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Results for “Spatial orientation”

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At least 883 records · Page 49Linked to original sources

PubMed1993

Effects of ablation of the presumed equivalent of the mammalian prefrontal cortex on pigeon homing.

Pigeons (Columba livia) with bilateral ablation of the postero-dorsolateral neostriatum and the overlying corticoid were compared with unoperated control subjects in homing from both familiar and unfamiliar sites. Before the operation all the pigeons were subjected to 8 training flights from a site destined to be the familiar one. Postoperatively, the groups did not differ in orientation from the familiar site. In their releases from unfamiliar sites, however, the operated birds oriented in the training flight direction, whereas the control subjects were oriented homeward. In all the releases the homing performance, including both the homing speed and the number of returned birds, was significantly higher in the control group. Thus, the ablated tissue plays a role in homing behavior possibly through mediation of spatial orientation, of olfactory navigation, or of both.

Animals↗

PubMed2005

Effect of 25-hydroxyl group orientation on biological activity and binding to the 1alpha,25-dihydroxy vitamin D3 receptor.

The hormonal form of vitamin D, 1alpha,25-dihydroxyvitamin D(3) (1,25D), generates many biological actions by interactions with its nuclear receptor (VDR). The presence of a carbon-25 hydroxyl group is necessary for optimizing binding to the VDR. To examine the effect of spatial orientation of the 25-hydroxyl, two pairs of 22,23-allene sidechain analogs were studied. The 22R orientation in analogs HR (52+/-2%) and LA (154+/-19%) resulted in higher affinity binding than the 22S orientation of analogs HQ (21+/-3%) and LB (3.5+/-1.3%; 1,25D=100%). Limited trypsin proteolysis showed that 22R analogs induced VDR conformational changes better able to protect VDR from digestion than 22S analogs. 22R analogs were also able to induce gene transcription at 10-100-fold lower concentrations than 1,25D; 22S analogs were less effective. Analog LA was at least 10-fold more potent than 1,25D at inducing differentiation, while the other analogs were less potent. None of the analogs were as potent as 1,25D in promoting in vivo intestinal calcium absorption or bone calcium mobilization. LA was the most potent of the analogs but required 20-30-fold higher doses than 1,25D. The 25-hydroxyl orientation combined with the 16,17-ene functionality of analog LA enhances its ability to interact with VDR and induce biological actions.

Animals↗

PubMed1990

Head-direction cells recorded from the postsubiculum in freely moving rats. II. Effects of environmental manipulations.

The discharge characteristics of postsubicular head-direction cells in a fixed environment were described in the previous paper (Taube et al., 1990). This paper reports changes in the firing properties of head-direction cells following changes in the animal's environment. Head-direction cells were recorded from rats as they moved freely in a 76-cm-diameter gray cylinder. A white card, occupying 100 degrees of arc, was taped to the inside wall of the cylinder and served as the major orienting spatial cue in the animal's environment. Rotation of the cue card produced near-equal rotation in the preferred firing direction of head-direction cells, with minimal changes in peak firing rate, directional firing range, or asymmetry of the firing-rate/head-direction function. Card removal had no effect on peak firing rate or range of firing, but in 8/13 cells the preferred direction rotated by at least 24 degrees. Similarly, changing the shape of the environment to a rectangular or square enclosure caused the preferred firing direction to rotate by at least 48 degrees for 8/10 cells in the rectangle and 3/8 cells in the square, with minimal changes in the peak firing rate or directional firing range. Hand holding the animals and moving them around the cylinder had no effect on the preferred direction or firing range of the cell, but decreased the maximal firing rate in 7/9 cells. On 2 occasions, 2 head-direction cells were recorded simultaneously. The rotation of the preferred firing direction for one cell was the same as the rotation of the preferred direction for the second cell after each environmental manipulation. These results demonstrate that specific visual cues in the environment can exert control over the preferred firing direction and indicate that head-direction cell firing is not a simple sensory response to visual cues, but rather represents more abstract information concerning the animal's spatial relationship with its environment. The constancy of the angle between the preferred firing directions of pairs of simultaneously recorded head-direction cells suggests that there is a fixed mapping of the population onto direction within the environment. Thus, environmental manipulations appear to cause only a change in the reference direction, but leave all other discharge characteristics of directional cells unchanged. In the discussion, comparisons are drawn between the responses of head-direction cells and hippocampal place cells to similar environmental manipulations (Muller and Kubie, 1987), and ways in which these 2 spatial systems interact in navigation are discussed.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1986

Decreased response of human milk leukocytes to chemoattractant peptides.

To test the hypothesis that neutrophils and macrophages in human milk may not defend by classical inflammatory mechanisms, experiments were conducted to ascertain whether adherence, orientation, and directed motility of these leukocytes would be enhanced by exposure to chemoattractant peptides including N-formyl-L-methionyl-L-phenylalanine and N-formyl-L-methionyl-L-leucyl-L-phenylalanine and C5a generated from zymosan activated human serum. Adherence and spatial orientation were tested on coverglasses and in Zigmond chambers, and chemotaxis was examined by Boyden chambers and a subagarose technique. Whereas, the adherence, orientation, and directed movement of adult peripheral blood neutrophils and monocytes were significantly enhanced by those chemotactic agents, human milk leukocytes failed to respond. The failure of the response of human milk leukocytes was not due to alterations in maternal peripheral blood leukocytes but appeared to be due partially to inhibitors in human milk. The experiments suggest that human milk leukocytes may be modified in the mammary gland to protect by noninflammatory mechanisms.

Adult↗

PubMed1998

Updating visual space during passive and voluntary head-in-space movements.

The accuracy of our spatially oriented behaviors largely depends on the precision of monitoring the change in body position with respect to space during self-motion. We investigated observers' capacity to determine, before and after head rotations about the yaw axis, the position of a memorized earth-fixed visual target positioned 21 degrees laterally. The subjects (n=6) showed small errors (mean=-0.6 degrees) and little variability (mean=0.9 degrees) in determining the position of an extinguished visual-target position when the head (and gaze) remained in a straight-ahead position. This accuracy was preserved when subjects voluntary rotated the head by various magnitudes in the direction of the memorized visual target (head rotations ranged between 5 degrees and 60 degrees). However, when the chair on which the subjects were seated was unexpectedly rotated about the yaw axis in the direction of the target (chair rotations ranged between 6 degrees and 36 degrees ) during the head-on-trunk rotations, the performance was markedly decreased, both in terms of spatial precision (mean error=5.6 degrees ) and variability (mean=5.7 degrees). A control experiment showed that the prior knowledge of chair rotation occurrence had no effect on the perceived target position after head-trunk movements. Updating an earth-fixed target position during head-on-trunk rotations could be achieved through both cervical and vestibular signals processing, but, in the present experiment, the vestibular output was the only signal that had the potentiality to contribute to accurate coding of the target position after simultaneous head and trunk movements. Our results therefore suggest that the vestibular output is a noisy signal for the central nervous signal to update the visual space during head-in-space motion.

Adult↗

PubMed2005

Motor-maps, navigation and implicit space representation in the hippocampus.

Multiple sensory-motor maps located in the brainstem and the cortex are involved in spatial orientation. Guiding movements of eyes, head, neck and arms they provide an approximately linear relation between target distance and motor response. This involves especially the superior colliculus in the brainstem and the parietal cortex. There, the natural frame of reference follows from the retinal representation of the environment. A model of navigation is presented that is based on the modulation of activity in those sensory-motor maps. The actual mechanism chosen was gain-field modulation, a process of multimodal integration that has been demonstrated in the parietal cortex and superior colliculus, and was implemented as attraction to visual cues (colour). Dependent on the metric of the sensory-motor map, the relative attraction to these cues implemented as gain field modulation and their position define a fixed point attractor on the plane for locomotive behaviour. The actual implementation used Kohonen-networks in a variant of reinforcement learning that are well suited to generate such topographically organized sensory-motor maps with roughly linear visuo-motor response characteristics. In the following, it was investigated how such an implicit coding of target positions by gain-field parameters might be represented in the hippocampus formation and under what conditions a direction-invariant space representation can arise from such retinotopic representations of multiple cues. Information about the orientation in the plane--as could be provided by head direction cells--appeared to be necessary for unambiguous space representation in our model in agreement with physiological experiments. With this information, Gauss-shaped "place-cells" could be generated, however, the representation of the spatial environment was repetitive and clustered and single cells were always tuned to the gain-field parameters as well.

Algorithms↗

PubMed1988

Integrating stereopsis with monocular interpretations of planar surfaces.

Experiments are reported that involved spatial judgments of planar surfaces that had contradictory stereo and monocular information. Tasks included comparing the relative depths of two points on the depicted surface and judging the surface's apparent spatial orientation. It was found that for planar surfaces the 3D perception was dominated by the monocular interpretation, despite the strongly contradictory stereo information. We propose that stereo information is effectively integrated only where the surface exhibits curvature features or edge discontinuities, i.e. where the second spatial derivatives of disparity are nonzero. Planar surfaces induce constant gradients of disparity and are thus effectively featureless to stereopsis. Further observations are reported regarding nonplanar surfaces, where contradictory monocular information can still be effectively rivalrous with that suggested stereoscopically.

Depth Perception↗

PubMed2006

Specification of SUMO1- and SUMO2-interacting motifs.

SUMO proteins are ubiquitin-related modifiers implicated in the regulation of gene transcription, cell cycle, DNA repair, and protein localization. The molecular mechanisms by which the sumoylation of target proteins regulates diverse cellular functions remain poorly understood. Here we report isolation and characterization of SUMO1- and SUMO2-binding motifs. Using yeast two-hybrid system, bioinformatics, and NMR spectroscopy we define a common SUMO-interacting motif (SIM) and map its binding surfaces on SUMO1 and SUMO2. This motif forms a beta-strand that could bind in parallel or antiparallel orientation to the beta2-strand of SUMO due to the environment of the hydrophobic core. A negative charge imposed by a stretch of neighboring acidic amino acids and/or phosphorylated serine residues determines its specificity in binding to distinct SUMO paralogues and can modulate the spatial orientation of SUMO-SIM interactions.

Amino Acid Motifs↗

PubMed2005

Reference frame and haptic discrimination of orientations in infants.

Body-tilt effect on the haptic discrimination of orientations and the 'oblique effect' (better discrimination of the vertical orientation than of an oblique orientation) were examined in 5-month-old infants. Body tilt leads to a mismatch between egocentric and gravitational reference frames and indicates in which reference frame orientations and oblique effect are defined. A familiarization/reaction to novelty procedure was used in upright body and tilted body conditions. Results revealed the occurrence of a haptic oblique effect in the upright body position, which disappeared when the body was tilted. The results suggest that spatial orientations and the oblique effect depend on a mixed reference frame that integrates not only gravitational information but also egocentric information.

Analysis of Variance↗

PubMed2000

Three-dimensional transcranial color-coded sonography for the examination of the arteries of the circle of Willis.

Because examinations of the intracranial vessels using conventional transcranial color-coded sonography (TCCS) lack spatial orientation and reproducibility, development of a three-dimensional (3-D) imaging technique is required. Three patients with middle cerebral artery (MCA) stenosis, three with suspected intracranial aneurysm, two with vascular malformation, and one healthy volunteer were investigated by 3-D TCCS using a magnetic spatial positioning sensor mounted on the transducer for simultaneous recording of the probe coordinates to create a volumetric data set. Three-dimensional transcranial color-coded sonography enabled good visualization of intracranial aneurysms and MCA stenoses. However, it failed to detect morphological details in vascular malformations. In conclusion, 3-D TCCS is a promising technique that opens new perspectives in depicting intracranial vessels and provides volume measurement of intracranial aneurysms.

Adult↗

PubMed2003

Spatial disorientation in Alzheimer's disease: the remembrance of things passed.

BACKGROUND: Patients with Alzheimer's disease (AD) and many older adults become lost even in familiar surroundings. This is commonly attributed to memory impairment, but it may reflect impaired spatial cognition. METHODS: The authors examined the role of memory, perceptual, and cognitive mechanisms in spatial disorientation by comparing the performance of normal young (YN), middle-aged (MA), older adult (OA), and AD subjects on neuropsychological and spatial orientation tests. RESULTS: The tendency to become lost is shared by almost all patients with AD (93%) and some OA subjects (38%). This impairment is not related to memory impairment. Instead, it reflects an inability to link recognized scenes with locations in the environment. CONCLUSIONS: Spatial disorientation reflects the impaired linking of landmarks and routes that should be assessed in conjunction with routine memory testing in elderly patients.

Adult↗

PubMed1989

Orientation specificity in spatial memory: what makes a path different from a map of the path?

Three studies investigated the factors that lead spatial information to be stored in an orientation-specific versus orientation-free manner. In Experiment 1, we replicated the findings of Presson and Hazelrigg (1984) that learning paths from a small map versus learning the paths directly from viewing a world leads to different functional characteristics of spatial memory. Whether the route display was presented as the path itself or as a large map of the path did not affect how the information was stored. In Experiment 2, we examined the effects of size of stimulus display, size of world, and scale transformations on how spatial information in maps is stored and available for use in later judgments. In Experiment 3, we examined the effect of size on the orientation specificity of the spatial coding of paths that are viewed directly. The major determinant of whether spatial information was stored and used in an orientation-specific or an orientation-free manner was the size of the display. Small displays were coded in an orientation-specific way, whereas very large displays were coded in a more orientation-free manner. These data support the view that there are distinct spatial representations, one more perceptual and episodic and one more integrated and model-like, that have developed to meet different demands faced by mobile organisms.

Adult↗

PubMed2006

Hierarchical clustering analysis of flexible GBR 12909 dialkyl piperazine and piperidine analogs.

Pharmacophore modeling of large, drug-like molecules, such as the dopamine reuptake inhibitor GBR 12909, is complicated by their flexibility. A comprehensive hierarchical clustering study of two GBR 12909 analogs was performed to identify representative conformers for input to three-dimensional quantitative structure-activity relationship studies of closely-related analogs. Two data sets of more than 700 conformers each produced by random search conformational analysis of a piperazine and a piperidine GBR 12909 analog were studied. Several clustering studies were carried out based on different feature sets that include the important pharmacophore elements. The distance maps, the plot of the effective number of clusters versus actual number of clusters, and the novel derived clustering statistic, percentage change in the effective number of clusters, were shown to be useful in determining the appropriate clustering level. Six clusters were chosen for each analog, each representing a different region of the torsional angle space that determines the relative orientation of the pharmacophore elements. Conformers of each cluster that are representative of these regions were identified and compared for each analog. This study illustrates the utility of using hierarchical clustering for the classification of conformers of highly flexible molecules in terms of the three-dimensional spatial orientation of key pharmacophore elements.

Cluster Analysis↗

PubMed2000

Effects of the size of the morris water tank on spatial discrimination learning in the CFW1 mouse.

The spatial orientation of mice and rats in tasks such as the Morris water escape task is guided by extramaze cues. Using data from the control groups of mice used in two drug-finding experiments, we addressed the question whether the size of the Morris water tank affects spatial learning in mice. In these experiments, CFW1 mice had been tested in either a small or a large water tank. Reanalysis of the data revealed that pool size did not affect learning or bias for the previous training quadrant. The Morris water escape task appears to act as a severe stressor in particular mouse strains, and a high stress level may interfere with the learning ability or performance of mice, which may have serious consequences for the interpretation of data. This is of special relevance when assessing the Morris maze performance of strains of mice with a different sensitivity to stress. We conclude that mice can best be tested in a small pool, because the time and distance swam to find and escape onto the platform is decreased and the probability of success (that is, of encountering the platform) is increased. This will reduce stress and hence increase the comparability of data between different strains of mice.

Animals↗

PubMed1996

Lattice fringe continuity in the absence of crystal continuity in enamel.

Since high-resolution transmission electron microscopy (HRTEM) provides information on a nearly atomic level, the confidence level with this method is very high. Thus, when lattice fringe continuity is found between two enamel crystals in proximity, such continuity has been taken as evidence of crystal fusion (Daculsi and Kerebel, 1977). Similarly, selected-area dark-field (SADF) electron microscopic imaging has been used to study the axial and spatial orientation of crystals. These studies have shown that there is apparent continuity between enamel and dentin crystals (Arsenault and Robinson, 1989). This observation supported the hypothesis that enamel crystallites are initiated by crystallites in dentin. We have used both HRTEM and SADF methods to identify instances of spatial relationship between crystallites in sections of rat incisor enamel and shark enameloid. In each instance of apparent continuity, goniometric tilting was used to examine the continuous interface. All instances where two crystallites seemed to come into contact, and where HRTEM imaging showed the lattice fringes to be directly continuous, were separated into individual crystallites when the specimen was tilted a few degrees. Thus, adjacent crystallites can show lattice fringe continuity in the absence of real crystallite contact. When instances of overlapping crystallites were examined by SADF imaging, the overlapping crystallites gave a single bright image. Goniometric tilting revealed separate crystallites. Thus, neither lattice fringe continuity nor image continuity under SADF can be used as evidence of crystal continuity unless goniometric rotation and tilting are applied when spatial relationships are suspected.

Animals↗

PubMed2002

Crossmodal links in spatial attention are mediated by supramodal control processes: evidence from event-related potentials.

Crossmodal links in spatial attention were studied in an experiment where participants had to detect peripheral tactile or visual targets on the attended side, while ignoring all stimuli on the unattended side and in the currently irrelevant modality. Both relevant locations and relevant modalities were specified on a trial-by-trial basis by auditory precues. Spatial orienting in the cue-target interval was reflected in anterior negativities and occipital positivities contralateral to the cued side, either when vision or touch was cued as relevant. These effects resembled previously reported ERP modulations during shifts of visual attention, implicating supramodal mechanisms in the control of spatial attention and demonstrating their independence of cue modality. Early effects of spatial attention on somatosensory and visual ERPs were of equivalent size for currently relevant and irrelevant modalities. Results support the idea that crossmodal links in spatial attention are mediated by supramodal control mechanisms.

Adolescent↗

PubMed1997

Covert visual orienting across the lifespan.

Covert visual orienting was examined over a span of human life ranging from six to 73 years. The observer's task was the speeded discrimination of "X" from "O1" but of primary interest was the effect of a location cue that appeared prior to the target. Both an abrupt stimulus cue and a voluntary information cue were studied using response time (RT) measures. Eye movements were monitored to control for differences in the ability to maintain fixation. Experiment 1 showed that there were very few age differences in stimulus-cued orienting. In contrast, there were important differences when orienting was intentional. In comparison with young adults, children were less able to sustain orienting over time, and senior adults required more time to use the cue. Experiment 2 tested the relation between stimulus and information cues when they both occurred prior to a given target. All age groups were able to use information cues in the presence of conflicting stimulus cues, but young adults were better able to do so than either children or senior adults. These results are interpreted as support for the view that separate mechanisms underlie stimulus-based versus information-based spatial orienting.

Adolescent↗

PubMed1995

Secondary structure and orientation of phospholamban reconstituted in supported bilayers from polarized attenuated total reflection FTIR spectroscopy.

We have studied the secondary structure of native phospholamban (PLB), a 52-residue integral membrane protein that regulates calcium uptake into the cardiac sarcoplasmic reticulum, as well as its 27-residue carboxy-terminal transmembrane segment (PLB26-52). The relative contents of alpha-helix, beta-strand, and random coil, as well as the spatial orientations of the alpha-helices of these molecules, reconstituted in dimyristoylphosphatidylcholine (DMPC) and 1-palmitoyl-2-oleoylphosphatidylcholine (POPC) bilayer membranes, were determined using polarized attenuated total reflection (ATR) Fourier transform infrared (FTIR) spectroscopy. The major component of the amide I' bands of PLB and PLB26-52 was centered at 1654-1657 cm-1 and was assigned to alpha-helix. The fraction of alpha-helix in native PLB was 64-67% (33-35 residues), and the transmembrane peptide PLB26-52 contained 73-82% alpha-helix (20-22 residues); small fractions of beta- and random structures were also identified. The orientational order parameter (S) of the alpha-helical component of PLB26-52 in DMPC was S = 0.86 +/- 0.09, indicating that the transmembrane helix was oriented approximately perpendicular to the membrane plane. Assuming the transmembrane domain of PLB resembles the peptide PLB26-52, the additional alpha-helical residues in PLB were assigned to the cytoplasmic helix and determined to have an order parameter S = -0.15 +/- 0.30. This may imply that the cytoplasmic helix was tilted from the membrane normal by an angle of 61 +/- 13 degrees or, alternatively, may indicate a wide angular distribution.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗