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PubMed2002

The use of spatial modeling in an aquatic food web to estimate exposure and risk.

This paper quantitatively evaluates interactions among foraging behavior, habitat preferences, site characteristics and the spatial distribution of contaminants in estimating PCB exposure concentrations for winter flounder at a hypothetical open water dredged material disposal site in the coastal waters of New York and New Jersey (NY-NJ). The models implemented in this study include a spatial submodel to account for spatial and temporal characteristics of fish exposure and a probabilistic adaptation of the Gobas bioaccumulation model to account for temporal variation in concentrations of polychlorinated biphenyls (PCBs) in sediment and water. We estimated the geographic distribution of an offshore winter flounder subpopulation based on species biology, including such variables as foraging area, habitat size, disposal site size and migration characteristics. We incorporated these variables together with an estimate of differential attraction to a management site within a spatially explicit model to assess the range of expected PCB exposures to a winter flounder population. The output of this modeling effort, flounder PCB tissue concentrations, provides exposure point concentrations for estimates of human health risk through ingestion of locally caught flounder. The risks obtained for the spatially non-explicit case are as much as one order of magnitude higher than those obtained after incorporating spatial and temporal characteristics of winter flounder foraging and seasonal migration. Incorporating spatial and temporal variables in food chain models can help support sediment management decisions by providing a quantitative expression of the confidence in risk estimates.

Animals↗
PubMed2003

Dyslexia linked to talent: global visual-spatial ability.

Dyslexia has long been defined by deficit. Nevertheless, the view that visual-spatial talents accompany dyslexia has grown, due to reports of individuals with dyslexia who possess visual-spatial strengths, findings of elevated incidence of dyslexia in certain visual-spatial professions, and the hypothesis that left-hemisphere deficits accompany right-hemisphere strengths. Studies have reported superior, inferior, and average levels of visual-spatial abilities associated with dyslexia. In two investigations, we found an association between dyslexia and speed of recognition of impossible figures, a global visual-spatial task. This finding suggests that dyslexia is associated with a particular type of visual-spatial talent-enhanced ability to process visual-spatial information globally (holistically) rather than locally (part by part).

Aptitude↗
PubMed1989

Hyperthermia impairs retrieval of an overtrained spatial task in the Morris water maze.

Fifteen rats were trained to learn the location of a spatially fixed platform hidden in a Morris water maze (40 +/- 2 degrees C). Then retention of the spatial task was assessed immediately after raising core body temperature (Tc) to 42 or 40 degrees C or stabilizing at 37 degrees C (the normothermic control). The hyperthermic treatment order was counterbalanced according to a Latin-square design. Hyperthermia at 42 degrees C Tc significantly impaired spatial performance. Hyperthermic animals were cooled to normothermia (Tc = 37 degrees C) and spatial performance was tested again approximately 30 min later. Cooling resulted in a complete recovery of spatial performance. These results demonstrate that hyperthermia-induced amnesia can be obtained on an overtrained spatial-mapping strategy and cooling to normothermia initiates recovery of spatial performance.

Animals↗
PubMed2000

Spatial spectral analysis of human electrocorticograms including the alpha and gamma bands.

Spatial spectral analysis is essential for deriving spatial patterns from simultaneous recordings of electrocorticograms (ECoG), in order to determine the optimal interval between electrodes in arrays, and to design spatial filters, particularly for extraction of information about the dynamics of human gamma activity. ECoG were recorded from up to 64 electrodes 0.5 mm apart in a linear array 3.2 cm long, which was placed on the exposed superior temporal gyrus or motor cortex of volunteers undergoing diagnostic surgery. Visual displays of multiple traces revealed broad spectrum oscillations in episodic bursts having a common aperiodic wave form with recurring patterns of spatial amplitude modulation (AM patterns) on selected portions of the array. The one-dimensional spatial spectrum of the human ECoG was calculated at successive time samples and averaged over periods of up to 20 s. Log power decreased monotonically with increasing log spatial frequency in cycles/mm (c/mm) to the noise level approximately 2 log units below maximal power at minimal frequency (0.039+/-0.002 c/mm). The inflection point at 0.40+/-0.05 c/mm specified an optimal value for a low pass spatial filter to remove noise, and an optimal interelectrode spacing of 1.25 mm to avoid undersampling and aliasing. An 8 x 8 array with that spacing would be 10 x 10 mm.

Adolescent↗
PubMed1999

Effects of mammillary body lesions on spatial reference and working memory tasks.

This work examines the effects of electrolytic mammillary body (MB) lesions on the performance of rats in different spatial memory tasks in the Morris water maze. The first experiment assessed the effect of MB lesion on performance in a spatial reference memory task (place learning with multiple trials). The second experiment examined the effect of a lesion in this nucleus on performance in a spatial working memory task (single-trial place learning). The results show that lesion of the MB impairs the animals performance in spatial working memory tasks but does not impair acquisition in spatial reference memory tasks (place learning, transfer task, reversal task) or in a visual-cued task. However, the deficit in the spatial working memory task does not appear to vary with the delay between acquisition and retention trials (30 s and 5 min). Our results demonstrate a clear role of the mammillary bodies in the processing of spatial information in a working memory task. Lesion of the MB impairs performance in a working memory task but does not affect reference memory processes.

Animals↗
PubMed1999

Excitotoxic hippocampal lesions disrupt allocentric spatial learning in mice: effects of strain and task demands.

Spatial discrimination of ibotenic acid-lesioned C57BL/6 (B6) and DBA/2 (D2) mice was tested in two-choice water maze and plus maze tasks. B6 but not D2 mice learned the spatial discrimination in the water maze, but strains did not differ in learning a spatial discrimination in the plus maze paradigm. Ibotenic acid lesions of the hippocampus impaired percentage correct choices in the water maze spatial discrimination task in B6 but not in D2 mice, the latter of which may have been due to a floor effect. Furthermore, lesioned mice were more thigmotaxic, the distance travelled until a choice was made was longer and animals made more errors of omission. Despite the poor performance during water maze acquisition, lesioned animals, as well as sham-lesioned D2 mice, eventually acquired some place response in the water maze, as was evident when the location of the platform was reversed. However, hippocampus-lesioned mice of both strains were impaired when tested in the plus maze spatial discrimination task. Thus, ibotenic acid-induced lesions of the hippocampus impair acquisition of spatial discrimination in mice. These deficits were strain-dependent and likely comprise impaired accuracy as well as changes in non-mnemonic types of behaviour. Importantly, lesions in both strains impaired spatial learning, and whether a deficit was seen in mice of the D2 strain seemed to depend on the demands of the task.

Animals↗
PubMed2000

Reversal learning deficit in a spatial task but not in a cued one after telencephalic ablation in goldfish.

The fish telencephalon seems to be involved in spatial learning and memory in a similar manner to the hippocampus of the land vertebrates. For instance, telencephalon ablated goldfish are impaired in the post-operative retention of a 'spatial constancy' task, which requires the use of mapping strategies, but not in a directly cued task in which responses are based in a guidance strategy. In this regard, previous experiments showed that intact goldfish trained in the spatial constancy task presented considerable behavioral flexibility, as they showed fast reversal learning, that is, they required less training compared with animals trained in the directly cued task and made a lower number of errors to master the reversal than in acquisition. The purpose of the present work was to investigate if the goldfish telencephalon is involved in the faster reversal learning of the animals trained in the spatial constancy task. Goldfish with bilateral telencephalic ablation, sham operated or intact, were trained in the spatial constancy task or in the directly cued task. Telencephalic ablation selectively impaired reversal learning in the animals trained in the spatial constancy procedure. Ablated animals in this procedure reversed more slowly than control animals. By contrast, telencephalic ablation did not produce any significant deficit during reversal in the animals trained in the directly cued task. These results provide additional evidence that the fish telencephalon, as the land vertebrate hippocampus, plays a crucial role in the use of flexible spatial representations.

Animals↗
PubMed2002

A Bayesian model for spatial wildlife disease prevalence data.

The analysis of the geographical distribution of disease on the scale of geographic areas such as administrative boundaries plays an important role in veterinary epidemiology. Prevalence estimates of wildlife population surveys are often based on regional count data generated by sampling animals shot by hunters. The observed disease rate per spatial unit is not an useful estimate of the underlying disease prevalence due to different sample sizes and spatial dependencies between neighbouring areas. Therefore, it is necessary to account for extra-sample variation and spatial correlations in the data to produce more accurate maps of disease incidence. The detection of spatial patterns is complicated by missing data in many of the geographical areas as the complete coverage of all areas is nearly impossible in wildlife surveys. For this purpose a hierarchical Bayesian model in which structured and unstructured over dispersion is modelled explicitly in terms of spatial and non-spatial components was implemented by Markov chain Monte Carlo methods. The model was empirically compared with the results of a non-spatial beta-binomial model using surveillance data of pseudorabies virus infections of European wild boars (Sus scrofa scrofa L.) in the Federal State of Brandenburg, Germany.

Animal Diseases↗
PubMed2003

Spatial attention: normal processes and their breakdown.

Although "attention" is a general term in everyday folk and psychologic use, using research from cognitive psychology allows a focus on the processes associated with attention. A process-oriented definition of attention [2] makes "attention" a concept that can be studied rigorously. Attention is necessary for eliminating unwanted sensory inputs or irrelevant behavioral tasks and is useful when some cognitive system or process receives too many inputs. Attention acts to restrict the number of inputs and allow processing to continue in an effective manner. Although there are many forms of attentional selection, spatial attention is the most studied and perhaps the best understood form of selection. Spatial attention is the variety of attention most widely studied in neuropsychologic populations. As was evident from the authors' review, different neuropsychologic syndromes can be characterized as involving different difficulties with the component processes of spatial attention. Different neural structures work in concert to produce normal spatial selection, and damage to any of these neural structures, including the parietal and frontal lobes, pulvinar, and superior colliculus, produce an attentional impairment. Attentional impairments often have been studied in cases of focal brain damage resulting from stroke, traumatic brain injury, tumor, and surgical resection. Focal or multifocal lesions caused by neurodegenerative impairments, such as PSP and AD, however, also have marked effects on neural processes of attention. Patients with AD exhibit a range of impairments in spatial attention, and these impairments have been studied relatively little. Despite the understanding of attention provided by various patient populations, gaps remain in knowledge of the mechanisms involved in attending to space. For example, most studies of neurologic patients have used a simple spatial cuing paradigm with highly predictive cues. Although this task yields robust results and can be adapted for use with many different patient groups, the spatial cuing effects produced by such tasks have multiple interpretations (e.g., allocation of resources versus reduction of decision noise). This review highlights the general point that different neural sites seem to be responsible for different forms of attentional control, such as object-based attention, attentional task switching, and the executive control of attention [8.33]. Understanding the integration of these neural sites and their relationship to cognitive processes and, ultimately, behavior, will increase understanding of normal and disordered attentional selection.

Alzheimer Disease↗
PubMed2001

Age-independent and dose-response effects of ethanol on spatial memory in rats.

Results of previous studies have shown that ethanol impairs the acquisition of spatial memory in adolescent rats at doses below those required to impair the acquisition in adults. However, the previous work did not identify doses of ethanol that failed to impair acquisition in adolescents or that impaired acquisition in both adolescent and adult animals. This was our aim in the present study. Male, Long-Evans hooded rats (adolescent and adult) were treated intraperitoneally with 0.0, 0.5, or 2.5 g/kg of ethanol 30 min before daily training on a spatial or nonspatial version of the Morris water maze task. Twenty-four hours after training on the spatial task the animals were given a 1-min probe trial. The low dose of ethanol (0.5 g/kg) failed to impair the performance of animals from either age group on any tasks. It did, however, enhance the initial rate of acquisition on the spatial task. The 2.5-g/kg dose eliminated acquisition of spatial learning in animals of both ages and significantly attenuated performance on a nonspatial task in both age groups. However, the treatment effect in the nonspatial task was eliminated with controlling for baseline performance. These results establish a low dose of ethanol (0.5 g/kg) that does not impair acquisition of spatial memory in adolescent or adult rats. Moreover, the study findings show that 2.5 g/kg of ethanol markedly impairs acquisition of spatial memory in both adolescent and adult animals.

Aging↗
PubMed2003

A neural model of how the brain represents and compares multi-digit numbers: spatial and categorical processes.

Both animals and humans represent and compare numerical quantities, but only humans have evolved multi-digit place-value number systems. This article develops a Spatial Number Network, or SpaN, model to explain how these shared numerical capabilities are computed using a spatial representation of number quantities in the Where cortical processing stream, notably the inferior parietal cortex. Multi-digit numerical representations that obey a place-value principle are proposed to arise through learned interactions between categorical language representations in the What cortical processing stream and the Where spatial representation. Learned semantic categories that symbolize separate digits, as well as place markers like 'ty,' 'hundred,' and 'thousand,' are associated through learning with the corresponding spatial locations of the Where representation. Such What-to-Where auditory-to-visual learning generates place-value numbers as an emergent property, and may be compared with other examples of multi-modal cross-modality learning, including synesthesia. The model quantitatively simulates error rates in quantification and numerical comparison tasks, and reaction times for number priming and numerical assessment and comparison tasks. In the Where cortical process, transient responses to inputs are integrated before they activate an ordered spatial map that selectively responds to the number of events in a sequence and exhibits Weber law properties. Numerical comparison arises from activity pattern changes across the spatial map that define a 'directional comparison wave.' Variants of these model mechanisms have elsewhere been used to explain data about other Where stream phenomena, such as motion perception, spatial attention, and target tracking. The model is compared with other models of numerical representation.

Animals↗
PubMed2001

ERP time course of perceptual and post-perceptual mechanisms of spatial selection.

Event-related potentials (ERPs) were recorded from volunteers performing a task requiring simple judgements about the spatial location of a single target that could appear with equal probability to the left or right of fixation. A robust finding in the ERP literature is a dichotomy between attentional selection for spatial and non-spatial features. Visual spatial selection is manifest as a modulation of early components (P1, N1) that reveal exogenous processes, while non-spatial selection is revealed by the presence of longer latency endogenous components (N2). We present an analysis of several conditions that require different degrees of visual analysis to confirm the location of the single target, and show that spatial selection can be manifest at early (N1) or later (N2) stages. Observers identified the location of targets that were more salient (2D line drawings with abrupt onset) or less salient (2D line drawings without abrupt onset or 3D objects embedded in random-dot stereograms). We examined differences in amplitude, latency, and topography of early ERP components (P1, N1, P2, N2), and compared responses measured over the left and right hemispheres in response to left and right targets. The results support the hypothesis that the processes involved in spatial selection can be manifest at early or late stages, dependent on the quality of the incoming data. Moreover, the iterative process by which the percept is established benefits from a change in the visual input that is specific to the target.

Analysis of Variance↗
PubMed2003

Distinct neural substrates for visual search amongst spatial versus temporal distractors.

Whether the contribution of the superior parietal cortex (BA7) to attention-demanding tasks is strictly spatial in nature remains unresolved. We used functional magnetic resonance imaging to explore the behavioural and neuroanatomical correlates of non-spatial search for a conjunction of features within a stream of temporally-distracting stimuli. In addition, we compared these data to those from a conventional visuo-spatial search task, performed by the same subjects, in order to determine the specificity of right BA7 activation. Mode of stimulus-distribution (spatial versus temporal) and search type (target defined by a single feature or a conjunction of features) were manipulated in a 2 x 2 factorial design. Behaviourally, the temporal conjunction task was shown to index temporal selective attention. Accuracy of detecting a second target varied with the temporal proximity of two successive targets when subjects searched for a conjunction of features, but not a single feature. The temporal conjunction task activated a network of areas including right superior parietal cortex and bilateral regions of intraparietal sulcus, frontal operculum and putamen. The two latter regions were selectively activated by the attentional demands of the temporal conjunction task when compared directly to the attentional demands of the spatial conjunction task, implicating these regions specifically in selective attention among temporally-distracting stimuli. By comparison, only a very medial region of right BA7 was selectively activated by the spatial conjunction task. The more lateral region of BA7 previously reported by other groups was engaged to a similar degree by both spatial and temporal versions of the conjunction search task.

Adolescent↗
PubMed1996

Event-related potentials reveal topographical and temporal distinct neuronal activation patterns for spatial and object working memory.

This study examined whether working memory processes for object and spatial information are associated with different patterns of ERP activity. Subjects performed two versions of a delayed match-to-sample task in which either object forms or two-dimensional spatial configurations (S1) had to be encoded and retained in working memory for 6800 ms for comparison with a subsequent stimulus (S2). Event-related potentials (ERPs) were recorded from 29 electrode sites in the S1-S2 interval. Negative slow wave activity in the ERP varied with both, the type of memory task and the amount of materials held in working memory. When spatial information was maintained in working memory negative slow wave activity rapidly rose at recording sites overlying posterior parietal and occipital cortical areas. At these recording sites, slow wave increased in amplitude with increasing spatial memory load. For object information, load-sensitive negative slow wave activity was obtained approximately 2000 ms later than in the spatial task and it was focused to mid-frontal recording sites. Moreover, in the object memory task more pronounced negative slow wave activity was found at right inferior temporal recording sites indicating a larger involvement of the right temporal lobe in the processing of object as compared to spatial information. The results provide evidence for the notion that encoding and retention processes for object information and for spatial information can be functionally dissociated and involve differential patterns of neuronal activation rapidly shifting in time.

Adult↗
PubMed2003

Neural mechanisms of top-down control during spatial and feature attention.

Theories of visual selective attention posit that both spatial location and nonspatial stimulus features (e.g., color) are elementary dimensions on which top-down attentional control mechanisms can selectively influence visual processing. Neuropsychological and neuroimaging studies have demonstrated that regions of superior frontal and parietal cortex are critically involved in the control of visual-spatial attention. This frontoparietal control network has also been found to be activated when attention is oriented to nonspatial stimulus features (e.g., motion). To test the generality of the frontoparietal network in attentional control, we directly compared spatial and nonspatial attention in a cuing paradigm. Event-related fMRI methods permitted the isolation of attentional control activity during orienting to a location or to a nonspatial stimulus feature (color). Portions of the frontoparietal network were commonly activated to the spatial and nonspatial cues. However, direct statistical comparisons of cue-related activity revealed subregions of the frontoparietal network that were significantly more active during spatial than nonspatial orienting when all other stimulus, task, and attentional factors were equated. No regions of the frontal-parietal network were more active for nonspatial cues in comparison to spatial cues. These findings support models suggesting that subregions of the frontal-parietal network are highly specific for controlling spatial selective attention.

Adult↗
PubMed2003

Involvement of the hippocampal CA3-region in acquisition and in memory consolidation of spatial but not in object information in mice.

This study investigates the implication of the hippocampal CA3-region in the different phases of learning and memory in spatial and non-spatial tasks. For that purpose, we performed focal injections of diethyldithiocarbamate (DDC) into the CA3-region of the dorsal hippocampus. The DDC chelates most of the heavy metals in the brain which blocks selectively and reversibly the synapses containing heavy metals, i.e., the mossy fibres synaptic buttons and synapses of the dendrites of pyramidal cells. The effects of temporal inactivation of the CA3-region was examined in a non-associative task, the spatial open-field, designed to estimate the ability of mice to react to spatial changes, and in the object recognition task, designed to estimate the ability of mice to identify a familiar object. The results show that DDC induced a specific impairment on learning and memory consolidation in the spatial open-field but had no effect on recall in this task. In the object recognition task, DDC did not induce any impairment in the different phases of learning and memory. These data demonstrate that the hippocampal CA3-region is specifically implicated in spatial information processing and seems to be involved not only in acquisition but also in consolidation of spatial information.

Animals↗
PubMed2000

On the processing of spatial frequencies as revealed by evoked-potential source modeling.

OBJECTIVES AND METHODS: Visually evoked potentials (VEPs) are known to be sensitive to spatial frequency, especially in the time range between 50 and 100 ms post-stimulus. In two experiments we localized the cortical activity elicited by stimuli of varying spatial frequency in scalp-recorded brain potentials, using multi-electrode recordings and dipole-source analysis. RESULTS: Low spatial frequencies (<1 c/d) activated relatively lateral occipital areas, the orientation of the neural ensembles involved being predominantly perpendicular to the scalp surface. In contrast, high spatial frequencies (>4 c/d) induced activation of more medial occipital areas with the predominant orientation of the sources being much more parallel to the scalp surface. Furthermore, at about 100 ms latency the lateral-occipital response to low spatial frequencies was stronger in the right hemisphere; no such asymmetry was found for the responses to the high spatial frequencies. These findings were consistent across varying recording conditions, individual subjects, subject populations, stimulus characteristics (grating orientation, grating vs. checkerboard), and task conditions (active vs. passive). CONCLUSION: The results indicate that there are differences in sensitivity to specific spatial frequencies between primary and secondary visual areas, as well as between the right and the left hemispheres.

Adult↗
PubMed2002

Selective attention to spatial frequency: an ERP and source localization analysis.

OBJECTIVES: Physiological correlates of visual selective attention have been observed by recording ERPs to attended versus ignored target stimuli. Over many such studies, spatial attention has been observed to modulate early sensory components beginning 70 ms after stimulus onset, while effects of selection based on other stimulus features such as color and spatial frequency occur at longer latencies. Together, these findings argue for a primacy of location in early attentional selection. However, there have been some reports suggesting attention effects on short latency sensory-evoked potentials during selection of spatial frequency. The prime objective of the present study was to assess whether or not spatial frequency-dependent potentials are modulated by attention at a latency as early as 70-100 ms. METHODS: Checkerboard patterns were flashed to the subject, one being the target requiring a response. We investigated attentional effects using high-density scalp mapping and inverse dipole modeling. RESULTS: The earliest robust signs of selective attention to spatial frequencies consisted of an occipital selection negativity (OSN) and a frontal selection positivity (FSP). The OSN started at a latency of 140 ms, the FSP somewhat earlier at 120 ms. These attention effects were readily modeled by sources in cortical areas ventrally and laterally to the more primary areas generating the shorter-latency sensory components. CONCLUSIONS: This pattern of results has been found for non-spatial stimulus features in several studies, and is clearly different from the ERP correlates of spatial selection.

Adolescent↗