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PubMedDate not supplied

Neuromodulation, theta rhythm and rat spatial navigation.

Cholinergic and GABAergic innervation of the hippocampus plays an important role in human memory function and rat spatial navigation. Drugs which block acetylcholine receptors or enhance GABA receptor activation cause striking impairments in the encoding of new information. Lesions of the cholinergic innervation of the hippocampus reduce the amplitude of hippocampal theta rhythm and cause impairments in spatial navigation tasks, including the Morris water maze, eight-arm radial maze, spatial reversal and delayed alternation. Here, we review previous work on the role of cholinergic modulation in memory function, and we present a new model of the hippocampus and entorhinal cortex describing the interaction of these regions for goal-directed spatial navigation in behavioral tasks. These mechanisms require separate functional phases for: (1) encoding of pathways without interference from retrieval, and (2) retrieval of pathways for guiding selection of the next movement. We present analysis exploring how phasic changes in physiological variables during hippocampal theta rhythm could provide these different phases and enhance spatial navigation function.

Animals↗
PubMed1998

Shifts of visual spatial attention modulate a steady-state visual evoked potential.

Although the effects of static allocations of visual spatial attention have been investigated using event-related potentials, most studies of shifts in visual spatial attention have been limited to behavioural measures. This study applied electroencephalographic measures to shifts in visual spatial attention in an effort to elucidate the time courses of such shifts. Using a custom-developed steady-state evoked potential analysis system, we analysed amplitude changes in EEG responses to rapid, periodic visual stimulation during a behavioural task that required rapid, repetitive shifts in visual spatial attention. Both stimulus-evoked oscillations (that is, those signals whose phases matched the phase of the steady-state stimulus) and ongoing, background (non-phase-locked) oscillations were measured. This analysis revealed a transient increase in phase-locked amplitude, in the interval 0-300-ms post-stimulus, contralateral to the visual hemifield in which an attended target appeared. The magnitude of this increase varied with the length of the interval since the previous shift. In addition, by about 600-ms post-stimulus, phase-locked amplitude increased in the hemisphere contralateral to the newly-attended visual hemifield and decreased in the ipsilateral hemisphere. In the case of long inter-target intervals, phase-locked amplitude increased in the right hemisphere regardless of the laterality of the target. Non-phase-locked amplitude exhibited a complementary pattern of modulation: it decreased contralaterally to the newly-attended visual hemifield and increased ipsilaterally. These components may be electrophysiological concomitants of both transient and long-lasting alterations in neural function that implement shifts in visual spatial attention. In particular, we suggest that they may reflect orienting to a target stimulus, and reorienting to a cued location.

Adult↗
PubMed2002

Relationships among childhood sex-atypical behavior, spatial ability, handedness, and sexual orientation in men.

Moderate support was obtained in a sample of 101 gay, bisexual, and heterosexual males for the perinatal hormone theory, which hypothesizes that attenuated levels of androgens during critical periods of male fetal development fail to masculinize and defeminize the brain. Affected individuals develop female-typical sexual orientation (assessed here by a pie chart) and cerebral organization, reflected in visual-spatial abilities and gender nonconformity. Handedness, also thought to reflect in utero hormone exposure, was evaluated. Gay and bisexual males reported greater femininity and lesser masculinity than heterosexuals, with bisexuals intermediate in masculinity, suggesting a common biological mediator for homoeroticism and sex atypicality. Among bisexual males, increased masculinity was related to enhanced performance on all spatial tasks. Group mean differences in spatial ability and handedness were not found; however, among bisexuals, poorer visual-spatial performance predicted increased homoeroticism and right-handedness positively correlated with all spatial tasks. If perinatal hormones contribute to a generalized feminization of the brain, the current data indicate that it is most apparent among bisexual males. Sexing of their brains may involve several sexually dimorphic regions that are related in a continuous manner. Inferred cerebral feminization was more circumscribed among gay and heterosexual males, for whom childhood sex atypicality was most highly-distinguishing. Unspecified mechanisms responsible for homoeroticism in them may differ from those that produce same-sex attractions in bisexuals and thus have relatively little impact on other components of cerebral feminization.

Adolescent↗
PubMed1997

The metrics of spatial situation models.

The authors investigated the metrics of spatial distance represented in situation models of narratives. In 3 experiments, a spatial gradient of accessibility in situation models was observed: The accessibility of objects contained in the situation model decreased with increasing spatial distance between the object and the reader's focus of attention. The first 2 experiments demonstrated that this effect of spatial distance was purely categorical rather than Euclidean: Accessibility depended on the number of rooms located between the object and the focus of attention, not on the size of the rooms. Experiment 3 revealed, however, that participants were able to use information about Euclidean distance in a secondary task when necessary. The implications of these results for theories of narrative comprehension and hierarchical versus nonhierarchical theories of spatial memory are discussed.

Adult↗
PubMed2006

Chimpanzees (Pan troglodytes) remember the location of a hidden food item after altering their orientation to a spatial array.

Two chimpanzees (Pan troglodytes) had a direct view of an experimenter placing a food item beneath one of several cups within a horizontal spatial array. The chimpanzees then were required to move around the spatial array, shifting their orientation to the array by 180 degrees . Both chimpanzees remembered the location of the food item. In the next experiment, a visual barrier was placed between the chimpanzees and the spatial array after the food item had been hidden to prevent visual tracking of the location of the object during the chimpanzees' movement. One chimpanzee remembered the location of the hidden item in this variation. These results demonstrate another capacity for spatial memory in this species that complements data indicating chimpanzee spatial memory for invisible displacements, array rotations, and array transpositions.

Animals↗
PubMed2003

Extinction, renewal, and spontaneous recovery of a spatial preference in the water maze.

Four experiments with C57BL/6 mice investigated extinction of a spatial preference in the Morris water maze. In Experiment 1, a spatial preference was extinguished by exposing mice to the water maze in the absence of a platform but in the presence of the distal spatial cues. In Experiment 2, extinction occurred when the platform was removed from the pool, when it was presented in random locations, or when it was presented consistently in the opposite location. Contextual renewal (Experiment 3) and spontaneous recovery (Experiment 4) of spatial preferences argue against an interpretation of extinction in terms of unlearning and instead suggest that extinction in the water maze, like extinction in Pavlovian conditioning, suppresses the original association. Implications of these findings for theories of spatial learning and hippocampal function are discussed.

Animals↗
PubMed2004

Learning and retrieval of concurrently presented spatial discrimination tasks: role of the fornix.

In macaque monkeys (Macaco mulatta), memory for scenes presented on touch screens is fornix dependent. However, scene learning is not a purely spatial task, and existing direct evidence for a fornix role in spatial memory comes exclusively from tasks involving learning about food-reward locations. Here the authors demonstrate that fornix transection impairs learning about spatial stimuli presented on touch screens. Using a new concurrent spatial discrimination learning task, they found that fornix transection did not impair recall of preoperatively learned problems. Relearning, on the other hand, was mildly impaired, and new learning was strongly impaired. New learning of smaller sets of harder problems was also markedly impaired, as was spatial configured learning. This pattern supports a functional specialization according to stimulus domain in the medial temporal lobe.

Animals↗
PubMed2004

An fMRI study of episodic memory: retrieval of object, spatial, and temporal information.

Sixteen participants viewed a videotaped tour of 4 houses that highlighted a series of objects and their spatial locations. Participants were tested for memory of object, spatial, and temporal-order information while undergoing functional magnetic resonance imaging. Preferential activation was observed in the right parahippocampal gyrus during the retrieval of spatial-location information. Retrieval of contextual information (spatial location and temporal order) was associated with activation in the right dorsolateral prefrontal cortex. In bilateral posterior parietal regions, greater activation was associated with processing of visual scenes regardless of the memory judgment. These findings support current theories positing roles for frontal and medial temporal regions during episodic retrieval and suggest a specific role for the hippocampal complex in the retrieval of spatial-location information.

Adult↗
PubMed1995

Sex differences in visuo-spatial ability: task difficulty, speed-accuracy tradeoff, and other performance factors.

Males have consistently been found to perform better than females on a task that requires the subject to mentally rotate a figure. Recently, Goldstein. Haldane, and Mitchell (1990) suggested that performance factors are operative in explaining sex differences in spatial ability. However, Stumpf (1993) was unable to replicate all of Goldstein et al.'s (1990) findings and to generalize them to other measures of spatial ability. In this study, it was hypothesized (1) that females would take longer to respond and would get fewer correct items than males on a spatial rotation task, and (2) that only females would show a speed-accuracy tradeoff as the difficulty of the spatial task increased from the 90 degrees to 180 degrees rotated conditions. The results confirmed each of these hypotheses. Furthermore, as Stumpf (1993) found, when ratio scores from the number of items correct to number attempted were computed for both males and females, differences in spatial ability were reduced, though still evident.

Adolescent↗
PubMed1993

Landmark stability is a prerequisite for spatial but not discrimination learning.

Neurons sensitive to both place and direction from distinct regions of the hippocampal formation, allometric relationships between spatial learning and hippocampal structure and pronounced impairments in spatial learning after lesions in this area, indicate that the hippocampal formation subserves allocentric spatial learning. To learn more about the process of spatial representation, we have developed a task that provides independent control of both landmark and directional cues. On the basis of physiological and behavioural work, this task also makes it possible to investigate the relevance of associative learning principles, such as predictability, to the spatial domain. We report here that although rats learn to discriminate between landmarks on the basis of their proximity to a reliably predicted food reward, they will only learn to use them to represent its location if they maintain stable locations within a geometric frame of reference.

Animals↗
PubMed2003

Hippocampal map realignment and spatial learning.

The spatial selectivity of hippocampal neurons suggests that they contribute to an internal representation of current location. The activity of hippocampal pyramidal cells was recorded while adult (10-13 months old) and aged (24-28 months old) rats performed a task in which two spatial reference frames were put in conflict. Rats attempted to find an unmarked goal whose position was fixed relative to only one of the two reference frames. The ability of a rat's hippocampus to adjust to the conflicting information and use the 'correct' position estimate (hippocampal map 'realignment') was correlated with the rat's ability to find the hidden goal. In addition, aged rats were impaired relative to adult rats in both goal-finding accuracy and map realignment. Thus, changes in the effectiveness with which the hippocampal spatial representation is updated on the basis of external cues may contribute to both within-age-group spatial learning variability and age-related spatial learning deficits.

Adaptation, Physiological↗
PubMed2026

Beyond benchmarking: an expert-guided consensus approach to spatially aware clustering.

Spatial omics technologies have revolutionized the study of tissue architecture and cellular heterogeneity by integrating molecular profiles with spatial localization. In spatially resolved transcriptomics, delineating higher-order anatomical structures is critical for understanding how cellular organization affects function. However, the reliability of current benchmarks of spatially aware clustering (SAC) methods is undermined by their narrow focus on Visium and brain tissue datasets and the incorrect interpretation of manual annotation as ground truth. Here we present SACCELERATOR, a community-driven, extensible framework that standardizes data formatting, method integration and metric evaluation, enabling rapid inclusion of new methods and datasets. Our analysis revealed substantial limitations in the generalizability and reproducibility of SAC methods and shows that anatomical labels commonly used as ground truths are often biased, error prone and unsuitable for benchmarking. Rather than ranking methods, we propose a consensus-guided workflow where descriptive spatial metrics highlight high-entropy regions of method disagreement, enabling targeted feedback for tissue experts. Applied to brain and cancer datasets, this approach uncovered biologically meaningful patterns overlooked by individual SAC methods and manual annotations, highlighting the need for iterative, expert-in-the-loop evaluation.

Benchmarking↗
PubMed2002

Hippocampal long-term depression as an index of spatial working memory.

Long-term potentiation (LTP), a form of synaptic plasticity in the hippocampus, is a cellular model for the neural basis of learning and memory, but few studies have investigated the contribution of long-term depression (LTD), a counterpart of LTP. To address the possible relationship between hippocampal LTD and spatial performance, the spatial cognitive ability of a rat was assessed in a spontaneous alternation test and, thereafter, LTD in response to low-frequency burst stimulation (LFBS) was monitored in the dentate gyrus of the same rat under anaesthesia. To enhance a divergence in the ability for spatial performance, some of the animals received fimbria-fornix (FF) transection 14 days before the experiments. LTD was reliably induced by application of LFBS to the medial perforant path of intact rats, while no apparent LTD was elicited in rats with FF lesions. The behavioural parameters of spatial memory showed a significant correlation with the magnitude of LTD. We found no evidence that the cognitive ability correlated with other electrophysiological parameters, e.g. basal synaptic responses, stimulus intensity to produce half-maximal responses, paired-pulse facilitation or paired-pulse depression. These results suggest that the magnitude of LTD in the dentate gyrus serves as a reliable index of spatial cognitive ability, providing insights into the functional significance of hippocampal LTD.

Animals↗
PubMed2003

Deficits in spatial learning and synaptic plasticity induced by the rapid and competitive broad-spectrum cyclooxygenase inhibitor ibuprofen are reversed by increasing endogenous brain-derived neurotrophic factor.

Cyclooxygenase (COX), which is present in two isoforms (COX1 and 2), synthesizes prostaglandins from arachidonic acid; it plays a crucial role in inflammation in both central and peripheral tissues. Here, we describe its role in synaptic plasticity and spatial learning in vivo via an effect on brain-derived neurotrophic factor (BDNF) and prostaglandin E2 (PGE2; both measured by Elisa). We found that broad-spectrum COX inhibition (BSCI) inhibits the induction of long-term potentiation (LTP; the major contemporary model of synaptic plasticity), and causes substantial and sustained deficits in spatial learning in the watermaze. Increases in BDNF and PGE2 following spatial learning and LTP were also blocked. Importantly, 4 days of prior exercise in a running wheel increased endogenous BDNF levels sufficiently to reverse the BSCI of LTP and spatial learning, and restored a parallel increase in LTP and learning-related BDNF and PGE2. In control experiments, we found that BSCI had no effect on baseline synaptic transmission or on the nonhippocampal visible-platform task; there was no evidence of gastric ulceration from BSCI. COX2 is inhibited by glucorticoids; there was no difference in blood corticosterone levels as measured by radioimmunoassay in any condition. Thus, COX plays a previously undescribed, permissive role in synaptic plasticity and spatial learning via a BDNF-associated mechanism.

Animals↗
PubMed1997

Spatial memory is related to hippocampal subcellular concentrations of calcium-dependent protein kinase C isoforms in young and aged rats.

Relationships were examined between spatial learning and hippocampal concentrations of the alpha, beta2, and gamma isoforms of protein kinase C (PKC), an enzyme implicated in neuronal plasticity and memory formation. Concentrations of PKC were determined for individual 6-month-old (n = 13) and 24-month-old (n = 27) male Long-Evans rats trained in the water maze on a standard place-learning task and a transfer task designed for rapid acquisition. The results showed significant relationships between spatial learning and the amount of PKC among individual subjects, and those relationships differed according to age, isoform, and subcellular fraction. Among 6-month-old rats, those with the best spatial memory were those with the highest concentrations of PKCgamma in the particulate fraction and of PKCbeta2 in the soluble fraction. Aged rats had increased hippocampal PKCgamma concentrations in both subcellular fractions in comparison with young rats, and memory impairment was correlated with higher PKCgamma concentrations in the soluble fraction. No age difference or correlations with behavior were found for concentrations of PKCgamma in a comparison structure, the neostriatum, or for PKCalpha in the hippocampus. Relationships between spatial learning and hippocampal concentrations of calcium-dependent PKC are isoform-specific. Moreover, age-related spatial memory impairment is associated with altered subcellular concentrations of PKCgamma and may be indicative of deficient signal transduction and neuronal plasticity in the hippocampal formation.

Aging↗
PubMed2005

The role of large-scale spatially explicit and small-scale localized processes on the population dynamics of cereal aphids.

A field-scale study of the spatially explicit interaction between the carabid Poecilus cupreus Linnaeus, and two common aphid species (Sitobion avenae (Fabricius) and Metopolophium dirhodum (Walker)) in winter wheat was conducted. All three species showed considerable spatial pattern at the field scale. Activity-density of P. cupreus was an order of magnitude higher in the central part of the field compared to its periphery. Where P. cupreus activity-density was highest, S. avenae and M. dirhodum population peaks were delayed. Additionally, in the case of M. dirhodum, lower maximum counts were evident where P. cupreus activity-density was highest. An analysis of the movement of individual P. cupreus using release-recapture indicated that those beetles within the centre of the field exhibited reduced displacement, which may have caused the generation or maintenance of spatial pattern. Crop density was also measured throughout the field. Although crop density had no large-scale spatial pattern, its variability at the small-scale was consistent with an influence on aphid population dynamics. This study demonstrates empirically that both large-scale spatially explicit and small-scale localized processes influenced aphid population dynamics simultaneously.

Animals↗
PubMed1984

The relationship of spatial concept development to the acquisition of locative understanding.

A cross-sectional study of children in the preoperational period was conducted to investigate the potential constraints of spatial concept development on children's understanding of spatial prepositions. A battery of Piagetian tasks and a locative comprehension measure were administered to 60 children, ranging in age from 2 to 7 years. In general, children were functioning in Stage II on the Piagetian spatial tasks before they comprehended the prepositions, in front of and behind, in terms of their own perspective using nonfronted objects. The findings also indicated that the children were functioning in Stage III--i.e., they had projective/Euclidean understanding--before they could comprehend in front of and behind when these terms involved projective/Euclidean spatial notions. The majority of children accounted for the front/back features of the object in placing an object in front of or behind a fronted object. The results suggest that as the child's conception of space changes, his comprehension of spatial prepositions also changes.

Child↗
PubMed1996

The benefits of random variable practice for spatial accuracy and error detection in a rapid aiming task.

The role of blocked and random variable practice in the development of a spatial error detection mechanism in 2 experiments was investigated in the present study. Twenty-four (Experiment 1) and 40 (Experiment 2) college-aged participants made either 20, 40, 60 degrees quick lever reversal movements in the sagittal plane. During acquisition in both experiments, blocked practice resulted in less spatial absolute constant error (ICEI) relative to the random group. The blocked practice group showed a smaller mean absolute objective-subjective difference than the random practice group during acquisition (Experiment 1). On no-knowledge of results retention tests in both studies, the random practice group showed a smaller spatial ICEI and a smaller mean absolute objective-subjective difference than the blocked practice group, even on a novel amplitude (Experiment 2). The study demonstrated the advantage of random variable practice over blocked variable practice on retention tests for spatial performance and in developing a spatial error detection capability.

Adult↗