Associative Memory Recall Research Articles

A Hardware Chaotic Neural Network With Gap Junction Models

ABSTRACTWe aim at the engineering applications of reservoir computing using hardware chaotic neural networks, including associative memory recall. The reservoir layer used in reservoir computing is networked and constructed using pulse‐type hardware chaos neuron models (P‐HCNMs). The structure of the reservoir layer is simple, which is advantageous for hardware implementation. By inducing chaos in the reservoir layer, it is possible to use the “chaotic edge” where the reservoir reaches its highest efficiency. It has also been reported that incorporating self‐correction within the reservoir layer increases the efficiency of the task. In this paper, we constructed a hardware small‐world neural network using a synaptic model with spike timing‐dependent synaptic plasticity (STDP) and a gap junction model. As a result, it is clarified that all cell body models with synaptic model connections show chaotic firing by simulation at the same time, and that the STDP model enables learning while keeping the chaotic phenomena. In addition, comparison with the firing of cell body models coupled only with synaptic models suggested that the gap junction model works significantly in inducing chaos in neural networks.

Sequential involvements of the perirhinal cortex and hippocampus in the recall of item-location associative memory in macaques.

The standard consolidation theory suggests that the hippocampus (HPC) is critically involved in acquiring new memory, while storage and recall gradually become independent of it. Converging studies have shown separate involvements of the perirhinal cortex (PRC) and parahippocampal cortex (PHC) in item and spatial processes, whereas HPC relates the item to a spatial context. These 2 strands of literature raise the following question; which brain region is involved in the recall process of item-location associative memory? To solve this question, this study applied an item-location associative (ILA) paradigm in a single-unit study of nonhuman primates. We trained 2 macaques to associate 4 visual item pairs with 4 locations on a background map in an allocentric manner before the recording sessions. In each trial, 1 visual item and the map image at a tilt (-90° to 90°) were sequentially presented as the item-cue and the context-cue, respectively. The macaques chose the item-cue location relative to the context-cue by positioning their gaze. Neurons in the PRC, PHC, and HPC, but not area TE, exhibited item-cue responses which signaled retrieval of item-location associative memory. This retrieval signal first appeared in the PRC, followed by the HPC and PHC. We examined whether neural representations of the retrieved locations were related to the external space that the macaques viewed. A positive representation similarity was found in the HPC and PHC, but not in the PRC, thus suggesting a contribution of the HPC to relate the retrieved location from the PRC with a first-person perspective of the subjects and provide the self-referenced retrieved location to the PHC. These results imply distinct but complementary contributions of the PRC and HPC to recall of item-location associative memory that can be used across multiple spatial contexts.

Hippocampal CA1 volume is associated with higher p‐tau and diminished memory performance in normal older adults

AbstractBackgroundPrior work has demonstrated that elevated CSF biomarkers in older adults are associated with diminished performance across several hippocampally‐dependent memory tasks. It is unknown whether early structural changes in medial temporal lobe subfields (1) may be impacted by elevated p‐tau181, and (2) mediate the effect of p‐tau181 on memory performance in older adults.MethodThe current study draws on a cohort of 147 cognitively unimpaired older adults (Stanford Aging and Memory Study) that completed both 3T MRI and lumbar punctures. To examine memory performance, participants completed two hippocampally dependent tasks: a paired associate cued recall task and a mnemonic discrimination task (MST) that examined discrimination between previously studied “old” objects, novel “foil” objects and perceptually similar “lure” objects. Lure trials were binned in five difficulty levels, ranging from low to high similarity compared to previously presented stimuli. Hippocampal subregions (CA1, CA3/DG, subiculum) were manually delineated on T2*weighted images following Carr et al., (2017). CSF was processed with Lumipulse to measure Ab42:Ab40 ratio and p‐tau181. Multiple regression was used to assess the associative memory d’ from the paired associate task. Given the repeated measures design of the MST task, linear mixed models were conducted to understand the association between hippocampal subfields and p‐tau181 on performance as a function of similarity strength (Trelle et al., 2021). Age, sex, and education were controlled in all models.ResultP‐tau181 was correlated with reduced left CA1 volume (partial r2=0.043, p = 0.01), but not with volume in other hippocampal subfields. Increased CA1 volume was positively associated with better memory performance, including higher associative memory recall and old‐lure discrimination. After controlling for p‐tau181, CA1 volume was no longer associated with performance on the associative memory task but remained significantly correlated with old/lure discrimination. Notably, increased CA1 volume improved overall discrimination for old/lure trials, independent of the difficulty level, while the association between p‐tau181 and performance was strongest at the lower similarity level.ConclusionReduced CA1 volume and p‐tau explain unique variance in memory performance in older adults. This combination of biofluid biomarkers and high‐resolution MRI has the potential to understand mechanisms underlying age‐related memory decline.

Pharmacologically increased cortisol levels impair recall of associative background context memory in males, but not females

Laboratory studies have consistently shown that stress impairs memory retrieval of individual parts (items) of a memory. The stress-hormone cortisol has been particularly linked to this impairment. However, it is unclear whether cortisol similarly affects the binding of items to associative context information in memory, i.e. the constituents of episodic memory. Here, we examine memory retrieval of item and associative memory under pharmacologically elevated cortisol vs. normal levels. Given that previous studies have indicated potential sex differences in the stress- and cortisol-induced memory modulation, we additionally assessed whether there may be sex differences for the cortisol effect on memory retrieval. Eighty-four female and male participants were tested in a placebo controlled, double-blind between-subject design, assigned to either a cortisol (10 mg hydrocortisone) or a placebo group. Participants of both groups were presented foreground images of negative and neutral valence on different neutral background scenes. Twenty-four hours later, participants’ memory for the images and their associated background scene was tested with a recognition task 20 min after substance administration. Among the 78 participants of both groups included in the final analysis, cortisol levels were higher in the cortisol group in comparison to the placebo group, and female participants had higher cortisol levels after hydrocortisone intake in comparison to male participants. Item memory did not differ between the placebo and cortisol group. In contrast, in males, but not females, associative memory for the background scene of emotional foreground images was lower in the cortisol vs. placebo group. Moreover, the individual cortisol increase during the recognition task was negatively correlated to memory for the background scenes of the emotional foreground images only in male participants of the cortisol group. This study shows that pharmacologically increased cortisol levels distinctly affect associative memory in female and male participants, but have no effect on item memory, indicating a complex interaction for the stress effects on memory.

Structured sampling of olfactory input by the fly mushroom body

Associative memory formation and recall in the fruit fly Drosophila melanogaster is subserved by the mushroom body (MB). Upon arrival in the MB, sensory information undergoes a profound transformation from broadly tuned and stereotyped odorant responses in the olfactory projection neuron (PN) layer to narrowly tuned and nonstereotyped responses in the Kenyon cells (KCs). Theory and experiment suggest that this transformation is implemented by random connectivity between KCs and PNs. However, this hypothesis has been challenging to test, given the difficulty of mapping synaptic connections between large numbers of brain-spanning neurons. Here, we used a recent whole-brain electron microscopy volume of the adult fruit fly to map PN-to-KC connectivity at synaptic resolution. The PN-KC connectome revealed unexpected structure, with preponderantly food-responsive PN types converging at above-chance levels on downstream KCs. Axons of the overconvergent PN types tended to arborize near one another in the MB main calyx, making local KC dendrites more likely to receive input from those types. Overconvergent PN types preferentially co-arborize and connect with dendrites of αβ and α'β' KC subtypes. Computational simulation of the observed network showed degraded discrimination performance compared with a random network, except when all signal flowed through the overconvergent, primarily food-responsive PN types. Additional theory and experiment will be needed to fully characterize the impact of the observed non-random network structure on associative memory formation and recall.

Potential role for peripheral nerve stimulation on learning and long-term memory: A comparison of alternating and direct current stimulations

BackgroundIn the past decade, a rising interest in transcranial electrical stimulation has emerged owing to its advantageous capacity to facilitate the extraction of casual links between neuromodulation and the obtained behavioral effects in cognitive performance. However, an insufficient number of direct comparative studies between transcranial alternating current stimulation (tACS) and transcranial direct current stimulation (tDCS) effects on associative memory have caused optimal parameters and procedural application to remain undefined. ObjectiveThe current study aimed to comparatively investigate the effects of tDCS and tACS applied to the occipital nerve (ON), targeting the locus coeruleus, on associative memory performance. MethodsWe employed a randomized, double-blind, two-visit, active-controlled study design. 85 cognitively normal adults were assigned to receive either active ON-tDCS, 40 Hz ON-tACS, sham ON-tDCS, or 1 Hz ON-tACS during encoding of a 50-word Swahili-English associative memory recall task. To evaluate the effects of electrical stimulation, we measured the cumulative rate of learning on Day 1 and to assess possible long-term effects, we measured the number of words recalled on Day 7. ResultsResults presented two notable findings: (1) participants who received 40 Hz ON-tACS learned significantly more words on Day 1 (F3,81 = 4.37, p = .007, η2 = 0.14), and (2) participants who received 40 Hz ON-tACS or active ON-tDCS recalled significantly more words on Day 7 (F3,81 = 11.08, p < .001, η2 = 0.29). ConclusionsThe evidence from this study alludes to 40 Hz ON-tACS and active ON-tDCS inducing distinct behavioral effects, whereby 40 Hz ON-tACS generated an effect during memory encoding via enhanced attention, however, active ON-tDCS elicited an offline effect transpiring during consolidation. Further neuroimaging studies are needed to validate these findings and proposed mechanisms of action.

ヒスタミン神経による連合記憶の想起促進

ヒスタミン神経による連合記憶の想起促進

Theta rhythmicity governs human behavior and hippocampal signals during memory-dependent tasks

Memory formation and reinstatement are thought to lock to the hippocampal theta rhythm, predicting that encoding and retrieval processes appear rhythmic themselves. Here, we show that rhythmicity can be observed in behavioral responses from memory tasks, where participants indicate, using button presses, the timing of encoding and recall of cue-object associative memories. We find no evidence for rhythmicity in button presses for visual tasks using the same stimuli, or for questions about already retrieved objects. The oscillations for correctly remembered trials center in the slow theta frequency range (1-5 Hz). Using intracranial EEG recordings, we show that the memory task induces temporally extended phase consistency in hippocampal local field potentials at slow theta frequencies, but significantly more for remembered than forgotten trials, providing a potential mechanistic underpinning for the theta oscillations found in behavioral responses.

Worse associative memory recall in healthy older adults compared to young ones, a face-name study in Spain and Mexico

ABSTRACT Introduction The Face Name Associative Memory Exam (FNAME) is sensitive to associative memory changes early in the Alzheimer’s disease spectrum, but little is known about how healthy aging affects FNAME performance. We aimed to assess aging effects on an extended version of the test, which captures further associative memory abilities beyond the recall and recognition domains measured in the original version. Method We adapted FNAME versions in Spain and Mexico, adding new subtests (Spontaneous Name Recall, Face-Name Matching). We compared the performance of 21 young adults (YA) and 27 older adults (OA) in Spain, and 34 YA and 36 OA in Mexico. Recall was analyzed using a mixed-model ANOVA including subtest scores as dependent variables, age group as a fixed-factor independent variable, and recall subtest as a three-level repeated-measure independent variable. The rest of the associative memory domains were analyzed through t-tests comparing the performance of YA and OA. Results In Spain, we found significant effects for age group and recall subtest, with large effect sizes. The recognition subtests (Face Recognition, Name Recognition) displayed ceiling effects in both groups. The new subtests displayed medium-to-large effect sizes when comparing age groups. In Mexico, these results were replicated, additionally controlling for education. In both studies, recall performance improved after repeated exposures and it was sustained after 30 minutes in YA and OA. Conclusions We document, in two different countries, a clear aging pattern on the extended FNAME: regardless of education, OA remember fewer stimuli than YA through recall subtests. The new subtests provide evidence on associative memory changes in aging beyond recall.

Abstract PD6-11: Altered regional cerebral blood flow in adjuvant-treated breast cancer survivors after chemo- and endocrine therapy

Abstract Objectives: In the first published observation of altered brain metabolism in patients exposed to chemotherapy (Breast Cancer Res Treat. 2007; 103:303-311), we described diminished metabolism in prefrontal cortex in proportion to magnitude of diminishment of short-term memory performance, 5-10 years following patients’ last chemotherapy dose. Subsequently, at least 7 other groups of investigators have independently demonstrated altered cerebral metabolism of frontal cortex as assessed by FDG-PET (J Nucl Med. 2019; 60:16821690). We now offer the first report of regional cerebral blood flow (rCBF) changes assessed by [O-15]water PET in prospectively recruited subjects with newly diagnosed breast cancer, longitudinally followed from time of initial therapy for one year. Methods: A total of 204 brain [O-15]water PET scans were obtained of 17 right-handed female subjects newly diagnosed with breast cancer, with near-equal portions of 10 chemo-exposed (C) and 7 unexposed (U) subjects undergoing endocrine therapy in the ensuing year (5/10, 3/7). For each subject, 12 scans were obtained – 6 during short-term memory, long-term memory, and control tasks presented in counterbalanced order soon after completion of any adjuvant chemotherapy but prior to initiation of any endocrine therapy (baseline), and repeating one year later. PET data were assessed through paired t statistical tests at the voxel level, after Family Wise Error (FWE)-based corrections for multiple comparisons. Results: Across all subjects, scans at baseline during short-term recall revealed most marked activation of bilateral temporal-occipital cortex (peak voxel t=7.20; size 4,649 voxels, p&amp;lt;.0005 FWEcorr.) and similar activation occurred during long-term recall (t=6.48; 6,446 voxels, p&amp;lt;.0005 FWEcorr.). One year later, left prefrontal cortex, including Broca’s area, activated during short-term recall (t=5.74; 227 voxels, p=.02 FWEcorr), as did bilateral medial occipital cortex (t=5.45; 908 voxels, p&amp;lt;.0005 FWEcorr.); during long-term recall, prefrontal cortex activated with greater bilaterality, but with an extent in left frontal lobe (1031 voxels, p=.008 FWEcorr.) about double the size of right (452 voxels), and with less occipital activation. In therapy-stratified analyses, baseline short-term recall of left prefrontal cortex, including Broca’s area, activated more extensively (3253 voxels, p&amp;lt;.0005 FWEcorr.) in U, while C showed more extensive activation in medial occipital cortex (5670 voxels, p&amp;lt;.0005 FWEcorr.vs. 423 voxels, p=.001). One year later, short-term recall in U continued to activate left prefrontal cortex including Broca’s area (4035 voxels, p&amp;lt;.0005 FWEcorr.), while C still primarily activated medial occipital cortex (976 voxels, p=.008 FWEcorr.), though demonstrating a shift of activation away from this region relative to one year prior, with more voxels of activation tending to appear in left prefrontal cortex over that interval. Similar, though less striking, differences were observed during long-term recall. Conclusions: Activation of rCBF during recall of verbal associative memories was diminished in left prefrontal brain areas critical to verbal memory performance in C relative to U. Concomitantly, C demonstrated apparent compensatory activation of primary visual cortex, involved in perceiving the visually presented verbal memory cues, in lieu of specific activation of the prefrontal cortical regions in the dominant hemisphere involved in processing language information. The strengths of these therapy-associated differences were generally diminished one year later, consistent with partial interim recovery in C of cerebral processing by language-specialized areas. Citation Format: Claire L Vandenberg, Patricia A Ganz, Stephen S Liu, Daniel HS Silverman. Altered regional cerebral blood flow in adjuvant-treated breast cancer survivors after chemo- and endocrine therapy [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PD6-11.

Enhanced Retrieval of Taste Associative Memory by Chemogenetic Activation of Locus Coeruleus Norepinephrine Neurons.

The ability of animals to retrieve memories stored in response to the environment is essential for behavioral adaptation. Norepinephrine (NE)-containing neurons in the brain play a key role in the modulation of synaptic plasticity underlying various processes of memory formation. However, the role of the central NE system in memory retrieval remains unclear. Here, we developed a novel chemogenetic activation strategy exploiting insect olfactory ionotropic receptors (IRs), termed "IR-mediated neuronal activation," and used it for selective stimulation of NE neurons in the locus coeruleus (LC). Drosophila melanogaster IR84a and IR8a subunits were expressed in LC NE neurons in transgenic mice. Application of phenylacetic acid (a specific ligand for the IR84a/IR8a complex) at appropriate doses induced excitatory responses of NE neurons expressing the receptors in both slice preparations and in vivo electrophysiological conditions, resulting in a marked increase of NE release in the LC nerve terminal regions (male and female). Ligand-induced activation of LC NE neurons enhanced the retrieval process of conditioned taste aversion without affecting taste sensitivity, general arousal state, and locomotor activity. This enhancing effect on taste memory retrieval was mediated, in part, through α1- and β-adrenergic receptors in the basolateral nucleus of the amygdala (BLA; male). Pharmacological inhibition of LC NE neurons confirmed the facilitative role of these neurons in memory retrieval via adrenergic receptors in the BLA (male). Our findings indicate that the LC NE system, through projections to the BLA, controls the retrieval process of taste associative memory.SIGNIFICANCE STATEMENT Norepinephrine (NE)-containing neurons in the brain play a key role in the modulation of synaptic plasticity underlying various processes of memory formation, but the role of the NE system in memory retrieval remains unclear. We developed a chemogenetic activation system based on insect olfactory ionotropic receptors and used it for selective stimulation of NE neurons in the locus coeruleus (LC) in transgenic mice. Ligand-induced activation of LC NE neurons enhanced the retrieval of conditioned taste aversion, which was mediated, in part, through adrenoceptors in the basolateral amygdala. Pharmacological blockade of LC activity confirmed the facilitative role of these neurons in memory retrieval. Our findings indicate that the LC-amygdala pathway plays an important role in the recall of taste associative memory.

Memory impairment in patients with spleen deficiency syndrome: Evidence from a resting-state fMRI study

IntroductionAccording to the basic theory of traditional Chinese medicine (TCM), the gastrointestinal function is considered the main function of spleen. The function of spleen is considered to be associated with memory. However, less evidence supports the notion from neuropsychological level. Our aim was to investigate the change of memory function and spontaneous brain activity in patients with spleen deficiency syndrome. MethodsTwenty patients and 16 healthy subjects took part in the memory function test. Eighteen patients and 14 healthy controls underwent functional magnetic resonance imaging examination. ResultsCompared with healthy subjects, patients with spleen deficiency syndrome revealed significantly lower scores of memory quotient (P = 0.001), directed memory (P ≤ 0.001), associative memory (P ≤ 0.001) and free recall of images (P = 0.025), higher aptitude of low-frequency fluctuation (ALFF) values in bilateral temporal occipital fusiform cortices (TOC) and lateral occipital cortices(LOC), and lower ALFF values in left frontal pole cortex (FPC). Moreover, scores of clinical memory scale were significantly correlated with ALFF values in bilateral TOCs and LOCs, and left FPC. ConclusionsOur results indicated that the abnormal brain regions were mainly involved in memory function, providing evidence for the memory functional impairment in patients with spleen deficiency syndrome.

Acute and chronic neurobehavioral effects of the designer drug and bath salt constituent 3,4-methylenedioxypyrovalerone in the rat.

The substantial increase in use of 3,4-methylenedioxypyrovalerone (MDPV), a popular recreational synthetic cathinone, has raised legitimate questions about its behavioral consequences and abuse liability. The aim of this study was to study MDPV-induced neurobehavioral effects in the rat, using different paradigms traditionally developed to study drug-attributed addictive properties. Different patterns of intraperitoneal 3 mg/kg MDPV administration were investigated. Consequences on rat horizontal locomotion and behavior of acute, intermittent (once daily dosing over 10 days), and binge (three-time daily dosing for 3 days) MDPV administration as well as challenge after 10 day MDPV withdrawal were studied. The dopamine receptor-D1 antagonist, SCH23390, was bilaterally infused in the nucleus accumbens to determine the role of D1-receptors in MDPV-related effects on the associative memory recall using the conditioned place preference paradigm. In addition, in a separate experience using western blot, we investigated the effects of chronic MDPV administration (four injections during 24 h) on ΔFosB expression in the nucleus accumbens, caudate putamen, and prefrontal cortex. Acute MDPV administration increased stereotypies and open arm entries in the elevated plus maze while SCH23390 abolished MDPV-induced enhancing effects on memory consolidation. Intermittent MDPV administration resulted in sensitization of MDPV-induced locomotor effects and tolerance during the following challenge. With binge MDPV administration, locomotor activity was not altered despite tolerance onset after challenge. SCH23390 abolished MDPV-induced conditioned place preference. Chronic MDPV administration induced ΔFosB accumulation in the nucleus accumbens, caudate putamen, and prefrontal cortex. Our findings clearly show that MDPV produces profound behavioral alterations mediated by the activation of the dopaminergic system similarly to other amphetamines.

Evidence that neural information flow is reversed between object perception and object reconstruction from memory

Remembering is a reconstructive process, yet little is known about how the reconstruction of a memory unfolds in time in the human brain. Here, we used reaction times and EEG time-series decoding to test the hypothesis that the information flow is reversed when an event is reconstructed from memory, compared to when the same event is initially being perceived. Across three experiments, we found highly consistent evidence supporting such a reversed stream. When seeing an object, low-level perceptual features were discriminated faster behaviourally, and could be decoded from brain activity earlier, than high-level conceptual features. This pattern reversed during associative memory recall, with reaction times and brain activity patterns now indicating that conceptual information was reconstructed more rapidly than perceptual details. Our findings support a neurobiologically plausible model of human memory, suggesting that memory retrieval is a hierarchical, multi-layered process that prioritises semantically meaningful information over perceptual details.

Nonboolean Pattern Recognition Using Chains of Coupled CMOS Oscillators as Discriminant Circuits

Networks of weakly coupled oscillators are special cases of Hopfield networks and as such may be used in building physical systems capable of associative memory recall and pattern recognition. However, the existing architectures are not suitable for hardware implementation mainly due to the complexity of required couplings between the oscillators. In this paper, we propose an alternative way of using coupled oscillators in what we call “discriminant circuits” in analogy to the concept of “discriminant functions” in the field of artificial intelligence and machine learning. The main advantage of our system is in the simplicity of its architecture, which relies only on local couplings between adjacent oscillators. Using this architecture, we design a network of coupled CMOS oscillators as the core of a physical non-Boolean pattern recognition engine. The simplicity of the proposed circuit makes it readily implementable on any standard CMOS technology.

Inhibitory engrams in perception and memory.

Nervous systems use excitatory cell assemblies to encode and represent sensory percepts. Similarly, synaptically connected cell assemblies or "engrams" are thought to represent memories of past experience. Multiple lines of recent evidence indicate that brain systems create and use inhibitory replicas of excitatory representations for important cognitive functions. Such matched "inhibitory engrams" can form through homeostatic potentiation of inhibition onto postsynaptic cells that show increased levels of excitation. Inhibitory engrams can reduce behavioral responses to familiar stimuli, thereby resulting in behavioral habituation. In addition, by preventing inappropriate activation of excitatory memory engrams, inhibitory engrams can make memories quiescent, stored in a latent form that is available for context-relevant activation. In neural networks with balanced excitatory and inhibitory engrams, the release of innate responses and recall of associative memories can occur through focused disinhibition. Understanding mechanisms that regulate the formation and expression of inhibitory engrams in vivo may help not only to explain key features of cognition but also to provide insight into transdiagnostic traits associated with psychiatric conditions such as autism, schizophrenia, and posttraumatic stress disorder.

Effects of low level lead exposure on associative learning and memory in the rat: Influences of sex and developmental timing of exposure.

Lead (Pb) exposure during development impairs a variety of cognitive, behavioral and neurochemical processes resulting in deficits in learning, memory, attention, impulsivity and executive function. Numerous studies have attempted to model this effect of Pb in rodents, with the majority of studies focusing on hippocampus-associated spatial learning and memory processes. Using a different paradigm, trace fear conditioning, a process requiring coordinated integration of both the medial prefrontal cortex and the hippocampus, we have assessed the effects of Pb exposure on associative learning and memory. The present study examined both female and male long evans rats exposed to three environmentally relevant levels of Pb (150 ppm, 375 ppm and 750 ppm) during different developmental periods: perinatal (PERI; gestation-postnatal day 21), early postnatal (EPN; postnatal days 1-21) and late postnatal (LPN; postnatal days 1-55). Testing began at postnatal day 55 and consisted of a single day of acquisition training, and three post training time points (1, 2 and 10 days) to assess memory consolidation and recall. All animals, regardless of sex, developmental window or level of Pb-exposure, successfully acquired conditioned-unconditioned stimulus association during training. However, there were significant effects of Pb-exposure on consolidation and memory recall at days 1-10 post training. In females, EPN and LPN exposure to 150 ppm Pb (but not PERI exposure) significantly impaired recall. In contrast, only PERI 150 ppm and 750 ppm-exposed males had significant recall deficits. These data suggest a complex interaction between sex, developmental window of exposure and Pb-exposure level on consolidation and recall of associative memories.

Adiabatic quantum optimization for associative memory recall

Hopfield networks are a variant of associative memory that recall information stored in the couplings of an Ising model. Stored memories are fixed points for the network dynamics that correspond to energetic minima of the spin state. We formulate the recall of memories stored in a Hopfield network using energy minimization by adiabatic quantum optimization (AQO). Numerical simulations of the quantum dynamics allow us to quantify the AQO recall accuracy with respect to the number of stored memories and the noise in the input key. We also investigate AQO performance with respect to how memories are stored in the Ising model using different learning rules. Our results indicate that AQO performance varies strongly with learning rule due to the changes in the energy landscape. Consequently, learning rules offer indirect methods for investigating change to the computational complexity of the recall task and the computational efficiency of AQO.

The hippocampus is essential for completely unconscious as well as conscious flexible memories.

This scientific commentary refers to ‘Unconscious relational encoding depends on hippocampus’ by Duss et al. (doi: 10.1093/brain/awu270). Several beliefs about the nature of organic amnesia were deeply entrenched by the early 1990s. It was believed that damage to the medial temporal lobe or its connections in the midline diencephalon and basal forebrain did not disrupt intelligence, perception, processing of information at input and immediate (short-term) memory, but selectively disrupted—following even a brief distraction—recall and recognition of recently encountered personal events or facts/concepts. In other words, amnesia was thought to affect only episodic and semantic memory, whether for pre-morbid events (retrograde amnesia) or post-morbid events (anterograde amnesia). With these kinds of memory, not only is the remembered information consciously apprehended at input and at retrieval, but the person remembering is also consciously aware that the information is a memory. That is, the person feels that the information has been encountered before, often in a particular context. In contrast, it was believed that amnesics acquired and retained other kinds of memory, such as habits and skills, normally. Although these latter types of non-declarative memory are functionally heterogeneous, they all lack the conscious feeling of memory that accompanies episodic and semantic memory. Since the late 1990s, several of these entrenched beliefs have been challenged. On the one hand, it has been argued that amnesia is not functionally unitary: while disruption of the hippocampal, fornix and anterior thalamic system impairs recall of flexible (relational) associative memories, disruption of the perirhinal cortex or its dorsomedial thalamic projection impairs inflexible item familiarity (for a review, see Montaldi and Mayes, 2010). Relational memory representations have components linked to each other as well as to other representations, which allows flexible access through multiple cues both to the representation and from it to other representations (Cohen and Eichenbaum, …

Noise-Enhanced Information Systems

Noise, traditionally defined as an unwanted signal or disturbance, has been shown to play an important constructive role in many information processing systems and algorithms. This noise enhancement has been observed and employed in many physical, biological, and engineered systems. Indeed stochastic facilitation (SF) has been found critical for certain biological information functions such as detection of weak, subthreshold stimuli or suprathreshold signals through both experimental verification and analytical model simulations. In this paper, we present a systematic noise-enhanced information processing framework to analyze and optimize the performance of engineered systems. System performance is evaluated not only in terms of signal-to-noise ratio but also in terms of other more relevant metrics such as probability of error for signal detection or mean square error for parameter estimation. As an important new instance of SF, we also discuss the constructive effect of noise in associative memory recall. Potential enhancement of image processing systems via the addition of noise is discussed with important applications in biomedical image enhancement, image denoising, and classification.