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M Girelli

Publications and source records attributed to M Girelli.

At least 19 recordsLinked to original sources
PubMed2006

ERP and fMRI correlates of endogenous and exogenous focusing of visual-spatial attention.

The aim of this study was to investigate the neural correlates of the functional distinction underlying attentional mechanisms of endogenous-sustained and exogenous-transient spatial selection. We recorded event related potentials (ERPs) and used functional magnetic resonance imaging (fMRI) in separate experiments while subjects performed a simple reaction time (RT) to the same visual stimulus displayed to one of several field locations. Endogenous-sustained or exogenous-transient focusing of attention onto target location were obtained by presenting the stimulus in blocks of same-point vs. randomised-point trials, respectively. Same-point stimuli yielded overall faster RT than randomised stimuli, indicating a facilitating effect of endogenous-sustained spatial attention on the perceptual processing of the impending stimulus. Moreover, same-point vs. randomised presentations revealed significant increases in the fMRI signal in the bilateral lingual and fusiform gyri as well as in the right calcarine sulcus, in conjunction with a larger amplitude of the posterior P1 component of ERPs, but no modulation of the amplitude of the N1 component. Rather, a larger amplitude of N1 was found in the reverse contrast, randomised minus same-point trials, which revealed increases in the fMRI signal along the posterior left superior frontal sulcus and bilaterally in the superior precuneus. These findings indicate that N1 indexes exogenous orienting of attention and is likely to represent the activity of frontal and parietal components of the attention network involved in eliciting attention changes. In contrast, the effects of those changes, resulting in a modulation of activation in visual occipital areas, are indexed by P1.

Adolescent↗
PubMed2001

What exactly is extinguished in unilateral visual extinction? Neurophysiological evidence.

We propose a model of unilateral visual extinction following right hemisphere lesions based on competition between contralesional and ipsilesional input to access a decision centre located in the left hemisphere. During bilateral presentations, the contralesional signal is on average less likely to activate the decision centre than the ipsilesional signal. This is because an intra-hemispheric lack of top-down attentional influences and an inter-hemispheric impairment of callosal transmission delay and/or weaken the contralesional input. Here we provide behavioural as well as event-related potential evidence for both these impairments. Finally, we argue that an essential prerequisite for contralesional extinction is the presence of a restricted general attentional capacity which often follows large right hemisphere damage.

Adolescent↗
PubMed2001

Human vasculogenesis ex vivo: embryonal aorta as a tool for isolation of endothelial cell progenitors.

SUMMARY: Vasculogenesis, the de novo formation of new blood vessels from undifferentiated precursor cells or angioblasts, has been studied with experimental in vivo and ex vivo animal models, but its mechanism is poorly understood, particularly in humans. We used the aortic ring assay to investigate the angioforming capacity of aortic explants from 11- to 12-week-old human embryos. After being embedded in collagen gels, the aorta rings produced branching capillary-like structures formed by mesenchymal spindle cells that lined a capillary-like lumen and expressed markers of endothelial differentiation (CD31, CD34, von Willebrand factor [vWF], and fms-like tyrosine kinase-1 [Flk-1]/vascular endothelial growth factor receptor 2 [VEGFR2]). The cell linings of these structures showed ultrastructural evidence of endothelial differentiation. The neovascular proliferation occurred primarily in the outer aspects of aortic rings, thus suggesting that the new vessels mainly arose from immature endothelial precursor cells localized in the outer layer of the aortic stroma, ie, a process of vasculogenesis rather than angiogenesis. The undifferentiated mesenchymal cells (CD34+/CD31-), isolated and cultured on collagen-fibronectin, differentiated into endothelial cells expressing CD31 and vWF. Furthermore, the CD34+/CD31+ cells were capable of forming a network of capillary-like structures when cultured on Matrigel. This is the first reported study showing the ex vivo formation of human microvessels by vasculogenesis. Our findings indicate that the human embryonic aorta is a rich source of CD34+/CD31- endothelial progenitor cells (angioblasts), and this information may prove valuable in studies of vascular regeneration and tissue bioengineering.

Antigens, CD34↗
PubMed2000

Neural sources of focused attention in visual search.

Previous studies of visual search in humans using event-related potentials (ERPs) have revealed an ERP component called 'N2pc' (180-280 ms) that reflects the focusing of attention onto potential target items in the search array. The present study was designed to localize the neuroanatomical sources of this component by means of magnetoencephalographic (MEG) recordings, which provide greater spatial precision than ERP recordings. MEG recordings were obtained with an array of 148 magnetometers from six normal adult subjects, one of whom was tested in multiple sessions so that both single-subject and group analyses could be performed. Source localization procedures revealed that the N2pc is composed of two distinct neural responses, an early parietal source (180-200 ms) and a later occipito-temporal source (220-240 ms). These findings are consistent with the proposal that parietal areas are used to initiate a shift of attention within a visual search array and that the focusing of attention is implemented by extrastriate areas of the occipital and inferior temporal cortex.

Adult↗
PubMed2000

Electrophysiological correlates of conscious vision: evidence from unilateral extinction.

To study the electrophysiological correlates of conscious vision, we recorded event-related potentials (ERPs) in a patient with partial unilateral visual extinction as a result of right-hemisphere damage. When, following bilateral presentations, contralesional stimuli were not perceived, there was an absence of the early attention-sensitive P1 (80-120 msec) and N1 (140-180 msec) components of the ERP response. In contrast, following unilateral presentations, or in those bilateral presentations in which contralesional stimuli were perceived (about 60%), these ERP components were present. These results provide novel evidence that extinction involves the stage of early focusing of attention and that the P1 and N1 components of visual ERPs are reliable physiological correlates of conscious vision.

Attention↗
PubMed2000

Isolation and characterization of neural stem cells from the adult human olfactory bulb.

We have recently isolated stem cells deriving from the olfactory bulbs of adult patients undergoing particularly invasive neurosurgery. After improving our experimental conditions, we have now obtained neural stem cells according to clonal analysis. The cells can be expanded, established in continuous cell lines and differentiated into the three classical neuronal phenotypes (neurons, astrocytes, and oligodendrocytes). Also, after exposition to leukemia inhibitory factor, we are able to improve the number of neurons, an ideal biological source for transplantation in various neurodegenerative disorders.

Adult↗
PubMed1998

Neural site of the redundant target effect electrophysiological evidence.

The present study represents an attempt to find an electrophysiological correlate of the redundant targets effect, or RTE (i.e., the speeding up of reaction time, or RT, for redundant vs. single targets). Subjects made a speeded response either to one small checkerboard presented to the left or right of fixation or to a pair of identical checkerboards presented simultaneously to both hemifields. Both single and double targets could appear either in the upper or lower visual hemifield. The task required detection but not discrimination of the stimuli. During task performance, we recorded the event-related potentials (ERPs) elicited by the checkerboard targets. As in previous studies, we found that manual RTs to bilateral stimuli were faster than those to unilateral stimuli. This effect was more marked for lower- than for upper-field stimuli and could not be ascribed to probability summation. In addition, we found that the P1 and N1 components of the visual ERP had a shorter latency for bilateral than for summed unilateral stimuli presented to the two hemifields. In parallel with the behavioral findings, the latency values for the above components showed a larger RTE for lower-field stimuli. These findings indicate that the RTE occurs at the level of early visual processing, probably in the extrastriate visual cortex, rather than at late decisional or pre-motor stages.

Adult↗
PubMed1998

ERP and fMRI measures of visual spatial selective attention.

In two prior studies, we investigated the neural mechanisms of spatial attention using a combined event-related potential (ERP) and positron emission tomography (PET) approach (Heinze et al. [1994]: Nature 392:543-546; Mangun et al. [1997]: Hum Brain Mapp 5:273-279). Neural activations in extrastriate cortex were observed in the PET measures for attended stimuli, and these effects were related to attentional modulations in the ERPs at specific latencies. The present study used functional magnetic resonance imaging (fMRI) and ERPs in single subjects to investigate the intersubject variability in extrastriate spatial attention effects, and to qualitatively compare this to variations in ERP attention effects. Activations in single subjects replicated our prior group-averaged PET findings, showing attention-related increases in blood flow in the posterior fusiform and middle occipital gyri in the hemisphere contralateral to attended visual stimuli. All subjects showed attentional modulations of the occipital P1 component of the ERPs. These findings in single subjects demonstrate the consistency of extrastriate attention effects, and provide information about the feasibility of this approach for integration of electrical and functional imaging data.

Attention↗
PubMed1998

Fossa navicularis magna.

A notchlike bone defect in the basiocciput due to a prominent fossa navicularis was incidentally discovered in a patient referred for radiologic evaluation of sinusitis. MR images showed that the osseous defect was filled with lymphoid tissue of the pharyngeal tonsil. The occurrence of this anatomic variant is discussed, with reference to ancient anatomic works.

Adult↗
PubMed1997

Bridging the gap between monkey neurophysiology and human perception: an ambiguity resolution theory of visual selective attention.

When the visual system must process multiple objects simultaneously, as in the visual search paradigm, the neural coding of individual objects can become ambiguous due to the visual system's extensive use of coarse coding and distributed representations. Here we propose that the primary role of visual selective attention within the ventral object recognition pathway is to resolve these ambiguities. We begin by reviewing previous studies of the effects of attention on neural responses in monkeys, which provide the basis for this hypothesis, and then describe a new set of experiments showing that similar attentional mechanisms operate in the human brain. In these new experiments, event-related potentials (ERPs) were recorded from normal human observers while they performed tasks analogous to those used previously in monkeys. The central finding was that an attention-related ERP wave called the "N2pc component" was present under the same conditions that led to attentional modulations of neural responses in monkey visual cortex. These human electrophysiological results provide a bridge between cognitive-level theories of visual attention and the behavior of individual neurons in visual cortex.

Adolescent↗
PubMed1997

Blunt pancreatic trauma. Role of CT.

PURPOSE: To define the evolution patterns of blunt pancreatic trauma, and to point out the CT features most significant for the diagnosis. MATERIAL AND METHODS: Ten cases of pancreatic trauma, observed over a period of about 10 years, were analyzed in retrospect. The cases were divided into 3 groups according to the time that had elapsed between trauma and first CT: early phase (within 72 h: n=3/10); late phase (after 10 days: n=3/10); and following pancreatic drainage (n=4/10). RESULTS: In the early phase, one case showed a blood collection surrounding the pancreatic head and duodenum, and displacing the mesenteric vessels to the left. In the 2 other cases it was possible to demonstrate a tear in the pancreas at the neck, perpendicular to the main pancreatic axis. In the late phase in all 3 cases, one cystic lesion was present at the site of the tear, either surrounding the gland or embedded - more or less deeply - within the parenchyma. One of the lesions subsided spontaneously; the 2 others required surgery. In the postoperative phase, an external fistula was demonstrated in 2 cases following percutaneous drainage of pancreatic cysts; the fistula was fed by a cystic lesion in the pancreatic neck. In the 2 other cases a pseudocyst developed. CONCLUSION: Early demonstration of a parenchymal tear was difficult. At a later stage the diagnosis was easier owing to the demonstration of cystic lesions within the parenchyma at the site of the tear. The surgical drainage of this lesion does not usually lead to healing since an external fistula or a pseudocyst may develop.

Adult↗
PubMed1997

Interhemispheric transfer of visual information in humans: the role of different callosal channels.

We have assessed the interhemispheric transmission time (IHTT) by electrophysiological means in normal subjects performing a visuomotor reaction time task. We subtracted the latency of ERP components (P1 and N1) evoked by lateralized visual stimuli presented to the ipsilateral hemifield (indirect-callosal pathway) from the latency of the same components evoked by stimulation of the contralateral hemifield (direct pathway). Estimates of IHTT ranged between 5.77 msec and 12.54 depending upon the type of component and the location of the electrode sites. More anterior locations yielded shorter values of IHTT, and overall IHTT tended to be 7 msec shorter for the N1 component than for the P1 component. Moreover, there was an asymmetric IHTT for N1 in central sites with shorter latencies in the direction right-to-left hemisphere than in the opposite direction. Taken together, these results are in keeping with the idea that interhemispheric transfer of visuomotor information does not occur at the level of the primary visual areas but at more anterior cortical areas. The shorter IHTT for the N1 component suggests the involvement of the callosal connections between the inferotemporal areas of the two hemispheres.

Adult↗
PubMed1995

Abnormal spatial but normal temporal resolution in the Siamese cat: a behavioral correlate of a genetic disorder of the parallel visual pathways.

Six ordinary and one Siamese cat were tested for spatial frequency contrast sensitivity and for flicker discrimination thresholds. The Siamese cat was markedly impaired in the former task but performed normally in the latter. This result is consistent with single-cell physiological evidence showing an abnormally high Y/X cell ratio in the area centralis of Siamese cats. Under a more general perspective, this genetically related dissociation of visual impairments confirms the idea of parallel pathways subserving spatial and temporal resolution, respectively.

Albinism, Ocular↗
PubMed1991

Bilateral hemispheric control of foot distal movements: evidence from normal subjects.

Normal subjects have been tested for interhemispheric transfer (IT) of visuo-motor information using a simple reaction time (RT) paradigm and lateralized stimuli and responses (the so-called Poffenberger paradigm). In this paradigm IT time is assumed to correspond to the RT difference between crossed and uncrossed stimulus-response combinations (CUD). In Experiment 1, two types of movements were used: a unilateral flexion of the thumb and a unilateral plantar flexion of the big toe. A reliable CUD (7.4 msec) was found only with manual responses. Changing stimulus retinal eccentricity (10 degrees vs. 70 degrees) or attentional demands (blocked vs. random stimulus presentation) did not result in any reliable effect on the CUD. In Experiment 2 the number of RTs for each subject was considerably increased and several visual field sites (from areas close to the vertical meridian to the monocular crescent) were tested. Notwithstanding these modifications, this experiment confirmed the lack of CUD found for foot responses in Exp. 1. Taken together, these results are in keeping with a less lateralized hemispheric control of distal foot movements in comparison to hand movements.

Acoustic Stimulation↗
PubMed1990

[Methodological premises of statistical analysis of the data].

Most psychic disorders, such as anxiety, agitation and dementia are difficult to measure objectively since the scale of measure--psychometric tests--are often liable to subjective judgment--especially of clinicians or patients during self-rating scales. It become therefore necessary to use a complex way of measuring--a battery of tests--from which the results should be analyzed through multivariate statistic models. During this polycentric it was believed suitable to use the repeated multivariate analysis of variance, an instrument largely used in the data analysis of rating scale thanks to the flexibility of the generalized east squares methods. In this article the characteristics of this method and how to read its results will be discussed.

Acetylcarnitine↗
PubMed1988

Safety profile of ofloxacin in elderly patients.

In clinical trials co-ordinated in Italy by Glaxo S.p.A. from May 1984 to February 1988, 553 patients aged over 65 years (376 men and 177 women), suffering from different infectious diseases (mostly LRTI and UTI), were treated with ofloxacin, a new broad-spectrum quinolone. Of the patients studied, 75% presented one or more concurrent diseases and 72.3% were receiving one or more concurrent therapies. Daily dose of the drug varied, in most cases, between 400 and 800 mg in two oral administrations. In all, 21 adverse events were recorded in 19 patients (3.44%): 13 gastrointestinal events (gastric pain, nausea, vomiting), 3 cutaneous events and 5 others. The severity of the events was judged as mild in 56.3% of the cases and moderate in 43.7%. The treatment was stopped because of adverse events in three patients (0.54%). Abnormal laboratory parameters, probably related to the drug, were observed in four patients. In conclusion, ofloxacin appears to be a very safe drug in the treatment of bacterial infections in elderly patients.

Aged↗
PubMed1987

Effect of ranitidine on the absorption of aspirin.

Six healthy male volunteers received 1 week's pretreatment with ranitidine, 150 mg twice daily, and placebo in a double-blind cross-over trial. On the 8th day, each volunteer received 1 g of aspirin in order to study the pharmacokinetics of this nonsteroidal anti-inflammatory drug. The results of this study suggest that ranitidine does not induce clinically significant alterations to the kinetics of a single dose of aspirin in healthy males.

Adult↗