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PubMed2002

NGF induces appearance of adult-like response to spatial novelty in 18-day male mice.

We investigated the effects of Nerve Growth Factor (NGF) administration on the maturation of reactivity to spatial and non-spatial novelty in developing mice. CD-1 mice of both sexes received intracerebral administration of NGF on postnatal day (pnd) 15, and their response to object displacement (spatial novelty) and object substitution (object novelty) were assessed in a spatial open-field with four objects on pnd 18 or 28. On pnd 18, NGF induced only in males precocious appearance of spatial novelty discrimination, while increasing choline acetyltransferase activity in neocortex and hippocampus of both sexes. The behavioral and neurochemical effects disappeared by pnd 28. NGF triggers adult-like responding to spatial novelty in developing mice and such effect is gender-specific.

Animals↗
PubMed1992

Dissociation of spatial navigation and visual guidance performance in Purkinje cell degeneration (pcd) mutant mice.

Spatial learning in rodents requires normal functioning of hippocampal and cortical structures. Recent data suggest that the cerebellum may also be essential. Neurological mutant mice with dysgenesis of the cerebellum provide useful models to examine the effects of abnormal cerebellar function. Mice with one such mutation, Purkinje cell degeneration (pcd), in which Purkinje cells degenerate between the third and fourth postnatal weeks, were evaluated for performance of spatial navigation learning and visual guidance learning in the Morris maze swim-escape task. Unaffected littermates and C57BL/6J mice served as controls. Separate groups of pcd and control mice were tested at 30, 50 and 110 days of age. At all ages, pcd mice had severe deficits in distal-cue (spatial) navigation, failing to decrease path lengths over training and failing to express appropriate spatial biases on probe trials. On the proximal-cue (visual guidance) task, whenever performance differences between groups did occur, they were limited to the initial trials. The ability of the pcd mice to perform the proximal-cue but not the distal-cue task indicates that the massive spatial navigation deficit was not due simply to motor dysfunction. Histological evaluations confirmed that the pcd mutation resulted in Purkinje cell loss without significant depletion of cells in the hippocampal formation. These data provide further evidence that the cerebellum is vital for the expression of behavior directed by spatial cognitive processes.

Age Factors↗
PubMed1997

Subicular cells generate similar spatial firing patterns in two geometrically and visually distinctive environments: comparison with hippocampal place cells.

Cells in both the hippocampus and the subiculum show location related firing patterns, so that the momentary firing rate of a cell is related to the spatial location of a freely moving rat as it navigates in an environment. Since the subiculum receives a strong anatomical projection from the hippocampus, it seems possible that the subicular cell spatial patterns are simply driven by the spatial signals from hippocampal place cells. Data presented here, however, suggest that the two areas code space in fundamentally different ways. Here, spatial firing patterns of individual hippocampal and subicular cells were studied as rats navigated in two different environments. The two chambers were a cylinder and a square, of equal area. For some rats the two chambers were painted to have similar visual stimulus characteristics, while for others, the two were very different. The subicular cells showed very similar firing patterns in the two chambers, regardless of whether they were visually similar or different. In contrast, as predicted based on the findings of earlier studies, hippocampal place cells showed different patterns in the two (again, regardless of their visual similarity). These results suggest that the subicular cells have the ability to transfer a single, abstract spatial representation from one environment to another. This pattern is stretched to fit within the boundaries of the current environment. Thus, the subicular cells seem to provide a generic representation of the geometric relationships between different locations in an environment. It seems possible that this representation may contribute to some navigational abilities exhibited by animals, such as dead reckoning, and novel route generation in unfamiliar environments. In contrast, it appears that hippocampal place cells provide a spatial representation-which is unique for each environment and which is strongly influenced by the exact details and overall context of the situation.

Animals↗
PubMed1997

Dose-related impairment of spatial learning by intrahippocampal scopolamine: antagonism by ondansetron, a 5-HT3 receptor antagonist.

To study the role of hippocampal muscarinic receptors in spatial learning, various doses of scopolamine were injected bilaterally into the CA1 region of the dorsal hippocampus of rats trained in a two-platform spatial discrimination task. Scopolamine administered 10 min before each training session at doses ranging from 3.75 to 15 micrograms/microliter impaired choice accuracy, had no effect on choice latency and increased the errors of omission only with 7.5 micrograms on day 1 and with 15 micrograms on days 1 and 2 of training. No dose affected choice accuracy or latency of a non-spatial visual discrimination task. A subcutaneous dose of 1 microgram/kg ondansetron, a 5-HT3 receptor antagonist, 30 min before each training session prevented the impairment of choice accuracy by intrahippocampal 3.75 micrograms scopolamine but 0.1 microgram/kg ondansetron had no such effect. No dose of ondansetron by itself modified the acquisition of spatial learning. The results suggest that relatively low doses of scopolamine in the dorsal hippocampus selectively impair the acquisition of a spatial discrimination task, and that blockade of 5-HT3 receptors prevents the deficit caused by the muscarinic antagonist. The utility of the deficit of spatial learning induced by intrahippocampal scopolamine for modelling some aspects of memory disturbances in Alzheimer's disease is discussed.

Animals↗
PubMed2001

Small-scale spatial and temporal variance in the concentration of heavy metals in aquatic sediments: a review and some new concepts.

Uncertainty associated with data derived by the analyses of heavy metals in aquatic sediment is due to variance produced in the laboratory (precision), plus 'natural', small-scale spatial variance, (or field variance) at the sampling site. Precision is easily determined and is usually reported in contaminant studies, but field variance is poorly understood and seldom documented. It is important to have an understanding of the field variance because if small-scale spatial variance in the concentration of heavy metals is excessive, regional trends may be limited value. Similarly, if temporal change is large, the results of single synoptic surveys may be questionable and the ability to demonstrate anthropogenic contributions over time will be difficult. However, it is evident from the literature that the information needed to address problems of spatial and temporal variance in the field is beyond the resources of most researchers. Analytical precision of about 5% relative standard deviation (RSD) for heavy metal analysis is typical of a well-managed laboratory. Many studies of small-scale spatial variability made during the current investigation indicate that field variance is related to ambient energy and to the type of sedimentological environment. Total variance (analytical plus field variance) is approximately 10% RSD (mean for a suite of nine trace elements) for depositional parts of estuaries and the marine environment, but increases to about 20-35% RSD for the more dynamic parts of the estuarine environment and the fluvial system. Repeated sampling over periods of up to 7 years undertaken during the present study, indicate a similar order of magnitude for temporal variability in these sedimentological environments. A proposed scheme to provide information on field variance is to undertake small-scale spatial and temporal studies in discrete sedimentological environments in the study area after sediment sampling and characterisation has been completed. The comparatively large proportion of total variance associated with small-scale spatial and temporal variability in the field questions the often excessive cost and effort made in attempting minor reductions in analytical precision in contaminant investigations.

Ecosystem↗
PubMed2001

Deprivation and mortality: the implications of spatial autocorrelation for health resources allocation.

This paper aims at investigating whether the relationship between mortality and socio-economic deprivation is affected by the spatial autocorrelation of ecological data. A simple model is used in which mortality (all-ages and premature) is the dependent variable, and deprivation, morbidity and other socio-economic indicators are the explanatory variables. Deprivation is measured by the Townsend index; the other socio-economic variables are the median income, unequal income distribution (Gini coefficient) and population density. Morbidity is estimated on the basis of hospital admission rates and overweight prevalence. Spatial autocorrelation is measured by the Moran's I coefficient. All mortality and morbidity variables have significant, positive, and moderate-to-high spatial autocorrelation. Two multivariate models are explored: a weighted least-squares model ignoring spatial autocorrelation and a simultaneous autoregressive model. The paper concludes that spatial autocorrelation has a significant impact on the relationship between mortality and socio-economic variables. Future ecological models intended to inform health resources allocation need to pay greater attention to the spatial dimension of the data used.

Belgium↗
PubMed2000

Using survival analysis to study spatial point patterns in geographical epidemiology.

The spatial K-function has become a well accepted method of investigating whether significant clustering can be detected in spatial point patterns. Unlike nearest neighbor-based methods, the K-function approach has the advantage of exploring spatial pattern across a range of spatial scales. However, K-functions still have a number of drawbacks. For instance, although K-functions are based on inter-event distances, they only use a count of the number of point events within successive distance bands. This represents data aggregation and information loss. Secondly, and perhaps more significantly, K-functions are based on a cumulative count of point events with distance. This feature raises the possibility that the investigation of pattern at different scales is compromised by the dependency of any one count to previous counts. This paper proposes a new approach to the analysis of spatial point patterns based upon survival analysis. Although typically used in the temporal domain, there is no reason why survival analysis cannot be applied to any positively-valued, continuous variable as well as time. In this paper, survival analysis is applied to the inter-event distance measures of bivariate spatial point patterns to investigate the 'random labeling' hypothesis. It is shown, through both a controlled data situation and empirical epidemiological applications, that such an approach may be a very useful complement to K-function analysis.

Accidents, Traffic↗
PubMed2003

Cognition and affective style: Individual differences in brain electrical activity during spatial and verbal tasks.

Relations between brain electrical activity and performance on two cognitive tasks were examined in a normal population selected to be high on self-reported measures of Positive or Negative Affectivity. Twenty-five right-handed women, from an original pool of 308 college undergraduates, were the participants. EEG was recorded during baseline and during psychometrically matched spatial and verbal tasks. As predicted, participants who were high in Positive Affectivity performed equally well on the verbal and spatial tasks, while participants who were high in Negative Affectivity had spatial scores that were lower than their verbal scores. There were no group differences in baseline EEG. Both groups exhibited left central activation (i.e., alpha suppression) during the verbal and spatial tasks. When EEG data were analyzed separately for the group high in Positive Affectivity, there was evidence of parietal activation for the spatial task relative to the verbal task. The EEG data for the group high in Negative Affectivity had comparable EEG power values during verbal and spatial tasks at parietal scalp locations. These data suggest that, within a selected normal population, differences in affective style may interact with cognitive performance and with the brain electrical activity associated with that performance.

Adolescent↗
PubMed1998

The cerebellum in the spatial problem solving: a co-star or a guest star?

The experimental findings reviewed here indicate that the cerebellum has to be added to the regions known to be involved in the spatial learning. Cerebellar function is specifically linked to 'how to find an object' rather than 'where the object is in the space'. In the Morris water maze (MWM) hemicerebellectomized (HCbed) rats displayed a severe impairment in coping with spatial information, displaying only peripheral circling. And yet, when the MWM cue phase was prolonged, HCbed rats succeeded in acquiring some abilities to learn platform position, even in a pure place paradigm, such as finding a hidden platform with the starting points sequentially changed. Conversely, whether the searching strategy was acquired preoperatively, no exploration deficit appeared. Thus, cerebellar lesions appear to affect the procedural components of spatial function, sparing the declarative ones. When intact animals were non-spatially pre-trained and then HCbed, they exhibited an expanded scanning strategy, underlining the cerebellar involvement in procedural component acquisition. By testing HCbed rats in an active avoidance task, first without and then with a request for right/left discrimination, lesioned rats displayed severe deficits. Thus, besides a marked impairment in facing procedural components of spatial processing, cerebellar lesion provokes deficits also in right/left discrimination task. In conclusion, it is possible to propose the cerebellum as one part of a large system that includes frontal, posterior parietal, inferior temporal cortices, hippocampus and basal ganglia. These structures form an allocentric spatial system and an egocentric control system, that interlock to process the information involved in representing an object in the space.

Animals↗
PubMed2001

Strain compounding: spatial resolution and performance on human images.

Compounding has long been used to reduce speckle brightness variations by incoherently combining partially correlated measurements of the same image object. Conventionally, decorrelation between measurements is introduced by imaging from different spatial positions (i.e., spatial compounding) or within different frequency ranges (i.e., frequency compounding). An alternative compounding approach based on speckle decorrelation of an object under different strain conditions was recently proposed. The new approach was referred to as strain compounding. Speckle correlation of strain compounding was previously analyzed using simulations and radiofrequency (RF) data from a gelatin-based phantom. Results indicated that effective speckle reduction is possible at strains potentially achievable in certain clinical situations. In this paper, performance of strain compounding is further analyzed. Potential degradation in spatial resolution of strain compounding is compared to that of conventional approaches using computer simulations. Results show that strain compounding potentially can achieve the same level of speckle reduction, with less degradation in spatial resolution if a large compression can be applied. Performance of strain compounding is also tested using postdetection human images acquired by a commercial imaging system. Two-dimensional (2-D) speckle tracking is performed to correct for tissue motion resulting from external compression and to ensure that the images to be compounded are spatially matched. Thyroid images show that speckle brightness variations can be effectively reduced without significant degradation in spatial resolution. Speckle reduction in liver imaging is also demonstrated. However, speckle reduction is not as significant as in thyroid imaging, due to the fact that a large compression cannot be achieved.

Humans↗
PubMed1998

D1 agonist CY208-243 attenuates the pattern electroretinogram to low spatial frequency stimuli in the monkey.

We investigated whether or not the D1 agonist, CY 208-243, affects the spatial tuning function of pattern electroretinogram (PERG). Two lightly anaesthetised monkeys were studied before and after CY 208-243 or placebo administration. The results show that the PERG response to 0.5 cycles/degree (c/d; coarse), but not to 2.3 c/d (medium) spatial frequency stimuli disappears following systemic administration of this drug. Since previous results show that D2 blockers attenuate the PERG only above 2.3 c/d, foremost the peak of the normal spatial frequency response function, the current results suggest that dopamine itself, via D1 receptors, may be responsible for the low spatial frequency decline of normal spatial PERG tuning function. We infer that the synergistic activation of D1 and D2 receptors is needed to shape the spatially tuned primate ERG.

Animals↗
PubMed2000

Spatial properties and direction selectivity of single neurons in area 21b of the cat.

The receptive field properties of single units were assessed in area 21b of the cat visual cortex. Visual cells in this area were binocular and showed relatively large receptive fields. Most cells were strongly sensitive to the direction of drifting gratings. The mean value of the half-widths of the direction tuning curves (32 degrees ) suggests broader direction tunings than are typically found in other visual areas. The spatial frequency tuning functions were either band-pass or low-pass. Cells responded optimally to low spatial frequencies (mean =0.08c/deg) and also showed low spatial resolution (mean =0.29c/deg.). The estimated values of spatial bandwidths (mean=2.2 octaves) suggest that area 21b cells act as relatively good spatial filters. Although some cells exhibited a low contrast threshold, most cells began to respond at intermediate or high contrast values (mean threshold =15.5%). Temporal frequency tuning functions were mostly band-pass and usually broad (mean temporal bandwidth=3.3 octaves). Cells were found that responded optimally to various temporal frequencies (mean optimal temporal frequency=3.2Hz), although the majority preferred a temporal frequency below 4Hz.These results suggest that visual properties (receptive fields sizes, spatial resolution and orientation/direction selectivity) of cells in area 21b differ from those of cells previously observed in the adjoining area 21a. These differences provide evidence in support of functional distinction between these two visual areas.

Animals↗
PubMed1998

Spatial and temporal matching of receptive field properties of binocular cells in area 19 of the cat.

The spatial and temporal properties of single neurons were investigated in area 19 of the cat. We evaluated the matching of binocular receptive field properties with regard to the respective strength of the ipsilateral and contralateral inputs. Results indicate that most cells in area 19 are well tuned to spatial and temporal frequencies and exhibit relatively low contrast threshold (mean=6.8%) when assessed using optimal parameters and tested through the dominant eye. Spatial resolution (mean=0.75 c/degree), optimal spatial frequencies (mean=0.16 c/degree) were relatively low and spatial bandwidths (mean=2.1 octaves) were broader as compared to those of cells in area 17 but comparable to those of cells in other extrastriate areas. On the other hand temporal resolution (mean=10.7 Hz), optimal temporal frequency (mean=4.5 Hz) and temporal bandwidths (mean=2.9 octaves) were higher and broader than in primary visual cortex. A significant relationship exists between most of the cell's properties assessed through either eye. For some parameters, such as spatial and temporal resolution, ocular dominance was shown to be significantly related to the extent of matching between the two eyes. For these parameters, binocular cells that exhibited a balanced ocular dominance were generally well matched with regard to the receptive field properties of each eye whereas the largest mismatches were found in cells that were more strongly dominated by one eye. These results suggest that visual input contributes to the activation of cells in area 19 in a redundant manner, possibly attesting to the multiplicity of parallel pathways to this area in the cat.

Animals↗
PubMed1998

Spatial learning and hippocampal volume in male deer mice: relations to age, testosterone and adrenal gland weight.

Spatial learning and various physiological parameters were examined in old (57 month), middle aged (38 month), adult (18 month) and young (3-3.5 month) male deer mice (Peromyscus maniculatus). Performance during acquisition of a water maze task was not significantly reduced for middle aged and adult mice relative to young reproductively active (breeding) mice. Performance was deteriorated in old mice relative to young breeding mice on block 4 of training. Retention of this spatial task, however, was reduced in all three older groups relative to young breeding mice. Corrected hippocampal volume (corrected for brain weight) was reduced only in old mice relative to young breeding mice although absolute volumes of hippocampus were lower in all groups relative to young breeding mice. Old mice also were shown to have lower levels of plasma testosterone and lighter brains relative to young breeding mice. Spatial retention was not deficient in old, middle aged and adult mice relative to a group of young reproductively quiescent male (non-breeding) mice. Young breeding mice displayed better spatial performance and had significantly higher plasma testosterone levels, corrected hippocampal volume and brain weight relative to young non-breeding mice. These results indicate that retention of a spatial task is more sensitive to the age of male deer mice than acquisition of the task. Hippocampal volume, although a gross morphological feature, appears to be sensitive to the effects of ageing in male deer mice. Plasma testosterone levels do not appear to be a crucial factor underlying age-related deficits in retention of a spatial task.

Adrenal Glands↗
PubMed2003

Influence of bladder and rectal volume on spatial variability of a bladder tumor during radical radiotherapy.

PURPOSE: To assess the spatial variability of a bladder tumor relative to the planning target volume boundaries during radical radiotherapy, and furthermore to develop strategies to reduce spatial variability. METHODS AND MATERIALS: Seventeen patients with solitary T2-T4N0M0 bladder cancer were treated with a technique delivering 40 Gy/2 Gy in 20 fractions to the whole bladder with a concomitant boost to the bladder tumor of 20 Gy in 1 Gy fractions in an overall time of 4 weeks. CT scans were made weekly, immediately after treatment, and matched with the planning CT scan. Spatial variability of the tumor, as well as bladder volume and rectal diameter, were scored for each patient each week. RESULTS: In 65% of patients, a part of the tumor appeared outside the planning target volume boundaries at least one time during the course of radiotherapy. No consistent relation of this variability with time was found. Bladder volumes and rectal diameters showed marked variability during the course of treatment. A large initial bladder volume and rectal diameter predicted a large volume variation and a large tumor spatial variability. CONCLUSION: In this study, a margin of 1.5 to 2 cm seemed to be inadequate in 65% of the patients with respect to spatial variability. Bladder volume and rectal diameter were found to be predictive for spatial variability of a bladder tumor during concomitant boost radiotherapy.

Humans↗
PubMed1998

Spatial resolution threshold in pseudophakic patients with monofocal and multifocal intraocular lenses.

PURPOSE: To compare the spatial resolution threshold in the central visual field of pseudophakic patients with monofocal and multifocal intraocular lenses (IOLs). SETTING: Eye Clinic, University of Trieste, Italy. METHODS: Twenty phakic normal subjects and four groups of 20 pseudophakic patients each, implanted with refractive and diffractive multifocal IOLs (Domilens Progress 1, AMO Array MPC25NB, or Pharmacia 811X) or with monofocal IOLs (Allergan PC43NB), were studied. The spatial resolution threshold in the central visual field was assessed using high-pass resolution perimetry. Measurements were performed adding spherical correction to test the different foci of the IOL. RESULTS: No significant differences between phakic subjects and pseudophakic patients with monofocal IOLs were found. In distance vision, no significant differences between patients with refractive multifocal IOLs and those with monofocal IOLs were found. The group with the diffractive multifocal IOL showed a significantly higher spatial resolution threshold (P = .003). In intermediate vision, the AMO Array group showed a significantly lower spatial resolution threshold than the other groups (P < .01). The best performance at near distance was in the diffractive group, which was statistically significantly different from the other groups (P < .001). CONCLUSION: In the diffractive group, the high spatial resolution threshold in distance vision could be explained by the lower brightness of the principal focus, related to a different light energy division between the foci. In the Domilens group, the high spatial resolution threshold in near vision could be related to the light energy scattered in a large number of foci.

Aged↗
PubMed2001

Event-related brain response abnormalities in autism: evidence for impaired cerebello-frontal spatial attention networks.

Although under some conditions the attention-related late positive event-related potential (ERP) response (LPC) is apparently normal in autism during visual processing, the LPC elicited by visuospatial processing may be compromised. Results from this study provide evidence for abnormalities in autism in two components of the LPC generated during spatial processing. The early frontal distribution of the LPC which may reflect attention orienting was delayed or missing in autistic subjects during conditions in which attention was to peripheral visual fields. The later parietal distribution of the LPC which may be associated with context updating was smaller in amplitude in autistic subjects regardless of attention location. Both abnormalities suggest disruption of function in spatial attention networks in autism. Evidence that the cerebellar abnormalities in autism may underlie these deficits comes from: (1) similar results in ERP responses and spatial attention deficits in patients with cerebellar lesions; (2) brain-behavior correlations in normally functioning individuals associating the size of the posterior cerebellar vermis and the latency of the frontal LPC; and (3) a previously reported complementary correlation between the size of the posterior vermal lobules and spatial orienting speed. Although the scalp-recorded LPC is thought to be cortically generated, it may be modulated by subcortical neural activity. The cerebellum may serve as a modulating influence by affecting the task-related antecedent attentional process. The electrophysiological abnormalities reported here index spatial attention deficits in autism that may reflect cerebellar influence on both frontal and parietal spatial attention function.

Adolescent↗
PubMed2002

Age-related changes in fronto-parietal networks during spatial memory: an ERP study.

Spatial attention and memory were compared in young and old subjects using non-delayed and delayed matching-to-sample tests. Both young and older subjects revealed a right hemisphere superiority for spatial processing. Older subjects were as accurate as young controls in the non-delay task supporting preserved attention ability in this spatial task. However, older subjects were impaired at 3 s retention intervals supporting an encoding and/or retrieval deficit in spatial memory. Stimulus evaluation demands were highest in the non-delay task and younger subjects generated the largest posterior P3 in this condition plus an additional frontal P3. The frontal P3 was reduced in amplitude in the delay tasks in the young subjects. Retention of spatial information during the delay period was characterized by a negative slow wave maximal over Pz that predicted later memory performance and was enhanced in those subjects with high memory performance. Conversely, older subjects generated a frontal P3 in both delay and non-delay conditions and a reduced sustained posterior scalp negativity in some delay conditions. The results support age-related alterations in frontal-parietal networks during spatial memory.

Adolescent↗