Separate elements of episodic memory subserved by distinct hippocampal–prefrontal connections

Effects of long-term exposure to high-altitude on episodic memory: The moderating role of daytime dysfunction

Chronic exposure to high-altitude hypoxic environments may influence short-term memory and working memory. However, its impact on long-term memory, specifically episodic memory, remains understudied. In this study, we systematically investigated the effects of long-term exposure to high altitude (3650 m) on episodic memory, including item memory and source memory. Moreover, we examined the moderating role of daytime dysfunction on the relationship between altitude and episodic memory. In total, 97 participants were enrolled in the study: 49 were from the high-altitude (HA) group, comprising those born and raised in low altitude (LA) areas (< 500 m) and had migrated to HA for 2∼3 years after turning 18; and 48 were from the LA group, who had never lived at high altitudes. Episodic memory was evaluated using a what-when-where task, whereas daytime dysfunction was measured by the Pittsburgh Sleep Quality Index. For item memory, hit rate and correct rejection rate were significantly lower in the HA group relative to the LA group. For source binding memory, the performance in what-where binding and what-when-where binding were decreased in the HA group, but the what-when binding did not differ between the two groups. Furthermore, the effects of altitude on hit rate, what-where binding, and what-when-where binding were significantly pronounced in individuals with higher levels of daytime dysfunction. These findings suggest that long-term exposure to high-altitude hypoxic environments influences episodic memory performance, including item recognition and source-binding memory. Specifically, spatial source memory is affected by high-altitude exposure, whereas temporal source memory remains unaffected. Moreover, these results highlight the importance of considering sleep quality, especially good daytime function, in maintaining optimal episodic memory function following chronic exposure to high altitudes.

Don't ignore the middle: Distinct mnemonic functions of intermediate hippocampus

The dorsal region of the hippocampus (dHC) mediates many of the mnemonic functions traditionally associated with the hippocampus proper, such as spatial and episodic memory, whereas ventral hippocampus (vHC) has been extensively implicated in emotional memory and motivational processes. By contrast, the functions of the intermediate hippocampus (iHC) are far less understood. In this study, we aimed to investigate the mnemonic functions of iHC by reversibly inactivating iHC prior to testing memory in behavioral tasks dependent on the integrity of dHC, iHC, or vHC, namely, rapid place water maze, inhibitory avoidance, spontaneous alternation, and temporal ordering of odors. Given our previous findings showing that dHC and vHC are involved in mnemonic control of ingestive behavior, we also assessed the effects of iHC inactivation on sucrose intake. The results showed that pharmacological inhibition of iHC impairs rapid place water maze memory, which has been previously shown to be dependent on iHC but not dHC or vHC. iHC inactivation does not impact memory dependent on dHC (spontaneous alternation), vHC (temporal odor memory), or either dHC or vHC (inhibitory avoidance), and only modestly affects sucrose intake. These findings provide support for the involvement of iHC in mnemonic functions that are distinct from dHC and vHC and highlight the need to further advance our understanding of the functions of this hippocampal region that has been relatively understudied.

Effects of childhood maltreatment and major depressive disorder on functional connectivity in hippocampal subregions

Major Depressive Disorder (MDD) with childhood maltreatment is a prevalent clinical phenotype. Prior studies have observed abnormal hippocampal activity in MDD patients, considering the hippocampus as a single nucleus. However, there is limited research investigating the static and dynamic changes in hippocampal subregion functional connectivity (FC) in MDD patients with childhood maltreatment. Therefore, we employed static and dynamic FC analyses using hippocampal subregions, including the anterior hippocampus and posterior hippocampus, as seed regions to investigate the neurobiological alterations associated with MDD resulting from childhood maltreatment. This study involved four groups: MDD with (n = 48) and without childhood maltreatment (n = 30), as well as healthy controls with (n = 57) and without (n = 46) childhood maltreatment. Compared to MDD patients without childhood maltreatment, those with childhood maltreatment exhibit altered FC between the hippocampal subregion and multiple brain regions, including the anterior cingulate gyrus, superior frontal gyrus, putamen, calcarine gyrus, superior temporal gyrus, angular gyrus, and supplementary motor area. Additionally, dynamic FC between the right medial-2 hippocampal head and the right calcarine gyrus shows a positive correlation with childhood maltreatment across all its subtypes. Moreover, dFC between the right hippocampal tail and the left angular gyrus moderates the relationship between childhood maltreatment and the depression severity. Our findings of distinct FC patterns within hippocampal subregions provide new clues for understanding the neurobiological basis of MDD with childhood maltreatment.

Obesogenic diet induces circuit-specific memory deficits in mice

Obesity is associated with neurocognitive dysfunction, including memory deficits. This is particularly worrisome when obesity occurs during adolescence, a maturational period for brain structures critical for cognition. In rodent models, we recently reported that memory impairments induced by obesogenic high-fat diet (HFD) intake during the periadolescent period can be reversed by chemogenetic manipulation of the ventral hippocampus (vHPC). Here, we used an intersectional viral approach in HFD-fed male mice to chemogenetically inactivate specific vHPC efferent pathways to nucleus accumbens (NAc) or medial prefrontal cortex (mPFC) during memory tasks. We first demonstrated that HFD enhanced activation of both pathways after training and that our chemogenetic approach was effective in normalizing this activation. Inactivation of the vHPC-NAc pathway rescued HFD-induced deficits in recognition but not location memory. Conversely, inactivation of the vHPC-mPFC pathway restored location but not recognition memory impairments produced by HFD. Either pathway manipulation did not affect exploration or anxiety-like behaviour. These findings suggest that HFD intake throughout adolescence impairs different types of memory through overactivation of specific hippocampal efferent pathways and that targeting these overactive pathways has therapeutic potential.

Pathway specific interventions reveal the multiple roles of ventral hippocampus projections in cognitive functions

Since the 1950s study of Scoville and Milner on the case H.M., the hippocampus has attracted neuroscientists' attention. The hippocampus has been traditionally divided into dorsal and ventral parts, each of which projects to different brain structures and mediates various functions. Despite a predominant interest in its dorsal part in animal models, especially regarding episodic-like and spatial cognition, recent data highlight the role of the ventral hippocampus (vHPC), as the main hippocampal output, in cognitive processes. Here, we review recent studies conducted in rodents that have used advanced in vivo functional techniques to specifically monitor and manipulate vHPC efferent pathways and delineate the roles of these specific projections in learning and memory processes. Results highlight that vHPC projections to basal amygdala are implicated in emotional memory, to nucleus accumbens in social memory and instrumental actions and to prefrontal cortex in all the above as well as in object-based memory. Some of these hippocampal projections also modulate feeding and anxiety-like behaviours providing further evidence that the "one pathway-one function" view is outdated and future directions are proposed to better understand the role of hippocampal pathways and shed further light on its connectivity and function.

Subcortico-amygdala pathway processes innate and learned threats

Behavioral flexibility and timely reactions to salient stimuli are essential for survival. The subcortical thalamic-basolateral amygdala (BLA) pathway serves as a shortcut for salient stimuli ensuring rapid processing. Here, we show that BLA neuronal and thalamic axonal activity in mice mirror the defensive behavior evoked by an innate visual threat as well as an auditory learned threat. Importantly, perturbing this pathway compromises defensive responses to both forms of threats, in that animals fail to switch from exploratory to defensive behavior. Despite the shared pathway between the two forms of threat processing, we observed noticeable differences. Blocking β-adrenergic receptors impairs the defensive response to the innate but not the learned threats. This reduced defensive response, surprisingly, is reflected in the suppression of the activity exclusively in the BLA as the thalamic input response remains intact. Our side-by-side examination highlights the similarities and differences between innate and learned threat-processing, thus providing new fundamental insights.

Development and validation of the Mental-Physical Verb Norms (MPVN): A text analysis measure of mental state attribution

Attribution of mental states to self and others, i.e., mentalizing, is central to human life. Current measures are lacking in the ability to directly gauge the extent to which individuals engage in spontaneous mentalizing. Focusing on natural language use as an expression of inner psychological processes, we developed the Mental-Physical Verb Norms (MPVN). These norms are participant-derived ratings of the extent to which common verbs reflect mental (vs physical) activities and occurrences, covering a majority of verbs appearing in a given English text. Content validity was assessed against existing expert-compiled dictionaries of mental states and cognitive processes, as well as against normative ratings of verb concreteness. Criterion Validity was assessed through natural text analysis of both experimental data, and natural language use in a real-world online setting. Finally, incremental validity was assessed through a classification analysis. Results indicate the unique contribution of the MPVN ratings as a measure of the degree to which individuals adopt the intentional stance in describing targets, by describing both self and others in mental, opposite physical, terms. We discuss potential uses for future research across various psychological and neurocognitive disciplines, as well as theoretical implications regarding the use of mentalizing language within spontaneous contexts.

FiPhA: An Open-Source Platform for Fiber Photometry Analysis

Significance

Fiber photometry is a widely used technique in modern behavioral neuroscience, employing genetically encoded fluorescent sensors to monitor neural activity and neurotransmitter release in awake-behaving animals, However, analyzing photometry data can be both laborious and time-consuming.

Aim

We propose the FiPhA (Fiber Photometry Analysis) app, which is a general-purpose fiber photometry analysis application. The goal is to develop a pipeline suitable for a wide range of photometry approaches, including spectrally resolved, camera-based, and lock-in demodulation.

Approach

FiPhA was developed using the R Shiny framework and offers interactive visualization, quality control, and batch processing functionalities in a user-friendly interface.

Results

This application simplifies and streamlines the analysis process, thereby reducing labor and time requirements. It offers interactive visualizations, event-triggered average processing, powerful tools for filtering behavioral events and quality control features.

Conclusions

FiPhA is a valuable tool for behavioral neuroscientists working with discrete, event-based fiber photometry data. It addresses the challenges associated with analyzing and investigating such data, offering a robust and user-friendly solution without the complexity of having to hand-design custom analysis pipelines. This application thus helps standardize an approach to fiber photometry analysis.

Hippocampal-prefrontal long-term potentiation-like plasticity with transcranial direct current stimulation in rats

Transcranial direct current stimulation (tDCS) has been explored as a new treatment method for improving cognitive and motor functions. However, the neuronal mechanisms of tDCS in modulating brain functions, especially cognitive and memory functions, are not well understood. In the present study, we assessed whether tDCS could promote neuronal plasticity between the hippocampus and prefrontal cortex in rats. This is important because the hippocampus-prefrontal pathway is a key pathway in cognitive and memory functions and is involved in various psychiatric and neurodegenerative disorders. Specifically, the effect of anodal or cathodal tDCS on the medial prefrontal cortex was investigated in rats by measuring the medial prefrontal cortex response to electrical stimulation applied to the CA1 region of the hippocampus. Following anodal tDCS, the evoked prefrontal response was potentiated compared to that in the pre-tDCS condition. However, the evoked prefrontal response did not show any significant changes following cathodal tDCS. Furthermore, the plastic change of the prefrontal response following anodal tDCS was only induced when hippocampal stimulation was continuously applied during tDCS. Anodal tDCS without hippocampal activation showed little or no changes. These results indicate that combining anodal tDCS of the prefrontal cortex with hippocampal activation induces long-term potentiation (LTP)-like plasticity in the hippocampus-prefrontal pathway. This LTP-like plasticity can facilitate smooth information transmission between the hippocampus and the prefrontal cortex and may lead to improvements in cognitive and memory function.

The Recruitment of a Neuronal Ensemble in the Central Nucleus of the Amygdala During the First Extinction Episode Has Persistent Effects on Extinction Expression

BACKGROUND

Adaptive behavior depends on the delicate and dynamic balance between acquisition and extinction memories. Disruption of this balance, particularly when the extinction of memory loses control over behavior, is the root of treatment failure of maladaptive behaviors such as substance abuse or anxiety disorders. Understanding this balance requires a better understanding of the underlying neurobiology and its contribution to behavioral regulation.

METHODS

We microinjected Daun02 in Fos-lacZ transgenic rats following a single extinction training episode to delete extinction-recruited neuronal ensembles in the basolateral amygdala (BLA) and central nucleus of the amygdala (CN) and examined their contribution to behavior in an appetitive Pavlovian task. In addition, we used immunohistochemistry and neuronal staining methods to identify the molecular markers of activated neurons in the BLA and CN during extinction learning or retrieval.

RESULTS

CN neurons were preferentially engaged following extinction, and deletion of these extinction-activated ensembles in the CN but not the BLA impaired the retrieval of extinction despite additional extinction training and promoted greater levels of behavioral restoration in spontaneous recovery and reinstatement. Disrupting extinction processing in the CN in turn increased activity in the BLA. Our results also show a specific role for CN PKCδ+ neurons in behavioral inhibition but not during initial extinction learning.

CONCLUSIONS

We showed that the initial extinction-recruited CN ensemble is critical to the acquisition-extinction balance and that greater behavioral restoration does not mean weaker extinction contribution. These findings provide a novel avenue for thinking about the neural mechanisms of extinction and for developing treatments for cue-triggered appetitive behaviors.

Stimulation-induced entrainment of hippocampal network activity: Identifying optimal input frequencies

The hippocampus contains rich oscillatory activity, with continuous ebbs and flows of rhythmic currents that constrain its ability to integrate inputs. During associative learning, the hippocampus must integrate inputs from a range of sources carrying information about events and the contexts in which they occur. Under these circumstances, temporal coordination of activity between sender and receiver is likely essential for successful communication. Previously, it has been shown that the coordination of rhythmic activity between the lateral entorhinal cortex (LEC) and the CA1 region of the hippocampus is tightly correlated with the onset of learning in an associative learning task. We aimed to examine whether rhythmic inputs from the LEC in specific frequency ranges were sufficient to enhance the temporal coordination of activity in downstream CA1. In urethane-anesthetized rats, we applied extracellular low-intensity alternating current stimulation across the length of the LEC. Using this method, we aimed to phase-bias ongoing neuronal activity in LEC at a range of different frequencies (from 1.25 to 55 Hz). Rhythmic stimulation of LEC at both 35 and 50 Hz increased the proportion of CA1 neurons significantly entrained to the phase of the applied stimulation current. A subset of stimulation frequencies modified CA1 spiking relationships to the phase of local ongoing CA1 oscillations, with each stimulation frequency exerting a unique influence upon downstream CA1, often in frequency ranges outside the target stimulation frequency. These results suggest there are optimal frequencies for LEC-CA1 communication, and that different profiles of LEC rhythms likely have distinct outcomes upon CA1 processing.

Parallel Pathways Provide Hippocampal Spatial Information to Prefrontal Cortex

Long-range synaptic connections define how information flows through neuronal networks. Here, we combined retrograde and anterograde trans-synaptic viruses to delineate areas that exert direct and indirect influence over the dorsal and ventral prefrontal cortex (PFC) of the rat (both sexes). Notably, retrograde tracing using pseudorabies virus (PRV) revealed that both dorsal and ventral areas of the PFC receive prominent disynaptic input from the dorsal CA3 (dCA3) region of the hippocampus. The PRV experiments also identified candidate anatomical relays for this disynaptic pathway, namely, the ventral hippocampus, lateral septum, thalamus, amygdala, and basal forebrain. To determine the viability of each of these relays, we performed three additional experiments. In the first, we injected the retrograde monosynaptic tracer Fluoro-Gold into the PFC and the anterograde monosynaptic tracer Fluoro-Ruby into the dCA3 to confirm the first-order connecting areas and revealed several potential relay regions between the PFC and dCA3. In the second, we combined PRV injection in the PFC with polysynaptic anterograde viral tracer (HSV-1) in the dCA3 to reveal colabeled connecting neurons, which were evident only in the ventral hippocampus. In the third, we combined retrograde adeno-associated virus (AAV) injections in the PFC with an anterograde AAV in the dCA3 to reveal anatomical relay neurons in the ventral hippocampus and dorsal lateral septum. Together, these findings reveal parallel disynaptic pathways from the dCA3 to the PFC, illuminating a new anatomical framework for understanding hippocampal-prefrontal interactions. We suggest that the representation of context and space may be a universal feature of prefrontal function.SIGNIFICANCE STATEMENT The known functions of the prefrontal cortex are shaped by input from multiple brain areas. We used transneuronal viral tracing to discover multiple prominent disynaptic pathways through which the dorsal hippocampus (specifically, the dorsal CA3) has the potential to shape the actions of the prefrontal cortex. The demonstration of neuronal relays in the ventral hippocampus and lateral septum presents a new foundation for understanding long-range influences over prefrontal interactions, including the specific contribution of the dorsal CA3 to prefrontal function.

The role of metabotropic glutamate receptors in neurobehavioral effects associated with methamphetamine use

Metabotropic glutamate (mGlu) receptors are expressed throughout the central nervous system and act as important regulators of drug-induced neuroplasticity and behavior. Preclinical research suggests that mGlu receptors play a critical role in a spectrum of neural and behavioral consequences arising from methamphetamine (meth) exposure. However, an overview of mGlu-dependent mechanisms linked to neurochemical, synaptic, and behavioral changes produced by meth has been lacking. This chapter provides a comprehensive review of the role of mGlu receptor subtypes (mGlu1-8) in meth-induced neural effects, such as neurotoxicity, as well as meth-associated behaviors, such as psychomotor activation, reward, reinforcement, and meth-seeking. Additionally, evidence linking altered mGlu receptor function to post-meth learning and cognitive deficits is critically evaluated. The chapter also considers the role of receptor-receptor interactions involving mGlu receptors and other neurotransmitter receptors in meth-induced neural and behavioral changes. Taken together, the literature indicates that mGlu5 regulates the neurotoxic effects of meth by attenuating hyperthermia and possibly through altering meth-induced phosphorylation of the dopamine transporter. A cohesive body of work also shows that mGlu5 antagonism (and mGlu2/3 agonism) reduce meth-seeking, though some mGlu5-blocking drugs also attenuate food-seeking. Further, evidence suggests that mGlu5 plays an important role in extinction of meth-seeking behavior. In the context of a history of meth intake, mGlu5 also co-regulates aspects of episodic memory, with mGlu5 stimulation restoring impaired memory. Based on these findings, we propose several avenues for the development of novel pharmacotherapies for Methamphetamine Use Disorder based on the selective modulation mGlu receptor subtype activity.

Probing the nature of episodic memory in rodents

Episodic memory (EM) specifies the experience of retrieving information of an event at the place and time of occurrence. Whether non-human animals are capable of EM remains debated, whereas evidence suggests that they have a memory system akin to EM. We here trace the development of various behavioral paradigms designed to study EM in non-human animals, in particular the rat. We provide an in-depth description of the available behavioral tests which combine three spontaneous object exploration paradigms, namely novel object preference (for measuring memory for "what"), novel location preference (for measuring memory for "where") and temporal order memory (memory for "when"), into a single trial to gauge a memory akin to EM. Most important, we describe a variation of such a test in which each memory component interacts with the others, demonstrating an integration of diverse mnemonic information. We discuss why a behavioral model of EM must be able to assess the ability to integrate "what", "where" and "when" information into a single experience. We attempt an interpretation of the various tests and review the studies that have applied them in areas such as pharmacology, neuroanatomy, circuit analysis, and sleep. Finally, we anticipate future directions in the search for neural mechanisms of EM in the rat and outline model experiments and methodologies in this pursuit.

Assessing episodic memory in rodents using spontaneous object recognition tasks

Models of episodic memory are successfully established using spontaneous object recognition tasks in rodents. In this review, we present behavioral techniques devised to investigate this type of memory, emphasizing methods based on associations of places and temporal order of items explored by rats and mice. We also provide a review on the areas and circuitry of the medial temporal lobe underlying episodic-like memory, considering that a large number of neurobiology data derived from these protocols. Although spontaneous recognition tasks are commonplace in this field, there is need for careful evaluation of factors affecting animal performance. Such as the ongoing development of tools for investigating the neural basis of memory, efforts should be put in the refinement of experimental designs, in order to provide reliable behavioral evidence of this complex mnemonic system.

Effects of Personalized Cognitive Training with the Machine Learning Algorithm on Neural Efficiency in Healthy Younger Adults

To date, neural efficiency, an ability to economically utilize mental resources, has not been investigated after cognitive training. The purpose of this study was to provide customized cognitive training and confirm its effect on neural efficiency by investigating prefrontal cortex (PFC) activity using functional near-infrared spectroscopy (fNIRS). Before training, a prediction algorithm based on the PFC activity with logistic regression was used to predict the customized difficulty level with 86% accuracy by collecting data when subjects performed four kinds of cognitive tasks. In the next step, the intervention study was designed using one pre-posttest group. Thirteen healthy adults participated in the virtual reality (VR)-based spatial cognitive training, which was conducted four times a week for 30 min for three weeks with customized difficulty levels for each session. To measure its effect, the trail-making test (TMT) and hemodynamic responses were measured for executive function and PFC activity. During the training, VR-based spatial cognitive performance was improved, and hemodynamic values were gradually increased as the training sessions progressed. In addition, after the training, the performance on the trail-making task (TMT) demonstrated a statistically significant improvement, and there was a statistically significant decrease in the PFC activity. The improved performance on the TMT coupled with the decreased PFC activity could be regarded as training-induced neural efficiency. These results suggested that personalized cognitive training could be effective in improving executive function and neural efficiency.

Neuronal circuitry for recognition memory of object and place in rodent models

Rats and mice are used for studying neuronal circuits underlying recognition memory due to their ability to spontaneously remember the occurrence of an object, its place and an association of the object and place in a particular environment. A joint employment of lesions, pharmacological interventions, optogenetics and chemogenetics is constantly expanding our knowledge of the neural basis for recognition memory of object, place, and their association. In this review, we summarize current studies on recognition memory in rodents with a focus on the novel object preference, novel location preference and object-in-place paradigms. The evidence suggests that the medial prefrontal cortex- and hippocampus-connected circuits contribute to recognition memory for object and place. Under certain conditions, the striatum, medial septum, amygdala, locus coeruleus and cerebellum are also involved. We propose that the neuronal circuitry for recognition memory of object and place is hierarchically connected and constructed by different cortical (perirhinal, entorhinal and retrosplenial cortices), thalamic (nucleus reuniens, mediodorsal and anterior thalamic nuclei) and primeval (hypothalamus and interpeduncular nucleus) modules interacting with the medial prefrontal cortex and hippocampus.

Time to retire the serial Papez circuit: Implications for space, memory, and attention

After more than 80 years, Papez serial circuit remains a hugely influential concept, initially for emotion, but in more recent decades, for memory. Here, we show how this circuit is anatomically and mechanistically naïve as well as outdated. We argue that a new conceptualisation is necessitated by recent anatomical and functional findings that emphasize the more equal, working partnerships between the anterior thalamic nuclei and the hippocampal formation, along with their neocortical interactions in supporting, episodic memory. Furthermore, despite the importance of the anterior thalamic for mnemonic processing, there is growing evidence that these nuclei support multiple aspects of cognition, only some of which are directly associated with hippocampal function. By viewing the anterior thalamic nuclei as a multifunctional hub, a clearer picture emerges of extra-hippocampal regions supporting memory. The reformulation presented here underlines the need to retire Papez serially processing circuit.

Differences in memory for what, where, and when components of recently formed episodes

An integral feature of human memory is the ability to recall past events. What distinguishes such episodic memory from semantic or associative memory is the joint encoding and retrieval of "what," "where," and "when" (WWW) for such events. Surprisingly, little work has addressed whether all three components of WWW are retrieved with equal fidelity when remembering episodes. To study this question, we created a novel task where human participants identified matched or mismatched still images sampled from recently viewed synthetic movies. The mismatch images only probe one of the three WWW components at a time, allowing us to separately test accuracies for each component of the episodes. Crucially, each WWW component in the movies is easily distinguishable in isolation, thereby making any differences in accuracy between components due to how they are joined in memory. We find that memory for "when" has the lowest accuracy, with it being the component most influenced by primacy and recency. Furthermore, the memory of "when" is most susceptible to interference due to changes in task load. These findings suggest that episodes are not stored and retrieved as a coherent whole but instead their components are either stored or retrieved differentially as part of an active reconstruction process. NEW & NOTEWORTHY When we store and subsequently retrieve episodes, does the brain encode them holistically or in separate parts that are later reconstructed? Using a task where participants study abstract episodes and on any given trial are probed on the what, where, and when components, we find mnemonic differences between them. Accuracy for "when" memory is the lowest, as it is most influenced by primacy, recency, and interference, suggesting that episodes are not treated holistically by the brain.

Electrical stimulation mapping in the medial prefrontal cortex induced auditory hallucinations of episodic memory: A case report

It has been well documented that the auditory system in the superior temporal cortex is responsible for processing basic auditory sound features, such as sound frequency and intensity, while the prefrontal cortex is involved in higher-order auditory functions, such as language processing and auditory episodic memory. The temporal auditory cortex has vast forward anatomical projections to the prefrontal auditory cortex, connecting with the lateral, medial, and orbital parts of the prefrontal cortex. The connections between the auditory cortex and the prefrontal cortex thus help in localizing, recognizing, and comprehending external auditory inputs. In addition, the medial prefrontal cortex (MPFC) is believed to be a core region of episodic memory retrieval and is one of the most important regions in the default mode network (DMN). However, previous neural evidence with regard to the comparison between basic auditory processing and auditory episodic memory retrieval mainly comes from fMRI studies. The specific neural networks and the corresponding critical frequency bands of neuronal oscillations underlying the two auditory functions remain unclear. In the present study, we reported results of direct cortical stimulations during stereo-electro-encephalography (SEEG) recording in a patient with drug-resistant epilepsy. Electrodes covered the superior temporal gyrus, the operculum and the insula cortex of bilateral hemispheres, the prefrontal cortex, the parietal lobe, the anterior and middle cingulate cortex, and the amygdala of the left hemisphere. Two types of auditory hallucinations were evoked with direct cortical stimulations, which were consistent with the habitual seizures. The noise hallucinations, i.e., “I could hear buzzing noises in my head,” were evoked with the stimulation of the superior temporal gyrus. The episodic memory hallucinations “I could hear a young woman who was dressed in a red skirt saying: What is the matter with you?,” were evoked with the stimulation of MPFC. The patient described how she had met this young woman when she was young and that the woman said the same sentence to her. Furthermore, by analyzing the high gamma power (HGP) induced by direct electrical stimulation, two dissociable neural networks underlying the two types of auditory hallucinations were localized. Taken together, the present results confirm the hierarchical processing of auditory information by showing the different involvements of the primary auditory cortex vs. the prefrontal cortex in the two types of auditory hallucinations.

Episodic representation: A mental models account

This paper offers a modeling account of episodic representation. I argue that the episodic system constructs mental models: representations that preserve the spatiotemporal structure of represented domains. In prototypical cases, these domains are events: occurrences taken by subjects to have characteristic structures, dynamics and relatively determinate beginnings and ends. Due to their simplicity and manipulability, mental event models can be used in a variety of cognitive contexts: in remembering the personal past, but also in future-oriented and counterfactual imagination. As structural representations, they allow surrogative reasoning, supporting inferences about their constituents which can be used in reasoning about the represented events.

Neural circuit pathology driven by Shank3 mutation disrupts social behaviors

Dysfunctional sociability is a core symptom in autism spectrum disorder (ASD) that may arise from neural-network dysconnectivity between multiple brain regions. However, pathogenic neural-network mechanisms underlying social dysfunction are largely unknown. Here, we demonstrate that circuit-selective mutation (ctMUT) of ASD-risk Shank3 gene within a unidirectional projection from the prefrontal cortex to the basolateral amygdala alters spine morphology and excitatory-inhibitory balance of the circuit. Shank3 ctMUT mice show reduced sociability as well as elevated neural activity and its amplitude variability, which is consistent with the neuroimaging results from human ASD patients. Moreover, the circuit hyper-activity disrupts the temporal correlation of socially tuned neurons to the events of social interactions. Finally, optogenetic circuit activation in wild-type mice partially recapitulates the reduced sociability of Shank3 ctMUT mice, while circuit inhibition in Shank3 ctMUT mice partially rescues social behavior. Collectively, these results highlight a circuit-level pathogenic mechanism of Shank3 mutation that drives social dysfunction.

Plexin-A1 expression in the inhibitory neurons of infralimbic cortex regulates the specificity of fear memory in male mice

Maintaining appropriate levels of fear memory specificity is crucial for individual's survival and mental health, whereas overgeneralized fear commonly occurs in neuropsychiatric disorders, including posttraumatic stress disorder and generalized anxiety disorder. However, the molecular mechanisms regulating fear memory specificity remain poorly understood. The medial prefrontal cortex (mPFC) is considered as a key brain region in fear memory regulation. Previous transcriptomic studies have identified that plexin-A1, a transmembrane receptor critical for axon development, was downregulated in the mPFC after fear memory training. In this study, we identified that learning-induced downregulation of the mRNA and protein levels of plexin-A1 specifically occurred in the inhibitory but not excitatory neurons in the infralimbic cortex (IL) of mPFC. Further studies of plexin-A1 by virus-mediated over-expression of functional mutants selectively in the IL inhibitory neurons revealed the critical roles of plexin-A1 for regulating memory specificity and anxiety. Moreover, our findings revealed that plexin-A1 regulated the distribution of glutamic acid decarboxylase 67, a GABA synthetase, which in turn modulated the activity of IL and its downstream brain regions. Collectively, our findings elucidate the molecular modifier of IL inhibitory neurons in regulating memory specificity and anxiety, and provide candidates for developing therapeutic strategies for the prevention or treatment of a series of fear generalization-related neuropsychiatric disorders.

Changes in the level of fatty acids in the brain of rats during memory acquisition

Memory acquisition is accompanied by many cellular and molecular processes, and it is not always clear what role they play. Fatty acids (FAs) are known to be important for cognitive functions, but the details of their involvement in memory processes remain unknown. We investigated FAs in the prefrontal cortex and hippocampus of rats trained to perform a task with food reinforcement. The learning consisted of two training sessions, each of which included 10 trials. The results showed that such training altered individual FAs in the brains. The most significant changes were in the prefrontal cortex, where an increase in the level of many FAs occurred, especially after the second training session: palmitic (16:0), stearic (18:0), docosahexaenoic (22:6, n-3), arachidonic (22:4, n-6), docosapentaenoic (22:5, n-6) acids. Changes in the fatty acid level after training in rats were detected only in the left hippocampus, where the levels of palmitic, docosapentaenoic, and docosahexaenoic acids changed. The changes in the right hippocampus were not significant. In both the prefrontal cortex and the left hippocampus, 72 h after training, all FAs returned to control levels. We believe that the main role of a reversible increase in FA levels during memory acquisition is to support and protect cellular processes involved in memory acquisition. Consolidation of memory traces, which occurs mainly in the neocortex, requires protection from external influences, to which FAs makes a significant contribution. They are able to improve neuronal plasticity, enhance local blood flow, improve mitochondrial processes, and suppress pro-inflammatory signals.

Hippocampus-Prefrontal Coupling Regulates Recognition Memory for Novelty Discrimination

Recognition memory provides the ability to distinguish familiar from novel objects and places, and is important for recording and updating events to guide appropriate behavior. The hippocampus (HPC) and medial prefrontal cortex (mPFC) have both been implicated in recognition memory, but the nature of HPC-mPFC interactions, and its impact on local circuits in mediating this process is not known. Here we show that novelty discrimination is accompanied with higher theta activity (4-10 Hz) and increased c-Fos expression in both these regions. Moreover, theta oscillations were highly coupled between the HPC and mPFC during recognition memory retrieval for novelty discrimination, with the HPC leading the mPFC, but not during initial learning. Principal neurons and interneurons in the mPFC responded more strongly during recognition memory retrieval compared with learning. Optogenetic silencing of HPC input to the mPFC disrupted coupled theta activity between these two structures, as well as the animals' (male Sprague Dawley rats) ability to differentiate novel from familiar objects. These results reveal a key role of monosynaptic connections between the HPC and mPFC in novelty discrimination via theta coupling and identify neural populations that underlie this recognition memory-guided behavior.SIGNIFICANCE STATEMENT Many memory processes are highly dependent on the interregional communication between the HPC and mPFC via neural oscillations. However, how these two brain regions coordinate their oscillatory activity to engage local neural populations to mediate recognition memory for novelty discrimination is poorly understood. This study revealed that the HPC and mPFC theta oscillations and their temporal coupling is correlated with recognition memory-guided behavior. During novel object recognition, the HPC drives mPFC interneurons to effectively reduce the activity of principal neurons. This study provides the first evidence for the requirement of the HPC-mPFC pathway to mediate recognition memory for novelty discrimination and describes a mechanism for how this memory is regulated.

Promoting and Optimizing the Use of 3D-Printed Objects in Spontaneous Recognition Memory Tasks in Rodents: A Method for Improving Rigor and Reproducibility

Spontaneous recognition memory tasks are widely used to assess cognitive function in rodents and have become commonplace in the characterization of rodent models of neurodegenerative, neuropsychiatric and neurodevelopmental disorders. Leveraging an animal’s innate preference for novelty, these tasks use object exploration to capture the what, where and when components of recognition memory. Choosing and optimizing objects is a key feature when designing recognition memory tasks. Although the range of objects used in these tasks varies extensively across studies, object features can bias exploration, influence task difficulty and alter brain circuit recruitment. Here, we discuss the advantages of using 3D-printed objects in rodent spontaneous recognition memory tasks. We provide strategies for optimizing their design and usage, and offer a repository of tested, open-source designs for use with commonly used rodent species. The easy accessibility, low-cost, renewability and flexibility of 3D-printed open-source designs make this approach an important step toward improving rigor and reproducibility in rodent spontaneous recognition memory tasks.

Dimensions and mechanisms of memory organization

Memory formation is dynamic in nature, and acquisition of new information is often influenced by previous experiences. Memories sharing certain attributes are known to interact so that retrieval of one increases the likelihood of retrieving the other, raising the possibility that related memories are organized into associative mnemonic structures of interconnected representations. Although the formation and retrieval of single memories have been studied extensively, very little is known about the brain mechanisms that organize and link related memories. Here we review studies that suggest the existence of mnemonic structures in humans and animal models. These studies suggest three main dimensions of experience that can serve to organize related memories: time, space, and perceptual/conceptual similarities. We propose potential molecular, cellular, and systems mechanisms that might support organization of memories according to these dimensions.

NMDARs in prefrontal cortex - Regulation of synaptic transmission and plasticity

In this review we consider the various roles played by N-methyl-d-aspartate receptors (NMDARs) located on pyramidal neurones in medial prefrontal cortex (mPFC). We focus on recent data from our lab that has investigated how NMDARs contribute to ongoing synaptic transmission in a frequency dependent manner, the plasticity of NMDARs and how this impacts their contribution to synaptic transmission, and finally consider how NMDARs contribute to plasticity induced by synchronous activation of two separate inputs to mPFC.

Dysregulation of the Synaptic Cytoskeleton in the PFC Drives Neural Circuit Pathology, Leading to Social Dysfunction

Psychiatric disorders are highly heritable pathologies of altered neural circuit functioning. How genetic mutations lead to specific neural circuit abnormalities underlying behavioral disruptions, however, remains unclear. Using circuit-selective transgenic tools and a mouse model of maladaptive social behavior (ArpC3 mutant), we identify a neural circuit mechanism driving dysfunctional social behavior. We demonstrate that circuit-selective knockout (ctKO) of the ArpC3 gene within prefrontal cortical neurons that project to the basolateral amygdala elevates the excitability of the circuit neurons, leading to disruption of socially evoked neural activity and resulting in abnormal social behavior. Optogenetic activation of this circuit in wild-type mice recapitulates the social dysfunction observed in ArpC3 mutant mice. Finally, the maladaptive sociability of ctKO mice is rescued by optogenetically silencing neurons within this circuit. These results highlight a mechanism of how a gene-to-neural circuit interaction drives altered social behavior, a common phenotype of several psychiatric disorders.

Object and object-memory representations across the proximodistal axis of CA1

Episodic memory requires information about objects to be integrated into a spatial framework. Place cells in the hippocampus encode spatial representations of objects that could be generated through signaling from the entorhinal cortex. Projections from lateral (LEC) and medial entorhinal cortex (MEC) to the hippocampus terminate in distal and proximal CA1, respectively. We recorded place cells in distal and proximal CA1 as rats explored an environment that contained objects. Place cells in distal CA1 demonstrated higher measures of spatial tuning, stability, and closer proximity of place fields to objects. Furthermore, remapping to object displacement was modulated by place field proximity to objects in distal, but not proximal CA1. Finally, representations of previous object locations were closer to those locations in distal CA1 than proximal CA1. Our data suggest that in cue-rich environments, LEC inputs to the hippocampus support spatial representations with higher spatial tuning, closer proximity to objects, and greater stability than those receiving inputs from MEC. This is consistent with functional segregation in the entorhinal-hippocampal circuits underlying object-place memory.

Location and temporal memory of objects declines in aged marmosets (Callithrix jacchus)

Episodic memory decline is an early marker of cognitive aging in human. Although controversial in animals and called “episodic-like memory”, several models have been successfully developed, however they rarely focused on ageing. While marmoset is an emerging primate model in aging science, episodic-like memory has never been tested in this species and importantly in aged marmosets. Here, we examined if the recall of the what-when and what-where building blocks of episodic-like memory declines in ageing marmosets. We developed a naturalistic approach using spontaneous exploration of real objects by young and old marmosets in the home cage. We implemented a three-trial task with 1 week inter-trial interval. Two different sets of identical objects were presented in sample trials 1 and 2, respectively. For the test trial, two objects from each set were presented in a former position and two in a new one. We quantified the exploratory behaviour and calculated discrimination indices in a cohort of 20 marmosets. Young animals presented a preserved memory for combined what-where, and what-when components of the experiment, which declined with aging. These findings lead one to expect episodic-like memory deficits in aged marmosets.

Binge drinking is associated with altered resting state functional connectivity of reward-salience and top down control networks

Binge drinking is characterized by bouts of high-intensity alcohol intake and is associated with an array of health-related harms. Even though the transition from occasional impulsive to addictive alcohol use is not well understood, neurobiological models of addiction suggest that repeated cycles of intoxication and withdrawal contribute to the development of addiction in part through dysregulation of neurofunctional networks. Research on the neural sequelae associated with binge drinking is scant but resting state functional connectivity (RSFC) studies of alcohol use disorders (AUD) indicate that the development and maintenance of long-term excessive drinking may be mediated by network-level disruptions. The present study examined RSFC in young adult binge (BD) and light (LD) drinkers with seeds representing the networks subserving reward (the nucleus accumbens and caudate nucleus), salience (anterior cingulate cortex, ACC), and executive control (inferior frontal cortex, IFC). BDs exhibited enhanced connectivity between the striatal reward areas and the orbitofrontal cortex and the ACC, which is consistent with AUD studies and may be indicative of alcohol-motivated appetitive behaviors. Conversely, BDs demonstrated lower connectivity between the IFC and hippocampus which was associated with higher craving. This may indicate impaired ability to suppress unwanted thoughts and a failure to employ memory of the harmful consequences of heavy drinking in prospective plans and intentions. The observed greater connectivity of the reward/salience network and the lower prefrontal-hippocampal connectivity were associated with hazardous drinking levels indicating that dysregulation of neurofunctional networks may underlie binge drinking patterns.

Plasticity in Prefrontal Cortex Induced by Coordinated Synaptic Transmission Arising from Reuniens/Rhomboid Nuclei and Hippocampus

The nucleus reuniens and rhomboid nuclei of the thalamus (ReRh) are reciprocally connected to a range of higher order cortices including hippocampus (HPC) and medial prefrontal cortex (mPFC). The physiological function of ReRh is well predicted by requirement for interactions between mPFC and HPC, including associative recognition memory, spatial navigation, and working memory. Although anatomical and electrophysiological evidence suggests ReRh makes excitatory synapses in mPFC there is little data on the physiological properties of these projections, or whether ReRh and HPC target overlapping cell populations and, if so, how they interact. We demonstrate in ex vivo mPFC slices that ReRh and HPC afferent inputs converge onto more than two-thirds of layer 5 pyramidal neurons, show that ReRh, but not HPC, undergoes marked short-term plasticity during theta frequency transmission, and that HPC, but not ReRh, afferents are subject to neuromodulation by acetylcholine acting via muscarinic receptor M2. Finally, we demonstrate that pairing HPC followed by ReRh (but not pairing ReRh followed by HPC) at theta frequency induces associative, NMDA receptor dependent synaptic plasticity in both inputs to mPFC. These data provide vital physiological phenotypes of the synapses of this circuit and provide a novel mechanism for HPC-ReRh-mPFC encoding.

Akt-mTOR hypoactivity in bipolar disorder gives rise to cognitive impairments associated with altered neuronal structure and function

The Akt family of kinases exerts many of its cellular effects via the activation of the mammalian target of rapamycin (mTOR) kinase through a series of intermediary proteins. Multiple lines of evidence have identified Akt-family kinases as candidate schizophrenia and bipolar disorder genes. Although dysfunction of the prefrontal cortex (PFC) is a key feature of both schizophrenia and bipolar disorder, no studies have comprehensively assessed potential alterations in Akt-mTOR pathway activity in the PFC of either disorder. Here, we examined the activity and expression profile of key proteins in the Akt-mTOR pathway in bipolar disorder and schizophrenia homogenates from two different PFC subregions. Our findings identify reduced Akt-mTOR PFC signaling in a subset of bipolar disorder subjects. Using a reverse-translational approach, we demonstrated that Akt hypofunction in the PFC is sufficient to give rise to key cognitive phenotypes that are paralleled by alterations in synaptic connectivity and function.

Decreased neuronal synaptosome associated protein 29 contributes to poststroke cognitive impairment by disrupting presynaptic maintenance

Background: Poststroke cognitive impairments are common in stroke survivors, and pose a high risk of incident dementia. However, the cause of these cognitive impairments is obscure and required an investigation.

Methods: Oxygen-glucose deprivation (OGD) model and middle cerebral artery occlusion (MCAO) model were used to imitate in vitro or in vivo acute cerebral ischemia, respectively. The differentially expressed synaptosome associated protein 29 (SNAP29)-interacting proteins upon ischemia and reperfusion were analyzed with bioinformatics analysis and the results indicated that the changes of SNAP29 after acute ischemia were mainly involved in the synaptic functions. The outcomes of SNAP29 reduction were assessed with SNAP29 knockdown, which mimicked the distribution of SNAP29 along neuronal processes after acute ischemia. Using the whole-cell patch clamp recording method and transmission electron microscope, the pre-synaptic function and readily releasable pool (RRP) were observed after SNAP29 knock down. Using photogenetic manipulations and behavioral tests, the neuronal projection and cognitive functions of mice with SNAP29 knock down in hippocampus CA1 region were evaluated.

Results: It was found that SNAP29 protein levels decreased in both in vitro and in vivo ischemic models. Further, the SNAP29 reduction wasn't associated with impaired autophagy flux and neuronal survival. When SNAP29 was knocked down in primary cortical neurons, the frequency of AMPARs-mediated mEPSCs, but not the amplitude, significantly decreased. Meanwhile, the mice with SNAP29 knockdown at CA1 region of hippocampus developed an impairment in hippocampus-mPFC (middle prefrontal cortex) circuit and behavioral dysfunctions. Moreover, the size of RRP at presynaptic sites was diminished.

Conclusion: Since SNAP29 protein levels didn't significantly influence the neuronal survival and its decrease was sufficient to disturb the neural circuit via a presynaptic manner, the SNAP29-associated strategies may be an efficient target against poststroke synaptic dysfunction and cognitive deficits.

Delayed voluntary physical exercise restores "when" and "where" object recognition memory after traumatic brain injury

Physical exercise has been associated with improved cognition and may even reduce memory deficits after brain injuries. The aims of this work were to: 1) assess whether voluntary physical exercise can reduce the deficits associated with traumatic brain injury (TBI) in two different components of episodic-like memory based on object recognition, temporal order memory ("when"), and object location memory ("where"); and 2) determine whether changes in levels of brain-derived neurotrophic factor (BDNF) in the hippocampus and prefrontal cortex, as well as alterations in hippocampal cytokines, insulin-like growth factor-1 (IGF-1) and vascular endothelial growth factor (VEGF), may influence the effects exercise has on either or both tasks. The rats were distributed into a sham group, a TBI group that remained sedentary (TBI-sed), and a TBI group that had access to a running wheel for a 25-day period from post-injury day 11 (TBI-exe). The rats were sacrificed after the "where" memory task, at post-injury day 37. Physical exercise restored the "when" and "where" memories, which had been impaired by the TBI, and increased the concentration of BDNF in the hippocampus, but not the prefrontal cortex. Neither TBI nor exercise were found to significantly affect hippocampal cytokines, IGF-1 or VEGF at this time post-injury. BDNF levels showed significant positive correlations with exercise, and with "when" (but not "where") memory. These results indicate that post-injury physical exercise restores "when" and "where" object recognition memory tasks after TBI, and that increased BDNF seems to be involved in this effect, particularly with regard to "when" memory.

Associative recognition memory for identity, spatial and temporal relations in healthy aging

The ability to generate associative representations and to retrieve them from long-term episodic memory generally declines in healthy aging. However, it is unclear whether healthy aging has differential effects on associative memory for identity, spatial configuration, and temporal order relationships. In the current study, we assessed how healthy aging impacts on associative memory for identity, spatial, or temporal relationships between pairs of visual objects via discrimination of intact and rearranged pairs. Accuracy and response time performance of healthy older adults (aged 65-80) were compared with young adults (ages 19-30). Age-related declines in associative memory were observed equally for all types of associations, but these declines differed by associative status: aging most strongly affected ability to discriminate rearranged pairs. These results suggest that associative memory for identity, spatial, and temporal relationships are equally affected by healthy aging, and may all depend on a shared set of basic associative mechanisms.

Translation-Focused Approaches to GPCR Drug Discovery for Cognitive Impairments Associated with Schizophrenia

There are no effective therapeutics for cognitive impairments associated with schizophrenia (CIAS), which includes deficits in executive functions (working memory and cognitive flexibility) and episodic memory. Compounds that have entered clinical trials are inadequate in terms of efficacy and/or tolerability, highlighting a clear translational bottleneck and a need for a cohesive preclinical drug development strategy. In this review we propose hippocampal-prefrontal-cortical (HPC-PFC) circuitry underlying CIAS-relevant cognitive processes across mammalian species as a target source to guide the translation-focused discovery and development of novel, procognitive agents. We highlight several G protein-coupled receptors (GPCRs) enriched within HPC-PFC circuitry as therapeutic targets of interest, including noncanonical approaches (biased agonism and allosteric modulation) to conventional clinical targets, such as dopamine and muscarinic acetylcholine receptors, along with prospective novel targets, including the orphan receptors GPR52 and GPR139. We also describe the translational limitations of popular preclinical cognition tests and suggest touchscreen-based assays that probe cognitive functions reliant on HPC-PFC circuitry and reflect tests used in the clinic, as tests of greater translational relevance. Combining pharmacological and behavioral testing strategies based in HPC-PFC circuit function creates a cohesive, translation-focused approach to preclinical drug development that may improve the translational bottleneck currently hindering the development of treatments for CIAS.

Ontogeny of spontaneous recognition memory in rodents

Spontaneous recognition memory tasks explore thewhat,whereandwhencomponents of recognition memory. These tasks are widely used in rodents to assess cognitive function across the lifespan. While several neurodevelopmental and mental disorders present symptom onset in early life, very little is known about how memories are expressed in early life, and as a consequence how they may be affected in pathological conditions. In this review, we conduct an analysis of the studies examining the expression of spontaneous recognition memory in young rodents. We compiled studies using four different tasks: novel object recognition, object location, temporal order recognition and object place. First, we identify major sources of variability between early life spontaneous recognition studies and classify them for later comparison. Second, we use these classifications to explore the current knowledge on the ontogeny of each of these four spontaneous recognition memory tasks. We conclude by discussing the possible implications of the relative time of onset for each of these tasks and their respective neural correlates. In compiling this research, we hope to advance on establishing a developmental timeline for the emergence of distinct components of recognition memory, while also identifying key areas of focus for future research. Establishing the ontogenetic profile of rodent spontaneous recognition memory tasks will create a necessary blueprint for cognitive assessment in animal models of neurodevelopmental and mental disorders, a first step towards improved and earlier diagnosis as well as novel intervention strategies.

Organisation of cingulum bundle fibres connecting the anterior thalamic nuclei with the rodent anterior cingulate and retrosplenial cortices

Despite considerable interest in the properties of the cingulum bundle, descriptions of the composition of this major pathway in the rodent brain have not kept pace with advances in tract tracing. Using complementary approaches in rats and mice, this study examined the dense, reciprocal connections the anterior thalamic nuclei have with the cingulate and retrosplenial cortices, connections thought to be major contributors to the rodent cingulum bundle. The rat data came from a mixture of fluorescent and viral tracers, some injected directly into the bundle. The mouse data were collated from the Allen Mouse Brain Atlas. The projections from the three major anterior thalamic nuclei occupied much of the external medullary stratum of the cingulum bundle, where they were concentrated in its more medial portions. These anterior thalamic projections formed a rostral-reaching basket of efferents prior to joining the cingulum bundle, with anteromedial efferents taking the most rostral routes, often reaching the genu of the corpus callosum, while anterodorsal efferents took the least rostral route. In contrast, the return cortico-anterior thalamic projections frequently crossed directly through the bundle or briefly joined the internal stratum of the cingulum bundle, often entering the internal capsule before reaching the anterior thalamus. These analyses confirm that anterior thalamic connections comprise an important component of the rodent cingulum bundle, while also demonstrating the very different routes used by thalamo-cortical and cortico-thalamic projections. This information reveals how the composition of the cingulum bundle alters along its length.

Spatial encoding in dorsomedial prefrontal cortex and hippocampus is related during deliberation

Deliberation is thought to involve the internal simulation of the outcomes of candidate actions, the valuation of those outcomes, and the selection of the actions with the highest expected value. While it is known that deliberation involves prefrontal cortical areas, specifically the dorsomedial prefrontal cortex (dmPFC), as well as the hippocampus (HPC) and other brain regions, how these areas process prospective information and select actions is not well understood. We recorded simultaneously from ensembles in dmPFC and CA1 of dorsal HPC in rats during performance of a spatial contingency switching task, and examined the relationships between spatial and reward encoding in these two areas during deliberation at the choice point. We found that CA1 and dmPFC represented either goal locations or the current position simultaneously, but that when goal locations were encoded, HPC and dmPFC did not always represent the same goal location. Ensemble activity in dmPFC predicted when HPC would represent goal locations, but on a broad timescale on the order of seconds. Also, reward encoding in dmPFC increased during hippocampal theta cycles where CA1 ensembles represented the goal location. These results suggest that dmPFC and HPC share prospective information during deliberation, that dmPFC may influence whether HPC represents prospective information, and that information recalled about goal locations by HPC may be integrated into dmPFC reward representations on fast timescales.

Allocentric Spatial Memory Performance in a Virtual Reality-Based Task is Conditioned by Visuospatial Working Memory Capacity

Traditionally, the medial temporal lobe has been considered a key brain region for spatial memory. Nevertheless, executive functions, such as working memory, also play an important role in complex behaviors, such as spatial navigation. Thus, the main goal of this study is to clarify the relationship between working memory capacity and spatial memory performance. Spatial memory was assessed using a virtual reality-based procedure, the Boxes Room task, and the visual working memory with the computer-based Change Localization Task. One hundred and twenty-three (n = 123) participants took part in this study. Analysis of Covariance (ANCOVA) revealed a statistically significant relationship between working memory capacity and spatial abilities. Thereafter, two subgroups n = 60, were formed according to their performance in the working memory task (1st and 4th quartiles, n = 30 each). Results demonstrate that participants with high working memory capacity committed fewer mistakes in the spatial task compared to the low working memory capacity group. Both groups improved their performance through repeated trials of the spatial task, thus showing that they could learn spatial layouts independent of their working memory capacity. In conclusion, these findings support that spatial memory performance is directly related to working memory skills. This could be relevant for spatial memory assessment in brain lesioned patients.

Dorsal hippocampus- and ACC-projecting medial septum neurons differentially contribute to the recollection of episodic-like memory

Episodic memory refers to the recollection of previous experiences containing specific temporal, spatial, and emotional information. The ability to recollect episodic memory requires coordination of multiple brain regions, including the hippocampus (HPC) and the cingulate cortex. While the afferents into HPC and cingulate cortex that orchestrate the episodic memory remain unclear. The medial septum (MS), one of the anatomical location of cholinergic centers, innervates not only the dorsal HPC (dHPC), but also the cingulate and entorhinal cortices. By using "What-Where-When" episodic-like memory (ELM) behavioral model and viral tracing, we found that MS neurons projected to dHPC and anterior cingulate cortex (ACC), which exerted distinct impacts on ELM recollection. Chemogenetic inhibition of the dHPC-projecting MS neurons disrupted "What-Where-When" ELM recollection as well as object location, object-in-place, and recency recognition memories recollection, while chemogenetic inhibition of the ACC-projecting MS neurons only disrupted "What-Where-When" ELM recollection. Moreover, neither dHPC- nor ACC-projecting MS neurons were involved in novel object recognition memory recollection or locomotor activity. Immunostaining showed that ACC- and dHPC-projecting MS neurons are partially overlapped populations. These findings reveal an unsuspected division of ELM processing and provide the potential mechanism that the recollection of episodic memory need the coordination of MS neurons projecting to dHPC and ACC.

Distributed interactive brain circuits for object-in-place memory: A place for time?

Rodents will spontaneously learn the location of an individual object, an ability captured by the object-in-place test. This review considers the network of structures supporting this behavioural test, as well as some potential confounds that may affect interpretation. A hierarchical approach is adopted, as we first consider those brain regions necessary for two simpler, ‘precursor’ tests (object recognition and object location). It is evident that performing the object-in-place test requires an array of areas additional to those required for object recognition or object location. These additional areas include the rodent medial prefrontal cortex and two thalamic nuclei (nucleus reuniens and the medial dorsal nucleus), both densely interconnected with prefrontal areas. Consequently, despite the need for object and location information to be integrated for the object-in-place test, for example, via the hippocampus, other contributions are necessary. These contributions stem from how object-in-place is a test of associative recognition, as none of the individual elements in the test phase are novel. Parallels between the structures required for object-in-place and for recency discriminations, along with a re-examination of the demands of the object-in-place test, signal the integration of temporal information within what is usually regarded as a spatial-object test.

Developmental onset distinguishes three types of spontaneous recognition memory in mice

Spontaneous recognition memory tasks build on an animal’s natural preference for novelty to assess the what, where and when components of episodic memory. Their simplicity, ethological relevance and cross-species adaptability make them extremely useful to study the physiology and pathology of memory. Recognition memory deficits are common in rodent models of neurodevelopmental disorders, and yet very little is known about the expression of spontaneous recognition memory in young rodents. This is exacerbated by the paucity of data on the developmental onset of recognition memory in mice, a major animal model of disease. To address this, we characterized the ontogeny of three types of spontaneous recognition memory in mice: object location, novel object recognition and temporal order recognition. We found that object location is the first to emerge, at postnatal day (P)21. This was followed by novel object recognition (24 h delay), at P25. Temporal order recognition was the last to emerge, at P28. Elucidating the developmental expression of recognition memory in mice is critical to improving our understanding of the ontogeny of episodic memory, and establishes a necessary blueprint to apply these tasks to probe cognitive deficits at clinically relevant time points in animal models of developmental disorders.

Baduanjin mind-body exercise improves logical memory in long-term hospitalized patients with schizophrenia: A randomized controlled trial

Neurocognitive impairment is one of the core symptoms in schizophrenia and poses a great challenge to effective treatment. Sixty-one long-term hospitalized patients with schizophrenia were recruited and randomly assigned to two groups: Baduanjin exercise and brisk walking. Patients in the Baduanjin group received 24 weeks of Baduanjin training (5 days/week, 40 min/day), while patients in the brisk walking group received 24 weeks of brisk walking (5 days/week, 40 min/day). Scores on the Wechsler Memory Scale, Digit Symbol Substitution Test (DSST), and the positive and negative syndrome scale were used to evaluate the logical memory (LM), processing speed, and clinical symptoms of all participants, while the score of Trail Making Test-A (TMT-A) was applied to assess the visual attention and graphomotor speed, at baseline and the 16th week and 24th week of intervention. The one-way repeated measures analysis of variance (ANOVA) was used to test the differences in neurocognitive changes between the two groups. Repeated measures ANOVA showed significant differences between the two groups in the LM immediate (F = 6.21, p = 0.003) and LM delayed (F=5.60, p = 0.005) scores, but not in the completion times of TMT-A (F=.22, p = 0.806) or DSST scores (F=0.97, p = 0.328). A significant effect of time was also detected in the LM immediate (F=10.24, p = 0.000) and LM delayed (F=4.93, p = 0.009) scores and in the completion time of the TMT-A (F=33.10, p = 0.000), but not in the DSST scores (F=2.12, p = 0.122). Baduanjin exercise could improve logical memory in the long-term hospitalized patients with schizophrenia.

The medial prefrontal cortex - hippocampus circuit that integrates information of object, place and time to construct episodic memory in rodents: Behavioral, anatomical and neurochemical properties

Rats and mice have been demonstrated to show episodic-like memory, a prototype of episodic memory, as defined by an integrated memory of the experience of an object or event, in a particular place and time. Such memory can be assessed via the use of spontaneous object exploration paradigms, variably designed to measure memory for object, place, temporal order and object-location inter-relationships. We review the methodological properties of these tests, the neurobiology about time and discuss the evidence for the involvement of the medial prefrontal cortex (mPFC), entorhinal cortex (EC) and hippocampus, with respect to their anatomy, neurotransmitter systems and functional circuits. The systematic analysis suggests that a specific circuit between the mPFC, lateral EC and hippocampus encodes the information for event, place and time of occurrence into the complex episodic-like memory, as a top-down regulation from the mPFC onto the hippocampus. This circuit can be distinguished from the neuronal component memory systems for processing the individual information of object, time and place.

Dorsomedial prefrontal cortex and hippocampus represent strategic context even while simultaneously changing representation throughout a task session

Dorsomedial prefrontal cortex (dmPFC) and hippocampus (HPC) are thought to play complementary roles in a spatial working memory and decision-making network, where spatial information from HPC informs representations in dmPFC, and contextual information from dmPFC biases how HPC recalls that information. We recorded simultaneously from neural ensembles in rodent dmPFC and HPC as rats performed a rule-switching task, and found that ensembles in dmPFC and HPC simultaneously encoded task contingencies and other time-varying information. While ensembles in HPC transitioned to represent new contingencies at the same time as rats updated their strategies to be consistent with the new contingency, dmPFC ensembles transitioned earlier. Neural representations of other time-varying information also changed faster in dmPFC than in HPC. Our results suggest that HPC and dmPFC represent contingencies while simultaneously representing other information which changes over time, and that this contextual information is integrated into hippocampal representations more slowly than in dmPFC.

Multi-level analyses of associative recognition memory: the whole is greater than the sum of its parts

Associative recognition memory depends on the integration of information concerning an item and the spatio-temporal context in which it was encountered. Such an integration depends on dynamic interactions across a brain-wide memory network. Here we discuss evidence from multiple levels of analysis, behavioural, cellular and synaptic which demonstrating the existence of multiple overlapping, subnetworks embedded within these large-scale networks. Recent advances have revealed that of these subnetworks, a distinct hippocampal-prefrontal networks are engaged by different representations (object-spatial or object temporal). Other subnetworks are recruited by distinct processing demands, such as encoding and retrieval which are supported by distinct cellular and synaptic processes. One challenge to multi-level investigations of memory continues to be that conclusions are drawn from correlations of effects rather than from direct evidence of causation.