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Results for “spatial dependency”

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At least 703 records · Page 39Linked to original sources

PubMed1995

Increasing doses of l-sulpiride reveal dose- and spatial frequency-dependent effects of D2 selective blockade in the human electroretinogram.

The amplitude and phase of the second harmonic (15 Hz) of the electroretinographic responses to three different spatial frequency grating stimuli (0.25, 1 and 4 c/deg), reversed at 7.5 Hz, were studied i normal human subjects, before and 30 min after the systemic administration of three doses (0.071, 0.357 or 1.428 mg/kg) of a selective D2 blocker, l-sulpiride, to three populations of 18, 19, or 20 subjects. The effect of the drug on the pattern electroretinogram (PERG) was clearly dose-dependent, being greatest on the responses to 4 c/deg. The mean decrease in second harmonic amplitude was -13.8% after 0.071 mg/kg of l-sulpiride, -23.5% after 0.357 mg/kg and -28.5% after 1.428 mg/kg. The last two variations were significant at P < 0.01 and P < 0.01 respectively. These data suggest that a dose-dependent effect on the human retinal response to 4 c/deg stimuli exists, probably mediated by a coupling between l-sulpiride and D2 receptors. Lastly, our data suggest that D2 receptors may play an important role in the pathophysiology of visual dysfunction in Parkinson's disease, that has been described to be more significant at medium spatial frequency (2-5 c/deg).

Adult↗

PubMed1996

Responses in area V4 depend on the spatial relationship between stimulus and attention.

1. We studied the spatial interaction between stimulus and attention in macaque area V4. Monkeys were required to fixate a small spot while continuously attending to a ring-shaped target within a large array of identical rings. Meanwhile, the response of the V4 cell under study was tested by flashing behaviorally irrelevant bar stimuli in the cell's classical receptive field (CRF). The location of the attended ring was varied across four positions surrounding the CRF, and the location of the bar stimulus was varied across five positions spanning the CRF. 2. Response strength depended on two aspects of the spatial relationship between the stimulus driving the cell (the bar) and the position of attention (the target ring). First, for 49% of the cells studied, responses were greater for bar stimuli near the attended ring; i.e., the receptive field profile shifted toward the attentional focus. Second, for 84% of the cells, the overall response level depended on the direction in which attention lay relative to the stimulus in the CRF (e.g., to the left, right, above, or below). 3. This study confirms a key prediction of spatial models of attention, which postulate enhanced processing of all stimuli near the attentional focus. It also introduces the novel finding that responses are influenced by the relative direction of attention. This result indicates that area V4 carries information about the spatial relationship between visual stimuli and attention.

Animals↗

PubMed2005

[Spatial distribution pattern and space dependence of Contarinia sp. and Erigonidium graminicola in jujube orchard].

With the principles and methodologies of geostatistics, this paper studied the spatial structure and space dependence of Contarinia sp. and its natural enemy Erigonidium graminicola in a jujube orchard at different date. The results indicated that the semivariogram of Contarinia sp. on 8 June, 27 August and 19 October could be described by spherical model, showing an aggregated spatial distribution with the ranges of spatial dependence being 26.3, 7.8 and 22.0 m, and the degrees of spatial dependence being 88.05%, 85.77% and 87.58%, respectively. The semivariogram of Erigonidium graminicola could be also described by spherical model, showing an aggregated distribution with the ranges of spatial dependence being 28.3, 22.5 and 22.2 m, and the degrees of spatial dependence being 90.09%, 87.96% and 85.72%, respectively. It is suggested that Erigonidium graminicola is the dominant natural enemy against Contarinia sp. population in the examined jujube orchard.

Animals↗

PubMed2000

Olfactory based spatial learning in neonatal mice and its dependence on CaMKII.

Spatial learning and memory involves the ability to encode geometric relationships between perceived cues and depends critically on the hippocampus. Visually guided spatial learning has been demonstrated in adult animals. As infant animals rely heavily on olfaction, olfactory based spatial learning was assessed in infant mice. When 12-day-old pups were displaced from their nest, they learned within a few training trials to use the spatial pattern of odor cues to move back to the nest. However, mouse pups that over-expressed Ca2+/calmodulin-dependent protein kinase (CaMKII) in hippocampal neurons were impaired in olfactory based spatial learning.

Age Factors↗

PubMed2005

Lesions of specific and nonspecific thalamic nuclei affect prefrontal cortex-dependent aspects of spatial working memory.

Three studies compared lesions of specific mediodorsal (MD) and nonspecific midline/intralaminar (M/IL) and ventromedial (VM) thalamic nuclei placed to spare the anterior nuclei. Lesions of MD, M/IL, or VM impaired delayed matching trained with retractable levers, a measure of spatial memory affected by prefrontal cortical lesions. The effects of the MD lesion increased at longer retention intervals and thus appeared delay dependent. The effects of M/IL and VM lesions were delay independent. Even when combined, these lesions had no effect on varying choice radial maze delayed nonmatching, a task sensitive to hippocampal or anterior thalamic (but not prefrontal) lesions. These results demonstrate effects of MD, M/IL, and VM lesions distinct from the contributions of hippocampus or anterior thalamus to spatial memory.

Animals↗

PubMed1996

Spatial frequency-dependent asymmetry of visual evoked potential amplitudes.

The extent to which pattern reversal evoked potential amplitudes are distributed symmetrically over the scalp was investigated as a function of stimulus spatial frequency. Nine right-handed male subjects viewed sinusoidal grating stimuli of 4.0 and 0.5 c/deg phase reversed every 900 msec. A visual half-field configuration enabled selective stimulation of the right- or left-hemisphere visual cortex. Evoked responses were recorded from the 2 cm above the inion (Oz) and at 7 and 13 cm lateral to Oz. Analyses of normalized evoked response amplitudes showed a significant asymmetry for the 4.0 c/deg stimulus; right-hemisphere amplitudes declined as a function of distance from the midline, while left-hemisphere amplitudes were greatest at the 7 cm recording site. No hemispheric differences were observed for the 0.5 c/deg stimulus; amplitudes for both hemispheres declined as a function of distance from the midline. The data are discussed in terms of hemispheric differences in morphology and functional asymmetries at early levels of sensory processing.

Adolescent↗

PubMed1999

Age-dependent changes in spatial and temporal blood velocity distribution of early left ventricular filling.

This study describes early diastolic inflow dynamics based on three-directional magnetic resonance velocity data and investigates age-dependent changes in early diastolic inflow characteristics. We examined 26 young healthy volunteers age 25 (3) years (mean, SD), and 23 healthy older volunteers age 63 (8) years. Three-directional magnetic resonance velocity mapping was performed in a long axis plane through the heart. Transverse velocity profiles were read in five different positions in the early diastolic inflow stream of the left ventricle. The size and timing of the maximum velocities at each level were recorded and the repeatability of the method was tested. Compared with the younger group, the older group was characterized by: 1) lower maximum velocity in all positions, 2) increased deceleration of blood downstream from the mitral leaflet tips, and 3) delayed velocity propagation. The described method was repeatable and enabled detection of the age-dependent differences between groups of normal subjects. In conclusion, the early diastolic inflow pattern changes with age, probably reflecting changes in the diastolic function of the myocardium.

Adult↗

PubMed2004

Spatial and temporal dependence of interspark interactions in femtosecond-nanosecond dual-pulse laser-induced breakdown spectroscopy.

A femtosecond air spark has recently been combined with a nanosecond ablative pulse in order to map the spatial and temporal interactions of the two plasmas in femtosecond-nanosecond orthogonal preablation spark dual-pulse laser-induced breakdown spectroscopy (LIBS). Good spatial and temporal correlation was found for reduced atomic emission from atmospheric species (nitrogen and oxygen) and increased atomic emission from ablated species (copper and aluminum) in the femtosecond-nanosecond plasma, suggesting a potential role for atmospheric pressure or nitrogen/oxygen concentration reduction following air spark formation in generating atomic emission enhancements in dual-pulse LIBS.

Journal Article↗

PubMed2002

Spatial and structural dependence of mechanical properties of porcine intervertebral disc.

Structure-function relationship of natural tissues is crucial to design a device mimicking the structures present in human body. For this purpose, to provide guidelines to design an intervertebral disc (IVD) substitute, in this study the influence of the spatial location and structural components on the mechanical properties of porcine IVD was investigated. Local compressive stiffness (LCS) was measured on the overall disc, also constrained between the two adjacent vertebrae: the dependence on the lumbar position was evaluated. The compliance values in the anterior position (A) were higher than both in the central posterior (CP) and in the lateral-posterior (RP, LP) locations. The values of Young's Modulus (74.67+/-6.03 MPa) and compression break load (1.36x10(4)+/-0.09x10(4)N) of the disc were also evaluated by distributed compression test. The NP rheological behavior was typical of weak-gels, with elastic modulus G' always higher than viscous modulus G" all over the frequency range investigated (G' and G" respectively equal to 320 and 85 Pa at 1 Hz) and with the moduli trends were almost parallel to each other.

Journal Article↗

PubMed2005

Density-dependent dispersal and spatial population dynamics.

The synchronization of the dynamics of spatially subdivided populations is of both fundamental and applied interest in population biology. Based on theoretical studies, dispersal movements have been inferred to be one of the most general causes of population synchrony, yet no empirical study has mapped distance-dependent estimates of movement rates on the actual pattern of synchrony in species that are known to exhibit population synchrony. Northern vole and lemming species are particularly well-known for their spatially synchronized population dynamics. Here, we use results from an experimental study to demonstrate that tundra vole dispersal movements did not act to synchronize population dynamics in fragmented habitats. In contrast to the constant dispersal rate assumed in earlier theoretical studies, the tundra vole, and many other species, exhibit negative density-dependent dispersal. Simulations of a simple mathematical model, parametrized on the basis of our experimental data, verify the empirical results, namely that the observed negative density-dependent dispersal did not have a significant synchronizing effect.

Animals↗

PubMed1978

Mapping the ATP-binding site in the catalytic subunit of adenosine-3':5'-monophosphate-dependent protein kinase. Spatial relationship with the ATP site of the undissociated enzyme.

A set of 24 ATP analogs modified at various positions of the ATP molecule was used for mapping the ATP-binding site in the free catalytic subunit (C) of cAMP-dependent protein kinase (type I). Ki values for these analogs (of which 23 were shown to be competitive with ATP) were measured and compared with Ki values previously obtained for the same set of analogs upon binding to the undissociated form of the enzyme (R2C2). It was found that modifications at the adenine part of ATP bring about a considerable reduction in affinity between C and the resulting analog. The other parts of the ATP molecule play a less important, though definite, role in the binding of this nucleotide to C. By measuring the effect of each given modification in ATP on its binding to C, and comparing the effect of this modification on the binding of the same analog to R2C2, it was possible to obtain 'specificity profiles' for both forms of the kinase. Using such profiles it is shown that the adenine-binding subsite in C may well coincide with the adenine-binding subsite in R2C2. Two plausible models describing the spatial relationship between the ATP sites in C and R2C2 are proposed.

Adenosine Triphosphate↗

PubMedDate not supplied

[The dependence of spatial-motor asymmetry on the nature of the reinforcement].

Spatial-motor asymmetry (SMA) of rats goal-directed running was studied in condition of numerous alternative choices in complex T-maze. In condition of free choices SMA in trained rats depended on reinforcement biological significance, volume and disposition scheme. In condition of non-free choices a change was possible of asymmetry of sequence of goal-directed motor acts adequate to situation, i.e. SMA regulation. Examples of the presence of properties of ego- and allocentric systems in SMA are given. The results of experiments testify to SMA dependence on the motivation of running, to rightfulness of SMA interpretation as behavioural tactics and to non-coming of SMA of goal-directed running to a simple rotation of animals.

Animals↗

PubMed2005

Visual and proprioceptive representations in spatial memory.

It has been shown that spatial information can be acquired from both visual and nonvisual modalities. The present study explored how spatial information from vision and proprioception was represented in memory, investigating orientation dependence of spatial memories acquired through visual and proprioceptive spatial learning. Experiment 1 examined whether visual learning alone and proprioceptive learning alone yielded orientation-dependent spatial memory. Results showed that spatial memories from both types of learning were orientation dependent. Experiment 2 explored how different orientations of the same environment were represented when they were learned visually and proprioceptively. Results showed that both visually and proprioceptively learned orientations were represented in spatial memory, suggesting that participants established two different reference systems based on each type of learning experience and interpreted the environment in terms of these two reference systems. The results provide some initial clues to how different modalities make unique contributions to spatial representations.

Adolescent↗

PubMed1984

Fluorescence resonance energy transfer on the voltage-dependent sodium channel. Spatial relationship and site coupling between the batrachotoxin and Leiurus quinquestriatus quinquestriatus alpha-scorpion toxin receptors.

A fluorescent N- methylanthraniloyl derivative of the potent depolarizing agent batrachotoxin has been used to probe the structural and conformational properties of the neurotoxin receptor site on the voltage-dependent sodium channel. Batrachotoxin A 20-alpha-N- methylanthranilate (BTX-NMA) retains high affinity for its receptor site on the synaptosomal sodium channel with a Kd between 78 and 91 nM and an average site capacity of 2 pmol/mg of synaptosomal protein in the presence of Leiurus quinquestriatus quinquestriatus alpha-scorpion toxin. The fluorescence emission of BTX-NMA upon binding to synaptosomes indicates a hydrophobic environment. Toxin V from L. quinquestriatus, an allosteric activator, effects a 20-nm red shift in the spectrum of bound BTX-NMA and a 4-fold enhancement in the fluorescence quantum yield disclosing a conformational change into a hydrophilic environment. Fluorescence resonance energy transfer measurements show that the distance separating the receptor sites is 37 +/- 10 A. Thus, the binding of alpha-scorpion toxin must involve conformational changes that extend over large distances from the batrachotoxin-binding locus. This information together with the distance measurements between the tetrodotoxin and alpha-scorpion toxin receptors and the conformational transition associated with this distance upon batrachotoxin addition indicate a conformationally flexible channel with coupling of sites through the polyatomic framework of individual subunits or through extensive alterations in subunit/subunit interactions.

Animals↗

PubMed2006

Extensive enriched environments protect old rats from the aging dependent impairment of spatial cognition, synaptic plasticity and nitric oxide production.

In aged rodents, neuronal plasticity decreases while spatial learning and working memory (WM) deficits increase. As it is well known, rats reared in enriched environments (EE) show better cognitive performances and an increased neuronal plasticity than rats reared in standard environments (SE). We hypothesized that EE could preserve the aged animals from cognitive impairment through NO dependent mechanisms of neuronal plasticity. WM performance and plasticity were measured in 27-month-old rats from EE and SE. EE animals showed a better spatial WM performance (66% increase) than SE ones. Cytosolic NOS activity was 128 and 155% higher in EE male and female rats, respectively. Mitochondrial NOS activity and expression were also significantly higher in EE male and female rats. Mitochondrial NOS protein expression was higher in brain submitochondrial membranes from EE reared rats. Complex I activity was 70-80% increased in EE as compared to SE rats. A significant increase in the area of NADPH-d reactive neurons was observed in the parietotemporal cortex and CA1 hippocampal region of EE animals.

Aging↗

PubMed2005

Involvement of ventral pallidum in prefrontal cortex-dependent aspects of spatial working memory.

Ventral pallidum (VP) is an important source of limbic input to medial thalamus. Three studies examined the role of VP in spatial memory tasks impaired by medial thalamic lesions. In the 1st study, rats with VP lesions were impaired performing delayed matching trained with retractable levers (DMRL), a measure sensitive to prefrontal (but not hippocampal) damage. The 2nd study demonstrated dose-dependent DMRL impairment following microinjection of gamma-aminobutyric acidA, glutamate, or mu-opioid agonists in VP. In the 3rd study, VP lesions had no effect on varying choice radial-maze delayed nonmatching, a measure sensitive to hippocampal (but not prefrontal) lesions. These results suggest a common role in spatial memory for VP and other components of prefrontal-ventral striatopallidothalamic circuits distinct from hippocampal function.

Animals↗

PubMedDate not supplied

Enriched environment, nitric oxide production and synaptic plasticity prevent the aging-dependent impairment of spatial cognition.

In rodents, neuronal plasticity decreases and spatial learning and working memory deficits increase upon aging. Several authors have shown that rats reared in enriched environments have better cognitive performance in association with increased neuronal plasticity than animals reared in standard environments. We hypothesized that enriched environment could preserve animals from the age-associated neurological impairments, mainly through NO-dependent mechanisms of induction of neuronal plasticity. We present evidence that 27 months old rats from an enriched environment show a better performance in spatial working memory than standard reared rats of the same age. Both mtNOS and cytosolic nNOS activities were found significantly increased (73% and 155%, respectively) in female rats from enriched environment as compared with control animals kept in a standard environment. The enzymatic activity of complex I was 80% increased in rats from enriched environment as compared with control rats. We conclude that an extensively enriched environment prevents old rats from the aging-associated impairment of spatial cognition, synaptic plasticity and nitric oxide production.

Aging↗

PubMedDate not supplied

Retrieval induces hippocampal-dependent reconsolidation of spatial memory.

Nonreinforced retrieval can cause extinction and/or reconsolidation, two processes that affect subsequent retrieval in opposite ways. Using the Morris water maze task we show that, in the rat, repeated nonreinforced expression of spatial memory causes extinction, which is unaffected by inhibition of protein synthesis within the CA1 region of the dorsal hippocampus. However, if the number of nonreinforced retrieval trials is insufficient to induce long-lasting extinction, then a hippocampal protein synthesis-dependent reconsolidation process recovers the original memory. Inhibition of hippocampal protein synthesis after reversal learning sessions impairs retention of the reversed preference and blocks persistence of the original one, suggesting that reversal learning involves reconsolidation rather than extinction of the original memory. Our results suggest the existence of a hippocampal protein synthesis-dependent reconsolidation process that operates to recover or update retrieval-weakened memories from incomplete extinction.

Animals↗