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PubMed1987

Cranial variation in European populations: a spatial autocorrelation study at three time periods.

This study reports on spatial variation of 10 cranial variables in European populations at 3 time periods. Means for these variables, based on 137, 108, and 183 samples from the Early Medieval, Late Medieval, and Recent periods, were subjected to one-dimensional and directional spatial autocorrelation analyses. Significant spatial structure was found for most variables. It becomes more pronounced as time progresses. The spatial patterns are not strongly clinal. Correlograms based on distances computed from all variables are monotonic only to 900, 1,650, and 1,350 km for the three periods. Regional patterns are seen for most variables and become more structured and significant with time. There is little similarity among the correlograms of the variables at any one period and virtually none among periods. Inferences about spatial structure of these populations, based on spatial autocorrelation analysis, suggest a pattern dominated by migration, followed by expansion and admixture rather than selection or chance fluctuations. The patterns of morphometric change seem to reflect the patterns of linguistic change in these areas.

Cephalometry↗
PubMed2002

Assessment of spatial normalization of whole-brain magnetic resonance images in children.

Commonly used frameworks for spatial normalization of brain imaging data (e.g., Talairach-space) are based on one or more adult brains. As pediatric brains are different in size and shape from adult brains and continue to develop through childhood, we aimed to assess the influence of age on various spatial normalization parameters. One hundred forty-eight healthy children aged 5-18 years were included in this study. The linear scaling parameters and the deformations from the non-linear spatial normalization to both a standard adult and a custom pediatric template were analyzed within SPM99. The effect of using a brain mask on the linear and of using different levels of constraint on the non-linear spatial normalization was assessed. Of the linear scaling factors, only the X-dimension (left-right) showed a significant age-correlation when based on brain tissue, whereas the overall scaling was not correlated with age. When based on the whole head, a very strong age-effect can be found in all dimensions. Non-linear deformations also show localized correlations with age, most pronounced in parietal and frontal areas. The total amount of volume change is significantly lower when using a pediatric template. It is also substantially influenced by the degree of regularization that is exerted on the spatial normalization parameters. Our results suggest that in the cortical areas showing a strong correlation of deformation with age, caution should be used in assigning imaging results in children to a specific morphological structure. Also, to minimize the amount of deformation during non-linear spatial normalization, a pediatric template should be used. Further implications of our findings on developmental neuroimaging studies are discussed.

Adolescent↗
PubMed2001

Spatial and temporal independent component analysis of functional MRI data containing a pair of task-related waveforms.

Independent component analysis (ICA) is a technique that attempts to separate data into maximally independent groups. Achieving maximal independence in space or time yields two varieties of ICA meaningful for functional MRI (fMRI) applications: spatial ICA (SICA) and temporal ICA (TICA). SICA has so far dominated the application of ICA to fMRI. The objective of these experiments was to study ICA with two predictable components present and evaluate the importance of the underlying independence assumption in the application of ICA. Four novel visual activation paradigms were designed, each consisting of two spatiotemporal components that were either spatially dependent, temporally dependent, both spatially and temporally dependent, or spatially and temporally uncorrelated, respectively. Simulated data were generated and fMRI data from six subjects were acquired using these paradigms. Data from each paradigm were analyzed with regression analysis in order to determine if the signal was occurring as expected. Spatial and temporal ICA were then applied to these data, with the general result that ICA found components only where expected, e.g., S(T)ICA "failed" (i.e., yielded independent components unrelated to the "self-evident" components) for paradigms that were spatially (temporally) dependent, and "worked" otherwise. Regression analysis proved a useful "check" for these data, however strong hypotheses will not always be available, and a strength of ICA is that it can characterize data without making specific modeling assumptions. We report a careful examination of some of the assumptions behind ICA methodologies, provide examples of when applying ICA would provide difficult-to-interpret results, and offer suggestions for applying ICA to fMRI data especially when more than one task-related component is present in the data.

Algorithms↗
PubMed2004

Spatial reference memory in GluR-A-deficient mice using a novel hippocampal-dependent paddling pool escape task.

Genetically modified mice lacking the L-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA) receptor subunit, GluR-A (GluR1), and deficient in hippocampal CA3-CA1 long-term potentiation (LTP), were assessed on a novel, hippocampal-dependent spatial reference memory, paddling pool escape task. The mice were required to use the extramaze cues around the laboratory to find a hidden escape tube that was in a constant location at one of 12 possible positions around the perimeter of the paddling pool, in order to escape from shallow water. The knockout mice performed well on this task. They displayed a small initial impairment (in terms of both escape latencies and choice errors), but they were soon as efficient as the wild-type mice in escaping from the water. This was further demonstrated by performance during a 20-s probe trial in which the exit tube was blocked. Both groups of mice spent most of the time searching in the quadrant of the pool in which the exit tube had previously been located. In a subsequent experiment, entirely normal spatial acquisition was observed in the knockout mice when the paddling pool was moved to a novel spatial environment. The GluR-A -/- mice were also unimpaired in a further reversal phase in which the correct exit location was moved by 180 degrees around the perimeter wall. These results are consistent with previous watermaze studies, providing further demonstration of intact hippocampus-dependent spatial reference memory in GluR-A knockout mice. They contrast strikingly with the profound deficits in hippocampus-dependent, short-term, flexible spatial working memory observed in these knockout mice. This study also demonstrates a novel behavioral task for assessing spatial memory in genetically modified mice. This task shares the behavioral profile of the well-established watermaze paradigm, but may have advantages for the study of genetically modified mice.

Animals↗
PubMed1992

Bilateral knife cuts to the perforant path disrupt spatial learning in the Morris water maze.

Both the hippocampus and the entorhinal cortex are known to be crucial for spatial learning, but the contribution of the pathway linking the two structures, the perforant path (PP), has never been tested in a spatial learning paradigm. The present study examined the role of the PP in spatial learning using the Morris water maze. Seven days after bilateral transection of the PP with a fine-bladed knife, rats were habituated to the pool, then trained to swim from varying start locations to a platform submerged in a fixed location. After 28 training trials over 5 days, probe trials (without any platform present) were given to assess spatial memory for the location. Compared to sham-operated controls, lesioned rats showed slower learning and poorer asymptotic performance in terms of both swim path distance and escape latency, and less preference for the correct quadrant during probe trials. When the platform location was "reversed" to the opposite quadrant, the lesioned rats again showed poorer learning, poorer asymptotic performance, and reduced preference for the correct quadrant on the probe trial. When tested with a visible platform whose position varied from trial to trial, lesioned rats performed as well as controls. These results are congruent with previous analyses of the contributions of the entorhinal cortex and hippocampus to spatial learning and suggest that for spatial learning, the PP is a critical functional link between these two structures.

Animals↗
PubMed1995

Simulation of spatial learning in the Morris water maze by a neural network model of the hippocampal formation and nucleus accumbens.

Cells in the hippocampal formation show spatial firing correlates thought to be critical to the role played by this structure in spatial learning. Place cells in the hippocampus proper show location-specific activity, whereas cells in the postsubiculum fire as a function of momentary directional heading. One question which has received little attention is how these spatial signals are used by motor structures to actually guide spatial behavior. Here we present a model of how one kind of spatial behavior, instrumental learning in the Morris water maze, could be guided by the spatial information in the hippocampal formation. For this, we concentrate on the hippocampal projection to the nucleus accumbens, which is strongly implicated in instrumental learning. In the model, simulated firing patterns of place cells and head direction cells activate "motor" cells in the "accumbens." Each motor cell causes a particular locomotor movement in a simulated rat. In this way, the "rat" locomotes through the simulated environment. Each step places the animal in a slightly different location and directional orientation, which, in turn, activates a different set of place and head direction cells, thus causing the next locomotor response, and so on. Connection strengths between cells are initially set randomly. When the animal encounters the reward location, however, connections are altered, so that recently active synapses are strengthened. Thus, successful moves in a particular locational and directional context are "stamped in." Simulated rats show rapid learning, similar in many ways to that of actual rats. In particular, they generate efficient routes to the goal after minimal experience, and can do so from somewhat novel starting positions. Consideration of the model architecture shows that 1) combined use of directional and place information is an example of a linearly inseparable problem and that 2) some types of novel route generation, often thought to require a "cognitive mapping" strategy, can be generated from the S-R type model used here.

Animals↗
PubMed2003

Technique to study three-dimensional spatial arrangement of synaptic vesicles using data from single sections.

Synaptic vesicles are membrane-bound organelles storing neurotransmitters in presynaptic terminals and releasing them into the synaptic cleft. Coordinated movements of synaptic vesicles relate to synaptic function and their spatial arrangement can provide useful information about the activity of a synapse. This article presents a technique to extract quantitative information about three-dimensional (3D) spatial arrangement of synaptic vesicles from measurements performed on single ultrathin random sections of a presynaptic terminal. The technique presumes quantification of a 2D density as well as 2D spatial pattern formed by vesicle profiles using a minimum spanning tree (MST) algorithm, in digitized micrographs of a presynaptic terminal. Further, original software was used to simulate a 3D spatial arrangement of synaptic vesicles and their random sectioning. A 3D density and pattern of synaptic vesicles were used as basic input parameters of the model, while a 2D density and MST quantities for vesicle profiles served as output, model-derived parameters allowing one to compare and fit simulated distributions to experimental ones. Pilot simulations performed to check the validity of the technique have shown that a 2D density and MST quantities of vesicle profiles closely relate to a 3D density and spatial pattern of vesicles. The technique was demonstrated in the analysis of spatial distribution of synaptic vesicles in axonal terminals forming asymmetric synaptic densities in the stratum radiatum of the CA1 subfield of the murine hippocampus.

Animals↗
PubMed2002

Combined time-resolved and high-spatial-resolution 3D MRA using an extended adaptive acquisition.

PURPOSE: To combine the benefits of time-resolved dynamic imaging and single elliptical centric acquisitions in a reasonable scan time. MATERIALS AND METHODS: A time series of images with moderate spatial resolution was acquired using the 3D Time-Resolved Imaging of Contrast KineticS (3D TRICKS) technique with elliptical centric encoding during contrast arrival. Following venous opacification, a complete large centrically encoded k-space volume was acquired. The high-spatial-frequency portions of this volume were combined with a 3D TRICKS time frame to form a high-resolution image. An additional single image is formed by suppressing background and signal averaging all acquired data, including post-venous low-spatial-frequency data. For this image, 2D temporal correlation analysis is used to suppress low-spatial-frequency vein contributions. Arrival time and spatial correlations are used to suppress background. RESULTS: The 3D TRICKS time frame may be selected to ensure a combined high-resolution image that has optimal central k-space sampling for any vascular region. The single image formed by signal averaging all acquired data has increased contrast-to-noise (CNR) and signal-to-noise (SNR) ratios. CONCLUSION: The advantages of time-resolved and high-spatial-resolution imaging were combined using an extended dual-phase acquisition. Some SNR and CNR gain was achieved by signal averaging. This process is facilitated by background and vein suppression.

Animals↗
PubMed2003

Proton echo-planar spectroscopic imaging with highly effective outer volume suppression using combined presaturation and spatially selective echo dephasing.

A highly effective outer volume suppression (OVS) technique, termed spatially selective echo dephasing (SSED), which employs gradient dephasing of spatially selective spin echoes, is introduced. SSED, which is relatively insensitive to T(1) dispersion among lipid signals and B(1) inhomogeneity, was integrated with very high spatial resolution 2D proton echo-planar spectroscopic imaging (PEPSI) to assess residual lipid bleeding into cortical regions in the human brain. The method was optimized to minimize signal refocusing of secondary spin-echoes in areas of overlapping suppression slices. A comparison of spatial presaturation with single or double SSED, and with combined presaturation and SSED shows that the latter method has superior performance with spatially uniform lipid suppression factors in excess of 70. Metabolite mapping (choline, creatine, and NAA) with a 64 x 64 spatial matrix and 0.3 cm(3) voxels in close proximity to peripheral lipid regions was demonstrated at 1.5 T with a scan time of 32 min using the standard head coil.

Brain↗
PubMed1993

Spatial agraphia.

Twenty-one patients with right hemisphere damage were studied (11 men, 10 women; average age = 41.33; age range 19-65). Subjects were divided into two groups: pre-Rolandic (6) and retro-Rolandic (15) right hemisphere damaged patients. A special writing test was given to each patient. The writing errors observed included literal substitutions, feature omissions and additions, letter omissions and additions, inability to maintain horizontal writing, inappropriate grouping and fragmentation of elements, and changes in handwriting style. Associated disorders included left-hemiparesis, visual field defects, spatial hemi-neglect, constructional apraxia, spatial alexia, and spatial acalculia. It is proposed that spatial agraphia is related to: (1) left hemi-neglect, (2) constructional deficits, (3) general spatial defects, and (4) some motor disautomatization and tendency to perseverate. In cases of right frontal damage, motor-associated deficits (iterations of features and letters) predominated, whereas in cases of posterior right hemisphere damage, spatial defects (inappropriate distribution of written material in the space, grouping of letters belonging to different words, and splitting of words) were more evident. Writing impairments are in general more noticeable in cases of retro-Rolandic damage.

Adult↗
PubMed1999

Change of spatial field effects in 16- to 20-week-old infants.

Infants from 16 to 20 weeks were presented with objects moving across a 60-cm distance. Tracking increased between 16 and 18 weeks, reaching increased at 18 weeks, and arm lifts (swipes) showed no age change. A right spatial field bias in tracking disappeared gradually. Swipes occurred most often in front of the object, when it was moving in the center field, presumably as reactions due to spatial proximity. Reaching occurred in the peripheral spatial fields in the younger infants, but in the older infants most often in the center spatial field. Moreover, reaching occurred generally more often toward the left spatial field and predicted the emergence of tracking the left spatial field. Thus, it appeared that a bias in reaching corrected a bias in tracking. Similar effects of limb movements, especially when reaching, were found in the successful treatment of visual neglect patients in neuropsychological research.

Female↗
PubMed2001

Dyslexia and visual-spatial talents: compensation vs deficit model.

There are both theoretical and empirical reasons to support the hypothesis that dyslexia is associated with enhancement of right-hemisphere, visual-spatial skills. However, the neurological evidence is neutral with respect to whether dyslexic visual-spatial abilities should be superior (a compensation model) or inferior (a deficit model). In three studies we tested the hypothesis that dyslexia is associated with superior visual-spatial skills. Individuals with dyslexia not only failed to show superiority on a range of visual-spatial tasks, even when tasks were presented without time constraints, but also demonstrated a deficit on many tasks. Whereas we found attentional problems associated with dyslexia, these did not explain our findings. Results are discussed in terms of the apparent conflict between the failure to find any visual-spatial talent associated with dyslexia and the fact that dyslexia is overrepresented in certain visual-spatial professions.

Adult↗
PubMed2001

Development and validation of a spatially explicit individual-based mixed crop growth model.

Spatial disposition of plants in intercrops, and differences in sowing time between species, can strongly affect their ecological interactions and, in consequence, the system's viability and performance. Empirical exploration of a wide range of spatial and temporal plant arrangements is costly and time-consuming. Modelling the growth of mixed crops is a tool which, combined with empirical tests, can greatly reduce the time and investment required for this task. Spatially explicit, individual-based dynamic models seem well suited for this purpose; their exploration and experimental validation for the case of simple, two-species, artificial plant communities, can also provide further insight as to how the spatial and temporal scales of a plant's multispecific neighbourhood affect its growth and performance. The aim of this investigation was to further develop a published spatially explicit individual-based mixed crop growth model [Vandermeer, J. H. (1989). The Ecology of Intercropping, Cambridge, U.K.: Cambridge University Press, p. 237], and to validate it experimentally. With this purpose in mind: (1) computer programs to simulate individual plant growth and to perform statistical analysis of both deterministic and stochastic versions of the model were developed; (2) the model was parametrized using a complex experimental diculture with several cohorts and spatial arrangements; (3) the predictive capacity of the model was tested using independent spatio-temporal experimental arrangements; (4) a modified version of the model was written, which abandons the assumption of linearity of the neighbourhood index at the cost of increasing the number of parameters; (5) The performance of stochastic versions of both Vandermeer's and our modified model were compared, employing a non-parametric measure of goodness of fit. We conclude that this approach to modelling plant growth subject to intra and interspecific competition is a remarkably efficient, general, conceptually elegant, heuristic tool whose predictive power can be further improved when nonlinear terms are introduced into the neighbourhood competition index, as done in our modified version of Vandermeer's model.

Agriculture↗
PubMed1999

Interactions of spatial and luminance information in the retina of chickens during myopia development.

Degrading the retinal image by frosted eye occluders produces elongated eyes and 'deprivation myopia' in a variety of animal models. The postulated retinal 'deprivation detector' is quite sensitive to even small changes in image contrast or spatial frequency composition. Because psychophysical experiments have shown that a decline in luminance shifts the contrast sensitivity function to lower spatial frequencies, it is likely that only a reduced spatial frequency range is available for image analysis to control eye growth. It is even possible that the compression might be sufficient to promote deprivation myopia. We have tested this hypothesis, using the animal model of the chicken. (1) At an ambient illumination of 550 lux (about 76 cd m-2), neutral density (ND) filters placed in front of the eye with 0.0, 0.5 or 1.0 log unit attenuation did not change refractive development. However, monocularly or binocularly attached filters with 2 log units attenuation produced 5-7 D of myopia relative to normal eyes. Black occluders were not more effective. Frosted eye occluders with little effect on image brightness (about 0.5 log units attenuation) produced much more myopia (about 16 D compared with the controls). (2) The effects of the ND filters on refractive development could not be reproduced if the ambient illumination was reduced by 2 log units. Probably, minor effects on image quality were introduced by optical imperfections of the ND filters which were more critical at low retinal image brightness. (3) In an optomotor experiment (spatial frequency 0.2 cyc deg-1, stripe speed 57 deg sec-1), it was shown that the chickens' contrast sensitivity was severely reduced when the eyes were covered by 2.0 ND filters. (4) Since there is evidence that changes in dopamine release from the retina may be one of the factors affecting the development of myopia, we have tested how selective these changes were for spatial information. It was found that dopamine release was controlled by both spatial and luminance information and that the inputs of both could be scarcely separated. (5) Because the experiments show that the eye becomes more sensitive to image degradation at low light, the human eye may also be more prone to develop myopia if the light levels are low during extended periods of near work.

Animals↗
PubMed2000

BDNF protects against spatial memory deficits following neonatal hypoxia-ischemia.

Hypoxic-ischemic (H-I) brain injury in the human perinatal period often leads to significant long-term neurobehavioral dysfunction in the cognitive and sensory-motor domains. Using a neonatal H-I injury model (unilateral carotid ligation followed by hypoxia) in postnatal day seven rats, previous studies have shown that neurotrophins, such as brain-derived neurotrophic factor (BDNF), can be protective against neural tissue loss. The present study explored potential relationships between neural protective and behavioral protective strategies in this neonatal H-I model by determining if neonatal H-I was associated with behavioral spatial learning and memory deficits and whether the neurotrophin BDNF was protective against both brain injury and spatial learning/memory dysfunction. Postnatal day seven rats received vehicle or BDNF pretreatments (intracerebroventricular injections) followed by H-I or sham treatments and then tested for spatial learning and memory on the simple place task in the Morris water maze from postnatal days 20 to 30, and their brains were histologically analyzed at 4 weeks following treatments. H-I rats with vehicle pretreatment displayed significant tissue loss in the hippocampus (including CA1 neurons), cortex, and striatum, as well as severe spatial memory deficits (e.g., short probe times). BDNF pretreatment resulted in significant protection against both H-I-induced brain tissue losses and spatial memory impairments. These findings indicate that unilateral H-I brain injury in a neonatal rodent model is associated with cognitive deficits, and that BDNF pretreatment is protective against both brain injury and spatial memory impairment.

Animals↗
PubMed1998

Sex differences in the activational effect of ERalpha on spatial learning.

This study investigated the role of the estrogen receptor alpha (ERalpha) in mediating performance on a spatial discrimination task, the Morris water maze. Spatial discrimination on this water escape task was examined in eight groups of gonadectomized mice. Male and female wild-type (WT) and littermate mice lacking functional copies of the ERalpha gene (ERalphaKO), were treated with estradiol benzoate (EB) or sesame oil vehicle. Subjects were trained on the water escape task over a 4-day period (four trials per block, three blocks per day). Latency to find the hidden platform was measured. Only female WT mice treated with EB failed to learn this spatial discrimination task. All males, WT and ERalphaKO treated with EB or oil exhibited decreased latencies across blocks of trials, WT females treated with oil, and ERalphaKO females, regardless of treatment, learned the spatial discrimination task. In order to eliminate motivational or sensory-motor impairments as a factor in describing the poor spatial discrimination performance of WT females treated with EB, the cue version of the water maze task was employed. Results from the cue phase of the task indicate that EB and oil-treated WT females exhibited a similar decrease in escape latencies across blocks of trials, indicating good cue discrimination performance. Taken together, the results indicate that ERalpha activation impairs acquisition of spatial discrimination of the water escape task, but not cue discrimination, in female mice. Because ligand-bound ERalpha appears to operate differently in male and female mice we hypothesize that the ability of ERalpha to affect learning is organized during development.

Animals↗
PubMed2001

Menstrual cycle variation in spatial ability: relation to salivary cortisol levels.

This study examined whether menstrual cycle phase was associated with performance on the Primary Mental Abilities Test of Spatial Relations, a test of mental rotation, in undergraduate students (N = 82). As cortisol levels also vary across the menstrual cycle under conditions of stress and influence cognitive performance, saliva samples were obtained before and after the test session to examine whether cortisol levels were related to between- and within-group differences in spatial performance. Men scored higher on the spatial test than all the groups of women, although the difference between men and women in the menstrual phase was not significant. Women in the luteal phase scored lower than the menstrual, follicular, and oral contraceptive user groups of women. There were no sex or menstrual cycle differences in cortisol levels, and no association between cortisol levels and spatial performance. The poorer performance of women in the luteal phase was not related to differences in ratings of perceived stress, perceived success on the test, or mood. Although menstrual cycle phase accounted for a significant proportion of the variance (15%) in performance on the spatial test, this does not explain why men outperformed women regardless of the phase of the cycle. Thus, there are clearly several other variables, sociocultural and physiological, involved in mediating individual differences in spatial performance.

Adolescent↗
PubMed1997

Spatial and density effects in evolutionary game theory.

Two models are considered for the study of game dynamics in a spatial domain. Both models are continuous in space and time and give rise to reaction-diffusion equations. The spatial domain is homogeneous but the mobility of the individuals is allowed to depend upon the strategy. The models are analysed for spatial patterns (via a Turing instability) and also for the direction of the travelling wave that replaces one strategy by another. It is shown that the qualitative behaviour of the two models is quite different. When considering the existence of spatial patterns and deciding whether increased mobility is helpful or not, it is shown that the answers depend crucially upon the model equations. Since both models (in the absence of spatial variation) are quite standard, it is clear that considerable care has to be exercised in the formulation of spatial models and in their interpretation.

Animals↗