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Manuela Piazza

Publications and source records attributed to Manuela Piazza.

14 recordsLinked to original sources
PubMed2007

A magnitude code common to numerosities and number symbols in human intraparietal cortex.

Activation of the horizontal segment of the intraparietal sulcus (hIPS) has been observed in various number-processing tasks, whether numbers were conveyed by symbolic numerals (digits, number words) or by nonsymbolic displays (dot patterns). This suggests an abstract coding of numerical magnitude. Here, we critically tested this hypothesis using fMRI adaptation to demonstrate notation-independent coding of numerical quantity in the hIPS. Once subjects were adapted either to dot patterns or to Arabic digits, activation in the hIPS and in frontal regions recovered in a distance-dependent fashion whenever a new number was presented, irrespective of notation changes. This remained unchanged when analyzing the hIPS peaks from an independent localizer scan of mental calculation. These results suggest an abstract coding of approximate number common to dots, digits, and number words. They support the idea that symbols acquire meaning by linking neural populations coding symbol shapes to those holding nonsymbolic representations of quantities.

Adaptation, Physiological↗
PubMed2006

Exact and approximate judgements of visual and auditory numerosity: an fMRI study.

Human adults can assess the number of objects in a set (numerosity) by approximate estimation or by exact counting. There is evidence suggesting that numerosity estimation depends on a dedicated mechanism that is a-modal and non-verbal. By contrast, counting requires the coordination between the pre-existing numerosity estimation abilities with language and one-to-one correspondence principles. In this paper we investigate with fMRI the neural correlates of numerosity estimation and counting in human adults, using both visual and auditory stimuli. Results show that attending to approximate numerosity correlates with increased activity of a right lateralized fronto-parietal cortical network, and that this activity is independent of the stimuli presentation's modality. Counting activates additional left prefrontal, parietal, and bilateral premotor areas, again independently from stimulus modality. These results dissociate two neuronal systems that underlie different numerosity judgements.

Acoustic Stimulation↗
PubMed2005

Interactions between number and space in parietal cortex.

Since the time of Pythagoras, numerical and spatial representations have been inextricably linked. We suggest that the relationship between the two is deeply rooted in the brain's organization for these capacities. Many behavioural and patient studies have shown that numerical-spatial interactions run far deeper than simply cultural constructions, and, instead, influence behaviour at several levels. By combining two previously independent lines of research, neuroimaging studies of numerical cognition in humans, and physiological studies of spatial cognition in monkeys, we propose that these numerical-spatial interactions arise from common parietal circuits for attention to external space and internal representations of numbers.

Humans↗
PubMed2004

[13C]Methionine breath test: a novel method to detect antiretroviral drug-related mitochondrial toxicity.

OBJECTIVES: A major side effect of antiretroviral drugs is nucleoside reverse transcriptase inhibitor (NRTI)-related mitochondrial toxicity, the in vivo diagnosis of which is difficult and not yet standardized. We used the [(13)C]methionine breath test to investigate hepatic mitochondrial oxidation in HIV-1-infected patients receiving antiretroviral therapy. PATIENTS AND METHODS: The [(13)C]methionine breath test was performed in healthy subjects (n=10), HIV-infected patients on antiretroviral therapy with (n=6) and without (n=15) hyperlactataemia and naive HIV-infected patients (n=11). After oral administration of [(13)C]methionine (2 mg/kg body weight), hepatic methionine metabolism was measured by breath (13)CO(2) enrichment, expressed as delta over baseline (DOB) every 15 min for 120 min by mass spectrometry. RESULTS: The four study groups showed a significant difference in (13)CO(2) exhalation (P=0.001). HIV-infected patients on antiretroviral therapy with normal serum lactate had reduced exhalation of (13)CO(2) compared with healthy subjects (DOB mean peak: 8.82+/-0.62 versus 11+/-0.9, P<0.05). HIV patients with hyperlactataemia had even lower values when compared with patients with normal lactataemia (DOB mean peak: 4.98+/-0.68 versus 8.82+/-0.62, P<0.05). CONCLUSIONS: The [(13)C]methionine breath test possibly showed mitochondrial impairment in antiretroviral-treated HIV-positive patients, particularly with hyperlactataemia. This non-invasive test can be used to monitor drug-related mitochondrial toxicity in vivo and to discover early and asymptomatic damage of the respiratory chain.

Adult↗
PubMed2004

Tuning curves for approximate numerosity in the human intraparietal sulcus.

Number, like color or movement, is a basic property of the environment. Recently, single neurons tuned to number have been observed in animals. We used both psychophysics and neuroimaging to examine whether a similar neural coding scheme is present in humans. When participants viewed sets of items with a variable number, the bilateral intraparietal sulci responded selectively to number change. Functionally, the shape of this response indicates that humans, like other animal species, encode approximate number on a compressed internal scale. Anatomically, the intraparietal site coding for number in humans is compatible with that observed in macaque monkeys. Our results therefore suggest an evolutionary basis for human elementary arithmetic.

Adult↗
PubMed2004

Distributed and overlapping cerebral representations of number, size, and luminance during comparative judgments.

How are comparative judgments performed in the human brain? We scanned subjects with fMRI while they compared stimuli for size, luminance, or number. Regions involved in comparative judgments were identified using three criteria: task-related activation, presence of a distance effect, and interference of one dimension onto the other. We observed considerable overlap in the neural substrates of the three comparison tasks. Interestingly, the amount of overlap predicted the amount of cross-dimensional interference: in both behavior and fMRI, number interfered with size, and size with luminance, but number did not interfere with luminance. The results suggest that during comparative judgments, the relevant continuous quantities are represented in distributed and overlapping neural populations, with number and size engaging a common parietal spatial code, while size and luminance engage shared occipito-temporal perceptual representations.

Adult↗
PubMed2003

Single-trial classification of parallel pre-attentive and serial attentive processes using functional magnetic resonance imaging.

Theories of perception have proposed a basic distinction between parallel pre-attentive and serial attentive modes of processing. However, chronometric measures are often ambiguous in separating parallel and serial processes. We have used the activity of attention-related regions of the human brain, measured with functional magnetic resonance imaging, to separate parallel from serial processes at the single-trial level in a visual quantification task. In this task, some have suggested the deployment of two qualitatively different processes, a fast parallel 'subitizing' for sets of one, two or three objects and a slow serial counting for larger sets. Our results indicate that attention-related regions of the posterior parietal and frontal cortices show a sudden increase in activity only from numerosity four onwards, confirming the parallel-serial dichotomy of subitizing and counting. Moreover, using the presence or absence of attentional shifts, as inferred from the activation of posterior parietal regions, we successfully predict whether, on a given trial, subjects deployed a serial exploration of the display or a parallel apprehension. Beyond the subitizing/counting debate, this approach may prove useful to probe the attentional demands of other cognitive tasks.

Adult↗
PubMed2003

Correlates of risk of adipose tissue alterations and their modifications over time in HIV-1-infected women treated with antiretroviral therapy.

OBJECTIVE: To assess the correlates of risk of the different types of lipodystrophy and their modifications over time in a cohort of HIV-positive women receiving antiretroviral therapy (ART). METHODS: A consecutive series of HIV-infected women receiving ART was prospectively enrolled between 1 and 31 March 1998, and followed up for 2 years. Adipose tissue alterations (ATAs) and their variations over time were assessed by means of clinical observation and anthropometric measurements, and logistic regression analysis was used to describe the associated risk factors identified by univariate and multivariate analyses. RESULTS: One-hundred-and-seventeen of the 212 women (55.2%) developed ATAs during the 24 months of follow-up. Central adiposity was observed in 95 patients and peripheral lipoatrophy in 91, with 21 patients (9.9%) showing pure lipoatrophy, 26 (12.3%) pure fat accumulation and 70 (33%) combined forms. Only six of the 223 regional adipose tissue alterations identified in 74 patients during the first 12 months of the study had disappeared by month 24. Of the 43 patients who developed breast enlargement during the first 12 months, 11 (25.6%) showed a decrease in breast size during the second year of follow-up that was unrelated to changes in therapy or therapeutic success. The development of ATAs during the first 12 months of follow-up independently correlated with protease inhibitor (PI) use (OR 2.81, P=0.002) but, by the end of the second year of follow-up, the only factor significantly related to the development of ATAs was the overall duration of ART (OR 1.85, P=0.041). The use of PI significantly increased the risk of developing central adiposity during the first 12 months of the study (OR 2.27, P=0.002), whereas the only variable significantly influencing the risk at month 24 was HIV-infection due to intravenous drug use, which proved to be protective (OR 0.53, P=0.043). During the first 12 months of follow-up, the development of peripheral lipoatrophy was significantly associated with stavudine (OR 2.19, P=0.037) and PI use at enrolment (OR 2.27, P=0.023). At the end of the study, the variables associated with peripheral lipoatrophy were stavudine use at enrolment (OR 2.82, P=0.002), ART exposure for >1000 days at enrolment (OR 2.32, P=0.007), a CD4 cell count of >200/microl at enrolment (OR 2.89, P=0.002) and an age of >28 years (OR 1.91, P=0.036). The only factor significantly associated with an increased risk of breast enlargement during the first 12 months of follow-up was PI use (adjusted OR 2.51; 95% CI: 1.16-5.46, P=0.02); however, at month 24, none of the tested variables was associated with a significantly increased risk of this ATA. CONCLUSIONS: ATAs (particularly central adiposity) are frequent in women treated with ART, and the different forms have different correlates of risk. Once they have become clinically evident, they generally tend to remain or worsen, and improve in only a small minority of cases. The considerable variations in adipomasty over time are apparently unrelated to changes in ART.

Adipose Tissue↗
PubMed2002

Body habitus changes and metabolic alterations in protease inhibitor-naive HIV-1-infected patients treated with two nucleoside reverse transcriptase inhibitors.

BACKGROUND: Cross-sectional and retrospective surveys suggest that nucleoside reverse transcriptase inhibitors (NRTIs) contribute to the metabolic and morphologic alterations observed in patients on antiretroviral therapy (ART). OBJECTIVES: To assess the risk of developing body habitus changes (BHCs) and metabolic abnormalities in protease inhibitor (PI)-naive HIV-1-infected patients treated with two NRTIs, and the risk associated with each of these drugs. DESIGN: Prospective cohort study. PATIENTS AND METHODS: The BHCs occurring in 335 patients treated with two NRTIs were evaluated every 3 months. The laboratory tests included determination of CD4 cell counts and the measurement of HIV RNA, serum glucose, cholesterol, and triglyceride levels. Cox proportional hazard models were used to describe the factors associated with the development of BHCs. RESULTS: During a median exposure of 747.5 days, 46 patients (13.7%) developed BHCs: nine fat accumulation alone, 12 fat loss alone, and 25 combined fat loss and accumulation in different body regions. Fat loss alone occurred after a significantly longer median duration of treatment than the other two forms (p =.004). The risk of developing any BHC was significantly higher in female patients (p <.0001). Fat loss was the prevalent alteration in males. Hypertriglyceridemia was observed in 76 patients (22.7%), hypercholesterolemia in 35 (10.5%), and hyperglycemia in 48 (14.3%). The adjusted risk of developing hypertriglyceridemia was higher in the stavudine-treated patients (p =.04) and in those who had previously received ART (p =.02). The only independent factor associated with the development of hypercholesterolemia was to be ART experienced at baseline (p =.02), whereas age was associated with the development of hyperglycemia (p =.0096). CONCLUSIONS: Treatment with NRTIs may be responsible for the same morphologic alterations as those observed in patients treated with PIs. Moreover, altered triglyceride levels are also frequently observed. The different timing of presentation and gender distribution of BHCs suggest that multiple pathogenetic mechanisms are involved.

Adult↗
PubMed2002

Are subitizing and counting implemented as separate or functionally overlapping processes?

Enumeration of small groups of four or fewer objects is very fast and accurate (often called "subitizing"), but gets slower and more error prone for more than four items ("counting"). Many theories have been proposed to account for this dichotomy, most suggesting that "subitizing" and "counting" are two qualitatively different and separable processes. Others, in contrast, have proposed that the two operations reflect two different levels along a continuum of complexity. In this paper we present a PET study that attempts to characterize subitizing and counting at a neural level in order to investigate whether they are implemented as separate or functionally overlapping processes. Subjects performed an enumeration task on visual arrays of dots that varied in numerosity (1-4 and 6-9 dots) and spatial arrangement (canonical and random). The results demonstrated a common network for subitizing and counting that comprises extrastriate middle occipital and intraparietal areas. The intensity and spatial extent of this network were modulated by the number of dots and their spatial arrangement: activation increased as the number of items in the visual array increased, reaching maximum peak and extent for counting 6-9 randomly arranged items. Direct comparison between subitizing and counting showed that counting, relative to subitizing, was correlated with increased activity in this occipitoparietal network, while subitizing did not show areas of increased activation with respect to counting. Results speak against the idea of the two processes being implemented in separable neural systems.

Adult↗
PubMedDate not supplied

Prospective observational study of fever in hospitalized returning travelers and migrants from tropical areas, 1997-2001.

BACKGROUND: An estimated 50 million people each year from industrialized countries visit tropical areas: 3% to 11% of these travelers report a febrile illness on their return. We conducted a 5-year prospective observational study on the causes of fever in patients admitted to a university teaching hospital after returning from the tropics. METHODS: We enrolled in this study all consecutive patients admitted to the Division of Infectious Diseases of the University of Milan, Italy, between January 1997 and December 2001 presenting with fever (oral temperature > or =37.5 degrees C) and a history of travel to a tropical country in the previous 6 months. RESULTS: Seven percent (147/2,074) of all hospital admissions in the study period were due to fever in travelers and migrants returning from the tropics. Malaria accounted for 47.6 % of all admissions (70/147), followed by presumed self-limiting viral infections (12%). Pretravel screening and vaccination strategies could have prevented a considerable number of hospitalizations (e.g., hepatitis A and typhoid fever). The most useful investigations were blood examination and PCR for malaria, which gave positive results in 65% of cases in which they were performed. CONCLUSIONS: During a 5-year period, the number of patients returning from tropical areas who were admitted with fever to a university hospital in northern Italy remained stable; malaria was the most frequent diagnosis, and should be considered in any febrile patient returning from the tropics. With the exception of hepatitis A and dengue fever infections, in a real-world setting serology is of modest utility and is probably overused.

Adult↗