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Biomedical subjects

G G Mascetti

Publications and source records attributed to G G Mascetti.

At least 19 recordsLinked to original sources
PubMed2001

Neuroendocrine responses to experimentally-induced psychological stress in healthy humans.

Previous studies of hormonal and neurophysiological changes in response to psychological stress in humans have produced contrasting findings due to differing experimental procedures and consistent individual variability. Habituation effects, which influence physiological coping in response to exposure to repeated stress, need to be investigated more extensively. In the present study, twenty healthy male subjects were each exposed twice to the same psychosocial stressor (Stroop Color Word Interference task, public speaking and mental arithmetic in front of an audience) during a first session (day 1) and a second session (day 8). Plasma concentrations of norepinephrine (NE), epinephrine (EPI), adrenocorticotropic hormone (ACTH), cortisol (CORT) and prolactin (PRL) were measured immediately before the beginning of the tests and at their end, 30 min later, on both experimental days. For the total group, NE, EPI, ACTH, and CORT levels were significantly elevated, and PRL levels were significantly decreased, after stress exposure on day 1. ACTH and CORT levels showed less significant increases after stress on day 8. In contrast, NE and EPI responses to stress were not significantly blunted, and PRL response was unchanged on day 8. Cluster analysis revealed two groups of subjects who showed different habituation patterns for ACTH and CORT. The first group (n=12) of subjects showed a reduction of ACTH and CORT responses to stress on day 8. The subjects of the second group (n=8) displayed a significant increase of ACTH and cortisol in response to stress on day 8, without any habituation effect. These results increase the evidence concerning the involvement of the HPA axis and catecholamines in response to psychological stress, and suggest that possible individual differences in the neuroendocrine coping mechanisms may affect mood regulation and the state of health.

Adrenocorticotropic Hormone↗
PubMed2000

Visual-spatial attention in developmental dyslexia.

Orienting and focusing of visual attention are two processes strictly involved in reading. They were studied in a group of dyslexic children and normal readers. Shifting of attention by both peripheral and central visual cues was studied by means of the covert orienting paradigm. Focusing, consisting in the ability to control the size of the attentional focus, was investigated using simple reaction times in central vision. Results showed that dyslexics had a specific disability in the shifting of attention caused by a peripheral cue at short SOAs, and were also able to maintain attention focused for short periods of time only, presumably not long enough for efficient visual processing. Our results support the suggestion that visual selective attention deficits in disabled readers may be due to a specific difficulty in orienting and focusing.

Adult↗
PubMed2000

Automatic and voluntary focusing of attention.

In this study, we investigate whether attentional focusing, like attentional orienting, comprises two independent mechanisms. We provide direct empirical evidence in favor of the existence of two mechanisms--one exogenous, or automatic, and one endogenous, or voluntary--that play a role in adjusting the size of the focus of attention. When a new object suddenly occurs in the visual field, the focus is first automatically fitted to it, and then an endogenous effort has to be exerted to maintain attention in the focused mode. Also, we provide evidence that voluntary focusing needs a perceptual object in order to operate.

Adult↗
PubMed1999

Visuospatial attention in myopia.

Four experiments were conducted to ascertain whether myopia is associated with deficits of visuospatial attention. In myopic and emmetropic control subjects, we studied: (1) automatic and voluntary orienting of attention, (2) focusing of attention and (3) performance on a visual search task. The results indicated that automatic orienting was defective in myopics and their performance in visual search was less efficient than that of controls. By contrast, myopics showed no deficits in voluntary orienting and in focusing.

Analysis of Variance↗
PubMed1999

Visual lateralization and monocular sleep in the domestic chick.

Behavioural sleep during the first 2 weeks of life was investigated in female chicks reared with an imprinting object or in social (visual) isolation. Binocular sleep tended to decrease and monocular sleep to increase with age in both rearing conditions. In chicks reared with an imprinted object. during the first week, monocular sleep with either right or left eye closure occurred with approximately the same frequency, except that on day 5 in which right eye closure dominated; during the second week, however, there was a clear bias towards more monocular sleep with left eye closure. During the second week, the pattern of monocular sleep was similar in both rearing conditions, but during the first week chicks reared with the imprinting object showed relatively more right eye closure compared to chicks reared without the imprinting object, an effect that might tentatively be associated with consolidation of imprinting memories in the left hemisphere. Binocular sleep occurred in all four body postures adopted by chicks during sleep: standing sleep, sleep with bill forward, sleep with bill on the ground, and sleep with head on the ground. Monocular sleep, in contrast, only occurred when chicks adopted the bill forward posture. When the colour of the imprinting object was suddenly changed on day 8, a striking shift towards predominant right eye closure during monocular sleep was observed. The same occurred when the imprinting object was suddenly removed from the home-cage on day 8, but not with other types of changes (i.e., when a novel different object was inserted into the home-cage or when a novel-coloured imprinting object was inserted into the home-cage together with the original one). It is argued that this phenomenon could be associated with right hemisphere involvement in response to novelty.

Aging↗
PubMed1998

Binocular behavior of split-brain cats which have previously learned monocularly opposite visual discriminations.

Twelve adult split-brain cats were tested binocularly in visual tasks which had been previously learned monocularly in a two-choice paradigm. Eight experimental cats learned two opposite tasks with two eyes because contingencies of reinforcement changed with the open eye. Four control cats learned the same tasks but contingencies of reinforcement did not change with the open eye and therefore they learned the same problems with the two eyes. Thereafter, cats were submitted binocularly to the same tasks but in a free-choice paradigm. Experimental cats showed extinction of the discriminative response in 12 out of 16 binocular testings; in four the extinction criterion was not reached. In control cats no extinction behavior was observed in seven out of eight testings. It is suggested that extinction of the discriminative response in experimental cats could be caused by an inhibitory effect build-up because the two hemispheres attempted to control binocular behavior in opposite ways. Alternatively, these cats may develop a response alternative to discrimination in which one hemisphere takes the control of subcortical motor and/or attentional centers. In four testings no extinction was recorded for experimental cats and it is likely that control of those centers shifted from one hemisphere to the other every few trials.

Animals↗
PubMed1997

Interaction between the hemispheres in split-brain cats.

Functional interactions between the two hemispheres were studied in adult split-brain cats. The aims were to assess whether monocular learning developed independently or that there were clues for interactions between the two sides of the brain during acquisition of opposite learning tasks. Experimental cats learned two visual pattern discriminations in which one pattern was positive for the right eye, whereas the other pattern was positive for the left eye. Control cats learned the same problems, but the same pattern was positive for both eyes. The open eye was changed from one session to the next in both groups of cats. In general, monocular performances of experimental cats were asymmetrical because they learned better and faster with one eye than with the other eye. Instead, no differences between the eyes were found in control cats. Statistical analysis of the data indicated that learning in experimental cats was significantly slower than learning in control cats, and that the difference between monocular performances was significantly greater for the experimental group than for the control group. The slower and asymmetrical monocular learning of experimental cats may reflect a conflict and a competition between the hemispheres for the control of learning behaviour, resulting in the dominance of one of them. Thus, some information about the stimuli must have been transmitted via the remaining interhemispheric connections. Symmetrical monocular learning of control group indicated that the competition for the control of behaviour was not present because there was no conflict between the hemispheres.

Analysis of Variance↗
PubMed1989

The internal horizontal cell of the frog: spatial summation.

The receptive field properties of internal horizontal cells (IHCs) were studied in the frog Rana pipiens. The space constant of each cell was determined by the use of stimulus spots of various sizes or by moving a light slit across the retina, varied from 100-500 microns by the former and 100-720 microns by the latter method. A similar range of values has been reported for Xenopus although its IHCs are much larger than the IHCs of Rana. Apparently, coupling among the IHCs is more efficient in the latter than in the former retina. The large range in values suggests substantial variation in coupling efficiency among cells of the same retina.

Animals↗
PubMed1988

Visual cells in the inferior colliculus of the cat.

Extracellular recordings from 91 cells of the pericentral nucleus (ICP) of the inferior colliculus of the cat revealed that 83 of them were responsive to auditory stimuli and the other 8 to visual stimuli. All visually driven cells were binocular and showed large receptive fields located in the contralateral hemifield. The best stimulus was either a spot or a bar moved in any direction across the receptive field. No directional selectivity was found. It is suggested that the visual input to the ICP participates in an integrated reflex-orienting behavior, in which the visual information is important for the localization of the sound source.

Acoustic Stimulation↗
PubMed1988

Interocular transfer of extinction of visual pattern discriminations in split-chiasm and split-brain cats.

The interocular transfer of the extinction of visual pattern discrimination was studied in cats with either section of optic chiasm (split-chiasm cats) or combined sections of chiasm and forebrain commissures (split-brain cats). Visual pattern discriminations were monocularly learned and their interocular transfer was assessed through the opposite eye. Then, learning was unilaterally extinguished and interocular transfer of extinction was tested on the other side. In split-chiasm cats, the total number of trials to extinction criterion (EC) was significantly lower with the second eye than with the first eye, indicating a successful interocular transfer. In split-brain cats, EC with the second eye was attained faster than with the first in some performances; it was similar with both eyes in other tasks, and with the second eye was higher than with the first in still other tasks. Statistical analysis applied to this group of split-brain cats pointed out that extinction performances with the two eyes were not significantly different. These findings suggest that interocular transfer of extinction was abolished in split-brain cats and that memory for extinction was unilaterally established in the absence of forebrain commissures.

Animals↗
PubMed1985

The outer horizontal cell of the frog retina: morphology, receptor input, and function.

The outer horizontal cell (OHC) of the frog Rana pipiens was studied by light and electron microscopy of Golgi-stained and horseradish peroxidase-injected cells. Responses of OHCs were recorded with intracellular electrodes. The OHCs are probably axonless cells. Their dendritic terminals are lateral processes at synaptic ribbons and are involved frequently in reciprocal invaginating contacts with receptors, ie, contacts characterized by invagination of receptor membrane deeply into the horizontal cell process. Two classes of OHC were distinguished on the basis of size and receptor contacts. Small OHCs (dendritic area about 5,000 micron2) contact all classes of receptor. These cells were not successfully penetrated with microelectrodes. Giant OHCs (dendritic area about 30,000 micron2) apparently contact only blue-sensitive rods and red-sensitive cones. They generate chromaticity or C-type responses, hyperpolarizing to short and depolarizing to long wavelength light.

Animals↗
PubMed1984

Perfect interocular transfer of visual pattern discriminations in split-chiasm cats trained with fading.

It has been reported that the interocular transfer of visual pattern discrimination is imperfect in split-chiasm cats. Perhaps the efficiency of callosal transfer is to some extent determined by the training procedure employed. To test that possibility, we trained 3 split-chiasm cats with a Classical Procedure used in interocular transfer studies (CP cats) and 4 split-chiasm cats with Fading (Fading cats). The Fading procedure consisted of the presentation of two stimuli which differed maximally at the beginning of training; through a series of gradual steps their difference was reduced to a minimal value required to control the desired discriminative behavior. Confirming previous studies, CP cats showed a drop in the discriminative performance when the viewing eye was changed from trained to untrained and they needed additional trials to reattain criterion with the untrained eye. Fading cats, however, showed no difference when the viewing eye was changed; criterion was immediately reached with the untrained eye. It is suggested that the perfect interocular transfer shown by the Fading paradigm represents efficient callosal transmission and stabilized, well organized memory traces.

Animals↗
PubMed1984

The internal horizontal cell of the frog. Analysis of receptor input.

The inner horizontal cell (IHC) of the retina of Rana pipiens was studied by light and electron microscopy of Golgi stained or horseradish peroxidase injected cells. Responses of IHCs were recorded with intracellular electrodes. Both axon and dendritic terminals of the IHC make synaptic contact with all classes of receptor. The terminals occur as lateral or medial processes at synaptic ribbons. Reciprocal invaginations of receptor into horizontal cell process are common. Different classes of receptor are contacted in about the proportions with which they occur in the retina. No tendency for contacts of one type of receptor to occur on a particular part of the cell was found. The IHC generates L-type S-potentials. Both rod and cone input is evident in the waveform of the response, its spectral sensitivity, and the effect on it of adaptation.

Animals↗
PubMed1978

Effects of lesions of areas 17, 18 and 19 on interocular transfer of pattern discriminations in split-chiasm cats.

Split-chiasm cats with unilateral or bilateral lesions largely removing the commissurally connected portions of visual cortical areas 17, 18 and 19 showed good interocular transfer of monocularly learned pattern discriminations. The capacity for interocular transfer in these cats was in fact little or not different from that of split-chiasm cats with an intact cortex. Split-chiasm cats with an additional section of the forebrain commissures, as well as two split-chiasm cats with 17-18 lesions also submitted to forebrain commissurotomy after having shown good interocular transfer, were generally incapable of transferring pattern discriminations between the eyes. It is concluded that interocular transfer of pattern discriminations, in split-chiasm cats does not require areas 17, 18 and 19 and must therefore depend on other cortical areas.

Animals↗
PubMed1978

Effects of experience on interocular transfer of pattern discriminations in split-chiasm and split-brain cats.

Interocular transfer of monocularly learned pattern discriminations was found to be imperfect in split-chiasm cats but to improve as a result of specific practice with interocular transfer tasks. Section of the forebrain commissures subsequently performed in these animals abolished immediate interocular transfer of pattern discriminations. However, there were some savings in reattaining the learning criterion with the second eye. Other cats that learned the same discriminations monocularly but had sustained a combined section of optic chiasm and forebrain commissures before learning showed no indication of interocular transfer. These data suggest that the commissural systems involved in interocular and interhemispheric transfer of pattern discriminations may be modified by practice and learning. Further, it is possible that the intervening transfer experience between the section of the optic chiasm and that of the forebrain commissures results in the persistence of some capacity for interocular transfer of pattern discriminations after commissurotomy. However, this residual capacity may be negligible when compared with the capacity for interocular transfer of split-chiasm cats with intact forebrain commissures.

Animals↗