End-to-End Multi-task Learning Architecture for Brain Tumor Analysis with Uncertainty Estimation in MRI Images

Brain tumors are a threat to life for every other human being, be it adults or children. Gliomas are one of the deadliest brain tumors with an extremely difficult diagnosis. The reason is their complex and heterogenous structure which gives rise to subjective as well as objective errors. Their manual segmentation is a laborious task due to their complex structure and irregular appearance. To cater to all these issues, a lot of research has been done and is going on to develop AI-based solutions that can help doctors and radiologists in the effective diagnosis of gliomas with the least subjective and objective errors, but an end-to-end system is still missing. An all-in-one framework has been proposed in this research. The developed end-to-end multi-task learning (MTL) architecture with a feature attention module can classify, segment, and predict the overall survival of gliomas by leveraging task relationships between similar tasks. Uncertainty estimation has also been incorporated into the framework to enhance the confidence level of healthcare practitioners. Extensive experimentation was performed by using combinations of MRI sequences. Brain tumor segmentation (BraTS) challenge datasets of 2019 and 2020 were used for experimental purposes. Results of the best model with four sequences show 95.1% accuracy for classification, 86.3% dice score for segmentation, and a mean absolute error (MAE) of 456.59 for survival prediction on the test data. It is evident from the results that deep learning-based MTL models have the potential to automate the whole brain tumor analysis process and give efficient results with least inference time without human intervention. Uncertainty quantification confirms the idea that more data can improve the generalization ability and in turn can produce more accurate results with less uncertainty. The proposed model has the potential to be utilized in a clinical setup for the initial screening of glioma patients.

Recalling gist memory depends on CA1 hippocampal neurons for lifetime retention and CA3 neurons for memory precision

Why some of us remember events more clearly than others and why memory loses precision over time is a major focus in memory research. Here, we show that the recruitment of specific neuroanatomical pathways within the medial temporal lobe (MTL) of the brain defines the precision of the memory recalled over the lifespan. Using optogenetics, neuronal activity mapping, and studying recent to very remote memories, we report that the hippocampal subfield CA1 is necessary for retrieving the gist of events and receives maximal support from MTL cortical areas (MEC, LEC, PER, and POR) for recalling the most remote memories. In contrast, reduction of CA3's activity alone coincides with the loss of memory precision over time. We propose that a shift between specific MTL subnetworks over time might be a fundamental mechanism of memory consolidation.

No convincing evidence the hippocampus is associated with working memory

In a previous discussion paper , twenty-six working memory fMRI studies that reported activity in the hippocampus were systematically analyzed. None of these studies provided convincing evidence that the hippocampus was active during the late delay phase, the only period in which working memory can be isolated from long-term memory processes. Based on these results, it was concluded that working memory does not activate the hippocampus. Six commentaries on the discussion paper were received from Courtney (2022), Kessels & Bergmann (2022), Peters and Reithler (2022), Rose and Chao (2022), Stern & Hasselmo (2022), and Wood, Clark, and Nee (2022). Based on these commentaries, the present response paper considered whether there is evidence of sustained hippocampal activity during the working memory delay period based on depth-electrode recording, whether there are activity-silent working memory mechanisms in the hippocampus, and whether there is hippocampal lesion evidence indicating this region is important for working memory. There was no convincing electrophysiological or neuropsychological evidence that the hippocampus is associated with working memory maintenance, and activity-silent mechanisms were arguably speculative. Given that only a small fraction (approximately 5%) of fMRI studies have reported hippocampal activity in working memory tasks and lesion evidence indicates the hippocampus is not necessary for working memory, the burden of proof is on proponents of view that the hippocampus is important for working memory to provide compelling evidence to support their position. To date, in my view, there is no convincing evidence that the hippocampus is associated with working memory.

Does working memory activate the hippocampus during the late delay period?

The aim of the present discussion paper was to identify whether any fMRI studies have provided convincing evidence that the hippocampus is associated with working memory. The key outcome variable was the phase in which hippocampal activity was observed: study, early delay, late delay, and/or test. During working memory tasks, long-term memory processes can operate during the study phase, early delay phase (due to extended encoding), or test phase. Thus, working memory processes can be isolated from long-term memory processes during only the late delay period. Twenty-six working memory studies that reported hippocampal activity were systematically analyzed. Many experimental protocols and analysis parameters were considered including number of participants, stimulus type(s), number of items during the study phase, delay duration, task during the test phase, behavioral accuracy, relevant fMRI contrast(s), whether the information was novel or familiar, number of phases modeled, and whether activation timecourses were extracted. For studies that were able to identify activity in different phases, familiar information sometimes produced activity during the study phase and/or test phase, but never produced activity during the delay period. When early-delay phase and late-delay phase activity could be distinguished via modeling these phases separately or inspecting activation timecourses, novel information could additionally produce activity during the early delay phase. There was no convincing evidence of hippocampal activity during the late delay period. These results indicate that working memory does not activate the hippocampus and suggest a model of working memory where maintenance of novel information can foster long-term memory encoding.

Influence of target-distractor neural similarity on working memory performance in older and younger adults

According to the inhibitory deficit hypothesis, older adults often fail to selectively inhibit distractors and attend to relevant information in working memory, leading to poorer memory of target items but better recall of irrelevant distractors compared to younger adults. Here, we explored how neural similarity of activity patterns between relevant and irrelevant stimulus categories impacts memory performance. We found evidence that older adults may benefit from failing to inhibit distractors that are similar to targets, perhaps because sustained neural activation of distractors partially supports maintenance of targets when they share neural resources, allowing for better subsequent recognition of studied target items. We also found increased category-specific multivoxel pattern activity in medial temporal regions in younger compared to older adults as category similarity increased. We propose that this reduced category-specific activation in medial temporal regions in older adults may reflect more blended representations of all the information available in working memory.

Types and Aspects of Front-of-Package Labeling Preferred by Parents: Insights for Policy Making in China

The WHO recommends front-of-package labeling (FOPL) to help parents make healthier food choices for their children. But which type of FOPL resonates with parents in China? We performed a cross-sectional study to investigate parental preferences for five widely used formats of FOPL. A multi-stage cluster sampling method was applied to selected parents of students in primary and secondary schools in six provinces and municipalities from July 2020 to March 2021. A close-ended questionnaire was used to collect demographic information, parents’ preferences for five FOPL in three dimensions, perceptions of the importance of nutrients labeled on FOPL, and prepackaged foods that need FOPL most. Chi-square tests were used to examine the characteristics among five groups. The results showed that multiple traffic lights (MTL) was preferred by parents, followed by warning labels. Parents thought the most needed nutrients to label were sugar, salt, and total fat. The top three prepackaged foods to label were “baked food”, “milk and dairy products” and “sugar-sweetened beverages”. Our findings indicate that nutrient-specific FOPL formats with interpretive aids were preferred by Chinese parents. These new findings can help inform the planning and implementation of FOPL in China and help Chinese parents make healthier food choices.

Neurons in the human medial temporal lobe track multiple temporal contexts during episodic memory processing

Episodic memory requires associating items with temporal context, a process for which the medial temporal lobe (MTL) is critical. This study uses recordings from 27 human subjects who were undergoing surgical intervention for intractable epilepsy. These same data were also utilized in Umbach et al. (2020). We identify 103 memory-sensitive neurons in the hippocampus and entorhinal cortex, whose firing rates predicted successful episodic memory encoding as subjects performed a verbal free recall task. These neurons exhibit important properties. First, as predicted from the temporal context model, they demonstrate reinstatement of firing patterns observed during encoding at the time of retrieval. The magnitude of reinstatement predicted the tendency of subjects to cluster retrieved memory items according to input serial position. Also, we found that spiking activity of these neurons was locked to the phase of hippocampal theta oscillations, but that the mean phase of spiking shifted between memory encoding versus retrieval. This unique observation is consistent with predictions of the “Separate Phases at Encoding And Retrieval (SPEAR)” model. Together, the properties we identify for memory-sensitive neurons characterize direct electrophysiological mechanisms for the representation of contextual information in the human MTL.

Reactivated Spatial Context Guides Episodic Recall

The medial temporal lobe (MTL) is known as the locus of spatial coding and episodic memory, but the interaction between these cognitive domains as well as the extent to which they rely on common neurophysiological mechanisms is poorly understood. Here, we use intracranial electroencephalography and a hybrid spatial-episodic memory task (29 subjects, 15 female) to determine how spatial information is dynamically reactivated in subregions of the human MTL and how this reactivation guides recall of episodic information. Our results implicate theta oscillations across the MTL as a common neurophysiological substrate for spatial coding in navigation and episodic recall. We further show that our index of retrieved spatial context is high in the hippocampus (HC) in an early time window preceding recall. Closer to recall, it decreases in the HC and increases in the parahippocampal gyrus. Finally, we demonstrate that hippocampal theta phase modulates parahippocampal gamma amplitude during retrieval of spatial context, suggesting a role for cross-frequency coupling in coding and transmitting retrieved spatial information.SIGNIFICANCE STATEMENT By recording from the human medial temporal lobe (MTL) while subjects recall items experienced in a virtual environment, we establish a direct relation between the strength of theta activity during memory search and the extent to which memories are organized by their spatial locations. We thereby pinpoint a role for theta oscillations in accessing the "cognitive map" during episodic retrieval and further highlight the dynamic interplay of hippocampus and extrahippocampal MTL in representing retrieved spatial context. Our results provide an important step toward a unified theory of MTL function encompassing its role in spatial navigation and episodic memory.

The impact of focused attention on subsequent emotional recollection: A functional MRI investigation

In his seminal works, Endel Tulving argued that functionally distinct memory systems give rise to subjective experiences of remembering and knowing (i.e., recollection- vs. familiarity-based memory, respectively). Evidence shows that emotion specifically enhances recollection, and this effect is subserved by a synergistic mechanism involving the amygdala (AMY) and hippocampus (HC). In extreme circumstances, however, uncontrolled recollection of highly distressing memories may lead to symptoms of affective disorders. Therefore, it is important to understand the factors that can diminish such detrimental effects. Here, we investigated the effects of Focused Attention (FA) on emotional recollection. FA is an emotion regulation strategy that has been proven quite effective in reducing the impact of emotional responses associated with the recollection of distressing autobiographical memories, but its impact during emotional memory encoding is not known. Functional MRI and eye-tracking data were recorded while participants viewed a series of composite negative and neutral images with distinguishable foreground (FG) and background (BG) areas. Participants were instructed to focus either on the FG or BG content of the images and to rate their emotional responses. About 4 days later, participants' memory was assessed using the R/K procedure, to indicate whether they Recollected specific contextual details about the encoded images or the images were just familiar to them - i.e., participants only Knew that they saw the pictures without being able to remember specific contextual details. First, results revealed that FA was successful in decreasing memory for emotional pictures viewed in BG Focus condition, and this effect was driven by recollection-based retrieval. Second, the BG Focus condition was associated with decreased activity in the AMY, HC, and anterior parahippocampal gyrus for subsequently recollected emotional items. Moreover, correlation analyses also showed that reduced activity in these regions predicted greater reduction in emotional recollection following FA. These results demonstrate the effectiveness of FA in mitigating emotional experiences and emotional recollection associated with unpleasant emotional events.

Different types of associative encoding evoke differential processing in both younger and older adults: Evidence from univariate and multivariate analyses

Age-related deficits in associative processing are well-documented (e.g., Naveh-Benjamin, 2000) and have been assumed to be the result of a general deficit that affects all types of binding. However, recent behavioral research has indicated that the visual configuration of the information that is presented to older adults influences the degree to which this binding deficit is exhibited by older adults (Overman, Dennis et al, 2019; Overman, Dennis, et al., 2018). The purpose of the present study was to further clarify the neural underpinnings of the associative deficit in aging and to examine whether functional activity at encoding differs with respect to the visual configuration and the type of associative being encoded. Using both univariate and multi-voxel pattern analysis, we found differences in both the magnitude of activation and pattern of neural responses associated with the type of association encoded (item-item and item-context). Specifically, our results suggest that, when controlling for stimuli composition, patterns of activation in sensory and frontal regions within the associative encoding network are able to distinguish between different types of associations. With respect to the MTL, multivariate results suggest that only patterns of activation in the PrC in older, but not younger adults, can distinguish between associations types. These findings extend prior work regarding the neural basis of associative memory in young and older adults, and extends the predictions of the binding of item and context model (BIC; Diana, Yonelinas, Ranganath, 2007) to older adults.

Spatial Representations in the Human Brain

While extensive research on the neurophysiology of spatial memory has been carried out in rodents, memory research in humans had traditionally focused on more abstract, language-based tasks. Recent studies have begun to address this gap using virtual navigation tasks in combination with electrophysiological recordings in humans. These studies suggest that the human medial temporal lobe (MTL) is equipped with a population of place and grid cells similar to that previously observed in the rodent brain. Furthermore, theta oscillations have been linked to spatial navigation and, more specifically, to the encoding and retrieval of spatial information. While some studies suggest a single navigational theta rhythm which is of lower frequency in humans than rodents, other studies advocate for the existence of two functionally distinct delta-theta frequency bands involved in both spatial and episodic memory. Despite the general consensus between rodent and human electrophysiology, behavioral work in humans does not unequivocally support the use of a metric Euclidean map for navigation. Formal models of navigational behavior, which specifically consider the spatial scale of the environment and complementary learning mechanisms, may help to better understand different navigational strategies and their neurophysiological mechanisms. Finally, the functional overlap of spatial and declarative memory in the MTL calls for a unified theory of MTL function. Such a theory will critically rely upon linking task-related phenomena at multiple temporal and spatial scales. Understanding how single cell responses relate to ongoing theta oscillations during both the encoding and retrieval of spatial and non-spatial associations appears to be key toward developing a more mechanistic understanding of memory processes in the MTL.

Effects of Repetition Learning on Associative Recognition Over Time: Role of the Hippocampus and Prefrontal Cortex

When stimuli are learned by repetition, they are remembered better and retained for a longer time. However, current findings are lacking as to whether the medial temporal lobe (MTL) and cortical regions are involved in the learning effect when subjects retrieve associative memory, and whether their activations differentially change over time due to learning experience. To address these issues, we designed an fMRI experiment in which face-scene pairs were learned once (L1) or six times (L6). Subjects learned the pairs at four retention intervals, 30-min, 1-day, 1-week and 1-month, after which they finished an associative recognition task in the scanner. The results showed that compared to learning once, learning six times led to stronger activation in the hippocampus, but weaker activation in the perirhinal cortex (PRC) as well as anterior ventrolateral prefrontal cortex (vLPFC). In addition, the hippocampal activation was positively correlated with that of the parahippocampal place area (PPA) and negatively correlated with that of the vLPFC when the L6 group was compared to the L1 group. The hippocampal activation decreased over time after L1 but remained stable after L6. These results clarified how the hippocampus and cortical regions interacted to support associative memory after different learning experiences.

Theta Oscillations in the Human Medial Temporal Lobe during Real-World Ambulatory Movement

The theta rhythm-a slow (6-12 Hz) oscillatory component of the local field potential-plays a critical role in spatial navigation and memory by coordinating the activity of neuronal ensembles within the medial temporal lobe (MTL). Although theta has been extensively studied in freely moving rodents, its presence in humans has been elusive and primarily investigated in stationary subjects. Here we used a unique clinical opportunity to examine theta within the human MTL during untethered, real-world ambulatory movement. We recorded intracranial electroencephalographic activity from participants chronically implanted with the wireless NeuroPace responsive neurostimulator (RNS) and tracked their motion with sub-millimeter precision. Our data revealed that movement-related theta oscillations indeed exist in humans, such that theta power is significantly higher during movement than immobility. Unlike in rodents, however, theta occurs in short bouts, with average durations of ∼400 ms, which are more prevalent during fast versus slow movements. In a rare opportunity to study a congenitally blind participant, we found that both the prevalence and duration of theta bouts were increased relative to the sighted participants. These results provide critical support for conserved neurobiological characteristics of theta oscillations during ambulatory spatial navigation, while highlighting some fundamental differences across species in these oscillations between humans and rodents.

[Genetic regulatory mechanisms of Candida albicans biofilm formation]

Candida albicans is an important opportunistic fungal pathogen of humans. Phenotypic plasticity is a typical biological feature of C. albicans, which is associated with pathogenicity, host adaptation, and sexual reproduction. Biofilm of C. albicans is a complex community formed by different morphological types of cells (yeast, hyphae and pseudohyphae) and secreted extracellular matrix. C. albicans biofilms are intrinsically resistant to antifungal drugs, the host immune system, and environmental stresses. Biofilm is an important virulence factor and a major clinical challenge. With the development of new technologies in global gene expression profiles and genetic manipulation, the regulatory mechanisms that govern C. albicans biofilm development and drug resistance become more and more clear. Major regulatory mechanisms involve the MAPK and cAMP signaling pathways and transcriptional regulators such as Bcr1 and Tec1. In addition, morphological transitions and sexual reproduction are also involved in the regulation of biofilm development. In this review, we focus on the genetic regulatory mechanisms of biofilm including the roles of cell-wall related proteins, transcription factors, and the MTL locus. In the last section, we also summarize the mechanisms of drug resistance of biofilm in C. albicans.

Oscillations and Episodic Memory: Addressing the Synchronization/Desynchronization Conundrum

Brain oscillations are one of the core mechanisms underlying episodic memory. However, while some studies highlight the role of synchronized oscillatory activity, others highlight the role of desynchronized activity. We here describe a framework to resolve this conundrum and integrate these two opposing oscillatory behaviors. Specifically, we argue that the synchronization and desynchronization reflect a division of labor between a hippocampal and a neocortical system, respectively. We describe a novel oscillatory framework that integrates synchronization and desynchronization mechanisms to explain how the two systems interact in the service of episodic memory.

Data from rodent as well as human studies suggest that theta/gamma synchronization in the hippocampus (i.e., theta phase to gamma power cross-frequency coupling) mediates the binding of different elements in episodic memory.

In vivo and in vitro animal studies suggest that theta provides selective time windows for fast-acting synaptic modifications and recent computational models have implemented these mechanisms to explain human memory formation and retrieval.

Recent data from human experiments suggest that low-frequency power decreases in the neocortex, most evident in the alpha/beta frequency range, mediate encoding and reinstatement of episodic memories.

The content of reinstated memories can be decoded from cortical low-frequency patterns.

Temporal binding within and across events

Remembering the order in which events occur is a fundamental component of episodic memory. However, the neural mechanisms supporting serial recall remain unclear. Behaviorally, serial recall is greater for information encountered within the same event compared to across event boundaries, raising the possibility that contextual stability may modulate the cognitive and neural processes supporting serial encoding. In the present study, we used fMRI during the encoding of consecutive face and object stimuli to elucidate the neural encoding signatures supporting subsequent serial recall behavior both within and across events. We found that univariate BOLD activation in both the middle hippocampus and left ventrolateral prefrontal cortex (PFC) was associated with subsequent serial recall of items that occur across event boundaries. By contrast, successful serial encoding within events was associated with increased functional connectivity between the hippocampus and ventromedial PFC, but not with univariate activation in these or other regions. These findings build on evidence implicating hippocampal and PFC processes in encoding temporal aspects of memory. They further suggest that these encoding processes are influenced by whether binding occurs within a stable context or bridges two adjacent but distinct events.

What relates newspaper, definite, and clothing? An article describing deficits in convergent problem solving and creativity following hippocampal damage

Creativity relies on a diverse set of cognitive processes associated with distinct neural correlates, and one important aspect of creativity, divergent thinking, has been associated with the hippocampus. However, hippocampal contributions to another important aspect of creativity, convergent problem solving, have not been investigated. We tested the necessity of hippocampus for convergent problem solving using a neuropsychological method. Participants with amnesia due to hippocampal damage (N = 5) and healthy normal comparison participants (N = 5) were tested using a task that promoted solutions based on existing knowledge (Bowden and Jung-Beeman, 2003). During each trial, participants were given a list of three words (e.g., fly, man, place) and asked to respond with a word that could be combined with each of the three words (e.g., fire). The amnesic group produced significantly fewer correct responses than the healthy comparison group. These findings indicate that the hippocampus is necessary for normal convergent problem solving and that changes in the status of the hippocampus should affect convergent problem solving in the context of creative problem-solving across short intervals. This proposed contribution of the hippocampus to convergent problem solving is consistent with an expanded perspective on hippocampal function that acknowledges its role in cognitive processes beyond declarative memory. © 2016 Wiley Periodicals, Inc.

Dissociable contributions of amygdala and hippocampus to emotion and memory in patients with Alzheimer's disease

The amygdala and the hippocampus are associated with emotional processing and declarative memory, respectively. Studies have shown that patients with bilateral hippocampal damage caused by anoxia/ischemia, and patients with probable Alzheimer's disease (AD), can experience emotions for prolonged periods of time, even when they cannot remember what caused the emotion in the first place (Feinstein et al. (2010) Proc Natl Acad Sci USA 107:7674-7679; Guzmán-Vélez et al. (2014) Cogn Behav Neurol 27:117-129). This study aimed to investigate, for the first time, the roles of the amygdala and hippocampus in the dissociation between feelings of emotion and declarative memory for emotion-inducing events in patients with AD. Individuals with probable AD (N = 12) and age-matched healthy comparisons participants (HCP; N = 12) completed a high-resolution (0.44 × 0.44 × 0.80 mm) T2-weighted structural MR scan of the medial temporal lobe. Each of these individuals also completed two separate emotion induction procedures (sadness and happiness) using film clips. We collected real-time emotion ratings at baseline and multiple times postinduction, and administered a test of declarative memory shortly after each induction. Consistent with previous research, hippocampal volume was significantly smaller in patients with AD compared with HCP, and was positively correlated with memory for the film clips. Sustained feelings of emotion and amygdala volume did not significantly differ between patients with AD and HCP. Follow-up analyses showed a significant negative correlation between amygdala volume and sustained sadness, and a significant positive correlation between amygdala volume and sustained happiness. Our findings suggest that the amygdala is important for regulating and sustaining an emotion independent of hippocampal function and declarative memory for the emotion-inducing event. © 2015 Wiley Periodicals, Inc.

Neural activity in the medial temporal lobe reveals the fidelity of mental time travel

Neural circuitry in the medial temporal lobe (MTL) is critically involved in mental time travel, which involves the vivid retrieval of the details of past experience. Neuroscientific theories propose that the MTL supports memory of the past by retrieving previously encoded episodic information, as well as by reactivating a temporal code specifying the position of a particular event within an episode. However, the neural computations supporting these abilities are underspecified. To test hypotheses regarding the computational mechanisms supported by different MTL subregions during mental time travel, we developed a computational model that linked a blood oxygenation level-dependent signal to cognitive operations, allowing us to predict human performance in a memory search task. Activity in the posterior MTL, including parahippocampal cortex, reflected how strongly one reactivates the temporal context of a retrieved memory, allowing the model to predict whether the next memory will correspond to a nearby moment in the study episode. A signal in the anterior MTL, including perirhinal cortex, indicated the successful retrieval of list items, without providing information regarding temporal organization. A hippocampal signal reflected both processes, consistent with theories that this region binds item and context information together to form episodic memories. These findings provide evidence for modern theories that describe complementary roles of the hippocampus and surrounding parahippocampal and perirhinal cortices during the retrieval of episodic memories, shaping how humans revisit the past.

Less wiring, more firing: low-performing older adults compensate for impaired white matter with greater neural activity

The reliable neuroimaging finding that older adults often show greater activity (over-recruitment) than younger adults is typically attributed to compensation. Yet, the neural mechanisms of over-recruitment in older adults (OAs) are largely unknown. Rodent electrophysiology studies have shown that as number of afferent fibers within a circuit decreases with age, the fibers that remain show higher synaptic field potentials (less wiring, more firing). Extrapolating to system-level measures in humans, we proposed and tested the hypothesis that greater activity in OAs compensates for impaired white-matter connectivity. Using a neuropsychological test battery, we measured individual differences in executive functions associated with the prefrontal cortex (PFC) and memory functions associated with the medial temporal lobes (MTLs). Using event-related functional magnetic resonance imaging, we compared activity for successful versus unsuccessful trials during a source memory task. Finally, we measured white-matter integrity using diffusion tensor imaging. The study yielded 3 main findings. First, low-executive OAs showed greater success-related activity in the PFC, whereas low-memory OAs showed greater success-related activity in the MTLs. Second, low-executive OAs displayed white-matter deficits in the PFC, whereas low-memory OAs displayed white-matter deficits in the MTLs. Finally, in both prefrontal and MTL regions, white-matter decline and success-related activations occurred in close proximity and were negatively correlated. This finding supports the less-wiring-more-firing hypothesis, which provides a testable account of compensatory over-recruitment in OAs.

Functional contributions and interactions between the human hippocampus and subregions of the striatum during arbitrary associative learning and memory

The hippocampus and striatum are thought to have different functional roles in learning and memory. It is unknown under what experimental conditions their contributions are dissimilar or converge, and the extent to which they interact over the course of learning. In order to evaluate both the functional contributions of as well as the interactions between the human hippocampus and striatum, the present study used high-resolution functional magnetic resonance imaging (fMRI) and variations of a conditional visuomotor associative learning task that either taxed arbitrary associative learning (Experiment 1) or stimulus-response learning (Experiment 2). In the first experiment, we observed changes in activity in the hippocampus and anterior caudate that reflect differences between the two regions consistent with distinct computational principles. In the second experiment, we observed activity in the putamen that reflected content specific representations during the learning of arbitrary conditional visuomotor associations. In both experiments, the hippocampus and ventral striatum demonstrated dynamic functional coupling during the learning of new arbitrary associations, but not during retrieval of well-learned arbitrary associations using control variants of the tasks that did not preferentially tax one system versus the other. These findings suggest that both the hippocampus and subregions of the dorsal striatum contribute uniquely to the learning of arbitrary associations while the hippocampus and ventral striatum interact over the course of learning.

Anterior and posterior MTL networks in aging and MCI

Two neuroanatomically dissociable, large-scale cortical memory networks, referred to as the anterior and posterior medial temporal lobe (MTL) networks have recently been described in young adults using resting-state blood oxygen level-dependent (BOLD) functional magnetic resonance imaging (fMRI)-based functional connectivity (fc-BOLD). They have been hypothesized to subserve distinct mnemonic and non-memory cognitive functions and are thought to be associated with differential vulnerability in neurological disorders. In this article, we demonstrate the existence of these functional networks in an older adult population and in a cohort of patients diagnosed with amnestic mild cognitive impairment (aMCI). Anatomic subregions of interest in the MTL were defined using high-resolution T2-weighted MRI and used as seeds for defining the putative networks using fc-BOLD. Although the literature has suggested that the posterior MTL network is particularly vulnerable to early Alzheimer's disease, we show that both the networks are affected in MCI, to varying degrees, compared with the control group. Furthermore, cortical thickness in the brain regions defined by these networks was reduced in MCI.

Human hippocampal processing of environmental novelty during spatial navigation

The detection and processing of novel information encountered as we explore our environment is crucial for learning and adaptive behavior. The human hippocampus has been strongly implicated in laboratory tests of novelty detection and episodic memory, but has been less well studied during more ethological tasks such as spatial navigation, typically used in animals. We examined fMRI BOLD activity as a function of environmental and object novelty as humans performed an object-location virtual navigation task. We found greater BOLD response to novel relative to familiar environments in the hippocampus and adjacent parahippocampal gyrus. Object novelty was associated with increased activity in the posterior parahippocampal/fusiform gyrus and anterior hippocampus extending into the amygdala and superior temporal sulcus. Importantly, whilst mid-posterior hippocampus was more sensitive to environmental novelty than object novelty, the anterior hippocampus responded similarly to both forms of novelty. Amygdala activity showed an increase for novel objects that decreased linearly over the learning phase. By investigating how participants learn and use different forms of information during spatial navigation, we found that medial temporal lobe (MTL) activity reflects both the novelty of the environment and of the objects located within it. This novelty processing is likely supported by distinct, but partially overlapping, sets of regions within the MTL.

Medial prefrontal theta phase coupling during spatial memory retrieval

Memory retrieval is believed to involve a disparate network of areas, including medial prefrontal and medial temporal cortices, but the mechanisms underlying their coordination remain elusive. One suggestion is that oscillatory coherence mediates inter-regional communication, implicating theta phase and theta-gamma phase-amplitude coupling in mnemonic function across species. To examine this hypothesis, we used non-invasive whole-head magnetoencephalography (MEG) as participants retrieved the location of objects encountered within a virtual environment. We demonstrate that, when participants are cued with the image of an object whose location they must subsequently navigate to, there is a significant increase in 4–8 Hz theta power in medial prefrontal cortex (mPFC), and the phase of this oscillation is coupled both with ongoing theta phase in the medial temporal lobe (MTL) and perceptually induced 65–85 Hz gamma amplitude in medial parietal cortex. These results suggest that theta phase coupling between mPFC and MTL and theta-gamma phase-amplitude coupling between mPFC and neocortical regions may play a role in human spatial memory retrieval. © 2014 The Authors. Hippocampus Published by Wiley Periodicals, Inc.

Source recognition by stimulus content in the MTL

Source memory is considered to be the cornerstone of episodic memory that enables us to discriminate similar but different events. In the present fMRI study, we investigated whether neural correlates of source retrieval differed by stimulus content in the medial temporal lobe (MTL) when the item and context had been integrated as a perceptually unitized entity. Participants were presented with a list of items either in verbal or pictorial form overlaid on a colored square and instructed to integrate both the item and context into a single image. At test, participants judged the study status of test items and the color in which studied items were presented. Source recognition invariant of stimulus content elicited retrieval activity in both the left anterior hippocampus extending to the perirhinal cortex and the right posterior hippocampus. Word-selective source recognition was related to activity in the left perirhinal cortex, whereas picture-selective source recognition was identified in the left posterior hippocampus. Neural activity sensitive to novelty detection common to both words and pictures was found in the left anterior and right posterior hippocampus. Novelty detection selective to words was associated with the left perirhinal cortex, while activity sensitive to new pictures was identified in the bilateral hippocampus and adjacent MTL cortices, including the parahippocampal, entorhinal, and perirhinal cortices. These findings provide further support for the integral role of the hippocampus both in source recognition and in detection of new stimuli across stimulus content. Additionally, novelty effects in the MTL reveal the integral role of the MTL cortex as the interface for processing new information. Collectively, the present findings demonstrate the importance of the MTL for both previously experienced and novel events.

Sports and brain morphology - a voxel-based morphometry study with endurance athletes and martial artists

Physical exercises and motor skill learning have been shown to induce changes in regional brain morphology, this has been demonstrated for various activities and tasks. Also individuals with special skills show differences in regional brain morphology. This has been indicated for professional musicians, London taxi drivers, as well as for athletes like dancers, golfers and judokas. However little is known about whether sports with different metabolic profiles (aerobic vs. anaerobic) are associated with different patterns of altered brain morphology. In this cross-sectional study we investigated two groups of high-performance athletes, one group performing sports that are thought to be mainly aerobic, and one group performing sports known to have intermittent phases of anaerobic metabolism. Using high-resolution structural imaging and voxel-based morphometry (VBM), we investigated a group of 26 male athletes consisting of 13 martial artists and 13 endurance athletes as well as a group of non-exercising men (n=13). VBM analyses revealed higher gray matter (GM) volumes in the supplementary motor area/dorsal premotor cortex (BA 6) in both athlete groups as compared to the control group. In addition, endurance athletes showed significantly higher GM volume in the medial temporal lobe (MTL), specifically in the hippocampus and parahippocampal gyrus, which was not seen in the martial arts group. Our data suggest that high-performance sports are associated with changes in regional brain morphology in areas implicated in motor planning and motor learning. In addition high-level endurance sports seem to affect MTL structures, areas that have previously been shown to be modulated by aerobic exercise.

Interaction between serum BDNF and aerobic fitness predicts recognition memory in healthy young adults

Convergent evidence from human and non-human animal studies suggests aerobic exercise and increased aerobic capacity may be beneficial for brain health and cognition. It is thought growth factors may mediate this putative relationship, particularly by augmenting plasticity mechanisms in the hippocampus, a brain region critical for learning and memory. Among these factors, glucocorticoids, brain derived neurotrophic factor (BDNF), insulin-like growth factor-1 (IGF-1), and vascular endothelial growth factor (VEGF), hormones that have considerable and diverse physiological importance, are thought to effect normal and exercise-induced hippocampal plasticity. Despite these predictions, relatively few published human studies have tested hypotheses that relate exercise and fitness to the hippocampus, and none have considered the potential links to all of these hormonal components. Here we present cross-sectional data from a study of recognition memory; serum BDNF, cortisol, IGF-1, and VEGF levels; and aerobic capacity in healthy young adults. We measured circulating levels of these hormones together with performance on a recognition memory task, and a standard graded treadmill test of aerobic fitness. Regression analyses demonstrated BDNF and aerobic fitness predict recognition memory in an interactive manner. In addition, IGF-1 was positively associated with aerobic fitness, but not with recognition memory. Our results may suggest an exercise adaptation-related change in the BDNF dose-response curve that relates to hippocampal memory.

Identification of putative estrogen receptor-mediated endocrine disrupting chemicals using QSAR- and structure-based virtual screening approaches

Identification of endocrine disrupting chemicals is one of the important goals of environmental chemical hazard screening. We report on the development of validated in silico predictors of chemicals likely to cause estrogen receptor (ER)-mediated endocrine disruption to facilitate their prioritization for future screening. A database of relative binding affinity of a large number of ERα and/or ERβ ligands was assembled (546 for ERα and 137 for ERβ). Both single-task learning (STL) and multi-task learning (MTL) continuous quantitative structure-activity relationship (QSAR) models were developed for predicting ligand binding affinity to ERα or ERβ. High predictive accuracy was achieved for ERα binding affinity (MTL R(2)=0.71, STL R(2)=0.73). For ERβ binding affinity, MTL models were significantly more predictive (R(2)=0.53, p<0.05) than STL models. In addition, docking studies were performed on a set of ER agonists/antagonists (67 agonists and 39 antagonists for ERα, 48 agonists and 32 antagonists for ERβ, supplemented by putative decoys/non-binders) using the following ER structures (in complexes with respective ligands) retrieved from the Protein Data Bank: ERα agonist (PDB ID: 1L2I), ERα antagonist (PDB ID: 3DT3), ERβ agonist (PDB ID: 2NV7), and ERβ antagonist (PDB ID: 1L2J). We found that all four ER conformations discriminated their corresponding ligands from presumed non-binders. Finally, both QSAR models and ER structures were employed in parallel to virtually screen several large libraries of environmental chemicals to derive a ligand- and structure-based prioritized list of putative estrogenic compounds to be used for in vitro and in vivo experimental validation.

Secretagogin-containing neurons in the mouse main olfactory bulb

Secretagogin (SCGN) is a recently discovered calcium binding protein of the EF hand family. We studied the structural features of SCGN-positive neurons in the mouse main olfactory bulb (MOB). SCGN-positive neurons were localized throughout layers but clustered in the glomerular layer (GL), mitral cell layer (MCL) and granule cell layer (GCL). They were heterogeneous, including numerous juxtaglomerular neurons, granule cells, small to medium-sized neurons in the external plexiform layer (EPL), and a few small cells in the ependymal/subependymal layer. Calretinin and/or tyrosine hydroxylase occasionally colocalized in SCGN-positive juxtaglomerular neurons. Calretinin also frequently colocalized in SCGN-positive EPL and GCL neurons. Morphologically some of juxtaglomerular SCGN-positive neurons were classical periglomerular cells, whereas others were apparently different from those periglomerular cells, although they were further heterogeneous. Some extended one slender process into a glomerulus which passed the glomerulus and further penetrated into another nearby glomeruli, and thus their dendritic processes spanned two or three or more glomeruli. We named this type of juxtaglomerular neurons "transglomerular cells." With the stereological analysis we estimated total number of juxtaglomerular SCGN-positive neurons at about 80,000/single MOB. The present study revealed the diversity of SCGN-positive neurons in the mouse MOB and their particular structural properties hitherto unknown.

The Effect of Retrieval Focus and Emotional Valence on the Medial Temporal Lobe Activity during Autobiographical Recollection

Laboratory-based episodic memory studies, using micro-events (pictures/words), point to a role of the amygdala (AMY), an emotion-based region, in the encoding and retrieval of emotionally valenced memories. However, autobiographical memory (AM) studies, using real-life personal events, do not conclusively support AMY’s involvement in AM recollection. This could be due to differences in instructions across the AM studies – i.e., whether emotional aspects were explicitly emphasized or not. The present study investigated the effect of retrieval focus on activity in emotion (AMY) and memory (hippocampus – HC) based regions of the medial temporal lobe in 17 subjects, who remembered emotional AMs while event-related fMRI data were recorded. The retrieval focus was manipulated by instructions to focus either on emotional (Emotion condition) or on other contextual (Context condition) details of the recollected AMs. The effect of retrieval focus according to the valence of AMs was also investigated by involving an equal proportion of positive and negative AMs. There were four main findings, showing both similarities and differences in retrieving positive and negative AMs. Regarding similarities, (1) focusing on Emotion was associated with increased scores of subjective re-experience of emotion and increased activity in the left AMY, for both positive and negative AMs, compared to focusing on Context; (2) the subjective emotional ratings were also positively correlated with bilateral AMY activity for both positive and negative AMs. Regarding differences, (3) focusing on Emotion was associated with increased activity for positive but not for negative AMs in the right AMY, and with (4) opposing patterns of activity linked to the valence of AMs in the left HC – i.e., increased activity for positive and decreased activity for negative AMs. These findings shed light on the role of AMY and HC in emotional AM recollection, linked to the retrieval focus and the valence of memories.

From perception to memory: changes in memory systems across the lifespan

Human memory is not a unitary entity; rather it is thought to arise out of a complex architecture involving interactions between distinct representational systems that specialize in perceptual, semantic, and episodic representations. Neuropsychological and neuroimaging evidence are combined in support of models of memory systems, however most models only capture a 'mature' state of human memory and there is little attempt to incorporate evidence of the contribution of developmental and senescence changes in various processes involved in memory across the lifespan. Here we review behavioral and neuroimaging evidence for changes in memory functioning across the lifespan and propose specific principles that may be used to extend models of human memory across the lifespan. In contrast to a simplistic reduced version of the adult model, we suggest that the architecture and dynamics of memory systems become gradually differentiated during development and that a dynamic shift toward favoring semantic memory occurs during aging. Characterizing transformations in memory systems across the lifespan can illustrate and inform us about the plasticity of human memory systems.

The parahippocampal gyrus links the default-mode cortical network with the medial temporal lobe memory system

The default-mode network (DMN) is a distributed functional-anatomic network implicated in supporting memory. Current resting-state functional connectivity studies in humans remain divided on the exact involvement of medial temporal lobe (MTL) in this network at rest. Notably, it is unclear to what extent the MTL regions involved in successful memory encoding are connected to the cortical nodes of the DMN during resting state. Our findings using functional connectivity MRI analyses of resting-state data indicate that the parahippocampal gyrus (PHG) is the primary hub of the DMN in the MTL during resting state. Also, connectivity of the PHG is distinct from connectivity of hippocampal regions identified by an associative memory-encoding task. We confirmed that several hippocampal encoding regions lack significant functional connectivity with cortical DMN nodes during resting state. Additionally, a mediation analysis showed that resting-state connectivity between the hippocampus and posterior cingulate cortex--a major hub of the DMN--is indirect and mediated by the PHG. Our findings support the hypothesis that the MTL memory system represents a functional subnetwork that relates to the cortical nodes of the DMN through parahippocampal functional connections.

Medial temporal lobe damage impairs representation of simple stimuli

Medial temporal lobe (MTL) damage in humans is typically thought to produce a circumscribed impairment in the acquisition of new enduring memories, but recent reports have documented deficits even in short-term maintenance. We examined possible maintenance deficits in a population of MTL amnesics, with the goal of characterizing their impairments as either representational drift or outright loss of representation over time. Patients and healthy comparisons performed a visual search task in which the similarity of various lures to a target was varied parametrically. Stimuli were simple shapes varying along one of several visual dimensions. The task was performed in two conditions, one presenting a sample target simultaneously with the search array and the other imposing a delay between sample and array. Eye-movement data collected during search revealed that the duration of fixations to items varied with lure-target similarity for all participants, i.e., fixations were longer for items more similar to the target. In the simultaneous condition, patients and comparisons exhibited an equivalent effect of similarity on fixation durations. However, imposing a delay modulated the effect differently for the two groups: in comparisons, fixation duration to similar items was exaggerated; in patients, the original effect was diminished. These findings indicate that MTL lesions subtly impair short-term maintenance of even simple stimuli, with performance reflecting not the complete loss of the maintained representation but rather a degradation or progressive drift of the representation over time.