Sequential Memory Research Articles

Synthesis of circuits based on all-optical Mach-Zehnder Interferometers using Binary Decision Diagrams

The advancement of fabrication technology in VLSI (Very Large Scale Integration) and photonic industry has gained significant interest due to the feasibility of performing functional computations on-chip using ultra-high speed optical devices and low-power interconnects. Here, the necessity of optical circuits arises as they are inevitable components in developing optical Integrated Circuits (ICs). In this conjuncture, methodologies to design highly scalable optical circuits and their synthesis schemes have received interest. In recent years, several works and their findings have been reported in various research articles where researchers have mainly designed combinational and sequential memory elements using optical devices. The use of Binary Decision Diagrams (BDDs) to construct optical circuits has been reported recently. However, the costs of the resulting circuits are still rather high. Furthermore, they include a substantial amount of splitters, which is a significant drawback as they degrade the signal strength in the circuits.In this paper, we propose an improved design technique where we use BDDs to construct optical circuits. Rather than generating a single graph for multi-output functions, we consider individual graphs for each output separately which, afterwards are combined to realize the entire function. In our experiments, we find that this approach performs better in comparison to related techniques – a cost improvement of approx. 34% is observed on average. As these optical circuits are mainly designed with MZIs, beam combiners and beam splitters, the use of beam splitters in the circuit degrades the signal quality at the receiver end. To address this concern, in a second phase of our design, we make all the circuits free from splitters. Experimental results for both the design schemes are given and analyzed.

Flexible Bayesian Dynamic Modeling of Correlation and Covariance Matrices.

Modeling correlation (and covariance) matrices can be challenging due to the positive-definiteness constraint and potential high-dimensionality. Our approach is to decompose the covariance matrix into the correlation and variance matrices and propose a novel Bayesian framework based on modeling the correlations as products of unit vectors. By specifying a wide range of distributions on a sphere (e.g. the squared-Dirichlet distribution), the proposed approach induces flexible prior distributions for covariance matrices (that go beyond the commonly used inverse-Wishart prior). For modeling real-life spatio-temporal processes with complex dependence structures, we extend our method to dynamic cases and introduce unit-vector Gaussian process priors in order to capture the evolution of correlation among components of a multivariate time series. To handle the intractability of the resulting posterior, we introduce the adaptive Δ-Spherical Hamiltonian Monte Carlo. We demonstrate the validity and flexibility of our proposed framework in a simulation study of periodic processes and an analysis of rat's local field potential activity in a complex sequence memory task.

Modeling individual variation in early literacy skills in kindergarten children with intellectual disabilities

In the present study, we investigated (i) to what extent the early literacy skills (phonological awareness, letter knowledge, and word decoding) along with cognitive (nonverbal reasoning, attention, phonological short-term memory, sequential memory, executive functioning) and linguistic (auditory discrimination, rapid naming, articulation, vocabulary) precursor measures of 53 six-year old children with intellectual disabilities (ID) differ from a group of 74 peers with normal language acquisition (NLA) and (ii) whether the individual variation of early literacy skills in the two groups to the same extent can be explained from the precursor measures. Results showed that children with ID scored below the NLA group on all literacy and precursor measures. Structural equation modeling evidenced that in the children with NLA early literacy was directly predicted by phonological awareness, PSTM and vocabulary, with nonverbal reasoning and auditory discrimination also predicting phonological awareness. In children with ID however, the variation in word decoding was predicted by letter knowledge and nonverbal reasoning, whereas letter knowledge was predicted by rapid naming, which on its turn was predicted by attentional skills. It can be concluded phonological awareness plays a differential role in the early literacy skills of children with and without ID. As a consequence, the arrears in phonological awareness in children with ID might put them on hold in gaining proper access to literacy acquisition. What this paper addsThis paper adds to the theoretical knowledge base on literacy acquisition in a special population, namely children with intellectual disabilities (ID). It addresses factors that influence early literacy learning, which have not been investigated thoroughly in this special and specific group. Furthermore, the children are not tested solely on literacy, but also on cognitive measures that may influence literacy acquisition. Whereas most research in ID focuses on groups with specific syndromes/etiologies, this paper takes a varied group of children with ID into account. The paper also adds to educational insights, since the findings imply that children with ID are able to use phonological pathways in learning to read. Educators could teach these children phonics-based literacy skills tailored to their individual learning needs.

Long Synfire Chains Emerge by Spike-Timing Dependent Plasticity Modulated by Population Activity.

Sequences of precisely timed neuronal activity are observed in many brain areas in various species. Synfire chains are a well-established model that can explain such sequences. However, it is unknown under which conditions synfire chains can develop in initially unstructured networks by self-organization. This work shows that with spike-timing dependent plasticity (STDP), modulated by global population activity, long synfire chains emerge in sparse random networks. The learning rule fosters neurons to participate multiple times in the chain or in multiple chains. Such reuse of neurons has been experimentally observed and is necessary for high capacity. Sparse networks prevent the chains from being short and cyclic and show that the formation of specific synapses is not essential for chain formation. Analysis of the learning rule in a simple network of binary threshold neurons reveals the asymptotically optimal length of the emerging chains. The theoretical results generalize to simulated networks of conductance-based leaky integrate-and-fire (LIF) neurons. As an application of the emerged chain, we propose a one-shot memory for sequences of precisely timed neuronal activity.

Nonspatial sequence coding varies along the CA1 transverse axis

The hippocampus plays a critical role in the memory for sequences of events, a defining feature of episodic memory. To shed light on the fundamental mechanisms supporting this capacity, we recently recorded neural activity in CA1 as rats performed a nonspatial odor sequence memory task. Our main finding was that, while the animals’ location and behavior remained constant, a proportion of CA1 neurons fired differentially to odors depending on whether they were presented in or out of sequence (sequence cells). Here, we further examined if such sequence coding varied along the distal-to-proximal axis of the dorsal CA1 region (distal: toward subiculum; proximal: toward CA3). Differences in information processing along this axis have been suggested by recent anatomical and electrophysiological evidence that odor information may be more strongly represented in the distal segment, whereas spatial information may be more strongly represented in the proximal segment. Recorded neurons were grouped into four arbitrary sections of dorsal CA1, ranging from distal to proximal. We found that, although sequence cell coding was observed across the distal-to-proximal extent of CA1 from which we recorded, it was significantly higher in intermediate CA1, a region with more balanced anatomical input from lateral and medial entorhinal regions. More specifically, in that particular segment of CA1, we observed a significant increase in the magnitude of sequence coding of all cells, as well as in the sequential information content of sequence cells. Importantly, a different pattern was observed when examining the distribution of spatial coding from the same electrodes. Consistent with previous reports, our results suggest that spatial information was more strongly represented in the proximal section of CA1 (higher proportion of cells with place fields). These findings indicate that nonspatial sequence memory coding is not uniformly distributed along the transverse axis of CA1, and that this distribution does not simply follow the expected gradient based on the stimulus modality or the degree of spatial selectivity. Instead, the observed distribution suggests this form of sequence coding may be associated with convergent input from lateral and medial entorhinal regions, which is present throughout the proximodistal axis but greater in intermediate CA1.

PSYCHOLINGUISTIC AGE-PROFILES OF LANGUAGE IMPAIRMENT: A COMPARISON BETWEEN CHILDREN WITH TYPICAL AND ATYPICAL LANGUAGE DEVELOPMENT

Background: Assessment of language is very important to detect atypically developed children. In this sense, psycholinguistic abilities are predictors of developmental functioning. The aim of this study was to compare ages of psycholinguistic processes between atypically and typically developed children. Material/Methods: In this cross-sectional study, six-, seven- and eight-year-old children from Cordoba (Argentina) (n= 28) were evaluated with the Spanish version of Illinois Test of Psycholinguistic Abilities (S-ITPA). Statistical analysis included Student’s t-test in order to find differences between groups. Results: In the six-year-old sample, those with atypical language showed significantly lower psycholinguistic ages in: global psycholinguistic age, auditory association, and verbal expression, auditory reception, auditory sequential memory, grammatical closu re, and auditory closure, manual expression. In seven-year-old sample differences were found in grammatical closure and auditory closure. In eight-year-old group, atypical language sample showed lower psycholinguistic ages in auditory association, verbal expression and auditory sequential memory. Conclusions: This evidence establishes a limit stage corresponding to 6 years of age, which reflects the consolidation and integrity of language and the aptitudes involved. In later ages (e.g. seven and eight years), results may be biased by acquired formal learning abilities.

Long-term impact of intensive lifestyle intervention on cognitive function assessed with the National Institutes of Health Toolbox: The Look AHEAD study

IntroductionThis study sought to determine whether 10 years of assignment to intensive lifestyle intervention (ILI) relative to diabetes support and education leads to better cognition. We examine intervention effects overall and among clinical subgroups, and report correlations between computer-administered and interviewer-administered cognitive batteries. MethodsThe Action for Health in Diabetes (Look AHEAD) was a 16-site randomized controlled trial with overweight/obese individuals (aged 45–76) who had type 2 diabetes. The NIH Toolbox Cognition Battery tests developed to measure cognition across the lifespan were used to evaluate cognition. Results were compared with standard paper-and-pencil tests. The Toolbox and paper-and-pencil tests were administered an average of 10.9 years after randomization to 1002 participants. ResultsToolbox measures significantly correlated with interviewer-administered measures, with the strongest correlations between the Toolbox Fluid Cognition Composite and Trails B (r = −0.64, P < .0001) and Digit Symbol Coding (r = 0.63, P < .0001), and between the Toolbox Dimensional Change Card Sort (r = 0.55, P < .0001) and the Digit Symbol Coding test. Overall, ILI and diabetes support and education groups had similar adjusted mean cognitive outcomes (P > .05 for all). Subgroup analyses identified different intervention effects within baseline body mass index groups for Picture Sequence Memory (P = .01), within baseline cardiovascular disease groups for Picture Vocabulary (P = .01) and Fluid Cognition Composite (P = .02) measures, and within baseline age groups for Picture Vocabulary (P = .02). DiscussionCorrelations between Toolbox and interviewer-administered outcomes provide a measure of internal validity. Findings suggest no overall effect of the intervention on cognition and that an ILI resulting in weight loss may have negative implications for cognition in individuals aged ≥60, with previous history of cardiovascular disease, and those with body mass index ≥40.

Effects of presentation style and musical elements on the sequential working memory of individuals with and without Autism Spectrum Disorder

BackgroundWhile information can be encoded and decoded via various channels, there is a lack of basic research investigating how presentation styles and musical elements might impact working memory of individuals with Autism Spectrum Disorder (ASD) as well as those who are neuro-typical (NT). ObjectiveThe purpose of this study was to examine the impact of presentation style (live versus recorded) and musical elements (melody versus rhythm) on the working memory of individuals with and without ASD. MethodParticipants (n=29 individuals with ASD and n=30 NT university students) listened to four separate sequences of seven randomized monosyllabic words. Sequences were delivered in live and recorded presentation styles with melodic or rhythmic musical elements. To assess working memory, the participants’ tasks were to sequentially recall the information within each condition. ResultsParticipants demonstrated significantly more accurate recall during the live versus the recorded conditions. There was no significant recall difference between the melodic and rhythmic musical elements. NT participants demonstrated more accurate recall than those with ASD. ConclusionsThe findings point to the possibility that information paired with music delivered in live presentation will increase the likelihood of recall and subsequent learning. Implications for clinical practice, limitations of the study, and suggestions for future research are provided.

Accelerating breadth-first graph search on a single server by dynamic edge trimming

Breadth-first graph search (a.k.a., BFS) is one of the typical in-memory computing models with complicated and frequent memory accesses. Existing single-server graph computing systems fail to take advantage of access pattern of BFS for performance optimization, hence suffering from a lot of extra memory latencies due to accessing no longer useful data elements of a big graph as well as wasting plenty of computing resources for processing them. In this article, we propose FastBFS, a new approach that accelerates breadth-first graph search on a single server by leverage of the access pattern during iterating over a big graph. First, FastBFS uses an edge-centric graph processing model to obtain the high bandwidth of sequential memory and/or disk access without expensive data preprocessing. Second, with a dynamic and asynchronous trimming mechanism, FastBFS can efficiently reduce the size of a big graph by eliminating useless edges in parallel with the computation. Third, FastBFS schedules I/O streams efficiently and can attain greater parallelism if an additional disk is available. We implement FastBFS by modifying the X-Stream system developed by EPFL. Our experimental results show that FastBFS can attain speedups of up to 7.9× and 10.4× in the computing speed compared with X-stream and GraphChi respectively. With an additional disk, the performance can be further improved.

Early intervention for children at risk for reading disabilities: The impact of grade at intervention and individual differences on intervention outcomes.

Across multiple schools in three sites, the impact of grade-at-intervention was evaluated for children at risk or meeting criteria for reading disabilities. A multiple-component reading intervention with demonstrated efficacy was offered to small groups of children in 1st, 2nd, or 3rd grade. In a quasi-experimental design, 172 children received the Triple-Focus Program (PHAST + RAVE-O), and 47 were control participants. Change during intervention and 1-3 years later (6-8 testing points), and the influence of individual differences in predicting outcomes, were assessed using reading and reading-related repeated measures. Intervention children out-performed control children at posttest on all 14 outcomes, with average effect sizes (Cohen's d) on standardized measures of .80 and on experimental measures of 1.69. On foundational word reading skills (standardized measures), children who received intervention earlier, in 1st and 2nd grade, made gains relative to controls almost twice that of children receiving intervention in 3rd grade. At follow-up, the advantage of 1st grade intervention was even clearer: First graders continued to grow at faster rates over the follow-up years than 2nd graders on six of eight key reading outcomes. For some outcomes with metalinguistic demands beyond the phonological, however, a posttest advantage was revealed for 2nd grade Triple participants and for 3rd grade Triple participants relative to controls. Estimated IQ predicted growth during intervention on seven of eight outcomes. Growth during follow-up was predicted by vocabulary and visual sequential memory. These findings provide evidence on the importance of early intensive evidence-based intervention for reading problems in the primary grades.

Postsynaptic adhesion GPCR latrophilin-2 mediates target recognition in entorhinal-hippocampal synapse assembly.

Synapse assembly likely requires postsynaptic target recognition by incoming presynaptic afferents. Using newly generated conditional knock-in and knockout mice, we show in this study that latrophilin-2 (Lphn2), a cell-adhesion G protein-coupled receptor and presumptive α-latrotoxin receptor, controls the numbers of a specific subset of synapses in CA1-region hippocampal neurons, suggesting that Lphn2 acts as a synaptic target-recognition molecule. In cultured hippocampal neurons, Lphn2 maintained synapse numbers via a postsynaptic instead of a presynaptic mechanism, which was surprising given its presumptive role as an α-latrotoxin receptor. In CA1-region neurons in vivo, Lphn2 was specifically targeted to dendritic spines in the stratum lacunosum-moleculare, which form synapses with presynaptic entorhinal cortex afferents. In this study, postsynaptic deletion of Lphn2 selectively decreased spine numbers and impaired synaptic inputs from entorhinal but not Schaffer-collateral afferents. Behaviorally, loss of Lphn2 from the CA1 region increased spatial memory retention but decreased learning of sequential spatial memory tasks. Thus, Lphn2 appears to control synapse numbers in the entorhinal cortex/CA1 region circuit by acting as a domain-specific postsynaptic target-recognition molecule.

Sleep-dependent motor sequence memory consolidation in individuals with periodic limb movements

Periodic limb movements (PLMs) during sleep increase with age and are associated with striatal neurodegeneration and dopamine deficiency. Limb movements are often associated with disruptions to non-rapid eye movement (NREM) sleep. Motor skill memory consolidation recruits the striatum, and learning-dependent striatal activation is associated with NREM sleep. Therefore, we investigated whether de novo individuals who significantly experience elevated levels of PLMs but have not been formally diagnosed with periodic limb movement disorder had learning and sleep-related memory deficits and whether these deficits were related to sleep quality and symptom severity.In total, 14 adults with significantly elevated PLMs (PLM condition), 15 age-matched controls (CTRL), and 14 age-matched “disturbed” sleep (through induced leg movements) controls (CTRL-ES) participated. The participants were trained (PM) and retested (AM) on procedural motor sequence learning (MSL) and declarative paired associates memory tasks.Baseline sleep quality was significantly worse in PLM than in CTRL. Despite the continued presence of PLMs in the PLM condition on the experimental night, remarkably, sleep quality improved and arousals decreased, vs. baseline, and did not differ from CTRL. MSL was significantly slower in the PLM condition than in CTRL at training but surprisingly exhibited overnight performance gains, which correlated with reduced arousals. As predicted, CTRL but not CTRL-ES had overnight gains in MSL. Taken together, this suggests that in the PLM condition, sleep quality was normalized following MSL, where they derived the same benefit of sleep to procedural memory consolidation as in CTRL. Sleep did not benefit declarative memory.Although preliminary, these results suggest that MSL in individuals with PLMs may provide a benefit to sleep, which in turn may benefit memory consolidation.

Phonological memory in sign language relies on the visuomotor neural system outside the left hemisphere language network.

Sign language is an essential medium for everyday social interaction for deaf people and plays a critical role in verbal learning. In particular, language development in those people should heavily rely on the verbal short-term memory (STM) via sign language. Most previous studies compared neural activations during signed language processing in deaf signers and those during spoken language processing in hearing speakers. For sign language users, it thus remains unclear how visuospatial inputs are converted into the verbal STM operating in the left-hemisphere language network. Using functional magnetic resonance imaging, the present study investigated neural activation while bilinguals of spoken and signed language were engaged in a sequence memory span task. On each trial, participants viewed a nonsense syllable sequence presented either as written letters or as fingerspelling (4–7 syllables in length) and then held the syllable sequence for 12 s. Behavioral analysis revealed that participants relied on phonological memory while holding verbal information regardless of the type of input modality. At the neural level, this maintenance stage broadly activated the left-hemisphere language network, including the inferior frontal gyrus, supplementary motor area, superior temporal gyrus and inferior parietal lobule, for both letter and fingerspelling conditions. Interestingly, while most participants reported that they relied on phonological memory during maintenance, direct comparisons between letters and fingers revealed strikingly different patterns of neural activation during the same period. Namely, the effortful maintenance of fingerspelling inputs relative to letter inputs activated the left superior parietal lobule and dorsal premotor area, i.e., brain regions known to play a role in visuomotor analysis of hand/arm movements. These findings suggest that the dorsal visuomotor neural system subserves verbal learning via sign language by relaying gestural inputs to the classical left-hemisphere language network.

A note on the normalizing sequences for sums of linear processes in the case of negative memory

We consider the partial-sum process $$ {S}_n(t)={\sum}_{k=0}^{\left\lfloor nt\right\rfloor }{X}_k $$ of linear processes $$ {X}_n={\sum}_{i=0}^{\infty }{c}_i{\upxi}_{n-i} $$ with independent identically distributed innovations {ξ i } belonging to the domain of attraction of α-stable law (0 < α ≤ 2). If |c k | = k −γ , k ∈ ℕ , γ > max(1, 1/α), and $$ {\sum}_{k=0}^{\infty}\kern0.5em ck=0 $$ (the case of negative memory for the stationary sequence {X n }), then it is known that the normalizing sequence of S n (1) can grow as n 1/α−γ+1 or remain bounded if the signs of the coefficients are constant or alternate, respectively. It is of interest to know whether it is possible, given ⋋ ∈ (0, 1/α − γ + 1), to change the signs of c k so that the rate of growth of the normalizing sequence would be n ⋋ . In this paper, we give the positive answer: we propose a way of choosing the signs and investigate the finite-dimensional convergence of appropriately normalized S n (t) to linear fractional Levy motion.

Re-stepping into the same river: competition problem rather than a reconsolidation failure in an established motor skill

Animal models suggest that consolidated memories return to their labile state when reactivated and need to be restabilized through reconsolidation processes to persist. Consistent with this notion, post-reactivation pharmacological protein synthesis blockage results in mnemonic failure in hippocampus-dependent memories. It has been proposed that, in humans, post-reactivation experience with a competitive task can also interfere with memory restabilization. However, several studies failed to induce performance deficit implementing this approach. Moreover, even upon effective post-reactivation interference, hindered performance may rapidly recover, raising the possibility of a retrieval rather than a storage deficit. Here, to address these issues in procedural memory domain, we used new learning to interfere with restabilization of motor memory acquired through training on a sequence of finger movements. Only immediate post-reactivation interference was associated with the loss of post-training delayed gains in performance, a hallmark of motor sequence memory consolidation. We also demonstrate that such performance deficit more likely indicates a genuine memory impairment rather than a retrieval failure. However, the reconsolidation view on a reactivation-induced plasticity is not supported. Instead, our results are in line with the integration model according to which new knowledge acquired during the interfering experience, is integrated through its consolidation creating memory competition.

Digit-color synaesthesia only enhances memory for colors in a specific context: A new method of duration thresholds to measure serial recall.

For digit-color synaesthetes, digits elicit vivid experiences of color that are highly consistent for each individual. The conscious experience of synaesthesia is typically unidirectional: Digits evoke colors but not vice versa. There is an ongoing debate about whether synaesthetes have a memory advantage over non-synaesthetes. One key question in this debate is whether synaesthetes have a general superiority or whether any benefit is specific to a certain type of material. Here, we focus on immediate serial recall and ask digit-color synaesthetes and controls to memorize digit and color sequences. We developed a sensitive staircase method manipulating presentation duration to measure participants' serial recall of both overlearned and novel sequences. Our results show that synaesthetes can activate digit information to enhance serial memory for color sequences. When color sequences corresponded to ascending or descending digit sequences, synaesthetes encoded these sequences at a faster rate than their non-synaesthetes counterparts and faster than non-structured color sequences. However, encoding color sequences is approximately 200 ms slower than encoding digit sequences directly, independent of group and condition, which shows that the translation process is time consuming. These results suggest memory advantages in synaesthesia require a modified dual-coding account, in which secondary (synaesthetically linked) information is useful only if it is more memorable than the primary information to be recalled. Our study further shows that duration thresholds are a sensitive method to measure subtle differences in serial recall performance. (PsycINFO Database Record

Task Complexity Modulates Sleep-Related Offline Learning in Sequential Motor Skills.

Recently, a number of authors have advocated the introduction of gross motor tasks into research on sleep-related motor offline learning. Such tasks are often designed to be more complex than traditional key-pressing tasks. However, until now, little effort has been undertaken to scrutinize the role of task complexity in any systematic way. Therefore, the effect of task complexity on the consolidation of gross motor sequence memory was examined by our group in a series of three experiments. Criterion tasks always required participants to produce unrestrained arm movement sequences by successively fitting a small peg into target holes on a pegboard. The sequences always followed a certain spatial pattern in the horizontal plane. The targets were visualized prior to each transport movement on a computer screen. The tasks differed with respect to sequence length and structural complexity. In each experiment, half of the participants initially learned the task in the morning and were retested 12 h later following a wake retention interval. The other half of the subjects underwent practice in the evening and was retested 12 h later following a night of sleep. The dependent variables were the error rate and total sequence execution time (inverse to the sequence execution speed). Performance generally improved during acquisition. The error rate was always low and remained stable during retention. The sequence execution time significantly decreased again following sleep but not after waking when the sequence length was long and structural complexity was high. However, sleep-related offline improvements were absent when the sequence length was short or when subjects performed a highly regular movement pattern. It is assumed that the occurrence of sleep-related offline performance improvements in sequential motor tasks is associated with a sufficient amount of motor task complexity.

Fractionating nonword repetition: The contributions of short-term memory and oromotor praxis are different.

The ability to reproduce novel words is a sensitive marker of language impairment across a variety of developmental disorders. Nonword repetition tasks are thought to reflect phonological short-term memory skills. Yet, when children hear and then utter a word for the first time, they must transform a novel speech signal into a series of coordinated, precisely timed oral movements. Little is known about how children’s oromotor speed, planning and co-ordination abilities might influence their ability to repeat novel nonwords, beyond the influence of higher-level cognitive and linguistic skills. In the present study, we tested 35 typically developing children between the ages of 5−8 years on measures of nonword repetition, digit span, memory for non-verbal sequences, reading fluency, oromotor praxis, and oral diadochokinesis. We found that oromotor praxis uniquely predicted nonword repetition ability in school-age children, and that the variance it accounted for was additional to that of digit span, memory for non-verbal sequences, articulatory rate (measured by oral diadochokinesis) as well as reading fluency. We conclude that the ability to compute and execute novel sensorimotor transformations affects the production of novel words. These results have important implications for understanding motor/language relations in neurodevelopmental disorders.

ERPs and oscillations during encoding predict retrieval of digit memory in superior mnemonists

Previous studies have consistently demonstrated that superior mnemonists (SMs) outperform normal individuals in domain-specific memory tasks. However, the neural correlates of memory-related processes remain unclear. In the current EEG study, SMs and control participants performed a digit memory task during which their brain activity was recorded. Chinese SMs used a digit-image mnemonic for encoding digits, in which they associated 2-digit groups with images immediately after the presentation of each even-position digit in sequences. Behaviorally, SMs’ memory of digit sequences was better than the controls’. During encoding in the study phase, SMs showed an increased right central P2 (150–250ms post onset) and a larger right posterior high-alpha (10–14Hz, 500–1720ms) oscillation on digits at even-positions compared with digits at odd-positions. Both P2 and high-alpha oscillations in the study phase co-varied with performance in the recall phase, but only in SMs, indicating that neural dynamics during encoding could predict successful retrieval of digit memory in SMs. Our findings suggest that representation of a digit sequence in SMs using mnemonics may recruit both the early-stage attention allocation process and the sustained information preservation process. This study provides evidence for the role of dynamic and efficient neural encoding processes in mnemonists.

A stochastic and mathematically integrative model of the control of human heart rate.

The innate variability of the heart rate contains both random and temporally scaled components. The objective of this study was to design a stochastic and mathematically integrative model (SIM) of the control of human heart rate that could replicate the cardiac rhythm during rest and two distinct states of exercise. Heartbeat-to-heartbeat interval (RRI) were recorded from 8 healthy subjects during rest and two exercise levels. Signal memory in RRI sequences was estimated with autocorrelation, and probability density functions (PDFs) were created by fitting polynomial curves to the normalized histograms of the RRI sequences. The SIM generated fictive RRI sequences by randomly selecting RRI values from a PDF and integrating the series using parameters derived from the autocorrelation analysis. Fractal-scaling in the model RRI sequences was quantified with detrended fluctuation analysis. After optimizing the model with the autocorrelation-based and PDF parameters, the SIM was able to produce fictive RRI sequences with significant fractal scaling (statistically assessed with surrogate analysis, p <; 0.001), and with fractal-scaling characteristics similar to the original human data (p = 0.62). Increasing the length of the SIM-generated sequences did not alter the temporal scaling of the model sequences. In conclusion, this research demonstrated a stochastic and integrative model that can replicate the temporally correlated characteristics of the human heart rate.