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Some aspects of our memory are enhanced by emotion, whereas other can be unaffected or even hinder. In particular, previous studies report impaired associative memory of emotional content, an effect termed associative 'emotional interference'. The current study utilized EEG and an associative recognition paradigm to investigate the cognitive and neural mechanisms associated with this effect. In two experiments, participants studied negative and neutral stimulus-pairs that were either semantically related or unrelated. In Experiment 1 emotions were relevant to the encoding task (valence judgment) whereas in Experiment 2 emotions were irrelevant (familiarity judgment). In a subsequent associative recognition test, EEG was recorded while participants discriminated between intact, rearranged, and new pairs. An associative emotional interference effect was observed in both experiments, but was attenuated for semantically related pairs when emotions were relevant to the study task. Moreover, a modulation of an early associative memory ERP component depended on task relevancy of emotions, and occurred for negative pairs when emotions were relevant, but for semantically related pairs when emotions were irrelevant. A later ERP component depicted a more general pattern, and was observed in all experimental conditions. These results suggest that both emotions and semantic relations can act as organizing principles that promote associative binding. Their ability to contribute to successful retrieval depends on specific task demands.

Memorizing the locations of environmental cues is crucial for survival and depends on the hippocampus. We recorded local field potentials (LFPs) from the hippocampus of freely moving mice during an object location task. The power of beta-band (23-30 Hz) oscillations increased immediately before approaching objects in a memory-encoding phase. The exploration-induced beta oscillations gradually decreased during the memory-encoding session. Mice that exhibited stronger beta oscillation power exhibited better performance in the subsequent memory-retrieval test. These results suggest that beta oscillations in the hippocampal CA1 region are involved in the memory encoding of object-location associations.

Adaptive memory requires the organism to form associations that bridge between events separated in time. Many studies show interactions between hippocampus (HPC) and prefrontal cortex (PFC) during formation of such associations. We analyze neural recording from monkey HPC and PFC during a memory task that requires the monkey to associate stimuli separated by about a second in time. After the first stimulus was presented, large numbers of units in both HPC and PFC fired in sequence. Many units fired only when a particular stimulus was presented at a particular time in the past. These results indicate that both HPC and PFC maintain a temporal record of events that could be used to form associations across time. This temporal record of the past is a key component of the temporal coding hypothesis, a hypothesis in psychology that memory not only encodes what happened, but when it happened.

The hippocampus and dorsal striatum are both associated with temporal processing, but they are thought to play distinct roles. The hippocampus has been reported to contribute to storing temporal structure of events in memory, whereas the striatum contributes to temporal motor preparation and reward anticipation. Here, we asked whether the striatum cooperates with the hippocampus in processing the temporal context of memorized visual associations. In our task, participants were trained to implicitly form temporal expectations for one of two possible time intervals associated to specific cue-target associations, and subsequently were scanned using 7T functional magnetic resonance imaging. During scanning, learned temporal expectations could be violated when the pairs were presented at either the learned or not-learned time intervals. When temporal expectations were not met during testing trials, activity in hippocampal subfields CA3/CA2 and CA1 decreased while right putamen activity increased, compared to when temporal expectations were met. Further, psycho-physiological interactions showed that functional connectivity between left CA1 and caudate, as well as between putamen and caudate, decreased when temporal expectations were not met. Our results indicate that the hippocampus and striatum cooperate to process implicit temporal expectation from mnemonic associations, with different but complementary contributions from caudate and putamen. Our findings provide further support for a hippocampal-striatal network in temporal associative processing.

Memory deficits in aging are characterized by impaired hippocampus-mediated relational binding-the formation of links between items in memory. By reducing reliance on relational binding, unitization of two items into one concept enhances associative recognition among older adults. Can a similar enhancement be obtained when probing memory with recall? This question has yet to be examined, because recall has been assumed to rely predominantly on relational binding. Inspired by recent evidence challenging this assumption, we investigated individual differences in older adults' recall of unitized and nonunitized associations. Compared with successfully aging individuals, older adults with mild memory deficits, typically mediated by the hippocampus, were impaired in recall of paired-associates in a task which relies on relational binding (study: "PLAY-TUNNEL"; test: PLAY-T?). In stark contrast, the two groups showed similar performance when items were unitized into a novel compound word (study: "LOVEGIGGLE"; test: LOVEG?). Thus, boosting nonrelational aspects of recall enhances associative memory among aging individuals with subtle memory impairments to comparable levels as successfully aging older adults.

As individuals explore their environment, they experience smells and recall memories associated with them. This close relationship between smell and memory has been extensively studied; however, less attention has been paid to the direct comparison of associative and non‐associative memory odours. This study aimed to measure responses to odours related to memories and responses to odours related to none or few memories using electroencephalography. In a within‐subject design, 25 individuals received two food odours (chocolate and apple strudel) while olfactory event‐related potentials (oERP) were recorded. These stimuli were chosen because individuals had an autobiographical memory associated with either one of the odours. Additionally, individuals rated the characteristics of the odours and were tested on their memory capacity. The results indicate that apple strudel, but not chocolate, produced larger oERP amplitudes when associated with a memory. Additionally, the apple strudel odour was found to be less pleasant and familiar than the chocolate odour, and fewer individuals had an association with the apple strudel odour. This indicates that oERP can be used to indicate the strength of odour‐related memories.

Adults struggle to recollect episodic memories from early life. This phenomenon-referred to as "infantile" and "childhood amnesia"-has been widely observed across species and is characterized by rapid forgetting from birth until early childhood. While a number of studies have focused on infancy, few studies have examined the persistence of memory for newly learned associations during the putative period of childhood amnesia. In this study, we investigated forgetting in 137 children ages 3-5 years old by using an interactive storybook task. We assessed associative memory between subjects after 5-min, 24-h, and 1-week delay periods. Across all delays, we observed a significant increase in memory performance with age. While all ages demonstrated above-chance memory performance after 5-min and 24-h delays, we observed chance-level memory accuracy in 3-year-olds following a 1-week delay. The observed age differences in associative memory support the proposal that hippocampal-dependent memory systems undergo rapid development during the preschool years. These data have the potential to inform future work translating memory persistence and malleability research from rodent models to humans by establishing timescales at which we expect young children to forget newly learned associations.

Unitization, the process of encoding previously independent units as one coherent representation, improves associative memory in both young and older adults, or in some cases, differentially benefits older adults. Unitization of verbal associative pairs may reduce reliance on the hippocampus (HC) for successful encoding and recognition by shifting to familiarity-based processing mediated by perirhinal cortex (PRC). However, this shift was not observed in a recent study of visual associative memory, with equivalent activation in HC and PRC during encoding of visually integrated (unitized) and nonintegrated object and scene pairs. Furthermore, behavioral findings from this study suggested an increase in recollection rather than familiarity during recognition of visually integrated pairs. The present study extends our previous work by focusing on the influence of visual integration on fMRI activation during associative recognition, rather than encoding and these patterns between young and older adults. In contrast to our findings from encoding, visual integration reduced HC and PRC activation during retrieval of object and scene associative pairs across both age groups. However, visual integration increased the correlation between bilateral HC and left parahippocampal (PHC) activation and behavioral performance among older adults, consistent with an increased reliance on recollection. In contrast, visual integration reduced the correlation between HC activation and behavioral performance in young adults, more consistent with findings from the verbal unitization literature. Taken together, these results suggest that associative memory for visually integrated pairs may involve differential recruitment of medial temporal regions in young and older adults.

Older adults demonstrate notable individual differences in associative memory. Here, resting-state functional magnetic resonance imaging (rsfMRI) was used to investigate whether intrinsic brain activity at rest could predict individual differences in associative memory among cognitively healthy older adults. Regional amplitude of low-frequency fluctuations (ALFF) analysis and a correlation-based resting-state functional connectivity (RSFC) approach were used to analyze data acquired from 102 cognitively normal elderly who completed the paired-associative learning test (PALT) and underwent fMRI scans. Participants were divided into two groups based on the retrospective self-reports on whether or not they utilized encoding strategies during the PALT. The behavioral results revealed better associative memory performance in the participants who reported utilizing memory strategies compared with participants who reported not doing so. The fMRI results showed that higher associative memory performance was associated with greater functional connectivity between the right superior frontal gyrus and the right posterior cerebellum lobe in the strategy group. The regional ALFF values in the right superior frontal gyrus were linked to associative memory performance in the no-strategy group. These findings suggest that the regional spontaneous fluctuations and functional connectivity during rest may subserve the individual differences in the associative memory in older adults, and that this is modulated by self-initiated memory strategy use.

Numerous studies seek to understand the role of oscillatory synchronization in cognition. This problem is particularly challenging in the context of complex cognitive behavior, which consists of a sequence of processing steps with uncertain duration. In this study, we analyzed oscillatory connectivity measures in time windows that previous computational models had associated with a specific sequence of processing steps in an associative memory recognition task (visual encoding, familiarity, memory retrieval, decision making, and motor response). The timing of these processing steps was estimated on a single-trial basis with a novel hidden semi-Markov model multivariate pattern analysis (HSMM-MVPA) method. We show that different processing stages are associated with specific patterns of oscillatory connectivity. Visual encoding is characterized by a dense network connecting frontal, posterior, and temporal areas as well as frontal and occipital phase locking in the 4-9Hz theta band. Familiarity is associated with frontal phase locking in the 9-14Hz alpha band. Decision-making is associated with frontal, and temporo-central interhemispheric connections in the alpha band. During decision making, a second network in the theta band that connects left-temporal, central, and occipital areas bears similarity to the neural signature for preparing a motor response. A similar theta band network is also present during the motor response, with additionally alpha band connectivity between right-temporal and posterior areas. This demonstrates, that the processing stages discovered with the HSMM-MVPA method are indeed linked to distinct synchronization patterns, leading to a closer understanding of the functional role of oscillations in cognition. This article is protected by copyright. All rights reserved.

The hippocampus (HC) interacts with distributed brain regions to support memory and shows significant volume reductions in aging, but little is known about age effects on hippocampal whole-brain structural covariance. It is also unclear whether the anterior and posterior HC show similar or distinct patterns of whole-brain covariance and to what extent these are related to memory functions organized along the hippocampal longitudinal axis. Using the multivariate approach partial least squares, we assessed structural whole-brain covariance of the HC in addition to regional volume, in young, middle-aged and older adults (n = 221), and assessed associations with episodic and spatial memory. Based on findings of sex differences in both memory and brain aging, we further considered sex as a potential modulating factor of age effects. There were two main covariance patterns: one capturing common anterior and posterior covariance, and one differentiating the two regions by capturing anterior-specific covariance only. These patterns were differentially related to associative memory while unrelated to measures of single-item memory and spatial memory. Although patterns were qualitatively comparable across age groups, participants' expression of both patterns decreased with age, independently of sex. The results suggest that the organization of hippocampal structural whole-brain covariance remains stable across age, but that the integrity of these networks decreases as the brain undergoes age-related alterations.

Introduction We present findings of a novel and ecologically relevant associative memory test, the Object Location Touchscreen Test (OLTT), which was posited as sensitive to early medial temporal lobe compromise associated with mild cognitive impairment (MCI). Methods A total of 114 participants, including healthy young and older controls and patients with MCI, completed the OLTT and standard neuropsychological testing. The OLTT required participants to recall the location of objects under free and cued recall conditions, with accuracy evaluated using distance measures (i.e., a continuous error score), and a standard recognition format. Correlations between performance and volumetric data were evaluated from a subset of 77 participants. Results Significant age effects were dwarfed by MCI effects across all test conditions. OLTT Cued Recall was strongly and specifically related to the volume of disease-relevant medial temporal lobe regions, generally more than traditional memory tests. Discussion The OLTT may be sensitive to early structural compromise in regions affected by Alzheimer's disease., Highlights • Evaluated age and mild cognitive impairment effects using ecologically relevant object location (OL) task. • Performance evaluated using both continuous and dichotomous measures of accuracy. • Greater decline in OL memory with mild cognitive impairment than with “healthy” aging. • Performance, especially continuous measure, reflected medial temporal integrity. • Novel OL memory task may be sensitive to early structural compromise.

Protein sequences have evolved to fold into functional structures, resulting in families of diverse protein sequences that all share the same overall fold. One can harness protein family sequence data to infer likely contacts between pairs of residues. In the current study, we combine this kind of inference from coevolutionary information with a coarse-grained protein force field ordinarily used with single sequence input, the Associative memory, Water mediated, Structure and Energy Model (AWSEM), to achieve improved structure prediction. The resulting Associative memory, Water mediated, Structure and Energy Model with Evolutionary Restraints (AWSEM-ER) yields a significant improvement in the quality of protein structure prediction over the single sequence prediction from AWSEM when a sufficiently large number of homologous sequences are available. Free energy landscape analysis shows that the addition of the evolutionary term shifts the free energy minimum to more native-like structures, which explains the improvement in the quality of structures when performing predictions using simulated annealing. Simulations using AWSEM without coevolutionary information have proved useful in elucidating not only protein folding behavior, but also mechanisms of protein function. The success of AWSEM-ER in de novo structure prediction suggests that the enhanced model opens the door to functional studies of proteins even when no experimentally solved structures are available.

This article describes a left-corner parser implemented within a cognitively and neurologically motivated distributed model of memory. This parser's approach to syntactic ambiguity points toward a tidy account both of surprisal effects and of locality effects, such as the parsing breakdowns caused by center embedding. The model provides an algorithmic-level (Marr, 1982) account of these breakdowns: The structure of the parser's memory and the nature of incremental parsing produce a smooth degradation of processing accuracy for longer center embeddings, and a steeper degradation when they are nested, in line with recall observations by Miller and Isard (1964) and speed-accuracy trade-off observations by McElree et al. (2003). Modeling results show that this effect is distinct from the effects of ambiguity and exceeds the effect of mere sentence length.

The hippocampus is critical for memory acquisition and consolidation. This function requires activity- and experience-induced neuronal plasticity. It is known that neuronal plasticity is largely dependent on synchronized activity. As has been well characterized, repetitive correlated activity of presynaptic and postsynaptic neurons can lead to long-term modifications at their synapses. Studies on network activity have also suggested that memory processing in the hippocampus may involve learning-induced changes of neuronal synchronization, as observed in vivo between hippocampal CA3 and CA1 networks as well as between the rhinal cortex and the hippocampus. However, further investigation of learning-induced synchronized activity in the hippocampus is needed for a full understanding of hippocampal memory processing. In this study, by performing paired whole-cell recording in vivo on CA1 pyramidal cells (PCs) in anaesthetized adult rats, we examined CA1 neuronal synchronization before and after associative fear learning. We first found in naive animals that there was a low level of membrane-potential (MP) synchronization and spike synchronization of CA1 PCs. In conditioned animals, we found a significant enhancement of both MP synchronization and spike synchronization, as observed on day 1 after learning, and this enhancement was transient and not observed on day 5. Accompanying learning-induced synchronized activity was a decreased firing threshold and rise time of suprathreshold MP changes as well as an increased spontaneous firing rate, possibly contributing to the enhanced spike synchronization. The transiently enhanced CA1 neuronal synchronization may have important roles in generating neuronal plasticity for hippocampal storage and consolidation of associative memory traces. This article is protected by copyright. All rights reserved

When meaningful stimuli such as words are encountered in groups or pairs (e.g., "elephant-ferry"), they can be processed either separately or as an integrated concept ("an elephant ferry"). Prior research suggests that memory for integrated associations is supported by different mechanisms than is memory for nonintegrated associations. However, little is known about the neurocognitive mechanisms that support the integration of novel stimulus pairs. We recorded ERPs while participants memorized sequentially presented, unrelated noun pairs using a strategy that either did or did not involve attempting to construct coherent definitions. We varied the concreteness of the first noun in each pair to examine whether conceptual combination instructions would induce compositional concreteness effects, or differences in ERPs evoked by the second noun as a function of the concreteness of the first noun. We found that the conceptual combination task, but not the noncombinatory encoding task, produced compositional concreteness effects on a late frontal negativity previously linked to visual imagery. Moreover, word pairs studied under conceptual combination instructions showed evidence of more unitized or holistic memory representations on associative recognition and free recall tests. Finally, item analyses indicated that (a) items with higher normed imageability ratings were rated by participants as easier to conceptually combine, and (b) in the conceptual combination task, ease-of-combination ratings mediated an indirect relationship between imageability and subsequent associative memory. These data are suggestive of a role of compositional imagery in the online formation of novel concepts via conceptual combination.

When encountering stimuli that vary slightly from previous experiences, neural signals within the CA3 and dentate gyrus (CA3DG) hippocampal subfields are thought to facilitate mnemonic discrimination, whereas CA1 may be less sensitive to minor stimulus changes, allowing for generalization across similar events. Studies have also posited a critical role for CA1 in the comparison of events to memory-derived expectations, but the degree to which these processes are impacted by explicit retrieval demands is yet unclear. To evaluate extant accounts of hippocampal subfield function, we acquired high-resolution fMRI data as participants performed a task in which famous names were used to cue the retrieval of previously paired images. Although both left CA3DG and CA1 showed match enhancement effects, responding more to original paired images (targets) than to never-before-seen images (novels), the sensitivity of these subfields to stimulus changes and task demands diverged. CA3DG showed a goal-independent, yet highly specific, preference for previously encountered stimuli, responding equally strongly to targets and mispaired associates, while showing equally weak responses to close lures and novels. In contrast, recognition signals in CA1 were goal-dependent (i.e., not evoked by mispaired associates), yet accommodating of subtle stimulus differences, such that close lures evoked comparable activity as targets. This article is protected by copyright. All rights reserved.

In today's clutter of marketing communications, creative advertisements are capable of grabbing the viewers’ attention with the aim of conveying the product's key benefit claim (KBC). A proven technique for drawing attention to an ad and communicating a KBC is the use of a “remote conveyor” that is seemingly unrelated to the product (e.g., a dolphin and a sports watch for conveying its waterproofness). Drawing on associative memory theory, this article investigates the potentially antagonistic relationship between five “curiosity-raising” (originality) and “benefit-conveying” (effectiveness) properties of a sample of 167 conveyors for communicating the KBC of four different products. The conveyors were generated in a nominal brainstorming session with 20 MBA students. This article also provides real-life examples to illustrate the role of the five conveyor properties in getting across the message creatively and effectively. Creatives and do-it-yourself advertisers alike can easily apply the outlined procedure for generating and selecting conveyors.

Current neuroscientific research has shown that the brain reconfigures its functional interactions at multiple timescales. Here, we sought to link transient changes in functional brain networks to individual differences in behavioral and cognitive performance by using an active learning paradigm. Participants learned associations between pairs of unrelated visual stimuli by using feedback. Interindividual behavioral variability was quantified with a learning rate measure. By using a multivariate statistical framework (partial least squares), we identified patterns of network organization across multiple temporal scales (within a trial, millisecond; across a learning session, minute) and linked these to the rate of change in behavioral performance (fast and slow). Results indicated that posterior network connectivity was present early in the trial for fast, and later in the trial for slow performers. In contrast, connectivity in an associative memory network (frontal, striatal, and medial temporal regions) occurred later in the trial for fast, and earlier for slow performers. Time-dependent changes in the posterior network were correlated with visual/spatial scores obtained from independent neuropsychological assessments, with fast learners performing better on visual/spatial subtests. No relationship was found between functional connectivity dynamics in the memory network and visual/spatial test scores indicative of cognitive skill. By using a comprehensive set of measures (behavioral, cognitive, and neurophysiological), we report that individual variations in learning-related performance change are supported by differences in cognitive ability and time-sensitive connectivity in functional neural networks. Hum Brain Mapp 37:3911-3928, 2016. © 2016 Wiley Periodicals, Inc.

Existing knowledge of the cerebellar microcircuitry structure and physiology allows a rather detailed description of what it in itself can and cannot do. Combined with a known mapping of different cerebellar regions to afferent systems and motor output target structures, there are several constraints that can be used to describe how specific components of the cerebellar microcircuitry may work during sensorimotor control. In fact, as described in this review, the major factor that hampers further progress in understanding cerebellar function is the limited insights into the circuitry-level function of the targeted motor output systems and the nature of the information in the mossy fiber afferents. The cerebellar circuitry in itself is here summarized as a gigantic associative memory element, primarily consisting of the parallel fiber synapses, whereas most other circuitry components, including the climbing fiber system, primarily has the role of maintaining activity balance in the intracerebellar and extracerebellar circuitry. The review explores the consistency of this novel interpretational framework with multiple diverse observations at the synaptic and microcircuitry level within the cerebellum.

Complex-valued associative memories (CAMs) are one of the most promising associative memory models by neural networks. However, the low noise tolerance of CAMs is often a serious problem. A projection learning rule with large constant terms improves the noise tolerance of CAMs. However, the projection learning rule can be applied only to CAMs with full connections. In this paper, we propose a gradient descent learning rule with large constant terms, which is not restricted by network topology. We realize large constant terms by regularization to connection weights. By computer simulations, we prove that the proposed learning algorithm improves noise tolerance. © 2016 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

The dramatic rise of data-intensive workloads has revived application-specific computational hardware for continuing speed and power improvements, frequently achieved by limiting data movement and implementing "in-memory computation". However, conventional complementary metal oxide semiconductor (CMOS) circuit designs can still suffer low power efficiency, motivating designs leveraging nonvolatile resistive random access memory (ReRAM), and with many studies focusing on crossbar circuit architectures. Another circuit primitive-content addressable memory (CAM)-shows great promise for mapping a diverse range of computational models for in-memory computation, with recent ReRAM-CAM designs proposed but few experimentally demonstrated. Here, programming and control of memristors across an 86 × 12 memristor ternary CAM (TCAM) array integrated with CMOS are demonstrated, and parameter tradeoffs for optimizing speed and search margin are evaluated. In addition to smaller area, this memristor TCAM results in significantly lower power due to very low programmable conductance states, motivating CAM use in a wider range of computational applications than conventional TCAMs are confined to today. Finally, the first experimental demonstration of two computational models in memristor TCAM arrays is reported: regular expression matching in a finite state machine for network security intrusion detection and definable inexact pattern matching in a Levenshtein automata for genomic sequencing.

To approach an advanced neuromorphic system, a significant unsettled problem is how to realize biologically plausible memory structures that are dramatically different from classical computers. Herein, a physical system based on memristors is simulated to realize associative memory based on discrete attractor networks, which is essentially content‐based storage, and the influence of device characteristics on network performance is systematically studied. An in situ unsupervised learning method is applied to make greater use of array structure and competitions between neurons, demonstrating significant performance improvement in memory capacity and noise tolerance compared with existing supervised approaches. By extending to continuous attractor neural networks (CANNs), working memory is realized based on memristors for the first time via simulation, and the write and read noises in memristor arrays are found to have different impacts on the ability of CANN in maintaining dynamic information. This work lays a foundation for the construction of future advanced neuromorphic computing systems.

When searching for concepts in memory-as in the verbal fluency task of naming all the animals one can think of-people appear to explore internal mental representations in much the same way that animals forage in physical space: searching locally within patches of information before transitioning globally between patches. However, the definition of the patches being searched in mental space is not well specified. Do we search by activating explicit predefined categories (e.g., pets) and recall items from within that category (categorical search), or do we activate and recall a connected sequence of individual items without using categorical information, with each item recalled leading to the retrieval of an associated item in a stream (associative search), or both? Using semantic representations in a search of associative memory framework and data from the animal fluency task, we tested competing hypotheses based on associative and categorical search models. Associative, but not categorical, patch transitions took longer to make than position-matched productions, suggesting that categorical transitions were not true transitions. There was also clear evidence of associative search even within categorical patch boundaries. Furthermore, most individuals' behavior was best explained by an associative search model without the addition of categorical information. Thus, our results support a search process that does not use categorical information, but for which patch boundaries shift with each recall and local search is well described by a random walk in semantic space, with switches to new regions of the semantic space when the current region is depleted.\ud

The study investigated the role of an associative information network as a mechanism underlying the relation of peer victimization and social anxiety disorder (SAD). A sample of N = 80 was divided according to diagnosis (SAD vs. no diagnosis) and amount of peer victimization (low vs. high). Responses to memory of a personally experienced aversive social situation and to imagining a standardized negative social situation were assessed. In terms of skin conductance level, subjects with SAD and peer victimization were more reactive to the memory script than the other three groups while responses to the standardized script did not vary. As to heart rate, there were no differences between the groups. Emotional responses presented with an inconsistent pattern. The results provide a first indication that associative memory structures resulting from aversive social experiences might play a role in the development and maintenance of SAD, but further research is needed.

Steganography is the art and science of hiding a message in a carrier, in such a manner that no one, except the sender and intended recipient, can guess the existence of the message; it is a form of security through obscurity. Often, steganography algorithms using discrete cosine transform are detectable through steganalysis attacks. To reduce detectability of the stego, we propose an image steganography algorithm in transform domain based on morphological associative memory, permutation approach, and matrix encoding. In our proposed algorithm, in order to insert a secret message in the cover image, first, we map the cover image to a morphological representation containing morphological coefficients, and then bits of secret message are inserted into the image by permutation approach and matrix encoding. Permutation approach leads to unique distribution of secret message in the carrier, and the use of matrix encoding minimizes the number of coefficients needed to be changed because of inserting secret message. In our experiments, we compared the quality of stego, time complexity, and robustness of our method with state-of-art image steganography algorithms F5 and morphological steganography with an equal payload. The experimental results showed that the proposed method is able to produce insignificant visual distortion compared with other traditional approaches. To test the robustness of our proposed algorithm, we used wavelet-based and block-based steganalysis methods. The obtained results showed a high level of robustness of our algorithm against steganalysis attacks. Copyright © 2014 John Wiley & Sons, Ltd.

Development introduces structured correlations among traits that may constrain or bias the distribution of phenotypes produced. Moreover, when suitable heritable variation exists, natural selection may alter such constraints and correlations, affecting the phenotypic variation available to subsequent selection. However, exactly how the distribution of phenotypes produced by complex developmental systems can be shaped by past selective environments is poorly understood. Here we investigate the evolution of a network of recurrent nonlinear ontogenetic interactions, such as a gene regulation network, in various selective scenarios. We find that evolved networks of this type can exhibit several phenomena that are familiar in cognitive learning systems. These include formation of a distributed associative memory that can “store” and “recall” multiple phenotypes that have been selected in the past, recreate complete adult phenotypic patterns accurately from partial or corrupted embryonic phenotypes, and “generalize” (by exploiting evolved developmental modules) to produce new combinations of phenotypic features. We show that these surprising behaviors follow from an equivalence between the action of natural selection on phenotypic correlations and associative learning, well-understood in the context of neural networks. This helps to explain how development facilitates the evolution of high-fitness phenotypes and how this ability changes over evolutionary time.

Memory deficits are a common complaint of patients with posttraumatic stress disorder (PTSD). Despite vivid trauma-related memory, previous studies report memory impairment for nontrauma-related stimuli when compared to controls, specifically in associative memory (Guez et al., 2011). Healthy individuals show hemispheric memory asymmetry with left-prefrontal lateralization of encoding and right-prefrontal lateralization of episodic retrieval, suggesting a role for interhemispheric communication in memory-related tasks (Gazzaniga, ; Ringo, Doty, Demeter, & Simard, ). Because brain magnetic resonance imaging (bMRI) studies in PTSD patients report volume changes in various regions, including white matter and corpus callosum (CC), we aimed to test the relationship between memory deficits and CC volume in PTSD patients. We probed for specific alterations in associative memory in PTSD and measured the volume of subportions within the CC employing bMRI. Our main finding was a reduction in CC white-matter volume in PTSD patients, as compared to controls, t(35) = -2.7, p = .010, that was correlated with lower associative performance (r = .76, p = .003). We propose that CC volume reduction is a substrate for the associative memory deficits found in PTSD.

Background and Purpose Recent human studies suggest that recreational cannabis strains that are relatively high in cannabidiol (CBD) content produce less cognitive impairment than do strains with negligible CBD and similar Δ9tetrahydrocannabinol (THC) content. Self-selection in such studies means it is impossible to rule out additional variables which may determine both cannabis strain selection and basal cognitive performance level. Controlled laboratory studies can better determine a direct relationship. Experimental Approach In this study, adult male rhesus monkeys were assessed on visuospatial Paired Associates Learning and Self-Ordered Spatial Search memory tasks, as well as additional tests of motivation and manual dexterity. Subjects were challenged with THC (0.2, 0.5 mg·kg−1, i.m.) in randomized order and evaluated in the presence or absence of 0.5 mg·kg−1 CBD. Key Results CBD attenuated the effects of THC on paired associates learning and a bimanual motor task without affecting the detrimental effects of THC on a Self-Ordered Spatial Search task of working memory. CBD did not significantly reverse THC-induced impairment of a progressive ratio or a rotating turntable task. Conclusions and Implications This study provides direct evidence that CBD can oppose the cognitive-impairing effects of THC and that it does so in a task-selective manner when administered simultaneously in a 1:1 ratio with THC. The addition of CBD to THC-containing therapeutic products may therefore help to ameliorate unwanted cognitive side-effects. Linked Article This article is commented on by Mechoulam and Parker, pp 1363–1364 of this issue. To view this commentary visit http://dx.doi.org/10.1111/bph.12400

High field strength functional magnetic resonance imaging (fMRI) has developed rapidly. However, it suffers from increased artifacts in brain regions such as the medial temporal lobe (MTL), challenging functional imaging of the hippocampus with the objective of high-spatial resolution, which is particularly useful for this region both from a clinical and cognitive neuroscience perspective. We set out to compare a BOLD sequence at 7 T versus 3 T to visualize the MTL activity during an associative memory-encoding task. Twenty-eight healthy volunteers underwent a blocked-design fMRI at either 3 T or 7 T while performing a face-profession associative memory encoding task. Qualitative analyses of overall image quality revealed that functional images at 7 T were of high quality, showing a good white/gray matter contrast, with reasonably acceptable signal dropouts and artifacts at the lower portion of the temporal lobe. Analyses of task-related fMRI data revealed robust activations in the bilateral MTL during associative memory encoding at both field strengths. Notably, we observed significantly stronger memory-related hippocampal activation at 7 T than at 3 T, suggesting higher BOLD sensitivity at 7 T. These results are discussed in the light of the feasibility of 7 T scanning protocols for the MTL.

The distinction between non-associative and associative forms of learning has historically been based on the behavioral training paradigm. Through discovering the molecular mechanisms that mediate learning, we can develop a deeper understanding of the relationships between different forms of learning. Here, we genetically dissect short- and long-term memory for a non-associative form of learning, habituation and an associative form of learning, context conditioning for habituation, in the nematode Caenorhabditis elegans. In short-term chemosensory context conditioning for habituation, worms trained and tested in the presence of either a taste (sodium acetate) or smell (diacetyl) context cue show greater retention of habituation to tap stimuli when compared with animals trained and tested without a salient cue. Long-term memory for olfactory context conditioning was observed 24 h after a training procedure that does not normally induce 24 h memory. Like long-term habituation, this long-term memory was dependent on the transcription factor cyclic AMP-response element-binding protein. Worms with mutations in glr-1 [a non-N-methyl-d-aspartate (NMDA)-type glutamate receptor subunit] showed short-term but not long-term habituation or short- or long-term context conditioning. Worms with mutations in nmr-1 (an NMDA-receptor subunit) showed normal short- and long-term memory for habituation but did not show either short- or long-term context conditioning. Rescue of nmr-1 in the RIM interneurons rescued short- and long-term olfactory context conditioning leading to the hypothesis that these interneurons function to integrate information from chemosensory and mechanosensory systems for associative learning.