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PubMed1997

Influence of the luminance and opponent chromatic channels on stereopsis with random-dot stereograms.

The present work examines the relationship between random-dot stereograms (via the disparity range parameter) and color-vision mechanisms (via the luminance channel and red-green and tritan directions at isoluminance). The results clearly indicate that the variations in the stereograms along red-green confusion lines contribute to stereopsis. Stereoscopic perception depends on spatial information for stereograms generated with variations along tritan confusion lines. For observers who perceive stereopsis via tritan directions, the results show a gradation in the disparity range, with the disparity range for stereograms generated by luminance variations being greater than for stereograms generated in red-green directions; the latter range is, in turn, greater than for stereograms generated along tritan directions.

Color Perception↗
PubMed1998

Perceived head-centric speed is affected by both extra-retinal and retinal errors.

When we make a smooth eye movement to track a moving object, the visual system must take the eye's movement into account in order to estimate the object's velocity relative to the head. This can be done by using extra-retinal signals to estimate eye velocity and then subtracting expected from observed retinal motion. Two familiar illusions of perceived velocity--the Filehne illusion and Aubert-Fleischl phenomenon--are thought to be the consequence of the extra-retinal signal underestimating eye velocity. These explanations assume that retinal motion is encoded accurately, which is questionable because perceived retinal speed is strongly affected by several stimulus properties. We develop and test a model of head-centric velocity perception that incorporates errors in estimating eye velocity and in retinal-motion sensing. The model predicts that the magnitude and direction of the Filehne illusion and Aubert-Fleischl phenomenon depend on spatial frequency and this prediction is confirmed experimentally.

Head↗
PubMed1999

Glycohistochemical investigation of canine and feline zonae pellucidae of preantral and antral oocytes.

Glycoconjugate modifications were analysed in the zona pellucida during development of oocytes in dog and cat using conventional histochemical staining methods with or without previous carbohydrate digestion. A series of lectins combined with desulphation and sialic acid degradation were applied. No differences were observed between dog and cat follicles using conventional histochemical staining methods. In both species, the zona pellucida and follicular fluid/intercellular matrix strongly reacted with PAS and high iron diamine stain (HID) and reacted moderately with low iron diamine stain (LID). Treatment with testicular hyaluronidase, chondroitinase ABC, chondroitinase AC and chondroitinase B treatment diminished HID and LID positivity of follicular fluid and intercellular matrix. Lectins that gave the most intense staining of the zona pellucida of both species were SBA, PNA, RCA-I, GSA-IB4 and WGA, indicating the presence of beta-D-GalNAc, D-Gal and GlcNAc residues. Sulpho- and asulpho-carbohydrates were identified in terminal and/or subterminal positions linked to sialic acid residues. In conclusion, the results indicate that glycosaminoglycans are not present in the zona pellucida of both species. Differences were observed in carbohydrate residues and in their spatial distribution, depending on species and developmental stage of the follicles. The similarity in lectin affinity between ooplasm and zona pellucida of oocytes present in follicles at different stages of development confirm the involvement of oocytes in zona pellucida production.

Animals↗
PubMed1998

A spatial scale factor for electrophysiological models of myocardium.

In the United States among males 20-64 years old about 1/3 of deaths are classified as 'sudden cardiac death', and 1/4 had no forewarning, nor did autopsy turn up any visible cause. The heart just switches from its normally periodic pumping to an alternative mode called 'fibrillation' more resembling electrical turbulence. In normal tissue its mechanism is a geometrically re-entrant mode of normal propagation. Everything about this spatial pattern depends upon the magnitude of 'D', the one term with dimension involving space in the pertinent biophysical equations. Explicit or implicit estimates in current literature span orders of magnitude. In this article I argue from a diversity of recent experiments for a narrower range of realistic values. It has an important role in the spatio-temporal evolution of fibrillation and in defibrillation.

Adult↗
PubMed1999

A stable prostacyclin-like substance produced by the medicinal leech Hirudo medicinalis.

The medicinal leech Hirudo medicinalis produces a low-molecular mass compound with properties similar to those of prostacyclin. It extracted with organic solvent, had affinity to 6-keto-PGF1alpha antibodies, inhibited human platelet aggregation induced in vitro by thrombin (by 50% at 4 pg/ml), and caused hypotension and secretion of plasminogen (t-PA) into the blood stream of rats. A main distinction from prostacyclin is stability of the substance due to covalent binding with the polypeptide chain of destabilase. Because of the high aggregability of destabilase, the molecules of the protein-lipid complex are organized into micelles that can change their spatial orientation depending on the nature of the solvent. Incorporation of hirudin and blood plasma kallikrein inhibitor into the micelle structure causes the formation of liposomes (with a molecular mass of the structural monomer 25 kDa). This complex with polypeptides provides not only stability but also rapid transmembrane penetration. The pure prostacyclin-like substance has a molecular mass of 391 Da and can be produced on destruction of the destabilase polypeptide chain.

Animals↗
PubMed2000

Chlordiazepoxide-induced spatial learning deficits: dose-dependent differences following prenatal malnutrition.

The sensitivity of prenatally protein-malnourished rats to the amnestic properties of the benzodiazepine (BZ) receptor agonist, chlordiazepoxide (CDP), was studied in the male offspring of rats provided with a protein-deficient diet (6% casein) for 5 weeks prior to mating and throughout pregnancy. Rats were tested during acquisition of the submerged platform version of the Morris water maze task using three systemic doses of CDP (3.2, 5.6, and 7.5 mg/kg i.p.) at two ages (day 30 and day 90). At 30 days, prenatally malnourished rats showed less sensitivity to the amnestic effect of the 5.6-mg/kg dose when compared with well-nourished controls by displaying shorter swim paths during acquisition and a more selective search of the target quadrant upon removal of the platform (probe trial). At 90 days, prenatally malnourished rats again showed less sensitivity to CDP at a dose of 5.6 mg/kg, but more sensitivity to the 3.2-mg/kg dose (indicated on the probe trial). No obvious relationship was identified between the nutritional group differences in behavioral sensitivity to CDP at 90 days and their BZ receptor density in the hippocampus or medial septum. It can be concluded that prenatal malnutrition alters the amnestic response to CDP in a dose-dependent and developmentally specific manner, thus providing further support for functional changes within the GABAergic system subsequent to malnutrition.

Animals↗
PubMed2002

Receptive field structure in cortical area 3b of the alert monkey.

More than 350 neurons with fingerpad receptive fields (RFs) were studied in cortical area 3b of three alert monkeys. Random dot patterns, which contain all stimulus patterns with equal probability, were scanned across these RFs at three velocities and eight directions to reveal the RFs' spatial and temporal structure. Area 3b RFs are characterized by three components: (1) a single, central excitatory region of short duration, (2) one or more inhibitory regions, also of short duration, that are adjacent to and nearly synchronous with the excitation, and (3) a region of inhibition that overlaps the excitation partially or totally and is temporally delayed with respect to the first two components. As a result of these properties, RF spatial structure depends on scanning direction but is virtually unaffected by changes in scanning velocity. This RF characterization, which is derived solely from responses to scanned random-dot patterns, predicts a neuron's responses to random patterns accurately, as expected, but it also predicts orientation sensitivity and preferred orientation measured with a scanned bar. Both orientation sensitivity and the ratio of coincident inhibition (number 2 above) to excitation are stronger in the supra- and infragranular layers than in layer IV.

Action Potentials↗
PubMed2000

The mechanisms of movement preparation: a precuing study.

It is well known that precues about the possible locations of upcoming targets reduce the manual reaction time. The present study investigates at which stage of the sensorimotor system such precues act. Several light dots were displayed as a precue; one of them became the target, and subjects had to produce a manual response to the target as fast as possible. Exp. A varied independently the number of precues and the area of space they occupy; we found that the reaction time of pointing movements depended on spatial extent, but not on the number of choices. The outcome was similar in Exp. B, where subjects produced stereotyped 'tapping' movements irrespective of target position. Taken together, both findings support the view that precues act mainly at a stage concerned with the internal representation of space, rather than with response selection or movement preparation. The effects of precues were preserved when subjects fixated throughout the precuing period (Exp. C), but not when precue and target positions were uncorrelated (Exp. D). These findings do not support the alternative interpretations, that precues act by guiding the eyes into the vicinity of targets, or by elevating the subjects' arousal level.

Adult↗
PubMed2000

A silastic positioner for a modiolus-hugging position of intracochlear electrodes: electrophysiologic effects.

HYPOTHESIS: It was postulated that an electrode array that achieved a close modiolar proximity would result in reduced threshold levels and amplitude slopes, as measured with electrically evoked auditory brainstem responses (EABRs). BACKGROUND: Quality and quantity of auditory information transmitted by a cochlear implant to patients with sensorineural hearing loss depend on spatial and temporal resolution achieved by the electrical intracochlear stimulation. METHODS: To improve spatial resolution, a new electrode system was developed by Advanced Bionics Corp., with the intention of obtaining greater modiolar proximity. The implant version specified for animal experiments consists of a straight electrode array of seven embedded platinum discs and a so-called Silastic-positioner. The Silastic positioner is shaped to follow the dimensions of the scala tympani with a concave (triangular) inner side, which fits the form of the electrode array. The aim of the study was to evaluate the influence of a modiolus-hugging electrode position in contrast to a conventional electrode position on EABR in short-term animal experiments. Short-term electrophysiologic studies were performed on six adult cats. After local intracochlear application of neomycin solution (50 mg/mL), electrodes were inserted into the scala tympani. Electrically evoked auditory brainstem response threshold levels and EABR amplitude slopes were systematically investigated with and without the positioner. RESULTS: Electrically evoked auditory brainstem response measurements revealed a distinct apicobasal threshold shift, with increasing thresholds toward the basal end of the electrode. After insertion of the positioner, this shift diminished or was inverted and EABR thresholds and amplitude slopes were reduced significantly. CONCLUSIONS: Threshold and amplitude slope data emphasize the functional benefit of the positioner system, especially for the stimulation of electrodes in the more basal channels.

Animals↗
PubMed2001

Effects of ageing on allocentric and egocentric spatial strategies in the Wistar rat.

This study was designed to assess the effect of ageing on spatial (allocentric and egocentric) strategies in rats. Two different tasks were designed for this purpose: one involving Morris' circular pool (distal extramaze cues) and another using the T water maze (egocentric cues). In the first task, the aged rats showed some difficulty in acquiring allocentric spatial learning skills. After increasing the number of trials in this task, there was no significant improvement in the performance of the aged group of rats compared to the adult group. However, in the second spatial task (using egocentric cues), both age groups gave a similar performance. Therefore, the effect of ageing on spatial learning depends on the strategy required to acquire this learning.

Journal Article↗
PubMed1999

Co-expression of human Kir3 subunits can yield channels with different functional properties.

To date, no comprehensive study has been done on all combinations of the human homologues of the Kir3.0 channel family, and the human homologue of Kir3.3 has not yet been identified. To obtain support for the contention that most of the functional data on non-human Kir3.0 channels can be extrapolated to human channels, we have cloned the human homologues of the Kir3.0 family, including the yet unidentified human Kir3.3, and the human Kir4.1. The expression pattern of these channels in various human brain areas and peripheral tissues, analysed by Northern blot analysis, allows for the existence of various homomeric and heteromeric forms of human Kir3.0 channels. Expression studies of all possible combinations in Xenopus oocytes indicated that in homomeric Kir3.2c and heteromeric Kir3.1/3.2c channels mediate, in our studies, inward currents with largest amplitude of any other Kir3.0 channel combinations, followed by heteromeric Kir3.1/3.4 and homomeric Kir4.1 channels. Channel combinations which include Kir3.3 are detrimental to the formation of functional channels. The co-expression experiments with different Kir channel subunits indicate the selective formation of certain channel combinations, suggesting that channel specificity is not solely dependent on spatial and temporal regulation of Kir subunit expression.

Amino Acid Sequence↗
PubMed1998

First- and second-order motion perception in Gabor micropattern stimuli: psychophysics and computational modelling.

This paper examines the perception of first- and second-order motion in human vision. In an extension of previous work by Boulton and Baker [J.B. Boulton, C.L. Baker, Motion detection is dependent on spatial frequency not size, Vision Res., 31 (1991) 77-87; J.B. Boulton, C.L. Baker, Different parameters control motion perception above and below a critical density, Vision Res., 33 (1993) 1803-1811], the direction of two-frame apparent motion is measured for stimuli composed of Gabor or Gaussian micropatterns. Three conditions are investigated. Condition 1 is that used by Boulton and Baker, in which motion is defined by the displacement of Gabor micropatterns. In condition 2, motion is defined by the displacement of Gaussian micropatterns. In condition 3, the envelopes of Gabor micropatterns are displaced while their carriers remain static. Using sparsely distributed micropatterns, direction judgements in all three conditions are determined by the spacing of the micropatterns. With a dense stimulus, direction judgements vary as a function of displacement in qualitatively different ways for the three conditions. The psychophysical results are predicted by a two-channel computational model. In one channel, motion is calculated directly from stimulus luminance, while in the other it is preceded by a texture-grabbing operation. The relative activities of the two channels dictates which governs direction judgements for any given stimulus.

Computer Simulation↗
PubMed2003

Variations in lectin-binding on the zona pellucida during oocyte growth in some wild ungulates.

The aim of the present study was to examine the glycoconjugate modifications occurring in the zona pellucida during oocyte growth in fallow, red and roe deer using a battery of lectins combined with sialidase digestion and chemical treatments. This histochemical approach allowed us to sequence the oligosaccharidic side chains of the zona pellucida glycoproteins in these wild ungulates. The most effective lectins in the zona pellucida of these species were SBA, PNA, RCA-I GSA-IB4, and WGA, indicating the presence of beta-D-N-Acetylgalactosamine, beta-D-Galactose, alpha-D-Galactose and N-Acetylglucosamine residues. Additionally, sialic acid moieties were demonstrated. We also observed differences in the glycosidic residue content and in their spatial distribution, depending on the species and stage of follicle development.

Animals↗
PubMed1998

An investigation of the imaging characteristics of the Y2O2S:Eu3+ phosphor for application in X-ray detectors of digital mammography.

Y2O2S:Eu laboratory prepared screens were evaluated as mammographic image receptors and were compared to similarly prepared screens of Gd2O2S:Tb and Y2O2S:Tb phosphor materials, often used in X-ray imaging detectors. The evaluation was performed by determining the Modulation Transfer Function (MTF) and the spatial frequency dependent Detective Quantum Efficiency (DQE). Y2O2S:Eu exhibited higher DQE values at low frequencies and given its good spectral matching with digital optical detectors, it may be appropriate for use in X-ray digital mammography.

Europium↗
PubMed2000

Dual resonant birdcage coils for 1H detected 13C microscopic imaging at 11.7 T.

Liquid state, rotating frame cross polarisation experiments are very sensitive to RF field inhomogeneity. In this work, we present an easily fabricated, co-resident high- and low-pass linear birdcage resonator, optimised to perform liquid state rotating frame polarisation transfer at 1H and 13C frequencies. Both the RF fields have been experimentally mapped, and used to validate the spatial signal dependence of a proton detected, 13C image. The predicted performance was then confirmed using PRAWN-based, cyclic J-cross polarisation (CYCLCROP) imaging. A novel variant of a B(1)-field mapping approach is also presented, using the signal enhancement of the CYCLCROP sequence to generate proton detected, 13C field maps.

Biophysical Phenomena↗
PubMed1999

Processing of affective pictures modulates right-hemispheric gamma band EEG activity.

The present study was designed to test differential hemispheric activation induced by emotional stimuli in the gamma band range (30-90 Hz). Subjects viewed slides with differing emotional content (from the International Affective Picture System). A significant valence by hemisphere interaction emerged in the gamma band from 30-50 Hz. Other bands, including alpha and beta, did not show such an interaction. Previous hypotheses suggested that the left hemisphere is more involved in positive affective processing as compared to the right hemisphere, while the latter dominates during negative emotions. Contrary to this expectation, the 30-50 Hz band showed relatively more power for negative valence over the left temporal region as compared to the right and a laterality shift towards the right hemisphere for positive valence. In addition, emotional processing enhanced gamma band power at right frontal electrodes regardless of the particular valence as compared to processing neutral pictures. The extended distribution of specific activity in the gamma band may be the signature of cell assemblies with members in limbic, temporal and frontal neocortical structures that differ in spatial distribution depending on the particular type of emotional processing.

Adult↗
PubMed2004

Adsorption, desorption, and conversion of thiophene on H-ZSM5.

The dynamics and stoichiometry of thiophene adsorption and of rearrangements of thiophene-derived adsorbed species in O(2), He, H(2), and C(3)H(8) carriers were measured using chromatographic methods and mass spectrometry on H-ZSM5 and H-Y zeolites. Thiophene adsorption obeyed Langmuir isotherms on both zeolites. Adsorption uptakes were 1.7 and 2.8 thiophene/Al at 363 K on H-ZSM5 and H-Y zeolites, respectively, after removal of physisorbed thiophene. These stoichiometries differed for these two zeolite structures but did not depend on their Al content (Si/Al = 13-85). Adsorption from a thiophene-toluene mixture showed thiophene selectivities ( approximately 10) greater than expected from van der Waals interactions. These adsorption stoichiometries, without contributions from physisorption, and the color changes detected indicate that thiophene adsorption occurs concurrently with oligomerization on acidic OH groups and that oligomer size depends on spatial constraints within channels. Thiophene oligomers decompose at approximately 534 K during subsequent thermal treatment to form molecular thiophene with all carriers, leaving behind unsaturated thiophene-derived species with a 0.9-1.1 thiophene/Al stoichiometry, confirming the specificity of OH groups and the oligomeric nature of bound thiophene during adsorption at 363 K. With He, H(2), and C(3)H(8), residual thiophene-derived species desorb as stable fragments, such as H(2)S, ethene, propene, arenes, and heavier organosulfur compounds (methylthiophene and benzothiophene) during thermal treatment; they also form unsaturated organic deposits that cannot desorb without hydrogenation events. H(2) and C(3)H(8) remove larger amounts of adsorbed species as unreacted thiophene than He, suggesting that dehydrogenation reactions are inhibited or reversed by a hydrogen source. C(3)H(8) removes a larger fraction of thiophene-derived intermediates as hydrocarbons and organosulfur compounds than H(2) or He; thus, hydrogen atoms formed during C(3)H(8) dehydrogenation are more effective in the removal of unsaturated deposits than those formed from H(2). Thiophene-derived adsorbed species are completely removed only with O(2)-containing streams at 873 K, a process that fully recovers initial adsorption capacities. This study provides a rigorous assessment of the nature and specificity of thiophene adsorption processes on acidic OH groups and of the identity and removal pathways of adsorbed species in various reactive environments.

Adsorption↗