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PubMed2005

Spatial auditory compensation in early-blind humans: involvement of eye movements and/or attention orienting?

Several studies have reported that the early-blind displays higher auditory spatial abilities than the sighted. Although many studies have attempted to delineate the cortical structures that undergo functional reorganization in blind people, few have tried to determine which auditory or non-auditory processes mediate these increased auditory spatial abilities. The aim of this paper is to investigate the role of eye movements and orientation of attention in auditory localization in blind humans. Although we found, in a first experiment, that the influence of eye movements on auditory spatial localization is preserved in spite of congenital visual deprivation, the saccade influence on spatial hearing is not more pronounced in the blind than in the sighted. In a second experiment, early-blind and sighted subjects undertook a task involving discrimination of sound elevation in which auditory targets followed uninformative auditory cues on either side with an intermediate elevation. When sounds were emitted from the frontal hemifield, both groups showed similar auditory localization performance. Although the auditory cue did not affect discrimination accuracy in both groups, early-blind subjects exhibited shorter reaction times than sighted subjects when sound sources were placed at far-lateral locations. Attentional cues, however, had similar effects on both groups of subjects, suggesting that improved auditory spatial abilities are not mediated by attention orienting mechanisms.

Adaptation, Physiological↗
PubMed2005

Visual spatial and visual pattern working memory: neuropsychological evidence for a differential role of left and right dorsal visual brain.

According to neurophysiological, neuroimaging, and behavioural evidence, visual working memory (WM) can be separated into a "what" and a "where" component, reflecting the duality of visual processing. Whereas a wealth of empirical data suggests a right-sided fronto-parietal network critical for the maintenance of spatial information, the cortical structures underlying maintenance of object information have remained controversial. Although visual object processing depends on ventral, inferior temporal areas, recent neuroimaging results suggest that maintenance of visual object information involves a left-sided or bilateral fronto-parietal network. The aim of the present study is to further clarify the role of the left and right parietal lobes for pattern and spatial visual WM. Seven patients with left-sided, seven with right-sided parietal brain injury, and two age-matched healthy control groups performed a delayed-matching-to-sample task using either pattern (shape) or spatial (location) information or both. In addition, eight patients with left-sided injury sparing parietal areas were tested to further examine the specific role of the left parietal cortex in pattern WM. Left parietal injury resulted in pattern WM impairment, only, while right parietal injury was associated with pattern and spatial WM deficits. Non-parietal injury was not associated with comparable deficits. These results suggest that visual spatial WM depends critically on right parietal areas; in contrast, pattern WM depends on both, left and right parietal areas.

Adult↗
PubMed2005

Vision and touch in ageing: crossmodal selective attention and visuotactile spatial interactions.

We investigated whether ageing affects crossmodal selective attention (the ability to focus on a relevant sensory modality and ignore an irrelevant modality) and the spatial constraints on such selective processing. Three groups of 24 participants were tested: Young (19-25 years), Young-Old (65-72 years) and Old-Old (76-92 years). The participants had to judge the elevation of vibrotactile targets (upper/index finger and lower/thumb), presented randomly to either hand while ignoring concurrent visual distractors. In a second task, the role of the target and distractor modalities was reversed. Crossmodal selective attention was assessed by comparing performance in the presence versus absence of distractors. Spatial constraints on selective attention were also investigated by comparing the effect of distractors presented on the same versus opposite side as the target. When attending to touch, the addition of visual distractors had a significantly larger effect on error rates in both of the older groups as compared to the Young group. This indicates that ageing has a detrimental effect on crossmodal selective attention. In all three age groups, performance was impaired when the target and distractor were presented at incongruent as compared to congruent elevations in both tasks. This congruency effect was modulated by the relative spatial location of the target and distractor in certain conditions for the Young and the Young-Old group. That is, participants in the two younger age groups found it harder to attend selectively to targets in one modality, when distractor stimuli came from the same side rather than from the opposite side. However, no significant spatial modulation was found in the Old-Old group. This suggests that ageing may also compromise spatial aspects of crossmodal selective attention.

Adult↗
PubMed2005

Dyslexics are impaired on implicit higher-order sequence learning, but not on implicit spatial context learning.

Developmental dyslexia is characterized by poor reading ability and impairments on a range of tasks including phonological processing and processing of sensory information. Some recent studies have found deficits in implicit sequence learning using the serial reaction time task, but others have not. Other skills, such as global visuo-spatial processing may even be enhanced in dyslexics, although deficits have also been noted. The present study compared dyslexic and non-dyslexic college students on two implicit learning tasks, an alternating serial response time task in which sequential dependencies exist across non-adjacent elements and a spatial context learning task in which the global configuration of a display cues the location of a search target. Previous evidence indicates that these implicit learning tasks are based on different underlying brain systems, fronto-striatal-cerebellar circuits for sequence learning and medial temporal lobe for spatial context learning. Results revealed a double dissociation: dyslexics showed impaired sequence learning, but superior spatial context learning. Consistent with this group difference, there was a significant positive correlation between reading ability (single real and non-word reading) and sequence learning, but a significant negative correlation between these measures and spatial context learning. Tests of explicit knowledge confirmed that learning was implicit for both groups on both tasks. These findings indicate that dyslexic college students are impaired on some kinds of implicit learning, but not on others. The specific nature of their learning deficit is consistent with reports of physiological and anatomical differences for individuals with dyslexia in frontal and cerebellar structures.

Adolescent↗
PubMed2006

Influences of time and spatial frequency on the perceptual bias: evidence for competition between hemispheres.

Perceptual biases for various visual features, such as size, luminance and numerosity, have been implicated with a right-hemisphere dominance in spatial and attentional functions and/or an asymmetrical competition between the two hemispheres. However, the mechanisms underlying these biases are poorly understood. For example, it has been largely ignored that processing of those features is closely interconnected with spatial frequency filters. To probe the influence of spatial frequencies on perceptual biases, here we used a new gratingscales task in neurologically healthy participants. We found that perceptual bias was strongly influenced within a bandwidth of spatial frequencies and that this bias correlated with a bias for luminance depending on presentation time. Furthermore, our participants, divided into two subgroups of perceptually "sensitive" and "insensitive" performers, showed considerably different, presentation time-dependent patterns of perceptual bias. While both groups were biased to the left, insensitive performers more than sensitive performers, these biases varied in a mirror-symmetric manner such that one group showed peaks of bias at times when the other group showed minima and vice versa. Our data suggest that perceptual bias results from an interhemispheric competition within a right-dominant system responsive to spatial frequencies, luminance and perhaps other magnitudes including abstract ones.

Adult↗
PubMed2004

Spatial learning in rats is impaired by microinfusions of protein kinase C-gamma antisense oligodeoxynucleotide within the nucleus accumbens.

The nucleus accumbens (NAcc) has been shown to play a role in motor and spatial learning. Protein kinase C (PKC) has been implicated in the mechanisms of initiation and maintenance of long-term potentiation that is thought to be involved in the storage of long-term memory. In the present study, the importance of de novo synthesis of PKC-gamma within the NAcc in the acquisition and retention of spatial discrimination learning was assessed using an antisense knockdown approach. Separate groups of Long-Evans rats were exposed to acute microinfusions (6microg/microl) of PKC-gamma antisense oligodeoxynucleotide (AS-ODN), control oligodeoxynucleotide (C-ODN) or vehicle into the NAcc at 24 and 3h before each training session. Behavioral findings showed that the blockade of NAcc-PKC-gamma translation caused impairments in the early phase of learning and retention of spatial information. Biochemical experiments showed that PKC-gamma expression was reduced and Ca(2+)/phospholipid-dependent protein kinase C (PKC) activity was blocked significantly in the AS-ODN-treated rats in comparison with control rats. The present findings suggest that NAcc-PKC-gamma plays a role during the early acquisition of spatial learning. Also, retention test results suggest that NAcc-PKC-gamma may be working as an intermediate factor involved in the onset of molecular mechanisms necessary for spatial memory consolidation within the NAcc.

Animals↗
PubMed2005

Medial septal galanin and acetylcholine: influence on hippocampal acetylcholine and spatial learning.

Neurochemical and behavioral studies in the rat have provided evidence for the view that galanin impairs learning via an inhibitory modulation of cholinergic neurons in the septohippocampal projection, believed to be important for learning and memory. To test this hypothesis, galanin was microinjected via a unilateral chronic cannula located in MS/dBB of rats. Infusion of galanin in the MS/dBB, which contains a high number of 125I-galanin binding sites, did not impair spatial acquisition or memory. On the contrary, spatial acquisition tended to be facilitated by 1 and 3 nmoles of galanin, while the 0.3 nmol dose had no effect. Intraseptal injections of scopolamine (10 microg/rat), a non-specific muscarinic antagonist, also failed to alter learning performance. In contrast, co-injections of galanin (3 nmol) and scopolamine (10 microg) resulted in a marked impairment of spatial acquisition. The effect of intraseptal galanin on basal acetylcholine release in the ventral hippocampus was examined by in vivo microdialysis and high-performance liquid chromatography. Both galanin (3 nmol/rat) and scopolamine (10 microg/rat) infused into the MS/dBB increased basal acetylcholine release in the ventral hippocampus. The combined injections of galanin and scopolamine resulted in an excessive increase in acetylcholine release. These results indicate, that galanin activates septohippocampal cholinergic neurons, suggesting that septal galanin may have a facilitatory role in spatial learning. Moreover, the level of muscarinic activity within the septal area appears to be critical for the effects of galanin on cognitive functions, since the combination of galanin and scopolamine produced a marked impairment in spatial learning, despite a marked increase in hippocampal acetylcholine release. In summary, a limited range of cholinergic muscarinic transmission may contribute to optimal hippocampal function, a finding that has important implications for therapeutic approaches in the treatment of disorders of memory function.

Acetylcholine↗
PubMed2004

Acute stress impairs spatial memory in male but not female rats: influence of estrous cycle.

We investigated how sex and estrous cycle influenced spatial recognition memory in the Y-maze after exposure to acute restraint stress. In Experiment 1, intact male and female rats were restrained for 1 h and then 2 h after the start of restraint, rats were trained on the Y-maze. After a 4 h delay, hippocampal-dependent spatial recognition memory was assessed. Acute stress produced opposite patterns between the sexes with spatial memory being impaired in males and facilitated in females. Serum corticosterone measures indicated that both sexes showed a robust corticosterone response after restraint and a moderate corticosterone response after Y-maze exposure. Serum corticosterone levels in response to restraint and Y-maze were not statistically different between the sexes. Experiment 2 examined the influence of the estrous cycle on spatial memory ability after acute stress. Acute stress facilitated spatial memory in females compared to controls, regardless of the estrous cycle phase (estrus and proestrus). Moreover, females in proestrus showed higher serum corticosterone levels during restraint compared to females in estrus. No differences in corticosterone levels were observed at baseline or following 2 h of recovery from restraint. These data show important differences in how sex and estrous cycle influence cognitive functions following acute stress.

Acute Disease↗
PubMed2006

The spatial distribution of atopic dermatitis cases in a population of insured Swedish dogs.

Canine atopic dermatitis (CAD) is manifested by pruritus and inflammation of the skin, and most affected dogs have specific IgE against environmental allergens. Our aim was to evaluate whether in Sweden the incidence of CAD varies spatially, and to investigate possible environmental causes of such variation in a longitudinal study of CAD incidence among insured Swedish dogs. The dataset consisted of >220,000 individuals which had been covered by an insurance plan between January 1, 1995 and December 31, 2002. Out of these, 1235 CAD cases were identified and matched to postal-code areas based upon the address of the owner. Environmental risk factors we considered included averages of long-term annual rainfall, and of January and July temperatures. Initial visualization of the incidence rate of CAD (cases/dog-years at risk) expressed as empirical Bayes smoothed spatial rates indicated geographic variation. Moran's I, adjusted for population at risk, revealed significant global clustering. Both the spatial scan statistic and a local indicator of spatial autocorrelation revealed a higher incidence of CAD in the major cities. In a Poisson-regression model (with a spatial covariance structure), the incidence of CAD increased with increasing human population density, increasing average annual rainfall, living in the southern half of Sweden, and having a veterinary dermatologist in the county.

Allergens↗
PubMed2005

Understanding the spatial diffusion process of severe acute respiratory syndrome in Beijing.

OBJECTIVES: To measure the spatial contagion of severe acute respiratory syndrome (SARS) in Beijing and to test the different epidemic factors of the spread of SARS in different periods. METHODS: A join-count spatial statistic study was conducted and the given hypothetical processes of the spread of SARS in Beijing were tested using various definitions of 'joins'. RESULTS: The spatial statistics showed that of the six diffusion processes, the highest negative autocorrelation occurred in the doctor-number model (M-5) and the lowest negative autocorrelation was found in the population-amount model (M-3). The results also showed that in the whole 29-day research period, about hour or more days experienced a significant degree of contagion. CONCLUSIONS: Spatial analysis is helpful in understanding the spatial diffusion process of an epidemic. The geographical relationships were important during the early phase of the SARS epidemic in Beijing. The statistic based on the number of doctors was significant and more informative than that of the number of hospitals. It reveals that doctors were important in the spread of SARS in Beijing, and hospitals were not as important as doctors in the contagion period. People are the key to the spread of SARS, but the population density was more significant than the population size, although they were both important throughout the whole period.

China↗
PubMed2004

Spatial working memory among middle-aged and older patients with schizophrenia and volunteers using fMRI.

OBJECTIVE: Goldman-Rakic and Selemon (Schizophr. Bull. 23 (1997)) hypothesized that many of the symptoms of schizophrenia can be explained by deficits of working memory (WM) that are, in turn, caused by dysfunction of dorsolateral prefrontal cortex (DLPFC). We examined whether older patients with schizophrenia would show an aberrant neural response in the DLPFC or other brain sites when performing a spatial working memory (WM) task adapted from McCarthy et al. (Proc. Natl. Acad. Sci. U. S. A. 91 (1994)). METHOD: Middle-aged and older patients with schizophrenia or schizoaffective disorder and healthy volunteers performed a spatial WM task contrasted with two baselines, passive and active viewing (PV and AV, respectively), while blood oxygen level dependent (BOLD) images were acquired in a functional magnetic resonance study. RESULTS: Patients did not perform significantly less well on the spatial tasks compared to the volunteers. Although we found no significant group effects in spatial WM activation of DLPFC, we did observe areas in medial frontal cortex including the left anterior cingulate gyrus, parietal areas of the both hemispheres, multiple sites within the basal ganglia of the left hemisphere, and the left superior temporal gyrus where healthy volunteers showed greater BOLD response to WM. In a second pattern, patients showed a greater BOLD response to WM in left fusiform gyrus [Brodmann's Area (BA) 19], peri-rolandic areas, medial frontal area; right anterior cerebellum (culmen), middle occipital lobe, and postcentral/supramarginal gyri (BA 2/40). CONCLUSIONS: Middle-aged and older patients with schizophrenia display normal or near-normal spatial WM activation of DLPFC when the processing demands of the WM task are within their performance capacity. Nonetheless, even when patients perform nearly normally, they demonstrate an aberrant pattern of brain response.

Age Factors↗
PubMed2005

Intact hemispheric specialization for spatial and shape working memory in schizophrenia.

OBJECTIVE: Using functional MRI, we investigated whether, like healthy subjects, patients with schizophrenia show a relative hemispheric specialization in ventrolateral prefrontal cortex (PFC) for spatial and shape working memory (WM). We hypothesized that reduced specialization in schizophrenia would reflect a failure to adopt optimal domain-specific strategies and would contribute to WM deficits. METHODS: Twelve healthy subjects and 16 schizophrenia patients performed spatial and shape WM tasks and a non-WM control task. Direct comparisons of the spatial and shape WM tasks assessed specialization. RESULTS: Despite deficient WM performance, both patients and controls showed a relative hemispheric specialization in ventrolateral PFC for spatial (right) and shape (left) WM and did not differ in this regard. CONCLUSIONS: The finding of intact hemispheric specialization in ventrolateral PFC suggests that patients employ the same domain-specific strategies as healthy subjects during spatial and shape WM. Rather than reflecting a failure to adopt the optimal strategy, we hypothesize that WM deficits in schizophrenia reflect impairments of executive processes that are required for WM performance regardless of domain. These processes are associated with activity in the dorsolateral PFC, a region that has been repeatedly implicated in studies of WM.

Adult↗
PubMed2004

Inter-comparison of multimedia modeling approaches: modes of transport, measures of long range transport potential and the spatial remote state.

Several evaluative multi-media models have been developed during the recent years to determine the long-range transport potential, LRTP, of non-polar organic chemicals. Here, these models are categorized and compared with respect to the modes of transport and the measures used to compute LRTP. Differences concerning the mode of transport include the transport mechanism (advective vs. dispersive transport) and the number and coupling of transport media (transport in a single moving medium vs. coupled transport in air and water). Measures used include the characteristic travel distance and the spatial range. The spatial remote state is defined as a benchmark for the comparison of the different measures. This is the state of the model system far-off the source that is independent of the release pattern. With the expected value in the spatial remote state as a benchmark, the maximum of the spatial ranges in air and water and the maximum of the characteristic travel distances in air and water as well as the spatial range in air in combination with release into water prove to be reliable measures of the LRTP. The framework developed allows one to overview the features of the different models used in the ranking and assessment of chemicals.

Air Movements↗
PubMed2005

Assessing spatial coupling in complex population dynamics using mutual prediction and continuity statistics.

A number of important questions in ecology involve the possibility of interactions or "coupling" among potential components of ecological systems. The basic question of whether two components are coupled (exhibit dynamical interdependence) is relevant to investigations of movement of animals over space, population regulation, food webs and trophic interactions, and is also useful in the design of monitoring programs. For example, in spatially extended systems, coupling among populations in different locations implies the existence of redundant information in the system and the possibility of exploiting this redundancy in the development of spatial sampling designs. One approach to the identification of coupling involves study of the purported mechanisms linking system components. Another approach is based on time series of two potential components of the same system and, in previous ecological work, has relied on linear cross-correlation analysis. Here we present two different attractor-based approaches, continuity and mutual prediction, for determining the degree to which two population time series (e.g., at different spatial locations) are coupled. Both approaches are demonstrated on a one-dimensional predator-prey model system exhibiting complex dynamics. Of particular interest is the spatial asymmetry introduced into the model as linearly declining resource for the prey over the domain of the spatial coordinate. Results from these approaches are then compared to the more standard cross-correlation analysis. In contrast to cross-correlation, both continuity and mutual prediction are clearly able to discern the asymmetry in the flow of information through this system.

Models, Theoretical↗
PubMed2006

Spatially extended host-parasite interactions: the role of recovery and immunity.

Techniques for determining the long-term dynamics of host-parasite systems are well established for mixed populations. The field of spatial modelling in ecology is more recent but a number of key advances have been made. In this paper, we use state-of-the-art approximation techniques, supported by simulations, in order to investigate the role of recovery and immunity in spatially structured populations. Our approach is to use correlation models, namely pair-wise models, to capture the spatial relationships of contacts and interactions between individuals. We use the pair-wise framework to address a number of key ecological questions; including, the persistence of endemic limit cycles and regions of parasite-driven extinction--features which differentiate spatial from non-spatial models--and the effects on invasion fitness. We demonstrate a loss of limit cycle behaviour, in addition to an increase in the critical transmissibility and extinction thresholds, when recovery is included. This approach allows for a better analytical understanding of the dynamics of host-parasite interactions and demonstrates the importance of recovery and immunity in local interactions.

Animals↗
PubMed2004

Criticality and disturbance in spatial ecological systems.

Classical criticality describes sudden changes in the state of a system when underlying processes change slightly. At this transition, patchiness develops which lacks a characteristic or dominant spatial scale. Thus, criticality lies at the interface of two important subjects in ecology, threshold behavior and patchiness. Most ecological examples of criticality involve processes of disturbance and recovery; the spatial and temporal scales of these processes enable three different types of critical system to be distinguished: classical phase transitions, self organized criticality (SOC) and 'robust' criticality. Here, we review the properties defining these three types and their implications for threshold behavior and large intermittent temporal fluctuations, with examples taken from spatial stochastic models for predator-prey, infected-susceptible, and disturbance-recovery interactions. In critical systems, spatial properties of patchiness alone are insufficient indicators of impending sudden changes, unless complemented by the spatial and temporal scales of disturbance and recovery themselves.

Journal Article↗
PubMed2005

Improvements in elastographic contrast-to-noise ratio using spatial-angular compounding.

Spatial-angular compounding is a new technique developed for improving the signal-to-noise ratio (SNR) in elastography. Under this method, elastograms of a region-of-interest (ROI) are obtained from a spatially weighted average of local strain estimated along different insonification angles. In this article, we investigate the improvements in the strain contrast and contrast-to-noise ratio (CNR) of the spatially compounded elastograms. Spatial angular compounding is also applied and evaluated in conjunction with global temporal stretching. Quantitative experimental results obtained using a single-inclusion tissue-mimicking phantom demonstrate that the strain contrast reduces slightly but the CNR improves by around 8 to 13 dB. We also present experimental spatial angular compounding results obtained from an in vitro thermal lesion in canine liver tissue embedded in a gelatin phantom that demonstrate the improved visual characteristics (due to the improved CNR) of the compound elastogram. The experimental results provide guidelines for the practical range of maximum insonification angles and estimates of the optimum angular increment.

Animals↗
PubMed2005

Spatial distribution of Dermacentor reticulatus and Ixodes ricinus in Hungary: evidence for change?

A survey was conducted to investigate the spatial distribution of Ixodes ricinus and Dermacentor reticulatus in Hungary and to compare these data with the results of a previous large-scale survey. In the survey conducted in the 1950s, D. reticulatus adults were detected in two isolated areas of two counties, and the presence of these ticks in the collection was explained by accidental introduction. In the present survey, D. reticulatus became the second most common species occurring in all 16 counties involved in the monitoring and showed high prevalence. The change in the spatial distribution of this tick species, the increase of incidence of Babesia canis infection in Hungary, and the increasing number of canine babesiosis case reports from other Central and Central Eastern European countries since the 1970s suggest an expansion of the geographic range of D. reticulatus and intensification of the transmission rate of B. canis and probably other D. reticulatus-borne diseases (e.g. tularemia and tick-borne lymphadenopathy) in the region. The spatial distribution of I. ricinus was roughly in line with the results of the earlier survey. I. ricinus was the most common tick species being present in all 16 counties with the highest prevalence. Nevertheless, the comparison of the data of the previous and current survey cannot be used for fine-scale analysis; thus, it cannot be dismissed that the spatial distribution of I. ricinus also changed during the past decades. The spatial distribution patterns of tick-borne encephalitis in Hungary and other Central Eastern European countries may indicate such a change.

Animals↗