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PubMed2006

Oxygen pressures in the interstitial space and their relationship to those in the blood plasma in resting skeletal muscle.

This study compared oxygen pressures (Po(2)), measured by oxygen-dependent quenching of phosphorescence, in the intravascular (blood plasma) space in the muscle with those in the interstitial (pericellular) space. Our hypothesis was that the capillary wall would not significantly impede oxygen diffusion from the blood plasma to the pericellular space. A new near-infrared oxygen sensitive probe, Oxyphor G3, was used to obtain oxygen distributions in the interstitial space. Oxyphor G3 is a Pd-tetrabenzoporphyrin encapsulated inside generation 2 poly-arylglycine (AG) dendrimer. The periphery of the dendrimer is modified with oligoethylene glycol residues (average molecular weight 350) to make the probe water soluble and biologically inert. Oxyphor G3 was injected into thigh muscle using a 30-gauge needle. Histograms of the Po(2) in the interstitial space were measured in awake and anesthetized animals and compared with those for Oxyphor G2 in the intravascular (blood plasma) space. For awake mice, the lowest 10% of Po(2) values for the interstitial and intravascular spaces (believed to represent capillary bed) were not significantly different [23.8 (SD 4.5) and 25 Torr (SD 4.3), respectively], whereas, in isoflurane-anesthetized mice, there was a small but significant (P = 0.01) difference [20.4 (SD 6.3) and 27.9 Torr (SD 3.5), respectively]. The peak values for the histograms for the interstitial space in awake and isoflurane-anesthetized mice were 40.8 (SD 7.5) and 36.9 Torr (SD 8.3), respectively, whereas those for the intravascular space were 52.2 (SD 4.9) and 55.9 Torr (SD 8.4), respectively, showing no significant difference due to isoflurane anesthesia. The histograms for the intravascular space were significantly wider, with more contribution at higher Po(2) values. A different anesthetic, ketamine plus xylazine injected intraperitoneally, caused a marked decrease in the tissue Po(2) values in both spaces, with the time course and extent of the decrease dependent on the time after injection and variable among mice. It was, therefore, not further used.

Animals↗
PubMed2002

Protein synthesis is required for the enhancement of long-term potentiation and long-term memory by spaced training.

Spaced training is generally more effective than massed training for learning and memory, but the molecular mechanisms underlying this trial spacing effect remain poorly characterized. One potential molecular basis for the trial spacing effect is the differential modulation, by distinct temporal patterns of neuronal activity, of protein synthesis-dependent processes that contribute to the expression of specific forms of synaptic plasticity in the mammalian brain. Long-term potentiation (LTP) is a type of synaptic modification that may be important for certain forms of memory storage in the mammalian brain. To explore the role of protein synthesis in the trial spacing effect, we assessed the protein synthesis dependence of hippocampal LTP induced by 100-Hz tetraburst stimulation delivered to mouse hippocampal slices in either a temporally massed (20-s interburst interval) or spaced (5-min interburst interval) fashion. To extend our studies to the behavioral level, we trained mice in fear conditioning using either a massed or spaced training protocol and examined the sensitivity of long-term memory to protein synthesis inhibition. Larger LTP was induced by spaced stimulation in hippocampal slices. This improvement of synaptic potentiation following temporally spaced synaptic stimulation in slices was attenuated by bath application of an inhibitor of protein synthesis. Further, the maintenance of LTP induced by spaced synaptic stimulation was more sensitive to disruption by anisomycin than the maintenance of LTP elicited following massed stimulation. Temporally spaced behavioral training improved long-term memory for contextual but not for cued fear conditioning, and this enhancement of memory for contextual fear was also protein synthesis dependent. Our data reveal that altering the temporal spacing of synaptic stimulation and behavioral training improved hippocampal LTP and enhanced contextual long-term memory. From a broad perspective, these results suggest that the recruitment of protein synthesis-dependent processes important for long-term memory and for long-lasting forms of LTP can be modulated by the temporal profiles of behavioral training and synaptic stimulation.

Animals↗
PubMed2006

Specialized face perception mechanisms extract both part and spacing information: evidence from developmental prosopagnosia.

It is well established that faces are processed by mechanisms that are not used with other objects. Two prominent hypotheses have been proposed to characterize how information is represented by these special mechanisms. The spacing hypothesis suggests that face-specific mechanisms primarily extract information about spacing among parts rather than information about the shape of the parts. In contrast, the holistic hypothesis suggests that faces are processed as nondecomposable wholes and, therefore, claims that both parts and spacing among them are integral aspects of face representation. Here we examined these hypotheses by testing a group of developmental prosopagnosics (DPs) who suffer from deficits in face recognition. Subjects performed a face discrimination task with faces that differed either in the spacing of the parts but not the parts (spacing task), or in the parts but not the spacing of the parts (part task). Consistent with the holistic hypothesis, DPs showed lower performance than controls on both the spacing and the part tasks, as long as salient contrast differences between the parts were minimized. Furthermore, by presenting similar spacing and part tasks with houses, we tested whether face-processing mechanisms are specific to faces, or whether they are used to process spacing information from any stimulus. DPs' normal performance on the tasks of two houses indicates that their deficit does not result from impairment in a general-purpose spacing mechanism. In summary, our data clearly support face-specific holistic hypothesis by showing that face perception mechanisms extract both part and spacing information.

Adolescent↗
PubMed1984

Some observations on spacing in the normal deciduous dentition of 100 Indian children from Gujarat.

Plaster casts of 50 boys and 50 girls aged 3-6 years, from Gujarat, India, were studied to observe the pattern of spacing in the normal deciduous dental arches. Spaced type of dental arches were more common than closed type or 'no spaces' type. Spacing/no spacing appeared to behave independently between upper and lower arches and between the sexes. The amount of spacing was greater in males than in females. Bilateral anthropoid spaces did not exist as a single phenomenon. They occurred when some other spaces were also present. Anthropoid spaces were more in the upper arch than in the lower and more in males than in females. If anthropoid spaces occurred in the upper arch, they were frequently missing from the lower arch; this was observed more in females than males. Spacing on the left side was more than the right side. Spacing between the mandibular incisors was the greatest of all.

Child↗
PubMed1993

Detection of focal hepatic lesions with spiral CT: comparison of 4- and 8-mm interscan spacing.

OBJECTIVE: The objective of this study was to determine if spiral CT with 4-mm interscan spacing results in increased confidence in or rate of detection of focal hepatic lesions when compared with spiral CT with 8-mm interscan spacing. MATERIALS AND METHODS: Spiral CT scans of the liver of 42 consecutive patients with suspected hepatic disease were independently reviewed by three senior radiologists in two sets: one set was reconstructed with 8-mm interscan spacing and one set was reconstructed with 4-mm interscan spacing. The slice thickness was 8 mm for both data sets. The number and sizes of focal hepatic lesions were documented. RESULTS: Thirty-three of the 42 patients had least one focal lesion. The lesion size varied from 2 mm to 21 cm. When 8-mm interscan spacing was used, 297 lesions were detected (212 were considered definite). When 4-mm interscan spacing was used, 318 lesions were detected (258 were considered definite). Therefore, 7% more lesions were detected with 4-mm interscan spacing than with 8-mm interscan spacing (p = .05), and 22% more were diagnosed definitively (p < .01). If lesions larger than 4 cm are excluded, 10% more lesions were detected with 4-mm interscan spacing, and 33% more were diagnosed definitively. Of the lesions detected exclusively with 4-mm interscan spacing, 69% were less than 1.0 cm in diameter. CONCLUSION: Spiral CT with smaller interscan spacing (4 instead of 8 mm) results in increased confidence in and rate of detection of focal liver lesions. The additional benefit is most significant with smaller lesions.

Adult↗
PubMed2003

The growth performance of the progeny of two swine sire lines reared under different floor space allowances.

A total of 736 pigs was used in a study with a 2 x 2 x 2 factorial arrangement to investigate the effects of and interactions between sire line (Line A vs. B), floor space (unrestricted vs. restricted), and gender (barrow vs. gilt) on growth performance, BW, and protein and estimated lipid accretion curves from 40 to 120 kg of BW. Pigs were by eight Line-A and nine Line-B sires mated with PIC C22 dams. Line A was of Pietrain ancestry and Line B was a synthetic line. The unrestricted floor space treatment consisted of small groups (four pigs) with 0.93 m2/pig of floor space for the entire grow-finish period. Pigs in the restricted floor space were in larger groups (12 pigs) with 0.37 and 0.56 m2/pig of floor space for the grower and finisher phases, respectively. Pigs were given ad libitum access to a three-phase dietary program, and one and three nipple waterers were available in the groups of 4 and 12 pigs, respectively. No sire line x floor space interactions were found for any of the traits measured. Line A pigs grew more slowly (50 g/d, P < 0.05), took longer (4.1 d, P < 0.05) to reach harvest weight (120.3 kg), and had similar feed intakes, but a lower gain:feed ratio (2.8%, P < 0.05) than Line B pigs. Line A pigs had greater longissimus muscle depth (P < 0.05) and estimated protein accretion rate (P < 0.05) than Line B pigs, but Line A and Line B pigs had a similar estimated percentage of lipid-free soft tissue. Pigs reared in the restricted floor space grew more slowly (105 g/d, P < 0.05) and consumed less feed (280 g/d, P < 0.05) but had a similar (P > 0.05) gain:feed ratio to pigs reared in the unrestricted floor space. Pigs reared in the unrestricted floor space had greater (P < 0.05) predicted protein and lipid accretion rates throughout the growth period than pigs reared in the restricted floor space. Differences between genders for growth traits and carcass measurements were in agreement with previous research. The differences in growth performance, carcass measures, and compositional growth curves between these two sire lines were similar in the two floor spaces.

Adipose Tissue↗
PubMed1999

Immune privilege is extended, then withdrawn, from allogeneic tumor cell grafts placed in the subretinal space.

PURPOSE: To determine whether the subretinal space can extend immune privilege to allogeneic tumor cell grafts that do not possess their own inherent immune privilege. METHODS: P815 tumor cells were injected into the anterior chamber (AC), the subretinal (SR) space, or subconjunctivally in eyes of BALB/c (allogeneic), SCID (immune incompetent), normal DBA/2 (syngeneic), or DBA/2 mice presensitized with P815 cells transfected with interleukin-12 and B7.1. Tumor growth was observed clinically and histologically for up to 50 days. BALB/c recipients were tested for suppression of DBA/2-specific delayed hypersensitivity and concomitant immunity. The SR space of tumor-containing eyes was assessed for its capacity to support ovalbumin (OVA)-specific anterior chamber associated immune deviation (ACAID). RESULTS: P815 cells injected into the SR space of presensitized and normal DBA/2 and SCID mice grew progressively, resulting eventually in recipient death. Tumor cells injected into the SR space of eyes of BALB/c mice grew progressively until day 14, followed by tumor regression resulting in phthisis bulbi (14/35) or tumor elimination (19/35) with preserved ocular anatomy by day 35. Despite elimination of tumors from the SR space, BALB/c recipients exhibited DBA/2-specific ACAID and concomitant immunity. In addition, OVA injected into the SR space of eyes from which tumor has been eliminated induced ACAID. CONCLUSIONS: Various parameters of immune privilege, originally described for the AC, are characteristic of immune privilege within the SR space. However, because P815 cells placed in the AC prove lethal for BALB/c recipients, but P815 cells placed in the SR space resolve without jeopardizing the host's life, immune privilege in the SR space can be distinguished from immune privilege in the AC, and this may have implications for grafts of retinal tissue placed within the SR space.

Animals↗
PubMed1995

Deep neck space infections.

The incidence of deep neck space infections has dramatically decreased since the advent of antibiotics, but with delayed treatment they carry the potential for significant morbidity and mortality. Odontogenic infections with involvement of the submandibular space are the most common source of deep neck space infections in adults, whereas in the pediatric population the most common cause is acute tonsillitis with involvement of the peritonsillar space. The newest group of patients at risk for deep neck space infections are intravenous drug abusers who inject the major vessels of the neck. Knowledge of neck spaces and fascial relationships is important in understanding the presentation, treatment, and complications of deep neck space infections. The spaces, which are created by various fasciae of the head and neck, are only potential spaces in that under normal conditions they cannot be examined clinically or radiographically. As the spaces are invaded by bacteria, a cellulitis or abscess occurs, and this infection may travel through paths of least resistance from one space to another.

Adult↗
PubMed1979

Space motion sickness.

Space motion sickness, presumably triggered by sudden entry into a weightless environment, occurred with unexpected frequency and severity among astronauts who flew the Skylab missions. Recovery from symptoms was complete within 3-5 days, and as revealed by the Skylab M131 Human Vestibular Function Experiment, all crewmembers were immune to experimentally induced motion sickness after mission day 8. This syndrome has been recognized as a possible threat to the early mission well-being and operational efficiency of at least some individuals who will fly space missions in the future. The causes of space motion sickness are not clearly understood, nor have satisfactory methods been identified to date for its prediction, prevention and treatment. In order to minimize the potential impact of this syndrome on Space Shuttle crew operations the National Aeronautics and Space Administration has organized a broad program of inter-disciplinary research involving a large number of scientists in the United States. Current research on the etiology of space motion sickness is based to a large extent on the so called sensory conflict theory. Investigations of the behavioral and neurophysiological consequences of intralabyrinthine, as well as intermodality sensory conflict are being performed. The work in this area is being influenced by the presumed alterations that occur in otolith behavior in weightlessness. In addition to sensory conflict, the possible relationship between observed cephalad shifts of body fluids in weightlessness and space motion sickness is being investigated. Research to date has failed to support the fluid shift theory. Research underway to identify reliable test methods for the prediction of susceptibility to space motion sickness on an individual basis includes attempts to (a) correlate susceptibility in different provocative environments; (b) correlate susceptibility with vestibular and non-vestibular response parameters, the latter including behavioral, hemodynamic and biochemical factors and (c) correlate susceptibility with rate of acquisition and length of retention of sensory adaptation. Controlled studies are also being performed during parabolic flight as a means of attempting to validate predictive tests for susceptibility to this syndrome. Research to develop new or improved countermeasures for space motion sickness is underway in two primary areas. One of these involves anti-motion sickness drugs. Significant achievements have been realized with regard to the identification of new highly efficacious drug combinations, dose levels and routes of administration. Although pronounced individual variations must be accounted for in selecting the optimum drug and dose level, combinations of promethazine plus ephedrine or scopolamine plus dexidrine are presently the drugs of choice. Work is also underway to identify side effects associated with anti-motion sickness drug use and to identify new drugs which may selectively modify activity in central neural pathways involved in motion sickness. In addition to research on drugs, efforts are being made to develop practical vestibular training methods. Variables which influence rate of acquisition of adaptation, length of retention of adaptation and transfer of protective adaptation to new environments are being evaluated. Also, included in this area is the use of biofeedback and autogenic therapy to train individuals to regulate autonomic responses associated with motion sickness. While valuable new knowledge is expected to evolve from these combined research programs, it is concluded that the final validation of predictive tests and countermeasures will require a series of controlled space flight experiments.

Adaptation, Physiological↗
PubMedDate not supplied

The Soviet-Russian space suits a historical overview of the 1960's.

The development of protective suits for space use started with the Vostok-suit SK-1, first used by Yu. Gagarin on April 12, 1961, and then used on all subsequent Vostok-flights. The technical background for the design of these suits was the work on full pressure protective suits for military pilots and stratospheric flights in the 1930's through 50's. The Soviet-Russian space programme contains a large number of 'firsts', and one of the most well known is the first EVA by Leonov in 1965. This event is also the starting point for a long series of space suit development for Extravehicular Activities over the last 35 years. The next step to come was the transfer in void space of crew members between the two spacecraft Soyuz 4 and 5 in 1969. As has later become known this was an essential element in the planned Soviet lunar exploration programme, which in itself required a new space suit. After the termination of the lunar programme in 1972, the space suit development concentrated on suits applicable to zero-gravity work around the manned space stations Salyut 6, Salyut 7 and MIR. These suits have become known as the ORLAN-family of suits, and an advanced version of this suit (ORLAN-M) will be used on the International Space Station together with the American EMU. This paper covers the space suit development in the Soviet Union in the 1960's and the experience used from the pre-space era.

Astronauts↗
PubMed1993

Interstitial space and collagen alterations of the developing rat diaphragm.

The effect of growth on the relative interstitial space [%total cross-sectional area (CSA)] and collagen content of the rat diaphragm muscle was examined at postnatal ages of 0, 7, 14, and 21 days as well as in adult males. The proportion of interstitial space relative to total muscle CSA was determined by computerized image analysis of lectin-stained cross sections of diaphragm muscle. To assess collagen content and extent of collagen maturation (i.e., cross-linking), high-pressure liquid chromatography analysis was used to measure hydroxyproline concentration and the nonreducible collagen cross-link hydroxylysylpyridinoline (HP), respectively. At birth, interstitial space accounted for approximately 47% of total diaphragm muscle CSA. During postnatal growth, the relative contribution of interstitial space decreased such that by adulthood the interstitial space accounted for approximately 18% of total muscle CSA. The change in relative interstitial space occurred without a concomitant change in hydroxyproline concentration. However, the concentration of HP markedly increased with age such that the adult diaphragm contained approximately 17 times more HP than at birth. These results indicate that during development the relative CSA occupied by interstitial space decreases as muscle fiber size increases. However, the reduction in relative interstitial space is not associated with a change in collagen concentration. Thus collagen density in the interstitial space may increase with age. It is possible that the observed changes in relative interstitial space and collagen influence the passive length-force properties of the diaphragm.

Animals↗
PubMed2000

The medical implications of space tourism.

UNLABELLED: Commercial space travel may soon be a reality. If so, microgravity, high acceleration, and radiation exposure, all known hazards, will be accessible to the general public. Therefore, space tourism has medical implications. Even though the first flights will feature space exposure times of only a few minutes, the potential may someday exist for exposure times long enough to warrant careful consideration of the potential hazards to the space-faring public. The effects of acceleration and microgravity exposure are well known on the corps of astronauts and cosmonauts. The effects of space radiation are partially known on astronauts, but much remains to be discovered. However, there are problems using astronaut data to make inferences about the general public. Astronauts are not necessarily representative of the general public, since they are highly fit, highly screened individuals. Astronaut data can tell us very little about the potential hazards of microgravity in pediatric, obstetric and geriatric populations, all of whom are potential space tourists. Key issues in standard setting will be determining acceptable limits of pre-existing disease and inferring medical standards from mission profiles. It will not be a trivial task drafting minimal medical standards for commercial space travel. It will require the collaboration of space medicine physicians, making the best guesses possible, based on limited amounts of data, with limited applicability. A helpful departure point may be the USAF Class 3 medical standard, applicable to NASA payload specialists. It is time to begin preliminary discussions toward defining those standards. KEYWORDS: acceleration, aerospace medicine, medical standards, microgravity, radiation, space, space tourism, environmental hazards, environmental medicine.

Aerospace Medicine↗
PubMed1997

Intracellular, interstitial and plasma spaces in the rat myocardium in vivo.

The aim of this study was to determine tissue water spaces in rat heart in vivo using [14C]-inulin or D-[14C]-mannitol as extracellular markers, and 2,3DPG as whole blood tissue marker. Tracer was injected into the jugular vein of anaesthetised male Sprague-Dawley rats (60 mg/kg) and allowed to equilibrate for 30 min. A blood sample was then taken and the heart was freeze-clamped at liquid N2 temperatures within 5 s of opening the chest cavity. Extracellular space was calculated by dividing the total tissue counts (d/min/g) by plasma counts (d/min/g). The extracellular inulin and mannitol spaces were 0.212+/-0.010 and 0.236+/-0.012 ml/g wet weight tissue, respectively (n=5). Expressed as a percentage of total tissue water (0.79+/-0.012 ml/g wet weight tissue, n=9), the intracellular space was found to be 73.1 (inulin) and 70.1% (mannitol). The interstitial space was calculated by subtracting the counts in tissue due to whole blood from total tissue counts and dividing by plasma counts. The interstitial space was 19.4 and 21. 9%; and the plasma space was 7.5 and 8.0% for the inulin and mannitol methods, respectively. We conclude that (i) there was no significant differences in the inulin or mannitol spaces in the in vivo heart (P<0.05), demonstrating that either marker provides a reliable and quantitative estimate of extracellular space, and (ii) 2,3-DPG can be used as a reliable indicator of tissue whole blood which can then be used in combination with the tracer method to calculate the interstitial and plasma spaces.

2,3-Diphosphoglycerate↗
PubMed2005

Saccadic search performance: the effect of element spacing.

In a saccadic search task, we investigated whether spacing between elements affects search performance. Since it has been suggested in the literature that element spacing can affect the eye movement strategy in several ways, its effects on search time per element are hard to predict. In the first experiment, we varied the element spacing (3.4 degrees -7.1 degrees distance between elements) and target-distracter similarity. As expected, search time per element increased with target-distracter similarity. Decreasing element spacing decreased the search time per element. However, this effect was surprisingly small in comparison to the effect of varying target-distracter similarity. In a second experiment, we elaborated on this finding and decreased element spacing even further (between 0.8 degrees and 3.2 degrees). Here, we did not find an effect on search time per element for element spacings from 3.2 degrees to spacings as small as 1.5 degrees . It was only at distances smaller than 1.5 degrees that search time per element increased with decreasing element spacing. In order to explain the remarkable finding that search time per element was not affected for such a wide range of element spacings, we propose that irrespective of the spacing crowding kept the number of elements processed per fixation more or less constant.

Adult↗
PubMed1988

Plasma and urine catecholamine levels in cosmonauts during long-term stay on Space Station Salyut-7.

The activity of the sympathetic adrenal system in cosmonauts exposed to a stay in space lasting for about half a year has so far been studied only by measuring catecholamine levels in plasma and urine samples taken before space flight and after landing. The device "Plasma 01", specially designed for collecting and processing venous blood from subjects during space flight on board the station Salyut-7 rendered it possible for the first time to collect and freeze samples of blood from cosmonauts in the course of a long-term 237-day space flight. A physician-cosmonaut collected samples of blood and urine from two cosmonauts over the period of days 217-219 of their stay in space. The samples were transported to Earth frozen. As indicators of the sympathetic adrenal system activity, plasma and urine concentrations of epinephrine and norepinephrine as well as urine levels of the catecholamine metabolites metanephrine, normetanephrine, and vanillylmandelic acid were determined before, during and after space flight. On days 217-219 of space flight plasma epinephrine and norepinephrine levels were slightly increased, yet not substantially different from normal. During stress situations plasma norepinephrine and epinephrine levels usually exhibit a manifold increase. On days 217-219 of space flight norepinephrine and epinephrine levels in urine were comparable with pre-flight values and the levels of their metabolites were even significantly decreased. All the parameters studied, particularly plasma norepinephrine as well as urine norepinephrine, normetanephrine, and vanillylmandelic acid, reached the highest values 8 days after landing. The results obtained suggest that, in the period of days 217-219 of the cosmonauts stay in space in the state of weightlessness, the sympathetic adrenal system is either not activated at all or there is but a slight activation induced by specific activities of the cosmonauts, whereas in the process of re-adaptation after space flight on Earth this system is considerably more markedly activated.

Adrenal Glands↗
PubMed1994

Ethological experiments on human orientation behavior within a three-dimensional space--in microgravity.

In weightlessness situation the subject has to realize domestic and professional tasks comparable to those performed under normal gravity, whereas the "body tool" available to him has been placed in new conditions which require significant behavioral changes. The loss of weight, the disappearance or modification of some ideothetic and allothetic cues, notably the absence of gravity for the body's referential verticality have the most obvious effect of diversifying the astronaut's orientations. The vertical position is thus no longer the only one possible. This means that in order to efficiently accomplish his tasks, the subject has to invent new motor strategies which transform the quality of displacements and manipulations on the basis of the new orientation possibilities in a three-dimensional space. The previous ethological studies have dealt, in a global way, with the astronaut's motor behavior in microgravity, revealed according to an exhaustive quantitative description of the behavioral manifestions as a whole in terms of movement, posture and orientation. We now propose focusing more specifically on his spatial behavior in a three-dimensional space in microgravity. Such a situation is an exceptional experimental paradigm since at every moment, the relationships of the body referential to the surrounding space are infinitely variable: a man in space has to extract, process or use spatial information between the referentials of his moving body in all directions of the three-dimensional space and the fixed referentials of the physical environment of the space habitat. Furthermore, in the temporal dynamics, the previous ethological results showed that the behavioral events change according to the duration of the space mission, passing through different adaptative stages from a large behavioral diversity to complete behavioral reorganization. On the first day of his space mission the astronaut has however acquired experience of microgravity through his training, simulated on the ground and realized in parabolic flights. Some immediate adaptative processes are already present. As a result, the subject's experience of such a situation has to be emphasized from the initial moments of adaptation to microgravity. We thus postulate that the subject, through his orientation behavior in a three-dimensional space, according to his experience and over time, would elaborate a new representation of the space, as part of the whole adaptative process to this new environment. In order to verify such hypotheses, the present study will propose three levels of observation, i.e. three experiments in conditions of orbital flight, parabolic flight, visual simulation.

Adult↗
PubMed2005

Visuospatial neglect in near and far space: dissociation between line bisection and letter cancellation.

The differential performance on a line bisection and a cancellation task in near and far space was studied. A group of 10 patients with severe left-sided visuospatial neglect and a group of 10 right-brain damaged patients without neglect were examined. The stimuli were presented at a distance of 60 cm (near space) and 160 cm (far space), respectively, and corrected for visual angle. In the line bisection task, patients were asked to point to the estimated line centre with a pencil (near space) or a stick (far space). In the cancellation task, patients pointed to all target stimuli they could detect using either a pencil (near space) or a stick (far space). Most patients with left hemineglect showed a more prominent neglect in far space as compared to near space for the line bisection task, whereas no difference of performance between near and far space was found in the control patients. In contrast, no group showed a distance effect in the cancellation task. The observation that only line bisection is influenced by the distance of the stimulus suggests that line bisection and cancellation are processed differentially. It is proposed that line bisection requires an allocentric reference system focusing attention on objects, whereas cancellation tasks are based on an egocentric reference system responsible for visuospatial attention. Our results indicate that distance changes perception within the allocentric but not within the egocentric system.

Adult↗
PubMed1998

Intrinsic optical signals in vitro: a tool to measure alterations in extracellular space with two-dimensional resolution.

In excitable tissues, extensive neuronal activity or pathophysiological conditions, such as spreading depression, ischemic infarct, or epileptic seizure, are accompanied by changes in extracellular space volume. Extracellular space volume, in turn, influences neuronal excitability and extracellular ion concentrations and is, therefore, an important parameter of brain activity. Unfortunately, determination of changes in extracellular space by ion-selective microelectrodes is tedious, restricted to one spot in space at a time and limited in time resolution. In this study we present intrinsic optical signals in vitro as a tool to measure relative changes in extracellular space volume in brain slice preparations with two-dimensional spatial and sufficient time resolution. Evidence is given that the intensity of intrinsic optical signals is linearly correlated to the amplitude of extracellular space volume changes. In contrast, the optical signal is poorly correlated to the concomitant increase in extracellular potassium concentration. We conclude that intrinsic optical signals in vitro are a useful tool to measure the spread of changes in extracellular space volume with high resolution in time and space. In combination with the measurement of the extracellular space at one location using ion-selective microelectrodes, it is possible to calibrate the optical signal to percentile alterations of extracellular space volume.

Animals↗