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PubMed1990

Comparison of spatial and temporal characteristics of neuronal activity in sequential stages of hippocampal processing.

The activity of individual pyramidal cells in the CA1 and CA3 subfields of the rodent hippocampus exhibits a remarkable selectivity for specific locations and orientations of the rat within spatially-extended environments. These cells exhibit high rates of activity when the animal is present within restricted regions of space, referred to as place fields, and are extremely quiet when it is elsewhere. Although this phenomenon has been well studied in the CA fields of the hippocampus, relatively little is known about the spatial and temporal firing characteristics either of the entorhinal cortical inputs to the hippocampus, or of the subicular recipients of the output of hippocampal place cells. We report here on a comparison of spatial and temporal discharge characteristics among entorhinal cortex, CA3 and CA1, and the subiculum. CA3 complex spike cells were significantly more spatially specific than their CA1 counterparts. Neither entorhinal cortex nor subiculum exhibited the highly localized patterns of spatial firing observed in the CA fields. In addition, average discharge rates in these areas were substantially higher. However, particularly in subiculum, there was evidence for spatially consistent, but dispersed, firing in some cells, suggestive of the convergence of a number of CA1 place cells. The patterns observed are not consistent with the hypothesis that spatial selectivity is progressively refined at the various levels of hippocampal processing. Rather, hippocampal output appears to be expressed as a much more highly distributed spatial code than activity within the hippocampus proper. We suggest that the sparse coding used within the hippocampus itself represents a mechanism for increasing the storage capacity of a network whose function is to form associations rapidly.

Action Potentials↗
PubMedDate not supplied

Effects of perinatal exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin on spatial and visual reversal learning in rats.

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a ubiquitous environmental contaminant that has been shown to alter spatial and visual learning following developmental exposure. The current study examined the effects of gestational and lactational exposure to TCDD on spatial and visual discrimination/reversal learning (spatial and visual RL) in rats using two-lever operant testing chambers. Pregnant Sprague-Dawley rats (10 per dose) received either 0 or 0.1 microg/kg TCDD per orem in corn oil from gestational day (GD) 10 to GD 16. One male and one female from each litter were tested beginning at 100 days of age. For spatial RL, animals were reinforced for pressing the lever associated with the correct spatial location (either left or right). For visual RL, the animals were reinforced for pressing the lever associated with the correct visual stimulus (either the illuminated or nonilluminated cuelight). After reaching 85% correct for two consecutive days, the opposite spatial location or visual cue was reinforced. Five reversals were conducted for spatial RL, and two reversals for visual RL. For spatial RL, there were no differences between the TCDD-exposed and control rats in total number of errors committed. However, an in-depth analysis of errors in four different phases of the learning process revealed that TCDD-exposed rats made more errors early in learning when they were just beginning to learn the new reinforcement contingencies. The importance of this increase in errors during the initial stage of learning is unclear, given that there was no increase in overall errors to criterion. For visual RL, there was a reduction in errors on original learning (OL) for TCDD-exposed males, while TCDD-exposed females exhibited a reduction in errors on the second reversal. Subsequent response pattern analyses revealed that the facilitation in performance was due to a more rapid transition through the early phase of learning. Why males were improved on OL and females were not until the second reversal is unknown, but the different patterns could reflect differences in learning style in male and female rats. In keeping with previous research, the results of the current study underscore the fact that (1) alterations in cognitive function observed following early TCDD exposure are very subtle and (2) under some conditions, learning is actually facilitated, rather than impaired, in TCDD-exposed animals.

Analysis of Variance↗
PubMedDate not supplied

Prenatal phenytoin exposure and spatial navigation in offspring: effects on reference and working memory and on discrimination learning.

Previous research has shown that rats exposed to phenytoin (PHT) in utero demonstrate abnormal circling, decreased learning, hyperactivity, and delayed air righting reflex development. The effects of prenatal PHT on offspring learning have been found on multiple-T mazes (Biel and Cincinnati types) and on spatial navigation (Morris maze). However, the specificity of the latter effects is unknown. Herein, we tested the effects of prenatal PHT in a Morris maze using six different procedures: cued versus spatial reference memory-based learning, cued versus spatial working memory-based learning, and cued versus spatial discrimination learning. PHT-exposed offspring showed increased preweaning mortality, growth reduction, and abnormal circling as noted in previous studies. PHT offspring were separated into those exhibiting circling and those not. PHT noncircling offspring demonstrated impaired reference memory-based spatial learning (acquisition and reversal), but no other effects. By contrast, PHT circling offspring demonstrated not only impaired reference memory-based spatial learning, but also impaired cued platform learning, impaired spatial discrimination, and impaired working memory-based learning. These data confirm that prenatal PHT induces a specific reference memory-based spatial learning deficit even in asymptomatic (noncircling) offspring that is distinct from the impairment induced in littermates exhibiting the circling impairment.

Analysis of Variance↗
PubMed2026

ARISE: RNA-anchored shared-edge topology and hierarchical fusion for spatial multi-omics integration.

MOTIVATION: Spatial multi-omics technologies jointly profile transcriptomes, proteins and chromatin accessibility in situ, enabling integrative analysis of tissue organization across molecular layers. However, most existing graph-based integration methods rely on independently constructed modality-specific k-nearest-neighbor graphs. When auxiliary modalities are sparse or noisy, these graphs can become topologically discordant, propagate spurious edges, weaken cross-modal alignment, and reduce spatial domain resolution. RESULTS: We present Anchored RNA for Integrated Spatial Embedding (ARISE), an RNA expression anchored framework for spatial multi-omics integration. ARISE defines a shared-edge topology by intersecting RNA feature-similarity and spatial-proximity graphs, encodes auxiliary modalities on this common scaffold, and integrates them through inside-out hierarchical fusion. We further show theoretically that graph intersection minimizes false-positive edges within a broad class of k-of-r graph fusion rules, providing a principled basis for topology anchoring. Across various spatial multi-omics benchmarks spanning simulated and real datasets in bi-modal and tri-modal settings, ARISE improves spatial domain identification, cross-modal consistency, and preservation of tissue structure relative to existing methods. Furthermore, the learned representation supports biologically meaningful downstream analyses, including marker-based domain annotation, pathway enrichment, and cis-regulatory inference, indicating that ARISE yields a robust and interpretable framework for spatial multi-omics integration. AVAILABILITY AND IMPLEMENTATION: The source code is available at https://github.com/XiangxiangWang-code/ARISE. The archived version used in this study is available at https://doi.org/10.6084/m9.figshare.32686137.v2.

Multiomics↗
PubMed2004

Spatial variation and density-dependent dispersal in competitive coexistence.

It is well known that dispersal from localities favourable to a species' growth and reproduction (sources) can prevent competitive exclusion in unfavourable localities (sinks). What is perhaps less well known is that too much emigration can undermine the viability of sources and cause regional competitive exclusion. Here, I investigate two biological mechanisms that reduce the cost of dispersal to source communities. The first involves increasing the spatial variation in the strength of competition such that sources can withstand high rates of emigration; the second involves reducing emigration from sources via density-dependent dispersal. I compare how different forms of spatial variation and modes of dispersal influence source viability, and hence source-sink coexistence, under dominance and pre-emptive competition. A key finding is that, while spatial variation substantially reduces dispersal costs under both types of competition, density-dependent dispersal does so only under dominance competition. For instance, when spatial variation in the strength of competition is high, coexistence is possible (regardless of the type of competition) even when sources experience high emigration rates; when spatial variation is low, coexistence is restricted even under low emigration rates. Under dominance competition, density-dependent dispersal has a strong effect on coexistence. For instance, when the emigration rate increases with density at an accelerating rate (Type III density-dependent dispersal), coexistence is possible even when spatial variation is quite low; when the emigration rate increases with density at a decelerating rate (Type II density-dependent dispersal), coexistence is restricted even when spatial variation is quite high. Under pre-emptive competition, density-dependent dispersal has only a marginal effect on coexistence. Thus, the diversity-reducing effects of high dispersal rates persist under pre-emptive competition even when dispersal is density dependent, but can be significantly mitigated under dominance competition if density-dependent dispersal is Type III rather than Type II. These results lead to testable predictions about source-sink coexistence under different regimes of competition, spatial variation and dispersal. They identify situations in which density-independent dispersal provides a reasonable approximation to species' dispersal patterns, and those under which consideration of density-dependent dispersal is crucial to predicting long-term coexistence.

Animals↗
PubMed2025

A Systematic Review of Spatial Epidemiological Modeling Approaches Applied During the COVID-19 Pandemic.

BACKGROUND: A wide range of epidemiological modeling approaches have been applied to the SARS-CoV-2 pandemic, which presents an opportunity to assess common approaches applied to specific research questions. Spatial models interrogate how heterogeneities and host movement dynamics influence local and regional patterns of disease, issues that were of great interest for understanding and controlling SARS-CoV-2. OBJECTIVE: Here we present a systematic review of spatial epidemiological modeling approaches of SARS-CoV-2. We describe common themes and highlight unique strategies, providing a foundation for researchers to devise spatial models most appropriate for future pathogens and epidemics. Our review also categorizes the research questions that were addressed with spatial models, highlights parameter estimation techniques, and describes the cyber infrastructure used for model development. METHODS: We conducted a systematic review using Web of Science and a standardized set of keywords, followed by thorough examination of abstracts and full texts to determine which studies met our inclusion criteria. To guide our description and comparisons of models, we developed a Geography, Population, Movement (GPM) framework that conceptualizes the interactions between three distinct subcomponents of any spatial model. The geographic model represents the physical arena in which the model is implemented, the intra-population model describes the transmission and disease processes that occur within distinct spatial units of the geography, and the movement model describes the algorithms that dictate how hosts move among spatial units within the geography. RESULTS: The search identified a total of 193 articles, of which 109 were included in our review. The most abundant intra-population modeling methods were agent-based (47.7%) and compartmental modeling (29.4%) approaches. Movement models ranged in complexity, with the most complex models implementing commuter movement among many points of interest in the geographic arena, which were sometimes parameterized by fine-scale mobility data. Geographic models ranged from describing microcosms, such as single classrooms, all the way up to multi-country models. Of the 63.3% of models studies that specified the programming language used, we detected ten different languages, with Matlab and Python being the most frequent, although only 30.6% of studies provided open-access code for their models. We also described eight specialized software systems that were used to construct agent-based or compartment models of COVID-19. CONCLUSIONS: Our review identified and characterized a variety of spatial modeling strategies and software that were usefully employed to address many relevant epidemiological questions for COVID-19. Future research is needed to quantitatively assess which modeling approaches are most appropriate in specific situations, to answer specific questions, or to apply to certain disease systems. Moreover, future cyberinfrastructure could help to modularize and standardize modeling approaches, which would increase transparency and reproducibility, and which would facilitate a detailed examination of which model attributes relate to model performance in a variety of contexts.

COVID-19↗
PubMed2026

Spatial Transcriptomics Identifies Characteristic Immunological Niches in Atopic Dermatitis.

BACKGROUND: Atopic dermatitis (AD) is primarily driven by a Type 2 immune response, with T helper (TH2) cells producing IL-4 and IL-13, thereby promoting inflammation, itch, and a compromised skin barrier. Yet, the spatial organization of pathogenic immune cells and their interactions with stromal and epithelial compartments in human AD skin remain incompletely understood. METHODS: We performed 10× Genomics Visium spatial transcriptomics on FFPE skin biopsies from patients with AD (n = 6), psoriasis (n = 2), and healthy controls (n = 5). Data were integrated with AD single-cell RNA sequencing (scRNA-seq) datasets and complemented by imaging mass cytometry (IMC) and multiplex immunofluorescence (IF) to validate the spatial localization of immune cells. Cell-cell communication analysis revealed putative signaling interactions within immune niches. RESULTS: Spatial clustering resolved tissue compartments and demonstrated transcriptional dysregulation in keratinocytes in AD and psoriasis. AD lesions showed a conserved spatial organization of immune aggregates within the superficial dermis. Integration of scRNA-seq signatures revealed spatially organized co-localization of T cells and mature migratory dendritic cells (mmDCs). We developed a ring-based neighborhood analysis to characterize the cellular organization of the immune-stromal niches, revealing T cell-enriched regions surrounded by inflammatory fibroblasts and activated keratinocytes. Intercellular communication analysis further identified putative signaling within mmDC-T cell niches that may promote pathogenic T cell recruitment and activation. Application of tertiary lymphoid structure (TLS) signatures indicated the presence of TLS-like regions. IMC and IF validated the close spatial proximity between activated TH2 cells and mmDCs. CONCLUSION: AD lesions contain spatially organized TLS-like immune niches at the dermal-epidermal junction, characterized by the close association of T cells and mmDCs and coordinated interactions with surrounding stromal and epithelial compartments. These mmDC-T cell niches may represent potential targets for future therapeutic strategies aimed at disrupting persistent local inflammatory pathways and improving long-term disease control.

atopic dermatitis↗
PubMed1997

Cerebellar contribution to spatial event processing: right/left discrimination abilities in rats.

Recently, we demonstrated the involvement of cerebellar circuits in the procedural components of spatial information processing by testing hemicerebellectomized (HCbed) rats in classical spatial paradigms, such as the Morris Water Maze and the water T-maze. Since procedural components are strongly present in these tests, an impairment also in processing more abstract spatial information, linked to 'where an object is' rather than to 'how to find it', could be hidden by the severe procedural deficits. On this basis, we investigated the influence of cerebellar lesions on spatial abilities strictly reducing procedural variables by employing an active avoidance task, first without and then with a request for right/left discrimination. In the two-way active avoidance task without spatial requests, controls and cerebellar operated rats developed active avoidance responses which were not statistically different, demonstrating that this kind of associative learning is not significantly affected by hemicerebellectomy (HCb). A second experimental group of cerebellar lesioned rats was tested in a modified version of this basic paradigm in which a right/left discrimination request was added. This group displayed severe deficits, which even in the last testing sessions prevented them from performing comparably to the control animals. Reversal of the rewarded choice, even if it affected the performances of both controls and operated rats in the first inversion trials, elicited the lowest number of correct responses in HCbed rats throughout the entire spatial reversal learning, suggesting a severe deficit in the ability to change an initially learned behaviour. These results demonstrate that, beside having a marked impairment in facing procedural components of spatial processing, cerebellar lesioned rats are severely defective also in right/left discrimination tasks, suggesting a role of cerebellar networks also in the discriminative spatial information processing.

Analysis of Variance↗
PubMed2026

Spatial Omics in High-Grade Gliomas: Mapping Immune-Tumor Niches for Precision Therapy.

High-grade gliomas (HGGs), particularly glioblastoma (GBM), remain among the most lethal human cancers despite decades of molecular profiling and therapeutic innovation. A primary reason for treatment failure is that HGG biology is spatial: malignant cell states, immune suppression, metabolic stress, and therapeutic resistance are organized into distinct anatomical and functional niches. Spatial omics technologies now enable high-dimensional mapping of gene expression, protein signaling, immune architecture, and metabolic activity within intact tumor tissue. These approaches reveal how proneural and mesenchymal transcriptional states coexist yet localize to distinct regions, alongside hypoxic, invasive, and stem-enriched niches. Spatial analyses show that key clinical determinants, including O6-methylguanine-DNA methyltransferase (MGMT)-associated temozolomide resistance, radiotherapy tolerance in hypoxic regions, and immunotherapy failure driven by myeloid-dominated immune exclusion, are influenced not only by molecular programs but also by cellular location. Beyond biological insight, spatial omics is reshaping clinical paradigms by enabling region-specific patient stratification, early assessment of treatment response, and identification of therapy-resistant reservoirs that seed recurrence. Prior bulk and single-cell studies defined HGG cell states and pathways but often treated resistance as tumor-wide. This review presents a spatially explicit framework that synthesizes spatial transcriptomic and immune-profiling studies to identify tumor-immune niches and spatial bottlenecks that drive therapeutic failure and recurrence.

Humans↗
PubMed2026

Spatial biology reveals altered macrophage states in immunosuppressed non-melanoma skin cancer.

Immunosuppressed patients with non-melanoma skin cancer experience worse clinical outcomes, yet the tumor immune microenvironment associated with systemic immunosuppression remains incompletely defined. Using integrated single-cell, spatial transcriptomic, multiplex immunofluorescence, and spatial epigenomic profiling across immunocompetent and immunosuppressed tumors, we found that overall immune-cell composition was largely preserved despite differences in immune-cell distribution, spatial organization, and T cell clonality. Immunosuppressed tumors demonstrated reduced intratumoral macrophage densities, decreased T cell clonal diversity, altered antigen-presenting cell and T cell spatial interactions, and distinct fibroblast- and macrophage-associated spatial niches. Multi-cohort validation across complementary spatial and single-cell platforms identified consistent alterations in innate-adaptive immune organization in immunosuppressed tumors. Together, these findings define spatial and functional remodeling of the tumor immune microenvironment under systemic immunosuppression and provide a framework for future therapeutic investigation in high-risk patients.

Humans↗
PubMed2004

Ibutilide-induced alterations in electrocardiographic and spatial vectorcardiographic descriptors of ventricular repolarization.

BACKGROUND: Ibutilide is used for the pharmacologic cardioversion of atrial fibrillation (AF) or flutter (AFl). Ibutilide-induced QT interval prolongation has been demonstrated previously. However, its effects on vectorcardiographic (VCG) descriptors of ventricular repolarization (VR) have not been studied so far. HYPOTHESIS: To evaluate the effects of ibutilide on electrocardiographic (ECG) and VCG descriptors of VR, one or two repeated 10-min infusions of 1 mg of ibutilide were given in 50 consecutively recruited patients (36 women, mean age 69.4 +/- 9.3 years) with AF or AFl of recent onset. METHODS: The maximum and the minimum QT intervals, QT dispersion, the rate-corrected QT maximum, and the spatial VCG descriptors, spatial T amplitude, and spatial QRS-T angle were calculated before (baseline ECG) and 30 min after the start of ibutilide infusion (postinfusion ECG). RESULTS: After ibutilide infusion, 40 (80%) patients were cardioverted to sinus rhythm (Group 1), while in the remaining 10 (Group 2) AF or AFl persisted. In both study groups, temporal measures of VR were significantly increased from baseline to the postinfusion ECG. In Group 1, spatial T amplitude and spatial QRS-T angle did not differ between those two ECGs, while in Group 2 spatial T amplitude was significantly increased (p = 0.005) and spatial QRS-T angle was significantly decreased (p = 0.002) post infusion compared with baseline ECG. CONCLUSIONS: While temporal measures of VR are significantly affected in all patients who receive ibutilide infusion for AF or AFl cardioversion, spatial VCG descriptors of VR are significantly altered only in those patients who fail to respond to the drug. A dose-related effect of ibutilide on the different aspects of VR should be suspected.

Aged↗
PubMed1986

Spatial cue utilization in chronically malnourished rats: task-specific learning deficits.

Rats whose mothers were maintained on either a 25% casein diet or an 8% casein diet and who were provided the same diet after weaning were tested on delayed spatial alternation or on one of a series of spatial localization problems using the Morris maze (Morris, 1981). Malnourished rats demonstrated perseverative deficits in the form of strings of consecutive errors on the delayed spatial alternation. Performance in the Morris maze indicated spatial localization ability and spatial memory processes were not impaired by chronic malnutrition in rats. The data suggest that complex processing of spatial information that includes flexible use of place cues over short intervals is impaired by malnutrition, while spatial localization per se and spatial mapping are not affected.

Animals↗
PubMed2001

GABAergic septohippocampal neurons are not necessary for spatial memory.

The medial septum/vertical limb of the diagonal band of Broca (MSDB) provides a major input to the hippocampus and is important for spatial memory. Both cholinergic and GABAergic MSDB neurons project to the hippocampus, and nonselective lesions of the MSDB or transections of the septohippocampal pathway impair spatial memory. However, selective lesions of cholinergic MSDB neurons using 192-IgG saporin (SAP) do not impair or only mildly impair spatial memory. Previously, intraseptal kainic acid was found to reduce levels of glutamic acid decarboxylase, a marker of GABAergic neurons, but not to alter the levels of choline acetyltransferase, a marker of cholinergic neurons. The present study further characterized the effects of kainic acid on GABAergic MSDB neurons and examined the effects of intraseptal kainic acid on spatial memory. Saline, kainic acid, SAP, or the combination of kainic acid and SAP was administered into the MSDB of rats. Spatial memory was assessed in an eight-arm radial maze and a water maze. Kainic acid destroyed GABAergic septohippocampal neurons, but spared cholinergic neurons. SAP eliminated MSDB cholinergic neurons, sparing noncholinergic neurons. Coadministration of kainic acid and SAP destroyed GABAergic and cholinergic MSDB neurons. Acquisition of the radial maze task and performance on this task with 4-h delays were unimpaired by intraseptal kainic acid or SAP, but were impaired by coadministration of kainic acid and SAP. Acquisition of the water maze task was unaffected by intraseptal kainic acid, delayed slightly by SAP, and impaired severely by coadministration of kainic acid and SAP. These results provide evidence that kainic acid at appropriate concentrations effectively destroys GABAergic septohippocampal neurons, while sparing cholinergic MSDB neurons. Furthermore, lesions of the GABAergic septohippocampal neurons do not impair spatial memory. While lesions of cholinergic MSDB neurons may mildly impair spatial memory, the combined lesion of GABAergic and cholinergic septohippocampal neurons resulted in a memory impairment that was greater than that observed after a selective lesion to either population. Thus, damage of GABAergic or cholinergic MSDB neurons, which together comprise the majority of the septohippocampal pathway, cannot totally account for the spatial memory impairment that is observed after nonselective lesions of the MSDB.

Animals↗
PubMed1999

Algorithmic behaviour and spatial memory are used by two intertidal fish species to solve the radial maze.

We used an eight-arm radial maze to assess the relative contributions of learned patterns of movement (algorithmic behaviour) and spatial memory to the foraging efficiency of two sympatric rocky-shore fish, fifteen-spined stickleback, Spinachia spinachia, and corkwing wrasse, Crenilabrus melops, exploiting nonrenewable food sources. To forage efficiently, subjects had to avoid arms already depleted within a trial. In the absence of spatial cues, sticklebacks and wrasse improved their foraging efficiency by developing the algorithm of visiting every third arm. In the presence of spatial cues (coloured tiles) algorithmic behaviour was largely subsumed by the use of spatial memory. Imposition of a delay within trials reset the behavioural algorithm, so depressing foraging efficiency in the absence of cues, but not in their presence when memory could be used to guide behaviour. Memory retention for previous choices (working memory) lay within the range 0.5-5.0 min, consistent with the characteristic timescale expected for habitats where prey distribution changes rapidly during the tidal cycle. We considered two hypotheses on the type of information memorized: the cue list hypothesis and the spatial configuration hypothesis. The cue list hypothesis predicts that neither random repositioning nor fixed rotation of spatial cues should impair foraging efficiency, whereas the spatial configuration hypothesis predicts that efficiency should be impaired by random repositioning of cues but not by rotation. Data supported the spatial configuration hypothesis. Copyright 1999 The Association for the Study of Animal Behaviour.

Journal Article↗
PubMed1999

Evolution of cooperation in spatially structured populations

Using a spatial lattice model of the Iterated Prisoner's Dilemma we studied the evolution of cooperation within the strategy space of all stochastic strategies with a memory of one round. Comparing the spatial model with a randomly mixed model showed that (1) there is more cooperative behaviour in a spatially structured population, (2) PAVLOV and generous variants of it are very successful strategies in the spatial context and (3) in spatially structured populations evolution is much less chaotic than in unstructured populations. In spatially structured populations, generous variants of PAVLOV are found to be very successful strategies in playing the Iterated Prisoner's Dilemma. The main weakness of PAVLOV is that it is exploitable by defective strategies. In a spatial context this disadvantage is much less important than the good error correction of PAVLOV, and especially of generous PAVLOV, because in a spatially structured population successful strategies always build clusters. Copyright 1999 Academic Press.

Journal Article↗
PubMed1999

Assessment of spatial normalization of PET ligand images using ligand-specific templates.

Recent advances allow robust computation of parametric maps of ligand-receptor binding from PET data sets. Parametric maps may be statistically analyzed at the voxel level, given suitable techniques for both the spatial normalization of image data into a standard space and the application of appropriate statistical tests. The purpose of this study was to spatially normalize parametric maps of [carbonyl-11C]WAY-100635 and [11C]raclopride binding using SPM 96 and ligand-specific templates. Ligand-specific templates were created from integral images taken from healthy subjects. For this, a MRI-based spatial normalization was used: T1-weighted MRI scans were coregistered to the PET integral images, and the spatial normalization of the MRI to the SPM 96 T1 MRI template was applied to the integral images. These integral images were meaned and smoothed to form [carbonyl-11C]WAY-100635 and [11C]raclopride templates. Reliability of spatial normalization using the ligand template method and the previous MRI-based spatial normalization was investigated by using a second set of integral images taken from a different cohort: Landmark coordinates were defined on all spatially normalized integral images. Mean coordinates were found in order to produce an overall (average) landmark for each location. For each image, at each location, the distance from the landmark coordinates to the overall landmark were found. A multivariate analysis of variance was used to examine the effects of observer variance, landmark location, and the method used. Visually acceptable templates were created. While observer variance was not significant, the landmark x method interaction was significant. The ligand template method had significantly smaller distances: Among the landmark locations with this method, the mean distances between individual image landmarks and overall image landmarks ranged from 1. 1 to 4.9 mm. The ligand template method provides a reliable approach for spatial normalization of PET ligand images.

Algorithms↗
PubMed1993

Spatial and temporal coding in single neurons.

Convergence between cells which differ in both spatial and temporal properties create higher order neurons with response properties that are distinctly different from those of the input neurons. The spatial properties of target neurons are not necessarily "cosine-tuned". In addition, unlike the independence between spatial and temporal properties in cosine-tuned afferent neurons, higher-order target cells generally exhibit a dependence of temporal dynamics on spatial properties. The response properties of target neurons receiving spatio-temporal convergence (STC) from tonic and phasic-tonic or phasic afferents is investigated here by considering a general case where the dynamic input is represented by a fractional, leaky, derivative transfer function. It is shown that, at frequencies below the corner frequency of the dynamic input, the temporal properties of target neurons can be described by leaky differentiators having time constants that are a function of spatial direction. Thus, STC target neurons exhibit tonic temporal response properties during stimulation along some spatial directions (having small time constants) and phasic properties along other directions (having large time constants). Specifically, target neurons encode the complete derivative of the stimulus along certain spatial directions. Thus, STC acts as a directionally specific high-pass filter and produces complete derivatives from fractional, leaky derivative afferent signals. In addition, spatio-temporal transformations can generate novel temporal dynamics in the central nervous system. These observations suggest that spatio-temporal computations might constitute an alternative to parallel, independent spatial and temporal channels.

Afferent Pathways↗
PubMed1990

Spatial frequency thresholds of single striate cortical cells in neonatal corpus callosum sectioned cats.

Following section of the corpus callosum at 1-6 postnatal weeks in cats, behavioral visual acuity was measured binocularly and monocularly from 6-29 postnatal weeks; physiological determination of spatial frequency thresholds of single striate cortical cells was performed when the cats were at least 8 months old. Results were compared between cats with callosum section at each postnatal week, as well as with normal cats. Cats with callosotomy at 1-3 postnatal weeks had deficits in behavioral visual acuity, and the deficits were greatest in the youngest operated cats. Cats with callosotomy at 1-2 postnatal weeks failed to resolve as high spatial frequencies as did normal cats, and the resolution of the 1 week operated cats was lower than the resolution of the 2 week operated cats. Cats with callosotomy at 3-6 postnatal weeks had spatial frequency thresholds that were equivalent to those of normal cats. To determine what kinds of striate cells had reduced spatial resolution following neonatal corpus callosum section, cells were categorized according to class (Simple, Complex), receptive field location (Central, Peripheral), and monocular behavioral acuity eye performance (Better Eye, Worse Eye). Cats with corpus callosum section during postnatal week 1 had the lowest spatial resolution for all cell categories compared to all groups tested. However, cats with callosum section during postnatal week 2 had normal spatial frequency thresholds for Simple, Central and Better Eye categories. The cats with callosum section in postnatal weeks 3-6 had normal spatial frequency thresholds for all cell categories. For corpus callosum sectioned cats with and without visual deficits, and for normal cats, visual acuity measured behaviorally is significantly related to visual acuity measured physiologically. The results show that neonatal corpus callosum section in cats can affect behavioral visual acuity, as well as the spatial frequency thresholds of many categories of striate cortical cells. However, callosum section at different ages affects different populations of cortical cells. Furthermore, the results suggest that neonatal corpus callosum section may directly affect a single fundamental property of cells in primary visual cortex with a resulting disruption of many visual functions.

Aging↗