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Biomedical subjects

M Carrasco

Publications and source records attributed to M Carrasco.

At least 37 records · Page 2Linked to original sources
PubMed2000

[Plasma levels of insulin and leptin in patients with morbid obesity and anorexia nervosa after weight loss or gain, respectively].

The present study was conducted in order to analyze the relationship existing between leptin and insulin levels in massive weight loss and weight recovery. Thirteen patients with severe obesity, 14 patients with anorexia nervosa and 13 healthy control subjects were studied. The patients with severe obesity underwent a vertical banded gastroplasty followed by an 800 kcal/day diet for 12 weeks. They were evaluated prior to (body mass index [BMI] 51.2 +/- 8.8 Kg/m2) and after drastic weight loss (BMI 40.6 +/- 6.7 Kg/m2). Patients with anorexia nervosa were treated exclusively with nutritional therapy during 12 weeks, and they were evaluated at their lowest weight status (BMI 16.2 +/- 2.2 Kg/m2) and after weight recovery (BMI 17.9 +/- 2.3 Kg/m2). The BMI of the normal subjects was in the normal range of 20 to 27 Kg/m2 (average 22.8 +/- 2.6 Kg/m2). BMI, percentage of body fat, waist circumference, and serum levels of leptin, insulin, and C-peptide were determined in each patient and normal subject. In severely obese patients, serum leptin and insulin decreased significantly after drastic weight reduction (leptin: from 51.8 +/- 22.3 to 23.7 +/- 10.2 ng/ml; insulin: from 27.1 +/- 13.3 to 17.2 +/- 7.2 mU/ml). In patients with anorexia nervosa, the mean serum leptin levels were significantly higher after weight recovery (5.5 +/- 3.2 vs 7.6 +/- 6 ng/ml). Serum leptin in the severe obesity group correlated positively with BMI, percentage body fat and waist circumference before and after weight loss. In those patients suffering from anorexia nervosa, serum leptin correlated positively with the BMI, percentage of body fat, and waist circumference in the low weight state and after weight recovery. In addition, their serum insulin correlated with BMI and waist circumference after weight recovery. These data reveal that serum leptin concentration correlates significantly with the BMI and body fat content 1) in subjects with a range of weight and caloric intake, 2) in obese patients after drastic weight loss; 3) in anorexic patients after weight gain; and that hyper- or normoinsulinemia do not seem to have any influence on the leptin changes caused by weight loss or gain.

Adipose Tissue↗
PubMed1999

Spatial attention improves performance in spatial resolution tasks.

This study used peripheral precueing to explore the effect of covert transient attention on performance in spatial resolution tasks. Experiments 1 (Landolt-square) and 2 ('broken-line') measured gap resolution and Experiment 3 measured vernier resolution. In all three tasks the target was presented alone in a large number of possible locations, ranging from 1.5-6 degrees of eccentricity in the vertical or horizontal axes. The precue indicated the target location but did not convey information regarding the correct response. Performance decreased as the gap size or the vernier offset size decreased and as target eccentricity increased. Precueing improved performance in terms of RT and accuracy in all three tasks; the eccentricity effect decreased in the cued trials of the gap resolution tasks. These findings support the idea that the performance improvement at attended locations results, to some extent, from an enhanced spatial resolution at the cued location, and not just from distractor exclusion, diminished uncertainty, or decisional factors.

Attention↗
PubMed1999

The temporal dynamics of visual search: evidence for parallel processing in feature and conjunction searches.

Feature and conjunction searches have been argued to delineate parallel and serial operations in visual processing. The authors evaluated this claim by examining the temporal dynamics of the detection of features and conjunctions. The 1st experiment used a reaction time (RT) task to replicate standard mean RT patterns and to examine the shapes of the RT distributions. The 2nd experiment used the response-signal speed-accuracy trade-off (SAT) procedure to measure discrimination (asymptotic detection accuracy) and detection speed (processing dynamics). Set size affected discrimination in both feature and conjunction searches but affected detection speed only in the latter. Fits of models to the SAT data that included a serial component overpredicted the magnitude of the observed dynamics differences. The authors concluded that both features and conjunctions are detected in parallel. Implications for the role of attention in visual processing are discussed.

Adolescent↗
PubMed1998

Attention improves or impairs visual performance by enhancing spatial resolution.

Covert attention, the selective processing of visual information at a given location in the absence of eye movements, improves performance in several tasks, such as visual search and detection of luminance and vernier targets. An important unsettled issue is whether this improvement is due to a reduction in noise (internal or external), a change in decisional criteria, or signal enhancement. Here we show that attention can affect performance by signal enhancement. For a texture segregation task in which performance is actually diminished when spatial resolution is too high, we observed that attention improved performance at peripheral locations where spatial resolution was too low, but impaired performance at central locations where spatial resolution was too high. The counterintuitive impairment of performance that we found at the central retinal locations appears to have only one possible explanation: attention enhances spatial resolution.

Attention↗
PubMed1998

Feature asymmetries in visual search: effects of display duration, target eccentricity, orientation and spatial frequency.

In Experiments 1-3, we monitored search performance as a function of target eccentricity under display durations that either allowed or precluded eye movements. The display was present either until observers responded, for 104 msec, or for 62 msec. In all three experiments an orientation asymmetry emerged: observers detected a tilted target among vertical distracters more efficiently than a vertical target among vertical distracters. As target eccentricity increased, reaction times and errors augmented, and the set size effect became more pronounced, more so for vertical than tilted targets. In Experiments 4-7, the stimulus spatial properties were manipulated: spatial frequency; size; and orientation. The eccentricity effect was more pronounced for vertical than tilted targets and for high- than low-spatial frequency targets. This effect was eliminated when either the size, the size and orientation, or the size and spatial frequency were magnified (M-cortical factor). By increasing the signal-to-noise ratio, magnification reduced the extent of both asymmetries; it aided more the detection of tilted than vertical and of high- than low-spatial frequency targets. Experiments 4-7 indicate that performance improvement in the magnified conditions was due to the specific pairing of stimulus size with retinal eccentricity and not to the larger stimulus size of the magnified conditions. We conclude that stimulus size, orientation and spatial frequency influence the extent of the eccentricity effect and the efficiency of search performance.

Eye Movements↗
PubMed1998

Modulation of murine lymphocyte functions by sulfated cholecystokinin octapeptide.

The effects in vitro of the sulfated octapeptide form of cholecystokinin (CCK-8) at concentrations ranging from 10(-13) M to 10(-6) M on several functions of murine lymphocytes were studied, i.e. adherence to substrate, mobility (spontaneous and directed by chemical gradient or chemotaxis) and spontaneous and phytohemagglutinin (PHA)-mediated proliferation. Lymphocytes were obtained from peritoneal suspension as well as from axillary nodes, spleen and thymus of BALB/c mice. CCK-8, at concentrations from 10(-10) M to 10(-8) M, significantly inhibited the mobility capacity and the PHA-induced proliferation and increased the adherence and the spontaneous proliferation of lymphocytes. A dose-response relationship was observed, with a maximum effect on lymphocyte functions at 10(-10) M. In addition, CCK-8 induced a significant decrease in membrane and cytosol protein kinase C (PKC) activity in murine lymphocytes, as well as an increase of intracellular cyclic AMP levels. These results suggest that CCK-8 is a negative modulator of two important lymphocyte functions in the immune response, i.e. mobility and mitogen-induced proliferation, and that the PKC activity inhibition and cAMP increase could be the mechanisms through which CCK inhibits these lymphocyte activities.

Animals↗
PubMed1998

Separate populations of neurons within the paraventricular hypothalamic nucleus of the rat project to vagal and thoracic autonomic preganglionic levels and express c-Fos protein induced by lithium chloride.

The role of different hypothalamic nuclei, particularly the paraventricular nucleus (PVN), in the control of food intake and feeding behaviour is well known. It is also well established that lithium chloride (LiCl) causes various disorders in feeding behaviour. In this study, we analyzed the precise distribution of hypothalamic neurons activated by i.p. LiCl administration (LCA neurons) and compared it to that of hypothalamic neurons which project to autonomic preganglionic levels (HAP neurons). We also analysed the possibility that some neurons belong to both populations of nerve cells. To this end, a multiple-labelling technique, using two retrograde fluorescent tracers together with c-Fos-like immunohistochemistry, was performed. Fast Blue was injected in the dorsal motor nucleus of the vagus and Fluorogold (FG) in the thoracic intermedial-lateral cell column, to trace parasympathetic and sympathetic pathways, respectively. LiCl was used as stimulus for c-Fos-like immunohistochemistry. HAP neurons were located mainly in the dorsal, ventral and lateral regions of the parvocellular PVN, while LCA neurons were observed predominantly in the magnocellular region of the PVN rostrally to HAP neurons. A significant number of FG/Fos double-labelled neurons were located in the dorsal parvocellular subnucleus of the PVN (dp) in the LiCl-stimulated rats. We concluded that there is a clear segregation of LCA neurons from HAP neurons within the PVN. The presence of FG/Fos double-labelled neurons in the dp suggests that this nucleus could mediate a sympathetic response after LiCl administration.

Animals↗
PubMed1998

The contribution of covert attention to the set-size and eccentricity effects in visual search.

To reexamine the role of covert attention in visual search, the authors directly manipulated attention by peripherally cueing the target location and analyzed its effects on the set-size and the eccentricity effects. Observers participated in feature and conjunction tasks. Experiment 1 used precues, and Experiment 2 used postcues in a yes-no task under valid-, invalid-, and neutral-cueing conditions. Experiments 3 and 4 used a 2-interval alternative forced-choice visual-search task under cued and neutral conditions. Precueing the target location improved performance in feature and conjunction searches; postcueing did not. For the cued targets, the eccentricity effect for features and conjunctions was diminished, suggesting that the attentional mechanism improves the quality of the sensory representation of the attended location. The conjunction set-size effect was reduced but not eliminated. This questions serial-search models that attribute a major role to covert attention in visual search.

Adult↗
PubMed1998

Multivariate time series analysis in nosocomial infection surveillance: a case study.

BACKGROUND: The present study describes the use of time series analysis in the evaluation of the incidence of nosocomial infection. The main hypothesis analysed was that monthly occurrence of nosocomial infection in a hospital may be related to work-related factors such as the control and training of personnel imposed by a surveillance system, strikes supported by medical personnel and movement of personnel. Time series analysis was used to quantify, model and statistically evaluate these interventions. METHODS: The data employed (March 1982-December 1990) were supplied by the nosocomial infection surveillance system of a primary-care general hospital. The monthly time series incidence of nosocomial infections (measured as percentage cumulative incidence) was analysed by curve fitting, autoregressive, integrated and moving average (ARIMA) modelling (Box-Jenkins) and intervention and dynamic regression analysis. RESULTS: The imposed control and training of personnel by the surveillance system was associated with a 3.63% decrease in the accumulated monthly incidence of nosocomial infection from 7.82% to a baseline level of 4.19%. There was a strong indication that an increase of infection incidence of 4.34% corresponded to a medical strike. This increase was maintained over the following months raising the baseline level to 4.84%. An increase of 0.18% was associated with each new nursing contract. Evidence was obtained for the possible relationship between incidence of nosocomial infection and vacation periods. CONCLUSIONS: The results suggest the need for strict control of the activities of hospital personnel and for the adoption of certain preventative measures during vacation periods to avoid an undesirable increase in the incidence of nosocomial infections.

Case-Control Studies↗
PubMed1998

The role of attention and study time in explicit and implicit memory for unfamiliar visual stimuli.

The effects of limited attentional resources and study time on explicit and implicit memory were studied using Schacter and Cooper's possible and impossible objects in their recognition and object decision paradigm. In one experiment, when attention at study was limited by a flanking digits procedure, object recognition was diminished but object decision priming for possible objects was unaffected; in another experiment, limiting attention plus reducing stimulus study time impaired object recognition and eliminated object priming. Recognition memory and perceptual priming for previously unfamiliar visual stimuli were both influenced by attention, although to different degrees. The intervening variable of study time determined the degree to which priming was affected by attentional resources. These results support a limited capacity attentional model for both recognition and perceptual priming of unfamiliar visual stimuli, and they highlight the need for assessing the interaction of attentional resources and study time in explicit and implicit memory tasks.

Adolescent↗
PubMed1998

"Transient structures": the effects of practice and distractor grouping on within-dimension conjunction searches.

It has been stated that whereas between-dimension (color x orientation) conjunctions can be searched in a "parallel" fashion, within-dimension (color x color) conjunctions are necessarily searched in a "serial self-terminating" fashion (Wolfe et al., 1990). We explored the effects of practice (within 1-h experimental session) and distractor grouping on within-dimension conjunction search tasks. In Experiments 1 and 3, the stimuli were rectangles formed by two adjacent squares; in Experiment 2, the stimuli were plus signs formed by two segments and an intersection. In Experiments 1 and 2, observers were assigned to one of two experimental conditions: In one, all the distractors shared a simple feature (the color blue); in the other, distractors did not share that simple feature. In the first condition, search became more efficient with practice and observers' performance was characterized by a shallow reaction time (RT) x set size slope; in the second condition, observers' performance did not improve as much with practice. We propose that the differential effects of practice between these two experimental conditions can be explained in terms of distractor grouping induced by the shared color of the distractors. Experiment 3 showed that, with practice, a shallow RT x set size slope characterized observers' search for a color x color target among four different distractors that shared a common color. The present results contradict a main tenet of some current visual search models--namely, that within-dimension conjunctions cannot be searched in parallel, and question the validity of using RT x set size slope functions to distinguish between preattentive versus attentive search.

Analysis of Variance↗