Spatial Navigation Task Research Articles

Trait affective differences influence behavioral flexibility in virtual spatial and non-spatial discrimination tasks

Affect and cognitive control processes are closely related, however, most studies have assessed state affect or affective disorders. The current study investigates the relationship between individual differences in trait affectivity and flexibility in spatial navigation and stimulus discrimination tasks. Beck Depression Inventory-II (BDI-II), Beck Anxiety Inventory (BAI), and the Positive and Negative Affectivity Scale (PANAS) were given to 82 participants followed by an intradimensional/extradimensional (ID/ED) set-shifting task in which navigation was reinforced based on visual stimuli colocalized with a goal or based on the spatial location of the goal. Higher BDI and NA predicted greater trials-to-criteria during ED shift, but not initial learning or ID shifting. Participants who failed to meet criteria during either ID or ED set-shifting (N = 16) had significantly higher scores for NA, BDI, and BAI compared to individuals who successfully met criterion (N = 56) with this relationship being primarily observed in males. The current findings indicate that negative affectivity is associated with poor performance in behavioral flexibility.

Short-term oral rapamycin prevents age-related learning impairment in mice.

Effective treatments to prevent or delay age-related learning impairment are not generally available. In a preliminary preclinical study, mice 20 months of age were fed a diet containing 14 ppm rapamycin, an inhibitor of mTOR, for three months and then tested in a spatial navigation task. Mice fed the nonmedicated control diet showed learning impairment while mice fed the rapamycin diet were not learning impaired. This observation provides support for additional preclinical studies and suggests that short-term rapamycin treatment could be a possible strategy for preventing or delaying age-related cognitive impairment in people.

Long-Term Music Exposure Prevents Age-Related Cognitive Deficits in Rats Independently of Hippocampal Neurogenesis.

Cognitive decline appears across aging. While some studies report beneficial effects of musical listening and practice on cognitive aging, the underlying neurobiological mechanisms remain unknown. This study aims to determine whether chronic (6h/day, 3times/week) and long-lasting (4-8months) music exposure, initiated at middle age in rats (15months old), can influence behavioral parameters sensitive to age effects and reduce age-related spatial memory decline in rats. Spontaneous locomotor, circadian rhythmic activity, and anxiety-like behavior as well as spatial working and reference memory were assessed in 14-month-old rats and then after 4 and 8months of music exposure (19 and 23months old, respectively). Spatial learning and reference memory data were followed up by considering cognitive status of animals prior to music exposure (14 months old) given by K-means clustering of individual Z-score. Hippocampal cell proliferation and brain-derived neurotrophic factor (BDNF) level in the hippocampus and frontal cortex were measured. Results show that music exposure differentially rescues age-related deficits in spatial navigation tasks according to its duration without affecting spontaneous locomotor, circadian rhythmic activity, and anxiety-like behavior. Hippocampal cell proliferation as well as hippocampal and frontal cortex BDNF levels was not affected by music across aging. Cognitive improvement by music in aging rats may require distinct neurobiological mechanisms than hippocampal cell proliferation and BDNF.

Computational Characteristics of the Striatal Dopamine System Described by Reinforcement Learning With Fast Generalization.

Generalization is the ability to apply past experience to similar but non-identical situations. It not only affects stimulus-outcome relationships, as observed in conditioning experiments, but may also be essential for adaptive behaviors, which involve the interaction between individuals and their environment. Computational modeling could potentially clarify the effect of generalization on adaptive behaviors and how this effect emerges from the underlying computation. Recent neurobiological observation indicated that the striatal dopamine system achieves generalization and subsequent discrimination by updating the corticostriatal synaptic connections in differential response to reward and punishment. In this study, we analyzed how computational characteristics in this neurobiological system affects adaptive behaviors. We proposed a novel reinforcement learning model with multilayer neural networks in which the synaptic weights of only the last layer are updated according to the prediction error. We set fixed connections between the input and hidden layers to maintain the similarity of inputs in the hidden-layer representation. This network enabled fast generalization of reward and punishment learning, and thereby facilitated safe and efficient exploration of spatial navigation tasks. Notably, it demonstrated a quick reward approach and efficient punishment aversion in the early learning phase, compared to algorithms that do not show generalization. However, disturbance of the network that causes noisy generalization and impaired discrimination induced maladaptive valuation. These results suggested the advantage and potential drawback of computation by the striatal dopamine system with regard to adaptive behaviors.

Blast-induced hearing loss suppresses hippocampal neurogenesis and disrupts long term spatial memory

Acoustic information transduced by cochlear hair cells is continuously relayed from the auditory pathway to other sensory, motor, emotional and cognitive centers in the central nervous system. Human epidemiological studies have suggested that hearing loss is a risk factor for dementia and cognitive decline, but the mechanisms contributing to these memory and cognitive impairments are poorly understood. To explore these issues in a controlled experimental setting, we exposed adult rats to a series of intense blast wave exposures that significantly reduced the neural output of the cochlea. Several weeks later, we used the Morris Water Maze test, a hippocampal-dependent memory task, to assess the ability of Blast Wave and Control rats to learn a spatial navigation task (memory acquisition) and to remember what they had learned (spatial memory retention) several weeks earlier. The elevated plus maze and open field arena were used to test for anxiety-like behaviors. Afterwards, hippocampal cell proliferation and neurogenesis were evaluated using bromodeoxyuridine (BrdU), doublecortin (DCX), and Neuronal Nuclei (NeuN) immunolabeling. The Blast Wave and Control rats learned the spatial navigation task equally well and showed no differences on tests of anxiety. However, the Blast Wave rats performed significantly worse on the spatial memory retention task, i.e., remembering where they had been two weeks earlier. Deficits on the spatial memory retention task were associated with significant decreases in hippocampal cell proliferation and neurogenesis. Our blast wave results are consistent with other experimental manipulations that link spatial memory retention deficits (long term memory) with decreased cell proliferation and neurogenesis in the hippocampus. These results add to the growing body of knowledge linking blast-induced cochlear hearing loss with the cognitive deficits often seen in combat personnel and provide mechanistic insights into these extra auditory disorders that could lead to therapeutic interventions.

Pathfinder: open source software for analyzing spatial navigation search strategies.

Spatial navigation is a universal behavior that varies depending on goals, experience and available sensory stimuli. Spatial navigational tasks are routinely used to study learning, memory and goal-directed behavior, in both animals and humans. One popular paradigm for testing spatial memory is the Morris water maze, where subjects learn the location of a hidden platform that offers escape from a pool of water. Researchers typically express learning as a function of the latency to escape, though this reveals little about the underlying navigational strategies. Recently, a number of studies have begun to classify water maze search strategies in order to clarify the precise spatial and mnemonic functions of different brain regions, and to identify which aspects of spatial memory are disrupted in disease models. However, despite their usefulness, strategy analyses have not been widely adopted due to the lack of software to automate analyses. To address this need we developed Pathfinder, an open source application for analyzing spatial navigation behaviors. In a representative dataset, we show that Pathfinder effectively characterizes the development of highly-specific spatial search strategies as male and female mice learn a standard spatial water maze. Pathfinder can read data files from commercially- and freely-available software packages, is optimized for classifying search strategies in water maze paradigms, and can also be used to analyze 2D navigation by other species, and in other tasks, as long as timestamped xy coordinates are available. Pathfinder is simple to use, can automatically determine pool and platform geometry, generates heat maps, analyzes navigation with respect to multiple goal locations, and can be updated to accommodate future developments in spatial behavioral analyses. Given these features, Pathfinder may be a useful tool for studying how navigational strategies are regulated by the environment, depend on specific neural circuits, and are altered by pathology.

Psychometric Tests and Spatial Navigation: Data From the Baltimore Longitudinal Study of Aging.

Spatial cognition is the process by which individuals interact with their spatial environment. Spatial cognition encompasses the specific skills of spatial memory, spatial orientation, and spatial navigation. Prior studies have shown an association between psychometric tests of spatial ability and self-reported or virtual measures of spatial navigation. In this study, we examined whether psychometric spatial cognitive tests predict performance on a dynamic spatial navigation task that involves movement through an environment. We recruited 151 community-dwelling adult participants [mean (SD) age 69.7 (13.6), range 24.6–93.2] from the Baltimore Longitudinal Study of Aging (BLSA). Spatial navigation ability was assessed using the triangle completion task (TCT), and two quantities, the angle and distance of deviation, were computed. Visuospatial cognitive ability was assessed primarily using the Card Rotations Test. Additional tests of executive function, memory, and attention were also administered. In multiple linear regression analyses adjusting for age, sex, race, and education, cognitive tests of visuospatial ability, executive function, and perceptual motor speed and integration were significantly associated with spatial navigation, as determined by performance on the TCT. These findings suggest that dynamic spatial navigation ability is related to spatial memory, executive function, and motor processing speed.

Cooling of Medial Septum Reveals Theta Phase Lag Coordination of Hippocampal Cell Assemblies

Hippocampal theta oscillations coordinate neuronal firing to support memory and spatial navigation. The medial septum (MS) is critical in theta generation by two possible mechanisms: either a unitary "pacemaker" timing signal is imposed on the hippocampal system, or it may assist in organizing target subcircuits within the phase space of theta oscillations. We used temperature manipulation of the MS to test these models. Cooling of the MS reduced both theta frequency and power and was associated with an enhanced incidence of errors in a spatial navigation task, but it did not affect spatial correlates of neurons. MS cooling decreased theta frequency oscillations of place cells and reduced distance-time compression but preserved distance-phase compression of place field sequences within the theta cycle. Thus, the septum is critical for sustaining precise theta phase coordination of cell assemblies in the hippocampal system, a mechanism needed for spatial memory.

Pathfinder: open source software for analyzing spatial navigation search strategies

Spatial navigation is a universal behavior that varies depending on goals, experience and available sensory stimuli. Spatial navigational tasks are routinely used to study learning, memory and goal-directed behavior, in both animals and humans. One popular paradigm for testing spatial memory is the Morris water maze, where subjects learn the location of a hidden platform that offers escape from a pool of water. Researchers typically express learning as a function of the latency to escape, though this reveals little about the underlying navigational strategies. Recently, a number of studies have begun to classify water maze search strategies in order to clarify the precise spatial and mnemonic functions of different brain regions, and to identify which aspects of spatial memory are disrupted in disease models. However, despite their usefulness, strategy analyses have not been widely adopted due to the lack of software to automate analyses. To address this need we developed Pathfinder, an open source application for analyzing spatial navigation behaviors. In a representative dataset, we show that Pathfinder effectively characterizes the development of highly-specific spatial search strategies as male and female mice learn a standard spatial water maze. Pathfinder can read data files from commercially- and freely-available software packages, is optimized for classifying search strategies in water maze paradigms, and can also be used to analyze 2D navigation by other species, and in other tasks, as long as timestamped xy coordinates are available. Pathfinder is simple to use, can automatically determine pool and platform geometry, generates heat maps, analyzes navigation with respect to multiple goal locations, and can be updated to accommodate future developments in spatial behavioral analyses. Given these features, Pathfinder may be a useful tool for studying how navigational strategies are regulated by the environment, depend on specific neural circuits, and are altered by pathology.

0090 Stage-Specific Sleep Disruption and its Effect on Spatial Navigational Memory

Abstract Introduction The mechanisms by which sleep disruption impact memory may depend on sleep stage, as rapid eye movement (REM) and slow wave sleep (SWS) differ in several significant ways, including degree of neuronal synchrony and frequency of cortical local field potential oscillations. Here we sought to examine the relationship between stage-specific disruption of sleep and its effect on spatial navigational memory. Methods 9 healthy adult subjects participated in this study which involved 3 in-lab polysomnograms (normal, REM-disruption, and SWS-disruption) accompanied by pre- and post-sleep functional neuroimaging of brain during a spatial navigational memory task. Graded auditory stimuli consisting of 0.5 second bursts of high-frequency tones (300-3000Hz) were used to disrupt sleep (REM/SWS) in real time. Primary metrics to ascertain the effect of these auditory tones on sleep were time in sleep stage (REM/SWS) as a % of total sleep time (TST), bout length. The primary metric for spatial navigational memory was %change in overnight completion time on a first-person-experience 3D maze task. Results Sleep macrostructure was normal during the normal night (TST:379.9±56.6 min; SWS:19.5±7.6%; REM:19.4±5.3%; mean±std). Stage-specific disruption of sleep was achieved using auditory tones during a) SWS-disruption condition (TST:388.9±47.4 mins; SWS:6.6±4.8%; REM:18.7±5.2%) and b) REM-disruption condition (TST:365.3±69.8 mins; SWS:17.1±7.7%; REM:12.1±6.6%). SWS-disruption reduced mean bout length of SWS as compared to no disruption (1.3±0.8 mins vs. 10.3±8.2 mins; p<0.01) and REM-disruption reduced mean bout length of REM as compared to no disruption (2.2±1.7 vs. 10.6±5.2 mins; p<0.01). When sleep was not disrupted, subjects achieved overnight improvements in performance (25.3±17%) which remained unchanged during REM-disruption (18.8±29.6%, p=0.5) and during SWS-disruption (38.8±24.4%; p=0.2). Morning psychomotor vigilance was also unaffected by condition. Conclusion Stage specific disruption of sleep can be achieved using graded auditory tones. While performance on a virtual 3D maze remain unchanged with stage specific sleep disruption, lower sample size may have limited our ability to detect the change. Activation patterns from functional neuroimaging that were acquired during the spatial navigation task may elucidate the interaction between stage-specific sleep disruption and performance. Support NIH R21AG059179

Functionally distinct high and low theta oscillations in the human hippocampus

Based on rodent models, researchers have theorized that the hippocampus supports episodic memory and navigation via the theta oscillation, a ~4–10 Hz rhythm that coordinates brain-wide neural activity. However, recordings from humans have indicated that hippocampal theta oscillations are lower in frequency and less prevalent than in rodents, suggesting interspecies differences in theta’s function. To characterize human hippocampal theta, we examine the properties of theta oscillations throughout the anterior–posterior length of the hippocampus as neurosurgical subjects performed a virtual spatial navigation task. During virtual movement, we observe hippocampal oscillations at multiple frequencies from 2 to 14 Hz. The posterior hippocampus prominently displays oscillations at ~8-Hz and the precise frequency of these oscillations correlates with the speed of movement, implicating these signals in spatial navigation. We also observe slower ~3 Hz oscillations, but these signals are more prevalent in the anterior hippocampus and their frequency does not vary with movement speed. Our results converge with recent findings to suggest an updated view of human hippocampal electrophysiology. Rather than one hippocampal theta oscillation with a single general role, high- and low-frequency theta oscillations, respectively, may reflect spatial and non-spatial cognitive processes.

Inactivation of the striatum in aged rats rescues their ability to learn a hippocampus-sensitive spatial navigation task.

Studies of age-related changes in learning and memory often focus on hippocampus-sensitive tasks and reveal age-associated impairments across numerous species and contexts. However, cognitive decline with advanced age is not all-encompassing; for example, forms of striatum-sensitive learning are conserved or enhanced with age. Under certain conditions, hippocampal and striatal memory systems function in opposition. In young adult rodents, disruption of one structure can enhance learning on tasks dependent on the other, suggesting that competitive interactions across memory systems contribute to learning and memory abilities. This report examines whether imbalances across memory systems might contribute to cognitive aging. We inactivated the striatum using central infusions of lidocaine (sodium channel blocker) prior to hippocampus-sensitive spatial (place) training in young (3-4-month-old) and old (24-25-month-old) F344 male rats. Consistent with prior work, vehicle-infused old rats exhibited place learning impairments relative to young rats. Additionally, striatal inactivation enhanced learning in old rats, but not young rats, abolishing the age-related impairment. These findings suggest that age-related declines in learning tasks thought to engage the hippocampus may stem from exaggerated interference from other memory systems and that interventions to target the striatum may reverse some age-related learning decrements.

Effects of aging on encoding of walking direction in the human brain

Human aging is characterized by impaired spatial cognition and reductions in the distinctiveness of category-specific fMRI activation patterns. Yet, little is known about age-related decline in neural distinctiveness of information that humans use when navigating spatial environments. Here, we asked whether neural tuning functions of walking direction are broadened in older versus younger adults. To test this idea, we developed a novel method that allowed us to investigate changes in fMRI-measured pattern similarity while participants navigated in different directions in a virtual spatial navigation task. We expected that directional tuning functions would be broader in older adults, and thus activation patterns that reflect neighboring directions would be less distinct as compared to non-adjacent directions. Because loss of distinctiveness leads to more confusions when information is read out by downstream areas, we analyzed predictions of a decoder trained on directional fMRI patterns and asked (1) whether decoder confusions between two directions increase proportionally to their angular similarity, (2) and how this effect may differ between age groups. Evidence for tuning-function-like signals was found in the retrosplenial complex and early visual cortex, reflecting the primarily visual nature of directional information in our task. Significant age differences in tuning width, however, were only found in early visual cortex, suggesting that less precise visual information could lead to worse directional signals in older adults. At the same time, only directional information encoded in RSC, but not visual cortex, correlated with memory on task. These results shed new light on neural mechanisms underlying age-related spatial navigation impairments and introduce a novel approach to measure tuning specificity using fMRI.

How cognitive and environmental constraints influence the reliability of simulated animats in groups.

Evolving in groups can either enhance or reduce an individual’s task performance. Still, we know little about the factors underlying group performance, which may be reduced to three major dimensions: (a) the individual’s ability to perform a task, (b) the dependency on environmental conditions, and (c) the perception of, and the reaction to, other group members. In our research, we investigated how these dimensions interrelate in simulated evolution experiments using adaptive agents equipped with Markov brains (“animats”). We evolved the animats to perform a spatial-navigation task under various evolutionary setups. The last generation of each evolution simulation was tested across modified conditions to evaluate and compare the animats’ reliability when faced with change. Moreover, the complexity of the evolved Markov brains was assessed based on measures of information integration. We found that, under the right conditions, specialized animats could be as reliable as animats already evolved for the modified tasks, and that reliability across varying group sizes correlated with evolved fitness in most tested evolutionary setups. Our results moreover suggest that balancing the number of individuals in a group may lead to higher reliability but also lower individual performance. Besides, high brain complexity was associated with balanced group sizes and, thus, high reliability under limited sensory capacity. However, additional sensors allowed for even higher reliability across modified environments without a need for complex, integrated Markov brains. Despite complex dependencies between the individual, the group, and the environment, our computational approach provides a way to study reliability in group behavior under controlled conditions. In all, our study revealed that balancing the group size and individual cognitive abilities prevents over-specialization and can help to evolve better reliability under unknown environmental situations.

Functional Connectivity of the Anterior and Posterior Hippocampus: Differential Effects of Glucose in Younger and Older Adults.

The hippocampus features structurally and functionally distinct anterior and posterior segments. Relatively few studies have examined how these change during aging or in response to pharmacological interventions. Alterations in hippocampal connectivity and changes in glucose regulation have each been associated with cognitive decline in aging. A distinct line of research suggests that administration of glucose can lead to a transient improvement in hippocampus-dependent memory. Here, we probe age, glucose and human cognition with a special emphasis on resting-state functional connectivity (rsFC) of the hippocampus along its longitudinal axis to the rest of the brain. Using a randomized, placebo-controlled, double-blind, crossover design 32 healthy adults (16 young and 16 older) ingested a drink containing 25 g glucose or placebo across two counter balanced sessions. They then underwent resting-state functional magnetic resonance imaging (rs-fMRI) and cognitive testing. There was a clear dissociation in the effects of glucose by age. Magnitude change in rsFC from posterior hippocampus (pHPC) to medial frontal cortex (mPFC) was correlated with individual glucose regulation and gains in performance on a spatial navigation task. Our results demonstrate that glucose administration can attenuate cognitive performance deficits in older adults with impaired glucose regulation and suggest that increases in pHPC-mPFC rsFC are beneficial for navigation task performance in older participants.

Spatial Navigation Is Distinctively Impaired in Persistent Postural Perceptual Dizziness.

Objective: To determine whether performance in a virtual spatial navigational task is poorer in persistent postural perceptual dizziness (PPPD) patients than in healthy volunteers and patients suffering other vestibular disorders.Methods: Subjects were asked to perform three virtual Morris water maze spatial navigational tasks: (i) with a visible target, (ii) then with an invisible target and a fixed starting position, and finally (iii) with an invisible target and random initial position. Data were analyzed using the cumulative search error (CSE) index.Results: While all subjects performed equally well with a visible target, the patients with PPPD (n = 19) performed poorer (p < 0.004) in the invisible target/navigationally demanding tasks (CSE median of 8) than did the healthy controls (n = 18; CSE: 3) and vestibular controls (n = 19; CSE: 4). Navigational performance in the most challenging setting allowed us to discriminate PPPD patients from controls with an area under the receiver operating characteristic curve of 0.83 (sensitivity 78.1%; specificity 83.3%). PPPD patients manifested more chaotic and disorganized search strategies, with more dispersion in the navigational pool than those of the non-PPPD groups (standard distance deviation of 0.97 vs. 0.46 in vestibular controls and 0.20 in healthy controls; p < 0.001).Conclusions: While all patients suffering a vestibular disorder had poorer navigational abilities than healthy controls did, patients with PPPD showed the worst performance, to the point that this variable allowed the discrimination of PPPD from non-PPPD patients. This distinct impairment in spatial navigation abilities offers new insights into PPPD pathophysiology and may also represent a new biomarker for diagnosing this entity.

Targeting Cannabinoid Receptor Activation and BACE-1 Activity Counteracts TgAPP Mice Memory Impairment and Alzheimer's Disease Lymphoblast Alterations.

Alzheimer's disease (AD), the leading cause of dementia in the elderly, is a neurodegenerative disorder marked by progressive impairment of cognitive ability. Patients with AD display neuropathological lesions including senile plaques, neurofibrillary tangles, and neuronal loss. There are no disease-modifying drugs currently available. With the number of affected individuals increasing dramatically throughout the world, there is obvious urgent need for effective treatment strategy for AD. The multifactorial nature of AD encouraged the development of multifunctional compounds, able to interact with several putative targets. Here, we have evaluated the effects of two in-house designed cannabinoid receptors (CB) agonists showing inhibitory actions on β-secretase-1 (BACE-1) (NP137) and BACE-1/butyrylcholinesterase (BuChE) (NP148), on cellular models of AD, including immortalized lymphocytes from late-onset AD patients. Furthermore, the performance of TgAPP mice in a spatial navigation task was investigated following chronic administration of NP137 and NP148. We report here that NP137 and NP148 showed neuroprotective effects in amyloid-β-treated primary cortical neurons, and NP137 in particular rescued the cognitive deficit of TgAPP mice. The latter compound was able to blunt the abnormal cell response to serum addition or withdrawal of lymphoblasts derived from AD patients. It is suggested that NP137 could be a good drug candidate for future treatment of AD.

MiR-195-Sirt3 Axis Regulates Angiotensin II-Induced Hippocampal Apoptosis and Learning Impairment in Mice.

ObjectiveApoptosis plays an essential role in cell development and aging, which is associated with a series of diseases, such as neurodegeneration. MircoRNAs exert important roles in the regulation of gene expression. As a stress-responsive deacetylase in mitochondria, sirtuin-3 (sirt3) is a key regulator for mitochondrial function and apoptosis. Also, miR-195 has been demonstrated to be involved in cell cycle and apoptosis. Therefore, this study aimed to investigate the effects of miR-195-sirt3 axis on angiotensin II (ANG II)-induced hippocampal apoptosis and behavioral influence.Materials and methodsANG II infusion was used to establish the hypertensive model in HT22 cells and 129S6/SvEvTac mice, respectively. TUNEL assay was used to evaluate the apoptosis level. Mitochondrial membrane potential (MMP) was measured to evaluate the mitochondrial property. Immunohistochemistry, RT-PCR, Western blotting, and luciferase reporter assay were conducted to determine the underlying molecular mechanism.ResultsThe results revealed that ANG II treatment promoted apoptosis in the hippocampal cells and tissues, along with increased sirt3 and decreased miR-195 expression. Silencing sirt3 by genetic engineering or siRNA reversed ANG II-induced hippocampal apoptosis. Sirt3 was identified as a direct target gene of miR-195. Forced expression of miR-195 could play counteractive roles in hippocampal apoptosis induced by ANG II. Furthermore, the behavioral assay demonstrated that ANG II-induced hippocampal apoptosis impaired the performance in the spatial navigation task, but not in the spatial memory task.ConclusionThe results suggested that miR-195-sirt3 axis plays an important role in the ANG II-induced hippocampal apoptosis via altering mitochondria-apoptosis proteins and mitochondria permeability and that hippocampal apoptosis is associated with impaired learning capability in hypertensive mice. This study provides insights into the molecular architecture of apoptosis-related neurodegenerative diseases.

P.172 Preliminary fMRI results exploring brain activity in a spatial navigation task in schizophrenia, Alzheimer's Disease, and healthy controls

P.172 Preliminary fMRI results exploring brain activity in a spatial navigation task in schizophrenia, Alzheimer's Disease, and healthy controls

A non-spatial account of place and grid cells based on clustering models of concept learning

One view is that conceptual knowledge is organized using the circuitry in the medial temporal lobe (MTL) that supports spatial processing and navigation. In contrast, we find that a domain-general learning algorithm explains key findings in both spatial and conceptual domains. When the clustering model is applied to spatial navigation tasks, so-called place and grid cell-like representations emerge because of the relatively uniform distribution of possible inputs in these tasks. The same mechanism applied to conceptual tasks, where the overall space can be higher-dimensional and sampling sparser, leading to representations more aligned with human conceptual knowledge. Although the types of memory supported by the MTL are superficially dissimilar, the information processing steps appear shared. Our account suggests that the MTL uses a general-purpose algorithm to learn and organize context-relevant information in a useful format, rather than relying on navigation-specific neural circuitry.