Memory systems in the brain

Spatially Resolved Transcriptomic Signatures of Hippocampal Subregions and Arc-Expressing Ensembles in Active Place Avoidance Memory

The rodent hippocampus is a spatially organized neuronal network that supports the formation of spatial and episodic memories. We conducted bulk RNA sequencing and spatial transcriptomics experiments to measure gene expression changes in the dorsal hippocampus following the recall of active place avoidance (APA) memory. Through bulk RNA sequencing, we examined the gene expression changes following memory recall across the functionally distinct subregions of the dorsal hippocampus. We found that recall induced differentially expressed genes (DEGs) in the CA1 and CA3 hippocampal subregions were enriched with genes involved in synaptic transmission and synaptic plasticity, while DEGs in the dentate gyrus (DG) were enriched with genes involved in energy balance and ribosomal function. Through spatial transcriptomics, we examined gene expression changes following memory recall across an array of spots encompassing putative memory-associated neuronal ensembles marked by the expression of the IEGs Arc, Egr1, and c-Jun. Within samples from both trained and untrained mice, the subpopulations of spatial transcriptomic spots marked by these IEGs were transcriptomically and spatially distinct from one another. DEGs detected between Arc+ and Arc- spots exclusively in the trained mouse were enriched in several memory-related gene ontology terms, including "regulation of synaptic plasticity" and "memory." Our results suggest that APA memory recall is supported by regionalized transcriptomic profiles separating the CA1 and CA3 from the DG, transcriptionally and spatially distinct IEG expressing spatial transcriptomic spots, and biological processes related to synaptic plasticity as a defining the difference between Arc+ and Arc- spatial transcriptomic spots.

Depth and hierarchies in the predictive brain: From reaction to action

The human brain is a prediction device, a view widely accepted in neuroscience. Prediction is a rational and efficient response that relies on the brain's ability to create and employ generative models to optimize actions over unpredictable time horizons. We argue that extant predictive frameworks while compelling, have not explicitly accounted for the following: (a) The brain's generative models must incorporate predictive depth (i.e., rely on degrees of abstraction to enable predictions over different time horizons); (b) The brain's implementation scheme to account for varying predictive depth relies on dynamic predictive hierarchies formed using the brain's functional networks. We show that these hierarchies incorporate the ascending processes (driven by reaction), and the descending processes (related to prediction), eventually driving action. Because they are dynamically formed, predictive hierarchies allow the brain to address predictive challenges in virtually any domain. By way of application, we explain how this framework can be applied to heretofore poorly understood processes of human behavioral thermoregulation. Although mammalian thermoregulation has been closely tied to deep brain structures engaged in autonomic control such as the hypothalamus, this narrow conception does not translate well to humans. In addition to profound differences in evolutionary history, the human brain is bestowed with substantially increased functional complexity (that itself emerged from evolutionary differences). We argue that behavioral thermoregulation in humans is possible because, (a) ascending signals shaped by homeostatic sub-networks, interject with (b) descending signals related to prediction (implemented in interoceptive and executive sub-networks) and action (implemented in executive sub-networks). These sub-networks cumulatively form a predictive hierarchy for human thermoregulation, potentiating a range of viable responses to known and unknown thermoregulatory challenges. We suggest that our proposed extensions to the predictive framework provide a set of generalizable principles that can further illuminate the many facets of the predictive brain. This article is categorized under: Neuroscience > Behavior Philosophy > Action Psychology > Prediction.

Relationships Among Structural Neuroimaging and Neurocognitive Outcomes in Adolescents and Young Adults with Congenital Heart Disease: A Systematic Review

Congenital heart disease (CHD) is the most common cause of major congenital anomalies in the world. Disruptions to brain development in this population may impact cognitive outcomes. As individuals with CHD age, understanding of long-term neurocognitive and brain outcomes is essential. Synthesis of the current literature of brain-behavior relationships in adolescents and young adults with CHD is needed to understand long-term outcomes and identify literature gaps. This systematic review summarizes and integrates the current literature on the relationship between structural neuroimaging and neurocognitive outcomes in adolescents and young adults with CHD. Included papers were published through August 2, 2021. Searches were conducted on Pubmed and APA PsycInfo. Studies were eligible for inclusion if they evaluated adolescents or young adults (ages 10-35) with CHD, and without genetic comorbidity. Studies explored relationships among structural neuroimaging and neurocognitive outcomes, were in English, and were an empirical research study. A total of 22 papers were included in the current review. Data from each study was extracted and included in a table for comparison along with a systematic assessment of study quality. Results suggest worse brain outcomes (i.e., brain abnormality, reduced volume, lower fractional anisotropy, and brain topology) are related to poorer performance in neuropsychological domains of intelligence, memory, and executive functioning. Consistently, poorer memory performance was related to lower hippocampal and temporal region volumes. Statistically significant brain-behavior relationships in adolescents and young adults with CHD are generally observed across studies but there is a lack of consistency in investigated neuropsychological constructs and brain regions to be able to make specific conclusions. Further research with adult samples of CHD is needed to better understand the long-term impacts of early neurological insult.

The Synergies Between Understanding Belief Formation and Artificial Intelligence

Understanding artificial intelligence (AI) and belief formation have interesting bidirectional synergies. From explaining the logical derivation of beliefs and their internal consistency, to giving a quantitative account of mightiness, AI still has plenty of unexploited metaphors that can illuminate belief formation. In addition, acknowledging that AI should integrate itself with our belief processes (mainly, the capacity to reflect, rationalize, and communicate that is allowed by semantic coding) makes it possible to focus on more promising lines such as Interpretable Machine Learning.

l-Lactate: Food for Thoughts, Memory and Behavior

More and more evidence shows how brain energy metabolism is the linkage between physiological and morphological synaptic plasticity and memory consolidation. Different types of memory are associated with differential inputs, each with specific inputs that are upstream diverse molecular cascades depending on the receptor activity. No matter how heterogeneous the response is, energy availability represents the lowest common denominator since all these mechanisms are energy consuming and the brain networks adapt their performance accordingly. Astrocytes exert a primary role in this sense by acting as an energy buffer; glycogen granules, a mechanism to store glucose, are redistributed at glance and conveyed to neurons via the Astrocyte–Neuron Lactate Shuttle (ANLS). Here, we review how different types of memory relate to the mechanisms of energy delivery in the brain.

Functional Decoupling of Emotion Coping Network Subsides Automatic Emotion Regulation by Implementation Intention

Automatic emotion regulation (AER) plays a vital role in the neuropathology underlying both suicide and self-harm via modifying emotional impact effortlessly. However, both the effortless account and the neural mechanisms of AER are undetermined. To investigate the neural changes at AER, we collected functional MRI (fMRI) in 31 participants who attended to neutral and disgust pictures in three conditions: watching, goal intention (GI), and reappraisal by implementation intention (RII). Results showed that RII (but not GI) decreased negative feelings and bilateral amygdala activity without increasing cognitive efforts, evidenced by the reduced effort rating and less prefrontal engagement during RII compared with during watching and GI. These emotion-regulatory effects of RII cannot be explained by emotional habituation, as the supplementary experiment (N = 31) showed no emotional habituation effects when the same disgust pictures were presented repeatedly three times for each watching and GI condition. Task-based network analysis showed both RII and GI relative to watching increased functional connectivities (FCs) of the ventral anterior cingulate cortex to the left insula and right precuneus during conditions, two FCs subserving goal setup. However, RII relative to GI exhibited weaker FCs in brain networks subserving effortful control, memory retrieval, aversive anticipation, and motor planning. In these FCs, the FC intensity of putamen-operculum/lingual and paracentral-superior temporal gyri positively predicted regulatory difficulty ratings. These findings suggest that the setup of implementation intention automatizes emotion regulation by reducing the online mobilization of emotion-coping neural systems.

Structural and functional consequences in the amygdala of leptin-deficient mice

On the one hand, the emotional state can influence food intake and on the other hand, hunger can have an impact on the emotional state. Leptin, which is encoded by the ob gene, is involved in the energy homeostasis and plays a role in development of obesity. Mice deficient for leptin (ob/ob) are obese and display several behavioral alterations. It has been shown that ob/ob mice display striking changes in neuronal plasticity within the limbic system, e.g., hippocampal formation. We focus on alterations in ob/ob mice that can be related to alter processing in another part of the limbic system, the amygdala. ob/ob mice have a higher food consumption than age-matched controls, which might have an impact on the emotional state of these mice. Since the amygdala is involved in emotional processing, we analyze whether ob/ob mice display alterations in plasticity at the electrophysiological and structural level. No changes were seen in dendritic spine densities in the basolateral and lateral (LA) nucleus of the amygdala. Interestingly and in contrast to the hippocampus (Porter et al. 2013), long-term potentiation in the LA was increased in ob/ob mice. Our results indicate that amygdalar and hippocampal synaptic plasticity are regulated in different ways by leptin deficiency in accordance with the different functions of these limbic structures in stress and anxiety.

A Review of the Historical Evolutionary Process of Dry and Water Maze Tests in Rodents

This research provides an overview of the historical advances of the maze tests that are widely used to assess the cognitive impairments in rodents. Particularly, this study focuses on the issue of learning and memory behavioral tests, including dry and water mazes. Several types of mazes have been used in this setting, but their real advantages and applications depend on the type selected by the researcher. We answered some of the basic questions that any interested researcher in such studies may be faced with. The reviewed topics are as follows: the definition of maze learning, the role of the memory in the maze learning, the differences between several types of mazes, and foremost the rationale behind the maze constructions and designs.

Neural evidence that disengaging memory retrieval is modulated by stimulus valence and rumination

To remember information from our personal past we need to be in a cognitive state where we treat stimuli as cues for memory retrieval. In this study we considered whether participants could exert control and disengage from a memory state when it was no longer required for the task at hand. In particular, we examined whether this ability was affected by the valence of the stimuli and participant's rumination scores. After a study phase participants completed test blocks where the task switched every two trials between a memory task (retrieving information from the study phase) and a perceptual task. Even though there was no episodic memory requirement in the perceptual task, a well-established event-related potential (ERP) index of memory retrieval was present for both trials when the stimuli were negative valenced pictures but not for neutral pictures. Furthermore, there was a positive correlation between the magnitude of this ERP memory index in the perceptual task and rumination scores but only for neutral stimuli and not negative. Thus, in this study participants generally had difficultly suppressing memory retrieval when negative stimuli were presented. However, for neutral stimuli only ruminators were more susceptible to memory intrusions.

Benefits of Implicit Regulation of Instructed Fear: Evidence From Neuroimaging and Functional Connectivity

Instructed fear, which denotes fearful emotions learned from others' verbal instructions, is an important form of fear acquisition in humans. Maladaptive instructed fear produces detrimental effects on health, but little is known about performing an efficient regulation of instructed fear and its underlying neural substrates. To address this question, 26 subjects performed an instructed fear task where emotional experiences and functional neuroimages were recorded during watching, explicit regulation (calmness imagination), and implicit regulation (calmness priming) conditions. Results indicated that implicit regulation decreased activity in the left amygdala and left insula for instructed fear; however, these effects were absent in explicit regulation. The implementation of implicit regulation did not increase activity in the frontoparietal control regions, while explicit regulation increased dorsolateral prefrontal cortex activity. Furthermore, implicit regulation increased functional connectivity between the right amygdala and right fusiform gyrus, and decreased functional connectivity between the right medial temporal gyrus and left inferior frontal gyrus, which are key nodes of memory retrieval and cognitive control networks, respectively. These findings suggest a favourable effect of implicit regulation on instructed fear, which is subserved by less involvement of control-related brain mechanisms.

Training the next generation of Africa's doctors: why medical schools should embrace the team-based learning pedagogy

BACKGROUND

As far back as 1995, the Cape Town Declaration on training Africa's future doctor recognized the need for medical schools to adopt active-learning strategies in order to nurture holistic development of the doctor. However, medical education in Africa remains largely stuck with traditional pedagogies that emphasize the 'hard skills' such as knowledge and clinical acumen while doing little to develop 'soft skills' such as effective communication, teamwork, critical thinking or life-long learning skills. By reviewing literature on Africa's epidemiologic and demographic transitions, we establish the need for increasing the output of well-trained doctors in order to match the continent's complex current and future healthcare needs. Challenges that bedevil African medical education such as outdated curricula, limited educational infrastructure and chronic resource constraints are presented and discussed. Furthermore, increased student enrollments, a trend observed at many schools, coupled with chronic faculty shortages have inadvertently presented specific barriers against the success of small-group active-learning strategies such as Problem-Based and Case-Based Learning. We argue that Team-Based Learning (TBL) offers a robust alternative for delivering holistic medical education in the current setting. TBL is instructor-driven and embodies key attributes that foster development of both 'hard' and 'soft' skills. We elaborate on advantages that TBL is likely to bring to the African medical education landscape, including increased learner enthusiasm and creativity, accountability, peer mentorship, deep learning and better knowledge retention. As with all new pedagogical methods, challenges anticipated during initial implementation of TBL are discussed followed by the limited pilot experiences with TBL in Africa.

CONCLUSION

For its ability to enable a student-centered, active learning experience delivered at minimum cost, we encourage individual instructors and African medical schools at large, to adopt TBL as a complementary strategy towards realizing the goal of training Africa's fit-for-purpose doctor.

Lesions of the Patch Compartment of Dorsolateral Striatum Disrupt Stimulus-Response Learning

The striatum mediates habit formation and reward association. The striatum can be divided into the patch and matrix compartment, which are two distinct regions that sub-serve different aspects of behavior. The patch compartment may mediate reward-related behaviors, while the matrix compartment may mediate adaptive motor functions. Previous studies indicate that enhanced relative activation of the patch versus matrix compartment is associated with inflexible behaviors, such as stereotypy. Habitual behaviors are also inflexible in nature, but whether enhanced activation of the patch compartment contributes to habitual behavior is not known. The goal of the current study was to examine the role of patch compartment in the development of habit formation. We used dermorphin-saporin to ablate neurons of the patch compartment in the dorsolateral striatum prior to training animals to self-administer sucrose on a random interval schedule of reinforcement. Our data showed that patch compartment lesions in the dorsolateral striatum reduced the reinstatement of sucrose self-administration after sucrose devaluation, indicating that destruction of this region prevented the development of habitual behavior. Additionally, in animals with patch compartment lesions in the DLS that did not develop habitual behavior, activation of the dorsolateral striatum and sensorimotor cortex was diminished, while activity in the dorsomedial striatum and prefrontal cortex was increased, suggesting less engagement of regions that mediate habitual behaviors and heightened engagement of regions that mediate goal-directed behaviors occurs with reduced habit formation. These data indicate that the dorsolateral patch compartment may mediate habit formation by altering information flow through basal ganglia circuits.

Sex differences in color discrimination and serial reversal learning in mollies and guppies

Behavioral flexibility provides an individual with the ability to adapt its behavior in response to environmental changes. Studies on mammals, birds, and teleosts indicate greater behavioral flexibility in females. Conversely, males appear to exhibit greater behavioral persistence. We, therefore, investigated sex differences in behavioral flexibility in 2 closely related molly species (Poecilia latipinna, P. mexicana) and their more distant relative, the guppy P. reticulata by comparing male and female individuals in a serial, visual reversal learning task. Fish were first trained in color discrimination, which was quickly learned by all females (guppies and mollies) and all molly males alike. Despite continued training over more than 72 sessions, male guppies did not learn the general test procedure and were, therefore, excluded from further testing. Once the reward contingency was reversed serially, molly males of both species performed considerably better by inhibiting their previous response and reached the learning criterion significantly faster than their respective conspecific females. Moreover, Atlantic molly males clearly outperformed all other individuals (males and females) and some of them even reached the level of 1-trial learning. Thus, the apparently universal pattern of higher female behavioral flexibility seems to be inverted in the 2 examined molly species, although the evolutionary account of this pattern remains highly speculative. These findings were complemented by the observed lower neophobia of female sailfin mollies compared with their male conspecifics. This sex difference was not observed in Atlantic mollies that were observed to be significantly less distressed in a novel situation than their consexuals. Hypothetically, sex differences in behavioral flexibility can possibly be explained in terms of the different roles that males and females play in mating competition, mate choice, and reproduction or, more generally, in complex social interactions. Each of these characteristics clearly differed between the closely related mollies and the more distantly related guppies.

Affective responses to uncertain real-world outcomes: Sentiment change on Twitter

We use data from Twitter.com to study the interplay between affect and expectations about uncertain outcomes. In two studies, we obtained tweets about candidates in the 2014 US Senate elections and tweets about National Football League (NFL) teams in the 2014/2015 NFL season. We chose these events because a) their outcomes are highly uncertain and b) they attract a lot of attention and feature heavily in the communication on social media. We also obtained a priori expectations for the events from political forecasting and sport betting websites. Using this quasi-experimental design, we found that unexpected events are associated with more intense affect than expected events. Moreover, the effect of expectations is larger for outcomes that fall below expectations than outcomes that exceed expectations. Our results are consistent with fundamental principles in psychological science, such as reference-dependence in experienced affect. We discuss how naturally occurring online data can be used to test psychological predictions and develop novel psychological insights.

Memory decline in elderly with cerebral small vessel disease explained by temporal interactions between white matter hyperintensities and hippocampal atrophy

White matter hyperintensities (WMH) constitute the visible spectrum of cerebral small vessel disease (SVD) markers and are associated with cognitive decline, although they do not fully account for memory decline observed in individuals with SVD. We hypothesize that WMH might exert their effect on memory decline indirectly by affecting remote brain structures such as the hippocampus. We investigated the temporal interactions between WMH, hippocampal atrophy and memory decline in older adults with SVD. Five hundred and three participants of the RUNDMC study underwent neuroimaging and cognitive assessments up to 3 times over 8.7 years. We assessed WMH volumes semi-automatically and calculated hippocampal volumes (HV) using FreeSurfer. We used linear mixed effects models and causal mediation analyses to assess both interaction and mediation effects of hippocampal atrophy in the associations between WMH and memory decline, separately for working memory (WM) and episodic memory (EM). Linear mixed effect models revealed that the interaction between WMH and hippocampal volumes explained memory decline (WM: β = .067; 95%CI[.024-0.111]; p < .01; EM: β = .061; 95%CI[.025-.098]; p < .01), with better model fit when the WMH*HV interaction term was added to the model, for both WM (likelihood ratio test, χ² [1] = 9.3, p < .01) and for EM (likelihood ratio test, χ² [1] = 10.7, p < .01). Mediation models showed that both baseline WMH volume (β = -.170; p = .001) and hippocampal atrophy (β = 0.126; p = .009) were independently related to EM decline, but the effect of baseline WMH on EM decline was not mediated by hippocampal atrophy (p value indirect effect: 0.572). Memory decline in elderly with SVD was best explained by the interaction of WMH and hippocampal volumes. The relationship between WMH and memory was not causally mediated by hippocampal atrophy, suggesting that memory decline during aging is a heterogeneous condition in which different pathologies contribute to the memory decline observed in elderly with SVD.

Gene-environment interactions informing therapeutic approaches to cognitive and affective disorders

Gene-environment interactions drive experience-dependent changes in the brain that alter cognition, emotion and behaviour. Positive engagement with the environment, through novel experience and physical activity, can improve brain function, although the mechanisms mediating such experience-dependent plasticity remain to be fully elucidated. In this article, we discuss the therapeutic value of environmental stimuli, exercise and environmental enrichment (EE), for cognitive and affective disorders, with implications for the understanding and treatment of depression and anxiety disorders. We demonstrate that environmental manipulations are potential therapeutic strategies for improving outcomes in these psychiatric disorders, including beneficial impacts on cognition. We discuss how EE and exercise are therapeutic environmental interventions impacting both affective and cognitive function. Serotonergic (5-HTergic) signaling is strongly implicated in the manifestation of psychiatric disorders and regulates cognitive and emotional processing that can underpin them. Thus, we focus on evidence implicating the serotonergic system in mediating gene-environment interactions to EE and exercise. Finally, we discuss robust gene-environment interactions associated with EE and exercise interventions, and their impacts on specific brain areas, particularly the hippocampus. We focus on potential mediators of this experience-dependent plasticity, including adult neurogenesis and brain-derived neurotrophic factor (BDNF). Furthermore, we explore molecular and cellular mechanisms of experience-dependent plasticity that potentially underlie the restoration of affective and cognitive phenotypes, thus identifying novel therapeutic targets. This article is part of the Special Issue entitled "Neurobiology of Environmental Enrichment".

Behavioral and biochemical evidences for nootropic activity of boldine in young and aged mice

Boldine, a bioactive compound, has been reported to be neuroprotective, but its effect on learning and memory has not been explored. So, the present study was aimed to study the effect of boldine on the learning and memory of the Swiss albino male young and aged mice. Boldine (1.5, 3 and 6mg/kg, po) and physostigmine salicylate (0.1mg/kg, ip) were administered to separate groups of mice for 7 successive days. Morris water maze was utilized as a behavioural model to study the effect of drugs on learning and memory of mice. Boldine and physostigmine significantly improved learning and memory of young as well as aged mice, as indicated by decrease in escape latency time during training session and increase in time spent in target quadrant during retrieval session. No significant effect on locomotor activities of mice was observed due to drug treatments. Memory-enhancing activity of boldine (3mg/kg) was found to be comparable to physostigmine. Boldine significantly reversed scopolamine-, sodium nitrite- and aging-induced amnesia in mice. Moreover, boldine attenuated oxidative stress, as shown by a significant decrease in brain malondialdehyde as well as brain nitrite levels and a significant increase in brain GSH level of young as well as aged mice. Brain acetylcholinesterase activity was also significantly inhibited by boldine in young as well as aged mice. In conclusion boldine administered for 7 successive days exhibited significant improvement of learning and memory of young and aged mice possibly through inhibition of brain acetylcholinesterase activity and alleviation of brain oxidative stress.

Emotions Are Rising: The Growing Field of Affect Neuropsychology

Thirty years ago, the neuropsychology of emotion started to emerge as a mainstream topic. Careful examination of individual patients showed that emotion, like memory, language, and so on, could be differentially affected by brain disorders, especially in the right hemisphere. Since then, there has been accelerating interest in uncovering the neural architecture of emotion, and the major steps in this process of discovery over the past 3 decades are detailed in this review. In the 1990s, magnetic resonance imaging (MRI) scans provided precise delineation of lesions in the amygdala, medial prefrontal cortex, insula and somatosensory cortex as underpinning emotion disorders. At the same time, functional MRI revealed activation that was bilateral and also lateralized according to task demands. In the 2000s, converging evidence suggested at least two routes to emotional responses: subcortical, automatic and autonomic responses and slower, cortical responses mediating cognitive processing. The discovery of mirror neurons in the 1990s reinvigorated older views that simulation was the means to recognize emotions and empathize with others. More recently, psychophysiological research, revisiting older Russian paradigms, has contributed new insights into how autonomic and other physiological indices contribute to decision making (the somatic marker theory), emotional simulation, and social cognition. Finally, this review considers the extent to which these seismic changes in understanding emotional processes in clinical disorders have been reflected in neuropsychological practice. (JINS, 2017, 23, 719-731).

Is the Alzheimer's disease cortical thickness signature a biological marker for memory?

Recent work suggests that analysis of the cortical thickness in key brain regions can be used to identify individuals at greatest risk for development of Alzheimer's disease (AD). It is unclear to what extent this "signature" is a biological marker of normal memory function - the primary cognitive domain affected by AD. We examined the relationship between the AD signature biomarker and memory functioning in a group of neurologically healthy young and older adults. Cortical thickness measurements and neuropsychological evaluations were obtained in 110 adults (age range 21-78, mean = 46) drawn from the Brain Resource International Database. The cohort was divided into young adult (n = 64, age 21-50) and older adult (n = 46, age 51-78) groups. Cortical thickness analysis was performed with FreeSurfer, and the average cortical thickness extracted from the eight regions that comprise the AD signature. Mean AD-signature cortical thickness was positively associated with performance on the delayed free recall trial of a list learning task and this relationship did not differ between younger and older adults. Mean AD-signature cortical thickness was not associated with performance on a test of psychomotor speed, as a control task, in either group. The results suggest that the AD signature cortical thickness is a marker for memory functioning across the adult lifespan.

Dammarane Sapogenins Ameliorates Neurocognitive Functional Impairment Induced by Simulated Long-Duration Spaceflight

Increasing evidence indicates the occurrence of cognitive impairment in astronauts under spaceflight compound conditions, but the underlying mechanisms and countermeasures need to be explored. In this study, we found that learning and memory abilities were significantly reduced in rats under a simulated long-duration spaceflight environment (SLSE), which includes microgravity, isolation confinement, noises, and altered circadian rhythms. Dammarane sapogenins (DS), alkaline hydrolyzed products of ginsenosides, can enhance cognition function by regulating brain neurotransmitter levels and inhibiting SLSE-induced neuronal injury. Bioinformatics combined with experimental verification identified that the PI3K-Akt-mTOR pathway was inhibited and the MAPK pathway was activated during SLSE-induced cognition dysfunction, whereas DS substantially ameliorated the changes in brain. These findings defined the characteristics of SLSE-induced cognitive decline and the mechanisms by which DS improves it. The results provide an effective candidate for improving cognitive function in spaceflight missions.

Memory in Neuroscience: Rhetoric Versus Reality

The central point of this article is that the concept of memory as information storage in the brain is inadequate for and irrelevant to understanding the nervous system. Beginning from the sensorimotor hypothesis that underlies neuroscience—that the entire function of the nervous system is to connect experience to appropriate behavior—the paper defines memories as sequences of events that connect remote experience to present behavior. Their essential components are (a) persistent events that bridge the time from remote experience to present behavior and (b) junctional events in which connections from remote experience and recent experience merge to produce behavior. The sequences comprising even the simplest memories are complex. This is both necessary—to preserve previously learned behaviors—and inevitable—due to secondary activity-driven plasticity. This complexity further highlights the inadequacy of the information storage concept and the importance of extreme simplicity in models used to study memory.

Memory deficit in patients with schizophrenia and posttraumatic stress disorder: relational vs item-specific memory

It has been well established that patients with schizophrenia have impairments in cognitive functioning and also that patients who experienced traumatic events suffer from cognitive deficits. Of the cognitive deficits revealed in schizophrenia or posttraumatic stress disorder (PTSD) patients, the current article provides a brief review of deficit in episodic memory, which is highly predictive of patients' quality of life and global functioning. In particular, we have focused on studies that compared relational and item-specific memory performance in schizophrenia and PTSD, because measures of relational and item-specific memory are considered the most promising constructs for immediate tangible development of clinical trial paradigm. The behavioral findings of schizophrenia are based on the tasks developed by the Cognitive Neuroscience Treatment Research to Improve Cognition in Schizophrenia (CNTRICS) initiative and the Cognitive Neuroscience Test Reliability and Clinical Applications for Schizophrenia (CNTRACS) Consortium. The findings we reviewed consistently showed that schizophrenia and PTSD are closely associated with more severe impairments in relational memory compared to item-specific memory. Candidate brain regions involved in relational memory impairment in schizophrenia and PTSD are also discussed.

The Basic-Systems Model of Episodic Memory

Behavior, neuropsychology, and neuroimaging suggest that episodic memories are constructed from interactions among the following basic systems: vision, audition, olfaction, other senses, spatial imagery, language, emotion, narrative, motor output, explicit memory, and search and retrieval. Each system has its own well-documented functions, neural substrates, processes, structures, and kinds of schemata. However, the systems have not been considered as interacting components of episodic memory, as is proposed here. Autobiographical memory and oral traditions are used to demonstrate the usefulness of the basic-systems model in accounting for existing data and predicting novel findings, and to argue that the model, or one similar to it, is the only way to understand episodic memory for complex stimuli routinely encountered outside the laboratory.

Immunohistochemical analysis of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) toxicity on the developmental dentate gyrus and hippocampal fimbria in fetal mice

Dioxins are widespread persistent environmental contaminants with adverse impacts on humans and experimental animals. Behavioral and cognitive functions are impaired by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) exposure. TCDD exerts its toxicity via the aryl hydrocarbon receptor (AhR), a ligand-activated transcription factor. The hippocampus, which plays important roles in episodic memory and spatial function, is considered vulnerable to TCDD-induced neurotoxicity, because it contains the AhR. We herein investigated the effects of TCDD toxicity on hippocampal development in embryonic mice. TCDD was administered to dams at 8.5 days postcoitum with a single dose of 20, 200, 2,000 and 5,000 ng/kg body weight (groups T20, T200, T2000 and T5000, respectively), and the brains were dissected from their pups at embryonic day 18.5. Immunohistochemical analysis demonstrated that the Glial Fibrillary Acidic Protein (GFAP) immunoreactivities in the dentate gyrus (DG) were reduced in the T5000 group. Granular GFAP immunoreactivity was observed in the hippocampal fimbria, and the number of immunoreactive fimbria was significantly decreased in the T5000 group. The number of Proliferating Cell Nuclear Antigen (PCNA)-positive cells was decreased in all TCDD-exposed groups and significantly reduced in the T20, T200 and T5000 groups. Together, these results demonstrate that maternal TCDD exposure has adverse impacts on neural stem cells (NSCs), neural precursor cells (NPCs) and granular cells in the DG and disrupts the NSC maintenance and timing of differentiation in the hippocampal fimbria, which in turn interrupt neuronal development in future generations of mice.

Cortical reinstatement and the confidence and accuracy of source memory

Cortical reinstatement refers to the overlap between neural activity elicited during the encoding and the subsequent retrieval of an episode, and is held to reflect retrieved mnemonic content. Previous findings have demonstrated that reinstatement effects reflect the quality of retrieved episodic information as this is operationalized by the accuracy of source memory judgments. The present functional magnetic resonance imaging (fMRI) study investigated whether reinstatement-related activity also co-varies with the confidence of accurate source judgments. Participants studied pictures of objects along with their visual or spoken names. At test, they first discriminated between studied and unstudied pictures and then, for each picture judged as studied, they also judged whether it had been paired with a visual or auditory name, using a three-point confidence scale. Accuracy of source memory judgments- and hence the quality of the source-specifying information--was greater for high than for low confidence judgments. Modality-selective retrieval-related activity (reinstatement effects) also co-varied with the confidence of the corresponding source memory judgment. The findings indicate that the quality of the information supporting accurate judgments of source memory is indexed by the relative magnitude of content-selective, retrieval-related neural activity.

A network convergence zone in the hippocampus

The hippocampal formation is a key structure for memory function in the brain. The functional anatomy of the brain suggests that the hippocampus may be a convergence zone, as it receives polysensory input from distributed association areas throughout the neocortex. However, recent quantitative graph-theoretic analyses of the static large-scale connectome have failed to demonstrate the centrality of the hippocampus; in the context of the whole brain, the hippocampus is not among the most connected or reachable nodes. Here we show that when communication dynamics are taken into account, the hippocampus is a key hub in the connectome. Using a novel computational model, we demonstrate that large-scale brain network topology is organized to funnel and concentrate information flow in the hippocampus, supporting the long-standing hypothesis that this region acts as a critical convergence zone. Our results indicate that the functional capacity of the hippocampus is shaped by its embedding in the large-scale connectome.

Dual reward prediction components yield Pavlovian sign- and goal-tracking

Reinforcement learning (RL) has become a dominant paradigm for understanding animal behaviors and neural correlates of decision-making, in part because of its ability to explain Pavlovian conditioned behaviors and the role of midbrain dopamine activity as reward prediction error (RPE). However, recent experimental findings indicate that dopamine activity, contrary to the RL hypothesis, may not signal RPE and differs based on the type of Pavlovian response (e.g. sign- and goal-tracking responses). In this study, we address this discrepancy by introducing a new neural correlate for learning reward predictions; the correlate is called "cue-evoked reward". It refers to a recall of reward evoked by the cue that is learned through simple cue-reward associations. We introduce a temporal difference learning model, in which neural correlates of the cue itself and cue-evoked reward underlie learning of reward predictions. The animal's reward prediction supported by these two correlates is divided into sign and goal components respectively. We relate the sign and goal components to approach responses towards the cue (i.e. sign-tracking) and the food-tray (i.e. goal-tracking) respectively. We found a number of correspondences between simulated models and the experimental findings (i.e. behavior and neural responses). First, the development of modeled responses is consistent with those observed in the experimental task. Second, the model's RPEs were similar to dopamine activity in respective response groups. Finally, goal-tracking, but not sign-tracking, responses rapidly emerged when RPE was restored in the simulated models, similar to experiments with recovery from dopamine-antagonist. These results suggest two complementary neural correlates, corresponding to the cue and its evoked reward, form the basis for learning reward predictions in the sign- and goal-tracking rats.

Higher-order conditioning is impaired by hippocampal lesions

Behavior in the real world is rarely motivated by primary conditioned stimuli that have been directly associated with potent unconditioned reinforcers. Instead, motivation and choice behavior are driven by complex chains of higher-order associations that are only indirectly linked to intrinsic reward and often exert their influence outside awareness. Second-order conditioning (SOC) [1] is a basic associative-learning mechanism whereby stimuli acquire motivational salience by proxy, in the absence of primary incentives [2, 3]. Memory-systems theories consider first-order conditioning (FOC) and SOC to be prime examples of hippocampal-independent nondeclarative memory [4, 5]. Accordingly, neurobiological models of SOC focus almost exclusively on nondeclarative neural systems that support motivational salience and reward value. Transfer of value from a conditioned stimulus to a neutral stimulus is thought to require the basolateral amygdala [6, 7] and the ventral striatum [2, 3], but not the hippocampus. We developed a new paradigm to measure appetitive SOC of tones in rats. Hippocampal lesions severely impaired both acquisition and expression of SOC despite normal FOC. Unlike controls, rats with hippocampal lesions could not discriminate between positive and negative secondary conditioned tones, although they exhibited general familiarity with previously presented tones compared with new tones. Importantly, normal rats' behavior, in contrast to that of hippocampal groups, also revealed different confidence levels as indexed by effort, a central characteristic of hippocampal relational memory. The results indicate, contrary to current systems models, that representations of intrinsic relationships between reward value, stimulus identity, and motivation require hippocampal mediation when these relationships are of a higher order.

Muscle tension induced after learning enhances long-term narrative and visual memory in healthy older adults

Arousing events are better remembered than mundane events. Indeed, manipulation of arousal, such as by muscle tension, can influence memory even when it occurs shortly after learning. Indeed, our founding study showed this approach can raise delayed memory performance in older adults to a level comparable to that of unaided young adults. Yet, systematic studies, especially those investigating different modalities or types of memory, have not been done. This study investigated the effects of a brief bout of isometric exercise via handgrip on narrative and visuospatial episodic memory in healthy elders. Forty-seven participants completed the Logical Memory subtest of the Wechsler Memory Scales III (LM) and the Benton Visual Retention Test (BVRT), followed alternately by no treatment and by moderately squeezing a sand-filled latex ball for 1-min (counterbalanced order and test forms). Isometric exercise significantly increased both positive and negative affect ratings. Retention was tested 2 weeks later. Delayed recall and recognition of LM was enhanced by arousal relative to control, as was recognition of the BVRT. The results extend past findings that muscle tension induced after learning modulates memory consolidation, extending findings in elders to suggest that a simple form of isometric exercise can have practical effects, such as aiding memory for stories and images.

Is Granger causality a viable technique for analyzing fMRI data?

Multivariate neural data provide the basis for assessing interactions in brain networks. Among myriad connectivity measures, Granger causality (GC) has proven to be statistically intuitive, easy to implement, and generate meaningful results. Although its application to functional MRI (fMRI) data is increasing, several factors have been identified that appear to hinder its neural interpretability: (a) latency differences in hemodynamic response function (HRF) across different brain regions, (b) low-sampling rates, and (c) noise. Recognizing that in basic and clinical neuroscience, it is often the change of a dependent variable (e.g., GC) between experimental conditions and between normal and pathology that is of interest, we address the question of whether there exist systematic relationships between GC at the fMRI level and that at the neural level. Simulated neural signals were convolved with a canonical HRF, down-sampled, and noise-added to generate simulated fMRI data. As the coupling parameters in the model were varied, fMRI GC and neural GC were calculated, and their relationship examined. Three main results were found: (1) GC following HRF convolution is a monotonically increasing function of neural GC; (2) this monotonicity can be reliably detected as a positive correlation when realistic fMRI temporal resolution and noise level were used; and (3) although the detectability of monotonicity declined due to the presence of HRF latency differences, substantial recovery of detectability occurred after correcting for latency differences. These results suggest that Granger causality is a viable technique for analyzing fMRI data when the questions are appropriately formulated.

The neural correlates of recollection: transient versus sustained FMRI effects

Prior research has identified several regions where neural activity is enhanced when recollection of episodic information is successful. Here, we investigated whether these regions dissociate according to whether recollection-related activity is transient or sustained across the time that recollected information must be maintained before a behavioral judgment. Human subjects studied a series of word-picture pairs under the requirement to judge which of the denoted objects was smaller. Following each of 4 study sessions, a scanned test phase occurred in which a series of studied and unstudied words was presented. The requirement at test was to judge whether each word was old or new and, if judged old, to retrieve the associated study picture and hold it in mind until a cue appeared. The delay interval varied between two and eight seconds. The cue instructed subjects which of three different judgments should be applied to the retrieved picture. Separate responses were required when words were either deemed new or the associated image was not retrieved. Relative to studied words for which the associated picture could not be retrieved, words giving rise to successful recollection elicited transient responses in the hippocampus/parahippocampal cortex and retrosplenial cortex, and to sustained activity in prefrontal cortex, the intraparietal sulcus, the left angular gyrus and the inferior temporal gyrus. The finding that recollection-related activity in the angular gyrus tracked the period over which recollected information was maintained is consistent with the proposal that this region contributes to the online representation of recollected information.

Neural correlates of the encoding of multimodal contextual features

Functional magnetic resonance imaging (fMRI) was employed to identify neural regions engaged during the encoding of contextual features belonging to different modalities. Subjects studied objects that were presented to the left or right of fixation. Each object was paired with its name, spoken in either a male or a female voice. The test requirement was to discriminate studied from unstudied pictures and, for each picture judged old, to retrieve its study location and the gender of the voice that spoke its name. Study trials associated with accurate rather than inaccurate location memory demonstrated enhanced activity in the fusiform and parahippocampal cortex and the hippocampus and reduced activity (a negative subsequent memory effect) in the medial occipital cortex. Successful encoding of voice information was associated with enhanced study activity in the right middle superior temporal sulcus and activity reduction in the right superior frontal cortex. These findings support the proposal that encoding of a contextual feature is associated with enhanced activity in regions engaged during its online processing. In addition, they indicate that negative subsequent memory effects can also demonstrate feature-selectivity. Relative to other classes of study trials, trials for which both contextual features were later retrieved demonstrated enhanced activity in the lateral occipital complex and reduced activity in the temporo-parietal junction. These findings suggest that multifeatural encoding was facilitated when the study item was processed efficiently and study processing was not interrupted by redirection of attention toward extraneous events.

The operation of pattern separation and pattern completion processes associated with different attributes or domains of memory

Pattern separation and pattern completion processes are central to how the brain processes information in an efficient manner. Research into these processes is escalating and deficient pattern separation is being implicated in a wide array of genetic disorders as well as in neurocognitive aging. Despite the quantity of research, there remains a controversy as to precisely which behavioral paradigms should be used to best tap into pattern separation and pattern completion processes, as well as to what constitute legitimate outcome measures reflecting impairments in pattern separation and pattern completion. This review will discuss a theory based on multiple memory systems that provides a framework upon which behavioral tasks can be designed and their results interpreted. Furthermore, this review will discuss the nature of pattern separation and pattern completion and extend these processes outside the hippocampus and across all domains of information processing. After these discussions, an optimal strategy for designing behavioral paradigms to evaluate pattern separation and pattern completion processes will be provided.

NMDA and kainate receptor expression, long-term potentiation, and neurogenesis in the hippocampus of long-lived Ames dwarf mice

In the current study, we investigated changes in N-methyl D-aspartate (NMDA) and kainate receptor expression, long-term potentiation (LTP), and neurogenesis in response to neurotoxic stress in long-living Ames dwarf mice. We hypothesized that Ames dwarf mice have enhanced neurogenesis that enables retention of spatial learning and memory with age and promotes neurogenesis in response to injury. Levels of the NMDA receptors (NR)1, NR2A, NR2B, and the kainate receptor (KAR)2 were increased in Ames dwarf mice, relative to wild-type littermates. Quantitative assessment of the excitatory postsynaptic potential in Schaffer collaterals in hippocampal slices from Ames dwarf mice showed an increased response in high-frequency induced LTP over time compared with wild type. Kainic acid (KA) injection was used to promote neurotoxic stress-induced neurogenesis. KA mildly increased the number of doublecortin-positive neurons in wild-type mice, but the response was significantly enhanced in the Ames dwarf mice. Collectively, these data support our hypothesis that the enhanced learning and memory associated with the Ames dwarf mouse may be due to elevated levels of NMDA and KA receptors in hippocampus and their ability to continue producing new neurons in response to neuronal damage.

Taste quality and intensity of 100 stimuli as reported by rats: the taste-location association task

The interpretation of neural activity related to sensory stimulation requires an understanding of the subject’s perception of the stimulation. Previous methods used to evaluate the perception of chemosensory stimuli by rodents have distinct limitations. We developed a novel behavioral paradigm, the taste–location association task, to complement these methods. First we tested if rats are able to learn associations between five basic taste stimuli and their spatial locations. This spatial task was based on four prototypical tastants and water. All four rats trained to perform the task reached levels of performance well above chance. Control trials demonstrated that the rats used only taste cues. Further, the learned stimulus set was resistant to interference, allowing for generalization experiments performed subsequently. We tested the rats’ gustatory generalizations of 100 tastants to the five trained stimuli, both regarding their taste qualities as well as intensity ratings. The taste profiles generated by these experiments contribute to the understanding of how perception of the specific taste stimuli relate to the perception of the five basic taste qualities in intact behaving rats. In this large taste space we found that intensity plays a major role. Furthermore, umami stimuli were not reported as being similar to other basic tastants. Our new paradigm enables neurophysiological studies of taste-based learning and memory in awake, freely moving animals.

Anatomy of the temporal lobe

Only primates have temporal lobes, which are largest in man, accommodating 17% of the cerebral cortex and including areas with auditory, olfactory, vestibular, visual and linguistic functions. The hippocampal formation, on the medial side of the lobe, includes the parahippocampal gyrus, subiculum, hippocampus, dentate gyrus, and associated white matter, notably the fimbria, whose fibres continue into the fornix. The hippocampus is an inrolled gyrus that bulges into the temporal horn of the lateral ventricle. Association fibres connect all parts of the cerebral cortex with the parahippocampal gyrus and subiculum, which in turn project to the dentate gyrus. The largest efferent projection of the subiculum and hippocampus is through the fornix to the hypothalamus. The choroid fissure, alongside the fimbria, separates the temporal lobe from the optic tract, hypothalamus and midbrain. The amygdala comprises several nuclei on the medial aspect of the temporal lobe, mostly anterior the hippocampus and indenting the tip of the temporal horn. The amygdala receives input from the olfactory bulb and from association cortex for other modalities of sensation. Its major projections are to the septal area and prefrontal cortex, mediating emotional responses to sensory stimuli. The temporal lobe contains much subcortical white matter, with such named bundles as the anterior commissure, arcuate fasciculus, inferior longitudinal fasciculus and uncinate fasciculus, and Meyer's loop of the geniculocalcarine tract. This article also reviews arterial supply, venous drainage, and anatomical relations of the temporal lobe to adjacent intracranial and tympanic structures.

Automaticity and multiple memory systems

A large number of criteria have been proposed for determining when a behavior has become automatic. Almost all of these were developed before the widespread acceptance of multiple memory systems. Consequently, popular frameworks for studying automaticity often neglect qualitative differences in how different memory systems guide initial learning. Unfortunately, evidence suggests that automaticity criteria derived from these frameworks consistently misclassify certain sets of initial behaviors as automatic. Specifically, criteria derived from cognitive science mislabel much behavior still under the control of procedural memory as automatic, and criteria derived from animal learning mislabel some behaviors under the control of declarative memory as automatic. Even so, neither set of criteria make the opposite error-that is, both sets correctly identify any automatic behavior as automatic. In fact, evidence suggests that although there are multiple memory systems and therefore multiple routes to automaticity, there might nevertheless be only one common representation for automatic behaviors. A number of possible cognitive and cognitive neuroscience models of this single automaticity system are reviewed. WIREs Cogn Sci 2012, 3:363-376. doi: 10.1002/wcs.1172 For further resources related to this article, please visit the WIREs website.

Study–Test Congruency Affects Encoding-related Brain Activity for Some but Not All Stimulus Materials

Memory improves when encoding and retrieval processes overlap. Here, we investigated how the neural bases of long-term memory encoding vary as a function of the degree to which functional processes engaged at study are engaged again at test. In an incidental learning paradigm, electrical brain activity was recorded from the scalps of healthy adults while they made size judgments on intermixed series of pictures and words. After a 1-hr delay, memory for the items was tested with a recognition task incorporating remember/know judgments. In different groups of participants, studied items were either probed in the same mode of presentation (word–word; picture–picture) or in the alternative mode of presentation (word–picture; picture–word). Activity over anterior scalp sites predicted later memory of words, irrespective of type of test probe. Encoding-related activity for pictures, by contrast, differed qualitatively depending on how an item was cued at test. When a picture was probed with a picture, activity over anterior scalp sites predicted encoding success. When a picture was probed with a word, encoding-related activity was instead maximal over posterior sites. Activity differed according to study–test congruency from around 100 msec after picture onset. These findings indicate that electrophysiological correlates of encoding are sensitive to the similarity between processes engaged at study and test. The time course supports a direct and not merely consequential role of encoding–retrieval overlap in encoding. However, because congruency only affected one type of stimulus material, encoding–retrieval overlap may not be a universal organizing principle of neural correlates of memory.