnosed as having either PD or PSP.

Right on in sign language

Abstract: Spoken language is dealt with by the left hemisphere of the brain. But does that apply to sign languages? A study employing functional magnetic resonance, which reveals the brain areas activated when subjects undertake a task such as understanding sentences, surprisingly finds that processing of sign language is carried out in parts of both hemispheres. This challenging result runs counter to observations from people with brain damage, and is open to various interpretations.

CHAPTER 29 – Use of Two- and Three-Dimensional PET and [11C](R)-PK11195 to Image Focal and Regional Brain Pathology1

Abstract: The ligand PK11195 is selective for the peripheral benzodiazepine binding site and exhibits minimal binding in normal brain. In brain lesions, however, there is a massive increase in binding, which in vitro studies have demonstrated is associated with infiltrating macrophages and activated microglia. Here, the binding of [11C]PK11195 was studied in the brains of multiple sclerosis patients using a CTI/Siemens 953B positron emission tomograph with retractable septa, acquiring data in either two-dimensional (2D) or 3D mode. Images acquired in 2D following injection of ~ 370 MBq were generally featureless. In some cases, poorly circumscribed signals were observed in brain stem or thalamus but with a minimal signal-to-noise ratio. However, regions showing gadolinium enhancement in magnetic resonance (MR) imaging, indicating a blood-brain barrier disturbance and known from histology to contain macrophages, never showed an elevated [11C]PK11195 signal. Three dimensional positron emission tomography (PET), using similar doses of radioligand, gave a fivefold increase in counts and produced a marked improvement in image quality. Gadolinium-enhancing lesions were clearly visualized, together with hot spots of binding in regions with apparently normal MR imaging appearance. The PET signals were often well delineated and, following coregistration with MR images, could be localized to well-defined anatomical structures such as individual thalamic nuclei and white matter tracts. In several cases, these structures identified pathways correlating with the clinical condition of the patient. It was concluded that while 2D PET and [11C]PK11195 can be used to image gross macrophage infiltration in the central nervous system, more subtle pathology requires 3D scanning in order to realize the full potential of the methodology.