Amylovis-201 enhances physiological memory formation and rescues memory and hippocampal cell loss in a streptozotocin-induced Alzheimer's disease animal model

Alzheimer's disease is the most common neurodegenerative disease, and its treatment is lacking. In this work, we tested Amylovis-201, a naphthalene-derived compound, as a possible therapeutic candidate for the treatment of AD. For this purpose, we performed three experiments. In the first and third experiment, animals received a bilateral administration of streptozotocin and, starting 24 h after injection, a daily dose of Amylovis-201 (orally), for 17 days or for the whole time of the experiment respectively (28 days), after which learning and memory, as well as the number of hippocampal dentate gyrus cells, were assessed. In the second experiment, healthy animals received a single dose of Amylovis-201, 10 min or 5 h after the learning section to assess whether this substance could promote specific mechanisms involved in memory trace formation. Our data show that, administration of a single dose of Amylovis-201, 10 min after the end of training, but not at 5 h, produces a prolongation in memory duration, probably because it modulates specific mechanisms involved in memory trace consolidation. Furthermore, daily administration of Amylovis-201 to animals with bilateral intracerebroventricular injection of STZ produces a reduction in the loss of the hippocampus dentate gyrus cells and an improvement in spatial memory, probably because Amylovis-201 can interact with some of the protein kinases of the insulin signaling cascade, also involved in neural plasticity, and thereby halt or reverse some of the effects of STZ. Taking to account these results, Amylovis-201 is a good candidate for the therapeutic treatment of AD.

Enhanced NMDA receptor pathway and glutamate transmission in the hippocampal dentate gyrus mediate the spatial learning and memory impairment of obese rats

Obesity has been linked with the impairment of spatial memory and synaptic plasticity but the molecular mechanisms remained unidentified. Since glutamatergic transmission and NMDA receptor neural pathways in hippocampal dentate gyrus (DG) are essential in the learning and memory, we aimed to investigate glutamate (Glu) and NMDA receptor signaling of DG in spatial learning and memory in diet-induced obesity (DIO) rats. Spatial learning and memory were assessed via Morris water maze (MWM) test on control (Ctr) and DIO rats. Extracellular concentration of Glu in the DG was determined using in vivo microdialysis and HPLC. The protein expressions of NMDA receptor subunit 2B (NR2B), brain-derived neurotrophic factor (BDNF), the activation of calcium/calmodulin-dependent kinase II (CaMKII) and cAMP-response-element-binding protein (CREB) in the DG were observed by western blot. Spatial learning and memory were impaired in DIO rats compared to those of Ctr. NR2B expression was increased, while BDNF expression and CaMKII and CREB activation were decreased in DG of DIO rats. Extracellular concentration of Glu was increased in Ctr on the 3rd and 4th days of the MWM test, but significant further increment was observed in DIO rats. Microinjection of an NMDA antagonist (MK-801) into the DG reversed spatial learning and memory impairment. Such effects were accompanied by greater BDNF expression and CaMKII/CREB activation in the DG of DIO rats. In conclusion, the enhancement of Glu-NMDA receptor transmission in the hippocampal DG contributes to the impairment of spatial learning and memory in DIO rats, maybe via the modulation of CaMKII-CREB-BDNF signaling pathway.

Effects of estrogen on spatial navigation and memory

RATIONALE

Animal studies suggest that the so-called "female" hormone estrogen enhances spatial navigation and memory. This contradicts the observation that males generally out-perform females in spatial navigation and tasks involving spatial memory. A closer look at the vast number of studies actually reveals that performance differences are not so clear.

OBJECTIVES

To help clarify the unclear performance differences between men and women and the role of estrogen, we attempted to isolate organizational from activational effects of estrogen on spatial navigation and memory.

METHODS

In a double-blind, placebo-controlled study, we tested the effects of orally administered estradiol valerate (E2V) in healthy, young women in their low-hormone menstrual cycle phase, compared to healthy, young men. Participants performed several first-person, environmentally rich, 3-D computer games inspired by spatial navigation and memory paradigms in animal research.

RESULTS

We found navigation behavior suggesting that sex effects dominated any E2 effects with men performing better with allocentric strategies and women with egocentric strategies. Increased E2 levels did not lead to general improvements in spatial ability in either sex but to behavioral changes reflecting navigation flexibility.

CONCLUSION

Estrogen-driven differences in spatial cognition might be better characterized on a spectrum of navigation flexibility rather than by categorical performance measures or skills.

A hippocampus-accumbens code guides goal-directed appetitive behavior

The dorsal hippocampus (dHPC) is a key brain region for the expression of spatial memories, such as navigating towards a learned reward location. The nucleus accumbens (NAc) is a prominent projection target of dHPC and implicated in value-based action selection. Yet, the contents of the dHPC→NAc information stream and their acute role in behavior remain largely unknown. Here, we found that optogenetic stimulation of the dHPC→NAc pathway while mice navigated towards a learned reward location was both necessary and sufficient for spatial memory-related appetitive behaviors. To understand the task-relevant coding properties of individual NAc-projecting hippocampal neurons (dHPC→NAc), we used in vivo dual-color two-photon imaging. In contrast to other dHPC neurons, the dHPC→NAc subpopulation contained more place cells, with enriched spatial tuning properties. This subpopulation also showed enhanced coding of non-spatial task-relevant behaviors such as deceleration and appetitive licking. A generalized linear model revealed enhanced conjunctive coding in dHPC→NAc neurons which improved the identification of the reward zone. We propose that dHPC routes specific reward-related spatial and behavioral state information to guide NAc action selection.

Contribution of the medial entorhinal cortex to performance on the Traveling Salesperson Problem in rats

In order to successfully navigate through space, animals must rely on multiple cognitive processes, including orientation in space, memory of object locations, and navigational decisions based on that information. Although highly-controlled behavioral tasks are valuable for isolating and targeting specific processes, they risk producing a narrow understanding of complex behavior in natural contexts. The Traveling Salesperson Problem (TSP) is an optimization problem that can be used to study naturalistic foraging behaviors, in which subjects select routes between multiple baited targets. Foraging is a spontaneous, yet complex, behavior, involving decision-making, attention, course planning, and memory. Previous research found that hippocampal lesions in rats impaired TSP task performance, particularly on measures of spatial memory. Although traditional laboratory tests have shown the medial entorhinal cortex (MEC) to play an important role in spatial memory, if and how the MEC is involved in finding efficient solutions to the TSP remains unknown. In the current study, rats were trained on the TSP, learning to retrieve bait from targets in a variety of spatial configurations. After recovering from either an MEC lesion or control sham surgery, the rats were tested on eight new configurations. Our results showed that, similar to rats with hippocampal lesions, MEC-lesioned rats were impaired on measures of spatial memory, but not spatial decision-making, with greatest impairments on configurations requiring a global navigational strategy for selecting the optimal route. These findings suggest that the MEC is important for effective spatial navigation, especially when global cue processing is required.

Event-related theta and gamma band oscillatory dynamics during visuo-spatial sequence memory in younger and older adults

Visuo-spatial working memory (VSWM) for sequences is thought to be crucial for daily behaviors. Decades of research indicate that oscillations in the gamma and theta bands play important functional roles in the support of visuo-spatial working memory, but the vast majority of that research emphasizes measures of neural activity during memory retention. The primary aims of the present study were (1) to determine whether oscillatory dynamics in the Theta and Gamma ranges would reflect item-level sequence encoding during a computerized spatial span task, (2) to determine whether item-level sequence recall is also related to these neural oscillations, and (3) to determine the nature of potential changes to these processes in healthy cognitive aging. Results indicate that VSWM sequence encoding is related to later (∼700 ms) gamma band oscillatory dynamics and may be preserved in healthy older adults; high gamma power over midline frontal and posterior sites increased monotonically as items were added to the spatial sequence in both age groups. Item-level oscillatory dynamics during the recall of VSWM sequences were related only to theta-gamma phase amplitude coupling (PAC), which increased monotonically with serial position in both age groups. Results suggest that, despite a general decrease in frontal theta power during VSWM sequence recall in older adults, gamma band dynamics during encoding and theta-gamma PAC during retrieval play unique roles in VSWM and that the processes they reflect may be spared in healthy aging.

Metabolic dysfunction induced by HFD + L-NAME preferentially affects hippocampal mitochondria, impacting spatial memory in rats

High-fat diet-induced metabolic changes are not restricted to the onset of cardiovascular diseases, but also include effects on brain functions related to learning and memory. This study aimed to evaluate mitochondrial markers and function, as well as cognitive function, in a rat model of metabolic dysfunction. Eight-week-old male Wistar rats were subjected to either a control diet or a two-hit protocol combining a high fat diet (HFD) with the nitric oxide synthase inhibitor L-NAME in the drinking water. HFD plus L-NAME induced obesity, hypertension, and increased serum cholesterol. These rats exhibited bioenergetic dysfunction in the hippocampus, characterized by decreased oxygen (O2) consumption related to ATP production, with no changes in H2O2 production. Furthermore, OPA1 protein expression was upregulated in the hippocampus of HFD + L-NAME rats, with no alterations in other morphology-related proteins. Consistently, HFD + L-NAME rats showed disruption of performance in the Morris Water Maze Reference Memory test. The neocortex did not exhibit either bioenergetic changes or alterations in H2O2 production. Calcium uptake rate and retention capacity in the neocortex of HFD + L-NAME rats were not altered. Our results indicate that hippocampal mitochondrial bioenergetic function is disturbed in rats exposed to a HFD plus L-NAME, thus disrupting spatial learning, whereas neocortical function remains unaffected.

A Spatial Memory Deficit in Male But Not Female Rats After Neonatal Diazepam Exposure: A New Model for Developmental Sedative Neurotoxicity

BACKGROUND

Developmental anesthetic neurotoxicity is well described in animal models for GABAergic, sedating drugs. Here we investigate the role of the benzodiazepine, diazepam on spatial and recognition memory of young adult rats after neonatal exposure.

METHODS

On postnatal day 7, male (n = 30) and female (n = 30) rats were exposed to diazepam (30 mg/kg intraperitoneally) or vehicle. On postnatal day 42, animals started a series of behavioral tests including Barnes maze (spatial memory), object recognition battery (recognition memory), and open field and elevated plus maze (anxiety). In a separate cohort, blood gases were obtained from diazepam-exposed animals and compared to isoflurane-exposed animals (1 MAC for 4 hours).

RESULTS

Male animals exposed to diazepam had impaired performance in the Barnes maze and were unable to differentiate the goal quadrant from chance (1-sample t test; tdiazepam/male (14) = 1.49, P = .158). Female rats exposed to diazepam performed the same as the vehicle controls ( tdiazepam/female (12) = 3.4, P = .005, tvehicle/female (14) = 3.62, P = .003, tvehicle/male (13) = 4.76, P < .001). There were no statistical differences in either males or females in measures of recognition memory, anxiety, or locomotor activity in other behavioral tests. Physiologic measurements of arterial blood gases taken from animals under sedation with diazepam were much less aberrant than those exposed to the volatile anesthetic isoflurane by t test (pH diazepam [M = 7.56, standard deviation {SD} = 0.11] versus pH Isoflurane [M = 7.15, SD = 0.02], t (10) = 8.93, P < .001; Paco 2diazepam [M = 32.8 mm Hg, SD = 10.1] versus Paco 2Isoflurane [M = 91.8 mm Hg, SD = 5.8], t (10) = 8.93, P < .001).

CONCLUSIONS

The spatial memory results are consistent with volatile anesthetic suggesting a model in which development of the GABA system plays a critical role in determining susceptibility to behavioral deficits.

Positive modulation of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors differentially alters spatial learning and memory in juvenile rats younger and older than three weeks

Remarkable performance improvements occur at the end of the third postnatal week in rodents tested in various tasks that require navigation according to spatial context. While alterations in hippocampal function at least partially subserve this cognitive advancement, physiological explanations remain incomplete. Previously, we discovered that developmental modifications to hippocampal glutamatergic α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors in juvenile rats was related to more mature spontaneous alternation behavior in a symmetrical Y-maze. Moreover, a positive allosteric modulator of AMPA receptors enabled immature rats to alternate at rates seen in older animals, suggesting an excitatory synaptic limitation to hippocampal maturation. We then validated the Barnes maze for juvenile rats in order to test the effects of positive AMPA receptor modulation on a goal-directed spatial memory task. Here we report the effects of the AMPA receptor modulator, CX614, on spatial learning and memory in the Barnes maze. Similar to our prior report, animals just over 3 weeks of age display substantial improvements in learning and memory performance parameters compared to animals just under 3 weeks of age. A moderate dose of CX614 enabled immature animals to move more directly to the goal location, but only after 1 day of training. This performance improvement was observed on the second day of training with drug delivery or during a memory probe trial performed without drug delivery after the second day of training. Higher doses created more search errors, especially in more mature animals. Overall, CX614 provided modest performance benefits for immature rats in a goal-directed spatial memory task.

Buildup and release from proactive interference: The forward testing effect in children's spatial memory

Previous work has indicated that testing can enhance memory for subsequently studied new information by reducing proactive interference from previously studied information. Here, we examined this forward testing effect in children's spatial memory. Kindergartners (5-6 years) and younger (7-8 years) and older (9-10 years) elementary school children studied four successively presented 3 × 3 arrays, each composed of the same 9 objects. The children were asked to memorize the locations of the objects that differed across the four arrays. Following presentation of each of the first three arrays, memory for the object locations of the respective array was tested (testing condition) or the array was re-presented for additional study (restudy condition). Results revealed that testing Arrays 1 to 3 enhanced children's object location memory for Array 4 relative to restudying. Moreover, children in the testing condition were less likely to confuse Array 4 locations with previous locations, suggesting that testing reduces the buildup of proactive interference. Both effects were found regardless of age. Thus, the current findings indicate that testing is an effective means to resolve proactive interference and, in this way, to enhance children's learning and remembering of spatial information even before the time of school entry.

Intermittent working memory training during adulthood protects against age-related long-term spatial reference memory decline in rats

Engagement in cognitive activity in adulthood is one of the factors that enable successful cognitive aging, both in humans and rodents. However, some studies emphasize that the beneficial effect on cognition of such an activity may reflect carry over from one test situation to another, including memory for procedural aspects of the behavioral tasks, and thus question whether this effect can be limited to the trained cognitive domain or whether it can be transferred to an untrained ones. In the current study, we assessed whether adulthood intermittent working memory training has beneficial effect on long-term memory of aged rats using two very different test situations. To this aim, rats trained in a delayed non-matching to position task in operant box at 3 and 15 months of age were tested in a place learning task in water maze when they were 24 months. The two tasks differ with regard to the cognitive domain but also in their spatial ability requirement and the nature of the reinforcer used. During the memory tests, accuracy of the platform search indicated age-related impairment only in the aged-untrained group. Thus, intermittent training during adult life in a task involving working memory protects aged animals from the deleterious effects of aging on spatial reference memory. This result highlights the long-term beneficial effects of training on a working memory task on an untrained cognitive domain.

The effects of orlistat on oxidative stress, recognition memory, spatial memory and hippocampal tissue in experimentally induced obesity in rats

This study investigates the impact of orlistat on oxidative stress, spatial memory, recognition memory, and hippocampal tissue in obese rats. The study groups were divided into control, high fat diet-induced obese (HFDIO), HFDIO+orlistat (HFDIO+ORL) groups, each consisting of 8 animals. While control fed with standart diet, HFDIO and HFDIO+ORL fed with high-fat diets for 8 weeks to induce obesity. Then, ORL treated 10 mg/kg for 7 weeks, while control and HFDIO get water. At 16th week, novel object recognition (NOR) and Morris water maze (MWM) tests were performed. TNF-alpha, IL-1beta levels in hippocampal tissue, and total/native thiol/disulphide levels in serum were measured. TNF-alpha level of HFDIO was higher than control, while lower in HFDIO+ORL compared to HFDIO as like IL-1beta level. On the contrary, serum total thiol level was lower in HFDIO than control and higher in HFDIO+ORL compared to the HFDIO, while disulphide level was opposite of the total thiol levels. While recognition index was higher in HFDIO+ORL, in MWM, latency of finding platform in HFDIO was higher than control and latency of HFDIO+ORL was very similar to control in 2-4 days. The HFDIO group demonstrated decrease in time spent in platform zone compared to control, whereas time spent of the HFDIO+ORL was higher than HFDIO. Our study demonstrates that orlistat administration exerts beneficial effects on oxidative stress, spatial memory, recognition memory, and hippocampal tissue in obese rats. It shows that orlistat may have potential therapeutic implications for obesity-related cognitive impairments and hippocampal dysfunction.

Disruption of awake sharp-wave ripples does not affect memorization of locations in repeated-acquisition spatial memory tasks

Storing and accessing memories is required to successfully perform day-to-day tasks, for example for engaging in a meaningful conversation. Previous studies in both rodents and primates have correlated hippocampal cellular activity with behavioral expression of memory. A key role has been attributed to awake hippocampal replay - a sequential reactivation of neurons representing a trajectory through space. However, it is unclear if awake replay impacts immediate future behavior, gradually creates and stabilizes long-term memories over a long period of time (hours and longer), or enables the temporary memorization of relevant events at an intermediate time scale (seconds to minutes). In this study, we aimed to address the uncertainty around the timeframe of impact of awake replay by collecting causal evidence from behaving rats. We detected and disrupted sharp wave ripples (SWRs) - signatures of putative replay events - using electrical stimulation of the ventral hippocampal commissure in rats that were trained on three different spatial memory tasks. In each task, rats were required to memorize a new set of locations in each trial or each daily session. Interestingly, the rats performed equally well with or without SWR disruptions. These data suggest that awake SWRs - and potentially replay - does not affect the immediate behavior nor the temporary memorization of relevant events at a short timescale that are required to successfully perform the spatial tasks. Based on these results, we hypothesize that the impact of awake replay on memory and behavior is long-term and cumulative over time.

Efficient encoding of aversive location by CA3 long-range projections

Memorizing locations that are harmful or dangerous is a key capability of all organisms and requires an integration of affective and spatial information. In mammals, the dorsal hippocampus mainly processes spatial information, while the intermediate to ventral hippocampal divisions receive affective information via the amygdala. However, how spatial and aversive information is integrated is currently unknown. To address this question, we recorded the activity of hippocampal long-range CA3 axons at single-axon resolution in mice forming an aversive spatial memory. We show that intermediate CA3 to dorsal CA3 (i-dCA3) projections rapidly overrepresent areas preceding the location of an aversive stimulus due to a spatially selective addition of new place-coding axons followed by spatially non-specific stabilization. This sequence significantly improves the encoding of location by the i-dCA3 axon population. These results suggest that i-dCA3 axons transmit a precise, denoised, and stable signal indicating imminent danger to the dorsal hippocampus.

Context memory formed in medial prefrontal cortex during infancy enhances learning in adulthood

Adult behavior is commonly thought to be shaped by early-life experience, although episodes experienced during infancy appear to be forgotten. Exposing male rats during infancy to discrete spatial experience we show that these rats in adulthood are significantly better at forming a spatial memory than control rats without such infantile experience. We moreover show that the adult rats' improved spatial memory capability is mainly based on memory for context information during the infantile experiences. Infantile spatial experience increased c-Fos activity at memory testing during adulthood in the prelimbic medial prefrontal cortex (mPFC), but not in the hippocampus. Inhibiting prelimbic mPFC at testing during adulthood abolished the enhancing effect of infantile spatial experience on learning. Adult spatial memory capability only benefitted from spatial experience occurring during the sensitive period of infancy, but not when occurring later during childhood, and when sleep followed the infantile experience. In conclusion, the infantile brain, by a sleep-dependent mechanism, favors consolidation of memory for the context in which episodes are experienced. These representations comprise mPFC regions and context-dependently facilitate learning in adulthood.

Learning shapes the development of migratory behavior

How animals refine migratory behavior over their lifetime (i.e., the ontogeny of migration) is an enduring question with important implications for predicting the adaptive capacity of migrants in a changing world. Yet, our inability to monitor the movements of individuals from early life onward has limited our understanding of the ontogeny of migration. The exploration-refinement hypothesis posits that learning shapes the ontogeny of migration in long-lived species, resulting in greater exploratory behavior early in life followed by more rapid and direct movement during later life. We test the exploration-refinement hypothesis by examining how white storks (Ciconia ciconia) balance energy, time, and information as they develop and refine migratory behavior during the first years of life. Here, we show that young birds reduce energy expenditure during flight while also increasing information gain by exploring new places during migration. As the birds age and gain more experience, older individuals stop exploring new places and instead move more quickly and directly, resulting in greater energy expenditure during migratory flight. During spring migration, individuals innovated novel shortcuts during the transition from early life into adulthood, suggesting a reliance on spatial memory acquired through learning. These incremental refinements in migratory behavior provide support for the importance of individual learning within a lifetime in the ontogeny of long-distance migration.

Impairments in the early consolidation of spatial memories via group II mGluR agonism in the mammillary bodies

mGluR2 receptors are widely expressed in limbic brain regions associated with memory, including the hippocampal formation, retrosplenial and frontal cortices, as well as subcortical regions including the mammillary bodies. mGluR2/3 agonists have been proposed as potential therapeutics for neurological and psychiatric disorders, however, there is still little known about the role of these receptors in cognitive processes, including memory consolidation. To address this, we assessed the effect of the mGluR2/3 agonist, eglumetad, on spatial memory consolidation in both mice and rats. Using the novel place preference paradigm, we found that post-sample injections of eglumetad impaired subsequent spatial discrimination when tested 6 h later. Using the immediate early gene c-fos as a marker of neural activity, we showed that eglumetad injections reduced activity in a network of limbic brain regions including the hippocampus and mammillary bodies. To determine whether the systemic effects could be replicated with more targeted manipulations, we performed post-sample infusions of the mGluR2/3 agonist 2R,4R-APDC into the mammillary bodies. This impaired novelty discrimination on a place preference task and an object-in-place task, again highlighting the role of mGluR2/3 transmission in memory consolidation and demonstrating the crucial involvement of the mammillary bodies in post-encoding processing of spatial information.

A persistent prefrontal reference frame across time and task rules

Behavior can be remarkably consistent, even over extended time periods, yet whether this is reflected in stable or 'drifting' neuronal responses to task features remains controversial. Here, we find a persistently active ensemble of neurons in the medial prefrontal cortex (mPFC) of mice that reliably maintains trajectory-specific tuning over several weeks while performing an olfaction-guided spatial memory task. This task-specific reference frame is stabilized during learning, upon which repeatedly active neurons show little representational drift and maintain their trajectory-specific tuning across long pauses in task exposure and across repeated changes in cue-target location pairings. These data thus suggest a 'core ensemble' of prefrontal neurons forming a reference frame of task-relevant space for the performance of consistent behavior over extended periods of time.

Hippocampal subfield plasticity is associated with improved spatial memory

Physical exercise studies are generally underrepresented in young adulthood. Seventeen subjects were randomized into an intervention group (24.2 ± 3.9 years; 3 trainings/week) and 10 subjects into a passive control group (23.7 ± 4.2 years), over a duration of 6 months. Every two months, performance diagnostics, computerized spatial memory tests, and 3 Tesla magnetic resonance imaging were conducted. Here we find that the intervention group, compared to controls, showed increased cardiorespiratory fitness, spatial memory performance and subregional hippocampal volumes over time. Time-by-condition interactions occurred in right cornu ammonis 4 body and (trend only) dentate gyrus, left hippocampal tail and left subiculum. Increases in spatial memory performance correlated with hippocampal body volume changes and, subregionally, with left subicular volume changes. In conclusion, findings support earlier reports of exercise-induced subregional hippocampal volume changes. Such exercise-related plasticity may not only be of interest for young adults with clinical disorders of hippocampal function, but also for sedentary normal cohorts.

Spatial working memory in a disappearing object task is impaired in female but not male dogs with chronic osteoarthritis

Chronic pain in humans is associated with impaired working memory but it is not known whether this is the case in long-lived companion animals, such as dogs, who are especially vulnerable to developing age-related chronic pain conditions. Pain-related impairment of cognitive function could have detrimental effects on an animal's ability to engage with its owners and environment or to respond to training or novel situations, which may in turn affect its quality of life. This study compared the performance of 20 dogs with chronic pain from osteoarthritis and 21 healthy control dogs in a disappearing object task of spatial working memory. Female neutered osteoarthritic dogs, but not male neutered osteoarthritic dogs, were found to have lower predicted probabilities of successfully performing the task compared to control dogs of the same sex. In addition, as memory retention interval in the task increased, osteoarthritic dogs showed a steeper decline in working memory performance than control dogs. This suggests that the effects of osteoarthritis, and potentially other pain-related conditions, on cognitive function are more clearly revealed in tasks that present a greater cognitive load. Our finding that chronic pain from osteoarthritis may be associated with impaired working memory in dogs parallels results from studies of human chronic pain disorders. That female dogs may be particularly prone to these effects warrants further investigation.

Rat spatial memory and foraging on dual radial mazes

Three experiments are reported that used a new test of spatial memory in rats. The apparatus used was dual eight-arm radial mazes that were connected at one arm of each maze, with a start arm and doors to each maze. Rats could be forced to go to one maze or the other or could make a free choice between mazes. In Experiment 1, rats formed reference memory for the arm containing food on one maze but had food randomly placed on different arms over trials on the other maze. In Experiment 2, rats formed working memory for the arm containing food on one maze but not the other. In Experiment 3, food location changed randomly among trials on both mazes, but one maze contained a cue for the location of food. Rats used reference and working memory to go directly to the food arm on one maze but found food only after searching several arms on the other maze. Most importantly, when given free-choice trials rats developed a significant preference for the maze where they knew the location of food reward or found the cue indicating the location of reward. We suggest these findings may be best interpreted by rats applying two successive rules: (1) choose the maze that leads to the most immediate reward, and (2) use extramaze or intramaze cues to find reward location on the maze.

Sex-specific variations in spatial reference memory acquisition: Insights from a comprehensive behavioral test battery in C57BL/6JRj mice

Sex differences in declarative memory are described in humans, revealing a female or a male advantage depending on the task. Specifically, spatial memory (i.e., spatial navigation) is typically most efficient in men. This sexual dimorphism has been replicated in male rats but not clearly in mice. In this study, sex differences in spatial memory were assessed in thirty-six C57BL/6 J mice (Janvier Labs; i.e., C57BL/6JRj mice), a widely used mouse substrain. Both male and female mice (12 weeks-old) were subjected to standard behavioral paradigms: the elevated plus maze, the open field test, the novel object and place tests, the forced swimming test, and the water maze test for spatial navigation. Across assessment, no sex differences were found in measures of locomotor activity, emotional and behavioral responses, and object and place recognition memories. In the water maze, male mice were faster in learning the platform location in the reference memory training and used more spatial strategies during the first training days. However, both sexes reached a similar asymptotic performance and performed similarly in the probe trial for long-term memory consolidation. No sex differences were found in the cued training, platform inversion sessions, or spatial working memory sessions. Hippocampal expression of the brain-derived neurotrophic factor was similar in both sexes, either in basal conditions or after performing the behavioral training battery. Importantly, female mice were not more variable than males in any measure analyzed. This outcome encourages the investigation of sex differences in animal models and the usefulness of including female mice in behavioral research.

Barnes maze test for spatial memory: A new, sensitive scoring system for mouse search strategies

The Barnes maze is a task used to assess spatial learning and memory in rodents. It requires animals to learn the position of a hole that can be used as an escape from a bright and open arena. The often-used parameters of latency and path length to measure learning and memory do not reflect the different navigation strategies chosen by the animals. Here, we propose an 11-point scoring scheme to classify the search strategies developed by the animals during the initial training as well as after the change of the escape target to a new position. Strategy scores add an important dimension to time and path length to assess the behavior in this popular maze.

Continuous high-frequency repetitive transcranial magnetic stimulation at extremely low intensity affects exploratory behavior and spatial cognition in mice

High-frequency repetitive transcranial magnetic stimulation (HF-rTMS) has been shown to be effective for cognitive intervention. However, whether HF-rTMS with extremely low intensity could influence cognitive functions is still under investigation. The present study systematically investigated the effects of continuous 40 Hz and 10 Hz rTMS on cognition in young adult mice at extremely low intensity (10 mT and 1 mT) for 11 days (30 min/day). Cognitive functions were assessed using diverse behavioral tasks, including the open field, Y-maze, and Barnes maze paradigms. We found that 40 Hz rTMS significantly impaired exploratory behavior and spatial memory in both 10 mT and 1 mT conditions. In addition, 40 Hz rTMS induced remarkably different effects on exploratory behavior between 10 mT and 1mT, compared to 10 Hz stimulation. Our results indicate that extremely low intensity rTMS can significantly alter cognitive performance depending on intensity and frequency, shedding light on the understanding of the mechanism of rTMS effects.

A clinical 3D pointing test differentiates spatial memory deficits in dementia and bilateral vestibular failure

BACKGROUND

Deficits in spatial memory, orientation, and navigation are often neglected early signs of cognitive impairment or loss of vestibular function. Real-world navigation tests require complex setups. In contrast, simple pointing at targets in a three-dimensional environment is a basic sensorimotor ability which provides an alternative measure of spatial orientation and memory at bedside. The aim of this study was to test the reliability of a previously established 3D-Real-World Pointing Test (3D-RWPT) in patients with cognitive impairment due to different neurodegenerative disorders, bilateral vestibulopathy, or a combination of both compared to healthy participants.

METHODS

The 3D-RWPT was performed using a static array of targets in front of the seated participant before and, as a transformation task, after a 90-degree body rotation around the yaw-axis. Three groups of patients were enrolled: (1) chronic bilateral vestibulopathy (BVP) with normal cognition (n = 32), (2) cognitive impairment with normal vestibular function (n = 28), and (3) combined BVP and cognitive impairment (n = 9). The control group consisted of age-matched participants (HP) without cognitive and vestibular deficits (n = 67). Analyses focused on paradigm-specific mean angular deviation of pointing in the azimuth (horizontal) and polar (vertical) spatial planes, of the preferred pointing strategy (egocentric or allocentric), and the resulting shape configuration of the pointing array relative to the stimulus array. Statistical analysis was performed using age-corrected ANCOVA-testing with Bonferroni correction and correlation analysis using Spearman's rho.

RESULTS

Patients with cognitive impairment employed more egocentric pointing strategies while patients with BVP but normal cognition and HP used more world-based solutions (pBonf 5.78 × 10-3**). Differences in pointing accuracy were only found in the azimuth plane, unveiling unique patterns where patients with cognitive impairment showed decreased accuracy in the transformation tasks of the 3D-RWPT (pBonf < 0.001***) while patients with BVP struggled in the post-rotation tasks (pBonf < 0.001***). Overall azimuth pointing performance was still adequate in some patients with BVP but significantly decreased when combined with a cognitive deficit.

CONCLUSION

The 3D-RWPT provides a simple and fast measure of spatial orientation and memory. Cognitive impairment often led to a shift from world-based allocentric pointing strategy to an egocentric performance with less azimuth accuracy compared to age-matched controls. This supports the view that cognitive deficits hinder the mental buildup of the stimulus pattern represented as a geometrical form. Vestibular hypofunction negatively affected spatial memory and pointing performance in the azimuth plane. The most severe spatial impairments (angular deviation, figure frame configuration) were found in patients with combined cognitive and vestibular deficits.

A consistent map in the medial entorhinal cortex supports spatial memory

The medial entorhinal cortex (MEC) is hypothesized to function as a cognitive map for memory-guided navigation. How this map develops during learning and influences memory remains unclear. By imaging MEC calcium dynamics while mice successfully learned a novel virtual environment over ten days, we discovered that the dynamics gradually became more spatially consistent and then stabilized. Additionally, grid cells in the MEC not only exhibited improved spatial tuning consistency, but also maintained stable phase relationships, suggesting a network mechanism involving synaptic plasticity and rigid recurrent connectivity to shape grid cell activity during learning. Increased c-Fos expression in the MEC in novel environments further supports the induction of synaptic plasticity. Unsuccessful learning lacked these activity features, indicating that a consistent map is specific for effective spatial memory. Finally, optogenetically disrupting spatial consistency of the map impaired memory-guided navigation in a well-learned environment. Thus, we demonstrate that the establishment of a spatially consistent MEC map across learning both correlates with, and is necessary for, successful spatial memory.

Impoverished details with preserved gist in remote and recent spatial memory following hippocampal and fornix lesions

INTRODUCTION

Cognitive Map Theory predicts that the hippocampus (HPC) plays a specialized, time-invariant role in supporting allocentric spatial memory, while Standard Consolidation Theory makes the competing prediction that the HPC plays a time-limited role, with more remote memories gaining independence of HPC function. These theories, however, are largely informed by the results of laboratory-based tests that are unlikely to simulate the demands of representing real-world environments in humans. Validation of these theories is further limited by an overall focus on spatial memory of newly encountered environments and on individuals with extensive lesions to the HPC and to surrounding medial temporal lobe (MTL) regions. The current study incorporates naturalistic tests of spatial memory based on recently and remotely encountered environments navigated by individuals with lesions to the HPC/MTL or that are limited to the HPC's major output, the fornix.

METHODS

Four participants with bilateral HPC/MTL and/or fornix lesions drew sketch maps of recently and remotely experienced neighbourhoods and houses. Tests of the appearance, distances, and routes between landmarks from the same real-world environments were also administered. Performance on the tasks was compared to that of control participants closely matched in terms of exposure to the same neighbourhoods and home environments as well as to actual maps.

RESULTS

The performance of individuals with fornix/MTL lesions was found to be largely comparable to that of controls on objective tests of spatial memory, other than one case who was impaired on remote and recent conditions for several tasks. The nature of deficits in recent and remote spatial memory were further revealed on house floorplan drawings, which contained spatial distortions, room/structure transpositions, and omissions, and on neighbourhood sketch maps, which were intact in terms of overall layout but sparse in details such as landmarks.

CONCLUSION

Lab-based tests of spatial memory of newly learned environments are unlikely to fully capture patterns of spared and impaired representations of real-world environments (e.g., peripheral features, configurations). Naturalistic tasks, including generative drawing tasks, indicate that contrary to Cognitive Map Theory, neither HPC nor MTL are critical for allocentric gross representations of large-scale environments. Conversely, the HPC appears critical for representing detailed spatial information of local naturalistic environments and environmental objects regardless of the age of the memory, contrary to Standard Consolidation Theory.

Potential Alzheimer's early biomarkers in a transgenic rat model and benefits of diazoxide/dibenzoylmethane co-treatment on spatial memory and AD-pathology

Alzheimer's disease (AD) is the major form of dementia prevalent in older adults and with a high incidence in females. Identification of early biomarkers is essential for preventive intervention to delay its progression. Furthermore, due to its multifactorial nature, a multi-target approach could be therapeutically beneficial. Our studies included 4- (pre-pathology) and 11-month (mild-pathology) TgF344-AD rats, a transgenic Alzheimer's model that exhibits age-dependent AD progression. We identified two potential early biomarker genes for AD, early growth response 2 (EGR2) and histone 1H2AA (HIST1H2AA), in the hippocampus of 4-month females. Out of 17,168 genes analyzed by RNA sequencing, expression of these two genes was significantly altered in 4-month TgF344-AD rats compared to wild-type littermates. We also evaluated co-treatment with diazoxide (DZ), a potassium channel activator, and dibenzoylmethane (DIB), which inhibits eIF2α-P activity, on TgF344-AD and wild-type rats. DZ/DIB-treatment mitigated spatial memory deficits and buildup of hippocampal Aβ plaques and tau PHF in 11-month TgF344-AD rats but had no effect on wild-type littermates. To our knowledge, this preclinical study is the first to report EGR2 and HIST1H2AA as potential AD biomarkers in females, and the benefits of DZ/DIB-treatment in AD. Evaluations across multiple AD-related models is warranted to corroborate our findings.

Forty-Hertz audiovisual stimulation does not have a promoting effect on visual threshold and visual spatial memory

Previous research has demonstrated that 40-Hz audiovisual stimulation can improve pathological conditions and promote cognitive function in mouse models of Alzheimer's disease. However, limited research has been conducted on humans, and the results have been inconsistent. In our study, we divided participants into an experimental group and a control group to investigate whether 40-Hz stimulation could enhance performance in visual threshold tasks and working memory task. In Experiment 1, we used a light bulb as the stimulus source and found a general practice effect, but no difference between the groups. In Experiment 2, we used a computer screen as the stimulus source and set the stimulation frequency to 48 Hz. In Experiment 3 , we used a computer screen and audio as stimulus sources, simultaneously applying a 40-Hz stimulation to both visual and auditory modalities. Both experiments only revealed the disappearance of practice effects in the 40-Hz (48-Hz) group. Experiment 4 focused on testing visual spatial memory, but did not identify any significant differences between or within groups. In Experiment 5, we tested various visual spatial frequencies; yet again, no significant differences were found. Based on the comprehensive results, we conclude that a 40-Hz stimulation does not have a promoting effect on visual threshold or visual spatial memory.

Repeated pre-exposure to morphine inhibited the amnesic effect of ethanol on spatial memory: Involvement of CaMKII and BDNF

Evidence has suggested that addiction and memory systems are related, but the signaling cascades underlying this interaction have not been completelyealed yet. The importance of calcium-calmodulin-dependent protein kinase II (CaMKII) and brain-derived neurotrophic factor (BDNF) in the memory processes and also in drug addiction has been previously established. In this present investigation, we examined the effects of repeated morphine pretreatment on impairment of spatial learning and memory acquisition induced by systemic ethanol administration in adult male rats. Also, we assessed how these drug exposures influence the expression level of CaMKII and BDNF in the hippocampus and amygdala. Animals were trained by a single training session of 8 trials, and a probe test containing a 60-s free-swim without a platform was administered 24 h later. Before training trials, rats were treated with a once-daily subcutaneous morphine injection for 3 days followed by a 5-day washout period. The results showed that pre-training ethanol (1 g/kg) impaired spatial learning and memory acquisition and down-regulated the mRNA expression of CaMKII and BDNF. The amnesic effect of ethanol was suppressed in morphine- (15 mg/kg/day) pretreated animals. Furthermore, the mRNA expression level of CaMKII and BDNF increased significantly following ethanol administration in morphine-pretreated rats. Conversely, this improvement in spatial memory acquisition was prevented by daily subcutaneous administration of naloxone (2 mg/kg) 15 min prior to morphine administration. Our findings suggest that sub-chronic morphine treatment reverses ethanol-induced spatial memory impairment, which could be explained by modulating CaMKII and BDNF mRNA expressions in the hippocampus and amygdala.

Chronic Pb exposure impairs learning and memory abilities by inhibiting excitatory projection neuro-circuit of the hippocampus in mice

Lead (Pb) is an environmental neurotoxic metal. Chronic Pb exposure causes behavioral changes in humans and rodents, such as dysfunctional learning and memory. Nevertheless, it is not clear whether Pb exposure disrupts the neural circuit. Thus, here we aim at investigating the effects the chronic Pb exposure on neural-behavioral and neural circuits in mice from prenatal to postnatal day (PND) 63. Pregnant mice and their male offspring were treated with Pb (150 ppm) until postnatal day 63. In this study, several behavior tests and Golgi-Cox staining methods were used to assess spatial memory ability and synaptogenesis. Virus-based tracing systems and immunohistochemistry assays were used to test the relevance of chronic Pb exposure with disrupted neural circuits. The behavioral experiments and Golgi-Cox staining results showed that Pb exposure impaired spatial memory and spine density in mice. The virus tracing results revealed that the Entorhinal cortex (EC) neurons could be directly projected to Cornuammonis 1 (CA1) and Dentate gyrus (DG), forming a critical circuit inhibited, in either a direct or indirect way, by Pb invasion. In addition, excitatory neural input from EC（labeled with CaMKII）to CA1 and DG was significantly attenuated by Pb exposure. In conclusion, our data indicated that Pb significantly impaired the excitatory connections from EC to the hippocampus (CA1 and DG), providing a novel neuro-circuitry basis for Pb neurotoxicity.

Neurodevelopment effects of early life bisphenol-A exposure on visual memory: Insights into recovery dynamics

Bisphenol A (BPA), a ubiquitous endocrine disruptor, is implicated in the cognitive deficits observed in both children and animals. Especially, BPA-induced spatial memory deterioration during the whole development phase of rodents has been well delineated. However, whether BPA exposure on the different development phases exerts similar effects on the prefrontal cortex (PFC) dependent visual memory is still elusive. Here, we chose two exposure windows, the whole gestation and lactation phases (E0∼P21) and the whole juvenile and adolescent phases (P22∼P60), for exposing rats to BPA. The visual memory of those rats was accessed by object recognition testing in the open field after BPA exposure and a constant recovery interval. The results revealed a substantial decline of visual memory under both exposure conditions, accompanied by an increase in anxiety-like behavior in BPA-exposed rats. Notably, after a 20-day recovery period, those behavioral changes induced by BPA exposure during P22∼60, not E0∼P21, were reversed compared to the control rats. According to morphological analysis of those rats after recovery, we found that the spine density of pyramidal neurons in the PFC were significant decreased in rats with BPA exposure during E0∼P21 and there was no difference between rats with or without BPA exposure during P22∼P60. Additionally, a similar change trend in excitatory receptors expression was observed under both exposure conditions. After an additional 20 days of recovery, the behavioral changes in rats with perinatal BPA exposure reverted to the normal status. Our present findings illuminate the dynamic effects of BPA on PFC-dependent functions across two crucial early developmental stages of life.

Mission impossible? Spatial context relearning following a target relocation event depends on cue predictiveness

Visual search for a target is faster when the spatial layout of distractors is repeatedly encountered, illustrating that statistical learning of contextual invariances facilitates attentional guidance (contextual cueing; Chun & Jiang, 1998, Cognitive Psychology, 36, 28-71). While contextual learning is usually relatively efficient, relocating the target to an unexpected location (within an otherwise unchanged search layout) typically abolishes contextual cueing and the benefits deriving from invariant contexts recover only slowly with extensive training (Zellin et al., 2014, Psychonomic Bulletin & Review, 21(4), 1073-1079). However, a recent study by Peterson et al. (2022, Attention, Perception, & Psychophysics, 84(2), 474-489) in fact reported rather strong adaptation of spatial contextual memories following target position changes, thus contrasting with prior work. Peterson et al. argued that previous studies may have been underpowered to detect a reliable recovery of contextual cueing after the change. However, their experiments also used a specific display design that frequently presented the targets at the same locations, which might reduce the predictability of the contextual cues thereby facilitating its flexible relearning (irrespective of statistical power). The current study was a (high-powered) replication of Peterson et al., taking into account both statistical power and target overlap in context-memory adaptation. We found reliable contextual cueing for the initial target location irrespective of whether the targets shared their location across multiple displays, or not. However, contextual adaptation following a target relocation event occurred only when target locations were shared. This suggests that cue predictability modulates contextual adaptation, over and above a possible (yet negligible) influence of statistical power.

Hippocampal-prefrontal high-gamma flow during performance of a spatial working memory

Working memory refers to a system that provides temporary storage and manipulation of the information necessary for complex cognitive tasks. The prefrontal cortex (PFC) and hippocampus (HPC) are major structures contributing to working memory. Accumulating evidence suggests that the HPC-PFC interactions are critical for the successful execution of working memory tasks. Nevertheless, the directional information transmission within the HPC-PFC pathway remains unclear. Using simultaneous multi-electrode recordings, we recorded local field potentials (LFPs) from the medial prefrontal cortex (mPFC) and ventral hippocampus (vHPC) while the rats performed a spatial working memory task in a Y-maze. The directionality of functional interactions between mPFC and vHPC was assessed using the phase-slope index (PSI). Our findings revealed a frequency-specific oscillatory synchrony in the two regions during the spatial working memory task. Furthermore, an increased high-gamma flow from vHPC to mPFC manifested exclusively during correctly performed trials, not observed during incorrect ones. This suggests that the enhanced high-gamma flow reflects behavioral performance in working memory. Consequently, our results indicate an major role of directional frequency-specific communication in the hippocampal-frontal circuit during spatial working memory, providing a potential mechanism for working memory.

Manipulating objects during learning shrinks the global scale of spatial representations in memory: a virtual reality study

Goal-directed approaches to perception usually consider that distance perception is shaped by the body and its potential for interaction. Although this phenomenon has been extensively investigated in the field of perception, little is known about the effect of motor interactions on memory, and how they shape the global representation of large-scale spaces. To investigate this question, we designed an immersive virtual reality environment in which participants had to learn the positions of several items. Half of the participants had to physically (but virtually) grab the items with their hand and drop them at specified locations (active condition). The other half of the participants were simply shown the items which appeared at the specified position without interacting with them (passive condition). Half of the items used during learning were images of manipulable objects, and the other half were non manipulable objects. Participants were subsequently asked to draw a map of the virtual environment from memory, and to position all the items in it. Results show that active participants recalled the global shape of the spatial layout less precisely, and made more absolute distance errors than passive participants. Moreover, global scaling compression bias was higher for active participants than for passive participants. Interestingly, manipulable items showed a greater compression bias compared to non-manipulable items, yet they had no effect on correlation scores and absolute non-directional distance errors. These results are discussed according to grounded approaches of spatial cognition, emphasizing motor simulation as a possible mechanism for position retrieval from memory.

Precision in spatial working memory examined with mouse pointing

The capacity of visuospatial working memory (VSWM) is limited. However, there is continued debate surrounding the nature of this capacity limitation. The resource model (Bays et al., 2009) proposes that VSWM capacity is limited by the precision with which visuospatial features can be retained. In one of the few studies of spatial working memory, Schneegans and Bays (2016) report that memory guided pointing responses show a monotonic decrease in precision as set size increases, consistent with resource models. Here we report two conceptual replications of this study that use mouse responses rather than pointing responses. Overall results are consistent with the resource model, as there was an exponential increase in localisation error and monotonic increases in the probability of misbinding and guessing with increases in set size. However, an unexpected result of Experiment One was that, unlike Schneegans and Bays (2016), imprecision did not increase between set sizes of 2 and 8. Experiment Two replicated this effect and ruled out the possibility that the invariance of imprecision at set sizes greater than 2 was a product of oculomotor strategies during recall. We speculate that differences in imprecision are related to additional visuomotor transformations required for memory-guided mouse localisation compared to memory-guided manual pointing localisation. These data demonstrate the importance of considering the nature of the response modality when interpreting VSWM data.

Morin improves learning and memory in healthy adult mice

BACKGROUND

Morin is a flavonoid found in many edible fruits. The hippocampus and entorhinal cortex play crucial roles in memory formation and consolidation. This study aimed to characterize the effect of morin on recognition and space memory in healthy C57BL/6 adult mice and explore the underlying molecular mechanism.

METHODS

Morin was administered i.p. at 1, 2.5, and 5 mg/kg/24 h for 10 days. The Morris water maze (MWM), novel object recognition, novel context recognition, and tasks were conducted 1 day after the last administration. The mice's brains underwent histological characterization, and their protein expression was examined using immunohistochemistry and Western blot techniques.

RESULTS

In the MWM and novel object recognition tests, mice treated with 1 mg/kg of morin exhibited a significant recognition index increase compared to the control group. Besides, they demonstrated faster memory acquisition during MWM training. Additionally, the expression of pro-brain-derived neurotrophic factor (BDNF), BDNF, and postsynaptic density protein 95 proteins in the hippocampus of treated mice showed a significant increase. In the entorhinal cortex, only the pro-BDNF increased. Morin-treated mice exhibited a significant increase in the hippocampus's number and length of dendrites.

CONCLUSION

This study shows that morin improves recognition memory and spatial memory in healthy adult mice.

The Role of the Cerebellum in Visual-Spatial Memory in Pediatric Posterior Fossa Tumor Survivors

The cerebellum is involved in motor and non-motor functions. Cerebellar lesions can underlie the disruption of various executive functions. The violation of executive functions in cerebellar lesions is a serious problem, since children, after completing treatment, must return to school, finish their education, and get a profession. One of the important executive functions is working memory, which contributes to academic success. Deficits of verbal working memory in cerebellar tumors have been studied, in contrast to visual-spatial working memory. To assess this issue, 101 patients who survived cerebellar tumors and 100 healthy control subjects performed a visual-spatial working memory test. As a result, in children who survived cerebellar tumors, visual-spatial working memory is impaired compared to the control group. Moreover, with age, and hence the time since the end of treatment, the number of elements that children can retain in visual-spatial working memory increases, but still remains smaller compared to the control group. Our findings complement the idea of cerebellar involvement in visual-spatial working memory and suggest that it is disrupted by cerebellar lesions in children.

What is it like to do a visuo-spatial working memory task: A qualitative phenomenological study of the visual span task

Working memory is typically measured with specifically designed psychological tasks. When evaluating the validity of working memory tasks, we commonly focus on the reliability of the outcome measurements. Only rarely do we focus on how participants experience these tasks. Accounting for lived experience of working memory task may help us better understand variability in working memory performance and conscious experience in general. We replicated recently established protocols for the phenomenological investigation of working memory using the visual span task. We collected subjective reports from eighteen healthy participants (10 women) aged 21 to 35 years. We observed that working memory can be phenomenologically characterized at three different time scales: background feelings, strategies, and tactics. On the level of tactics, we identified transmodality (i.e., how one modality of lived experience can be transformed into another one) as the central phenomenological dynamic at play during working memory task performance.

Strengthening of alpha synchronization is a neural correlate of cognitive transfer

Cognitive training can lead to improvements in both task-specific strategies and general capacities, such as visuo-spatial working memory (VSWM). The latter emerge slowly and linearly throughout training, in contrast to strategy where changes typically occur within the first days of training. Changes in strategy and capacity have not been separated in prior neuroimaging studies. Here, we used a within-participants design with dense temporal sampling to capture the time dynamics of neural mechanisms associated with change in capacity. In four participants, neural activity was recorded with magnetoencephalography on seven occasions over two months of visuo-spatial working memory training. During scanning, the participants performed a trained visuo-spatial working memory task, a transfer task, and a control task. First, we extracted an individual visuo-spatial working memory-load-dependent synchronization network for each participant. Next, we identified linear changes over time in the network, congruent with the temporal dynamics of capacity change. Three out of four participants showed a gradual strengthening of alpha synchronization. Strengthening of the same connections was also found in the transfer task but not in the control task. This suggests that cognitive transfer occurs through slow, gradual strengthening of alpha synchronization between cortical regions that are vital for both the trained task and the transfer task.

The neural correlates of memory integration in value-based decision-making during human spatial navigation

In daily life, we often make decisions based on relative value of the options, and we often derive these values from segmenting or integrating the outcomes of past episodes in memory. The neural correlates involved in value-based decision-making have been extensively studied in the literature, but few studies have investigated this topic in decisions that require segmenting or integrating episodic memory from related sources, and even fewer studies examine it in the context of spatial navigation. Building on the computational models from our previous studies, the current study investigates the neural substrates involved in decisions that require people either segment or integrate wayfinding outcomes involving different goals, across virtual spatial navigation tasks with differing demands. We find that when decisions require computation of spatial distances for navigation options, but also evaluation of one's prior spatial navigation ability with the task, the estimated value of navigational choices (EV) modulates neural activity in the dorsomedial prefrontal (dmPFC) cortex and ventrolateral prefrontal (vlFPC) cortex. However, superior parietal cortex tracked EV when decision-making tasks only require spatial distance memory but not evaluation of spatial navigation ability. Our findings reveal divergent neural substrates of memory integration in value-based decision-making under different spatial processing demands.

Voluntary exercise during puberty promotes spatial memory and hippocampal DG/CA3 synaptic transmission in mice

Physical exercise has been shown to have an impact on memory and hippocampal function across different age groups. Nevertheless, the influence and mechanisms underlying how voluntary exercise during puberty affects memory are still inadequately comprehended. This research aims to examine the impacts of self-initiated physical activity throughout adolescence on spatial memory. Developing mice were exposed to a 4-wk voluntary wheel running exercise protocol, commencing at the age of 30 d. After engaging in voluntary wheel running exercise during development, there was an enhancement in spatial memory. Moreover, hippocampal dentate gyrus and CA3 neurons rather than CA1 neurons exhibited an increase in the miniature excitatory postsynaptic currents and miniature inhibitory postsynaptic currents. In addition, there was an increase in the expression of NR2A/NR2B subunits of N-methyl-D-aspartate receptors and α1GABAA subunit of gamma-aminobutyric acid type A receptors, as well as dendritic spine density, specifically within dentate gyrus and CA3 regions rather than CA1 region. The findings suggest that voluntary exercise during development can enhance spatial memory in mice by increasing synapse numbers and improving synaptic transmission in hippocampal dentate gyrus and CA3 regions, but not in CA1 region. This study sheds light on the neural mechanisms underlying how early-life exercise improves cognitive function.

Curcumin Mitigates the High-Fat High-Sugar Diet-Induced Impairment of Spatial Memory, Hepatic Metabolism, and the Alteration of the Gut Microbiome in Alzheimer's Disease-Induced (3xTg-AD) Mice

The escalating prevalence of metabolic diseases and an aging demographic has been correlated with a concerning rise in Alzheimer's disease (AD) incidence. This study aimed to access the protective effects of curcumin, a bioactive flavonoid from turmeric, on spatial memory, metabolic functions, and the regulation of the gut microbiome in AD-induced (3xTg-AD) mice fed with either a normal chow diet (NCD) or a high-fat high-sugar diet (HFHSD). Our findings revealed an augmented susceptibility of the HFHSD-fed 3xTg-AD mice for weight gain and memory impairment, while curcumin supplementation demonstrated a protective effect against these changes. This was evidenced by significantly reduced body weight gain and improved behavioral and cognitive function in the curcumin-treated group. These improvements were substantiated by diminished fatty acid synthesis, altered cholesterol metabolism, and suppressed adipogenesis-related pathways in the liver, along with modified synaptic plasticity-related pathways in the brain. Moreover, curcumin enriched beneficial gut microbiota, including Oscillospiraceae and Rikenellaceae at the family level, and Oscillibacter, Alistipes, Pseudoflavonifractor, Duncaniella, and Flintibacter at the genus level. The observed alteration in these gut microbiota profiles suggests a potential crosswalk in the liver and brain for regulating metabolic and cognitive functions, particularly in the context of obesity-associated cognitive disfunction, notably AD.

rTMS reduces spatial learning and memory deficits induced by sleep deprivation possibly via suppressing the expression of kynurenine 3-monooxygenase in rats

INTRODUCTION

Impairment of learning and memory caused by sleep deprivation is a common symptom that significantly affects quality of life. Repetitive transcranial magnetic stimulation (rTMS) is a promising approach to exert a positive effect on cognitive impairment. However, there is less known about the mechanism of rTMS for learning and memory induced by chronic REM sleep deprivation (CRSD). This study was to detect the effects of rTMS on spatial learning and memory deficits by CRSD and explore possible mechanism.

METHODS

Sixty male Sprague-Dawley rats were randomly divided into four groups: wide platform (Control), sleep deprivation (SD), sleep deprivation + rTMS (TMS), and sleep deprivation + sham rTMS (Sham-TMS). Morris water maze (MWM) and open field test (OFT) assessed spatial learning and memory and anxiety of rats with pre/post-intervention. Golgi staining and transmission electron microscope (TEM) were used to observe structural variations of synapses in the hippocampus. The alteration in gene expression of different groups was analyzed by RNA-sequencing (RNA-Seq), and the key gene was screened and identified by quantitative polymerase chain reaction (qPCR) and subsequently verified with western blotting and immunofluorescence.

RESULTS

The behavioral test showed spatial learning and memory decreased and anxiety increased in the SD group compared to the Control and TMS groups. Moreover, rTMS improved spine density, ultrastructural damage, and quantities of synapses. In accordance with RNA-Seq, 56 differentially expressed genes (DEGs) were identified by comparing alternations in four groups and concentrated on kynurenine 3-monooxygenase (KMO). The expression of KMO increased significantly in rats of the SD group compared to the Control and TMS groups identified by qPCR, western blotting, and immunofluorescence.

CONCLUSION

1 Hz rTMS alleviated spatial learning and memory deficits induced by CRSD probably via down-regulating the expression of KMO and improving the structure and quantity of synapses in the hippocampus of rats.

Spatial memory requires hypocretins to elevate medial entorhinal gamma oscillations

The hypocretin (Hcrt) (also known as orexin) neuropeptidic wakefulness-promoting system is implicated in the regulation of spatial memory, but its specific role and mechanisms remain poorly understood. In this study, we revealed the innervation of the medial entorhinal cortex (MEC) by Hcrt neurons in mice. Using the genetically encoded G-protein-coupled receptor activation-based Hcrt sensor, we observed a significant increase in Hcrt levels in the MEC during novel object-place exploration. We identified the function of Hcrt at presynaptic glutamatergic terminals, where it recruits fast-spiking parvalbumin-positive neurons and promotes gamma oscillations. Bidirectional manipulations of Hcrt neurons' projections from the lateral hypothalamus (LHHcrt) to MEC revealed the essential role of this pathway in regulating object-place memory encoding, but not recall, through the modulation of gamma oscillations. Our findings highlight the significance of the LHHcrt-MEC circuitry in supporting spatial memory and reveal a unique neural basis for the hypothalamic regulation of spatial memory.

Effects of radiofrequency field from 5G communications on the spatial memory and emotionality in mice

The rapid development of 5G network technology has gained much popularity as well as concerns about its adverse effects. In this study, we investigated the effects of 4.9 GHz (one of working frequencies of 5G communication) radiofrequency (RF) field on emotional behaviours and spatial memory in adult male mice. Open field test (OFT), tail suspension test (TST) and Y maze were used to evaluate anxiety, depression-like behaviour and spatial memory ability, respectively. It was found that the anxiety-like behaviour and spatial memory ability of mice did not change, but the depression-like behaviour was induced in mice after 4.9 GHz RF exposure. In addition, the number of neurons significantly reduced and the level of pyroptosis obviously increased in amygdala rather than hippocampus. These results suggested that 4.9 GHz RF exposure could induce depression-like behaviour, which might be associated with the neuronal pyroptosis in amygdala.

Giant chess game enhances spatial navigational skills in 6-years-old children: preliminary findings

The game of chess is a valuable extracurricular activity for children, with positive effects on their cognitive skills and academic achievements. We investigated the extent to which the Giant Chess Game (GCG) played on a giant chessboard enhances working memory in "navigational-vista" space and "reaching" space. We also assessed if the GCG enhances mental rotation skills. For 10 weeks, 15 children (GCG group) were involved in a giant chess class, while 15 gender and age-matched children were involved in standard didactics (control group-CG). Children were tested twice, before (T0) and after (T1) the GCG, by tasks aimed at measuring: visuo-spatial working memory (VSWM) in the navigational-vista space (Walking Corsi test); VSWM in the reaching space (Corsi Block-Tapping task); mental rotation (Rotating Flowers test). We found that the GCG group significantly improved its performance more than the CG in VSWM in both navigational-vista space and reaching space, as well as in mental rotation. Our results suggest that the GCG has positive effects on visuo-spatial abilities underlying topographical skills. Therefore, the training using GCG can help enhancing spatial ability and may have a role in contrasting the spreading of navigational deficits such as the Developmental Topographical Disorientation (DTD).

Patients with Parkinson's disease demonstrate deficits in visual-spatial memory in the Chinese Visual Retention Test

OBJECTIVE

We aimed to explore the existence of visual-spatial memory deficit in patients with Parkinson's disease (PD) without dementia in the Chinese Visual Retention Test, as well as to assess whether their performance is related to age, duration, severity, stage, and dopamine (DA) dose.

METHODS

Forty-two patients with PD and 30 healthy controls were included in our study. The Chinese Visual Retention Test was used to evaluate the visual-spatial memory of the subjects. Parameters of the Chinese Visual Retention Test were compared between the two groups. Correlation analysis and multiple linear regression analysis were used to explore the associations of the Chinese Visual Retention Test with age, duration, severity, stage of PD, and DA dose.

RESULTS

Three correct scores in the Chinese Visual Retention Test were all significantly lower in the PD group than in the control group. The total error scores, error scores of omissions, deformation, and persistence in the PD group were significantly higher than those in the control group. Correlation analysis showed the total error scores in the Chinese Visual Retention Test was positively correlated with UPDRS III score and H-Y classification. Multiple linear regression analysis showed that the total error scores in the Chinese Visual Retention Test were associated with the UPDRS III score and H-Y classification.

CONCLUSION

Patients with PD without dementia had visual-spatial memory deficits in the Chinese Visual Retention Test which may be affected by the severity and clinical stage of PD.

Icariin rescues developmental BPA exposure induced spatial memory deficits in rats

Bisphenol A (BPA) has been implicated in cognitive impairment. Icariin is the main active ingredient extracted from Epimedium Herb with protective function of nervous system. However, the potential therapeutic effects of Icariin on spatial memory deficits induced by developmental BPA exposure in Sprague-Dawley rats have not been investigated. This study investigated the therapeutic effect of Icariin (10 mg/kg/day, from postnatal day (PND) 21 to PND 60 by gavage) on spatial memory deficits in rat induced by developmental BPA exposure (1 mg/kg/day, from embryonic to PND 60), demonstrating that Icariin can markedly improve spatial memory in BPA-exposed rat. Furthermore, intra-gastric administration of Icariin could attenuate abnormal hippocampal cell dispersion and loss, improved the dendritic spine density and Nissl bodies. Moreover, Icariin reversed BPA induced reduction of frequency of miniature excitatory postsynaptic currents(mEPSC) and decrease of Vesicular glutamate transporter 1(VGlut1). Collectively, Icariin could effectively rescue BPA-induced spatial memory impairment in male rats by preventing cell loss and reduction of dendritic spines in the hippocampus. In addition, we also found that VGlut1 is a critical target in the repair of BPA-induced spatial memory by Icariin. Thus, Icariin may be a promising therapeutic agent to attenuate BPA-induced spatial memory deficits.