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SUMMARYThe dorsomedial posterior parietal cortex is part of a higher-cognition network implicated in elaborate processes underpinning memory formation, recollection, episodes reconstruction, and temporal information processing. Neural coding for complex episodic processing is however under-documented. Here we revealed a set of neural codes of “neuroethogram” in the primate parietal cortex. Analyzing neural responses in macaque dmPPC to naturalistic videos, we discovered several groups of neurons that are sensitive to different categories of ethogram-items and to low-level sensory features, as well as saccadic eye movement. The amount of information coded within these multiplex representations in turn increases our trained classifier decodability for different video-types. We also discovered that the processing of category and feature information by these neurons is sustained by accumulation of temporal information over a long timescale up to 30 s, corroborating its reported long temporal receptive windows. We performed an additional behavioral experiment and found that saccade-related activities could not account for the mixed neuronal responses elicited by the video stimuli. We further observed monkeys’ scan-paths and gaze consistency are modulated by video content. Taken altogether, these neural findings explain how dorsomedial PPC weaves fabrics of ongoing experiences together in real-time. The high dimensionality of neural representations should motivate us to shift the focus of attention from pure selectivity neurons to mixed selectivity neurons, especially in increasingly complex naturalistic task designs.HIGHLIGHTSNeural codes for “neuroethogram” in macaque dorsomedial parietal cortexParietal neural codes exhibit mixed selectivity of event featuresDorsomedial PPC neurons support a long temporal receptive window for episodesSaccadic movement could not explain away mixed neuronal responsesEye movement scan-path and gaze consistency shown across viewing repetitions

Humans recall the past by replaying fragments of events temporally. Here, we demonstrate a similar effect in macaques. We trained six rhesus monkeys with a temporal-order judgement (TOJ) task and collected 5000 TOJ trials. In each trial, the monkeys watched a naturalistic video of about 10 s comprising two across-context clips, and after a 2 s delay, performed TOJ between two frames from the video. The data are suggestive of a non-linear, time-compressed forward memory replay mechanism in the macaque. In contrast with humans, such compression of replay is, however, not sophisticated enough to allow these monkeys to skip over irrelevant information by compressing the encoded video globally. We also reveal that the monkeys detect event contextual boundaries, and that such detection facilitates recall by increasing the rate of information accumulation. Demonstration of a time-compressed, forward replay-like pattern in the macaque provides insights into the evolution of episodic memory in our lineage.

Contains fulltext : 217200.pdf (Publisher’s version ) (Closed access) Nonhuman primate neuroimaging is on the cusp of a transformation, much in the same way its human counterpart was in 2010, when the Human Connectome Project was launched to accelerate progress. Inspired by an open data-sharing initiative, the global community recently met and, in this article, breaks through obstacles to define its ambitions. 4 p.

Studies have indicated that a cortical sensory system is capable of processing information from different sensory modalities. However, it still remains unclear when and how a cortical system integrates and retains information across sensory modalities during learning. Here we investigated the neural dynamics underlying crossmodal associations and memory by recording event-related potentials (ERPs) when human participants performed visuo-tactile (crossmodal) and visuo-visual (unimodal) paired-associate (PA) learning tasks. In a trial of the tasks, the participants were required to explore and learn the relationship (paired or non-paired) between two successive stimuli. EEG recordings revealed dynamic ERP changes during participants' learning of paired-associations. Specifically, (1) the frontal N400 component showed learning-related changes in both unimodal and crossmodal tasks but did not show any significant difference between these two tasks, while the central P400 displayed both learning changes and task differences; (2) a late posterior negative slow wave (LPN) showed the learning effect only in the crossmodal task; (3) alpha-band oscillations appeared to be involved in crossmodal working memory. Additional behavioral experiments suggested that these ERP components were not relevant to the participants' familiarity with stimuli per se. Further, by shortening the delay length (from 1300ms to 400ms or 200 ms) between the first and second stimulus in the crossmodal task, declines in participants' task performance were observed accordingly. Taken together, these results provide insights into the cortical plasticity (induced by PA learning) of neural networks involved in crossmodal associations in working memory.

We have developed a low-cost electromagnetic vibrotactile stimulator that uses the magnetic field of an MR scanner as a permanent magnet to power a vibrating motor. A simple variable current power supply is controlled by software using a USB data acquisition controller. In our study, the function of our novel stimulator was verified in a vibration frequency discrimination working memory task, in which various ranges of frequencies and amplitudes are delivered in MRI scanner. Furthermore, our functional MRI study revealed activations of the primary and secondary somatosensory cortices during the perception of tactile stimulation. Therefore, the new designed electromagnetic vibrotactile stimulator is capable of generating various frequencies of tactile stimuli and represents a powerful and useful tool for studying somatosensory functions with functional MRI.

People do not only feel guilty for transgressions that they are causally responsible for (i.e., personal guilt); they also feel guilty for transgressions committed by those they identify as in-group members (i.e., collective or group-based guilt). Decades of research using scenario-based imagination tasks and self-reported measures has shown that when reminded of transgressions committed by in-group members, people express guilt and are willing to make amends, even when they are not causally responsible for the transgressions. However, it remains elusive whether people genuinely experience guilt or simply display remorseful gestures deemed appropriate in those contexts. To resolve this puzzle, it is critical to closely examine the neurocognitive basis of group-based guilt and its relationship with personal guilt, a goal that self-reported measures alone cannot satisfactorily achieve. Here, we combined functional MRI with an interaction-based minimal group paradigm in which participants either directly caused harm to a group of victims (i.e., personal guilt), or observed in-group members cause harm to the victims (i.e., group-based guilt). In three experiments (N ​= ​90), we demonstrated and replicated that the perceived responsibility one shared with in-group members in transgression predicted both behavioral and neural manifestations of group-based guilt. Multivariate pattern analysis (MVPA) of the functional MRI data showed that group-based guilt recruited patterns of neural responses in anterior middle cingulate cortex that resembled personal guilt. These results have broadened our understanding of how group membership is integrated into the neurocognitive processes underlying social emotions.

Adaptive behavior usually requires accurate representations of body positions and ownership, which rely on integration of multiple sources of sensory information. The rubber hand illusion (RHI) presents a compelling example demonstrating that the combination of visual and tactile signals strongly influences the subjective experience of body ownership. However, it still remains unclear how the perception of body ownership in turn alters other aspects of sensory processing, such as pain perception. In the present study, we examined whether the RHI could modulate the subjective experience of pain. We set three conditions corresponding to different levels of ownership of the rubber hand: the synchronous condition in which the rubber and the real hand were simultaneously stroked; the asynchronous condition in which the two hands were asynchronously stroked; the own-hand-only condition in which only the real hand was stroked. Results from the screening experiment indicated that subjects experienced the stronger RHI in the synchronous condition, compared with the strength of RHI in the other two conditions. In the main experiment, subjects were requested to report the intensity and unpleasantness of pain evoked by laser stimuli under the three stroking conditions. Results showed that pain ratings were significantly lower under the synchronous condition than those under the other two conditions, suggesting the RHI could induce a significant analgesic effect. Furthermore, the correlation analysis showed that the degree of the analgesic effect was positively correlated with the RHI strength across individuals. Taken together, these results suggest an analgesic effect of the RHI and support the potential usage of visual illusions in future translational research on pain.

The combination of biological and artificial intelligence is a promising methodology to construct a novel intelligent modality, proposed as cyborg intelligence. The hierarchical conceptual framework is based on the interaction and combination of comparable components of biological cognitive units and computing intelligent units. The authors extend the previous conceptual framework and focus on sensorimotor circuits to explore the representation and integration of sensation. They then present a cognitive computing model for brain-computer integration and design efficient machine-learning algorithms for neural signal decoding. They also propose biological reconstruction methods for sensorimotor circuits to not only restore but enhance functionalities with AI. They develop a series of demonstrating systems to validate the conceptual framework of cyborg intelligence and possibly herald bright prospects and high values in diversified aspects of theoretical research, engineering techniques, and clinical applications. Finally, the authors summarize the latest research trends and challenges, which they believe will further boost new scientific frontiers in cyborg intelligence.

The neural processes underlying pain memory are not well understood. To explore these processes, contact heat-evoked potentials (CHEPs) were recorded in humans with electroencephalography (EEG) technique during a delayed matching-to-sample task, a working memory task involving presentations of two successive painful heat stimuli (S-1 and S-2) with different intensities separated by a 2-s interval (the memorization period). At the end of the task, the subject was required to discriminate the stimuli by indicating which (S-1 or S-2) induced more pain. A control task was used, in which no active discrimination was required between stimuli. All event-related potential (ERP) analysis was aligned to the onset of S-1. EEG activity exhibited two successive CHEPs: an N2-P2 complex (∼400 ms after onset of S-1) and an ultralate component (ULC, ∼900 ms). The amplitude of the N2-P2 at vertex, but not the ULC, was significantly correlated with stimulus intensity in these two tasks, suggesting that the N2-P2 represents neural coding of pain intensity. A late negative component (LNC) in the frontal recording region was observed only in the memory task during a 500-ms period before onset of S-2. LNC amplitude differed between stimulus intensities and exhibited significant correlations with the N2-P2 complex. These indicate that the frontal LNC is involved in maintenance of intensity of pain in working memory. Furthermore, alpha-band oscillations observed in parietal recording regions during the late delay displayed significant power differences between tasks. This study provides in the temporal domain previously unidentified neural evidence showing the neural processes involved in working memory of painful stimuli.

Whether nonhuman primate species can construct, still less reconstruct, order of past events remains controversial. Here we show that rhesus macaques are capable of reconstructing the temporal order of memory traces of dynamic videos. We made use of 2000 unseen naturalistic videos of wildlife content for encoding, and then probed monkeys' recollection of temporal-order of events with a temporal-order judgement (TOJ) test. This encoding-TOJ procedure was repeated at three different time points (day 1, day 2, and day 32+). We specifically tested for differential TOJ memory performance for videos that were displayed in a reverse sequence versus videos that were displayed in a normal sequence at these different time points. We observed that during TOJ monkeys committed more errors for video content that were shown in reverse but only upon re-exposures (i.e., day 2 and day 32+). Moreover, this memory distortion effect is significantly accentuated by social relevance of the video content. We interpret that the monkeys reversed the out-of-order events in accordance to their knowledge priors; such fallaciously re-ordered memory traces then led to higher rate of errors. Demonstrating in macaque monkeys a form of errors in temporal-order memory for reverse videos carries implications for studying memory retrospection in the primates.

Humans can perform episodic memory replay dynamically by replaying fragments of fine-grained temporal patterns of events and skipping flexibly across subevents. Here, we demonstrate a similar effect in macaque monkeys. We report evidence that the monkeys apply a time-compressed, forward replay mechanism during their judgement the order of cinematic events. We trained six macaque monkeys with a temporal order judgement (TOJ) task and collected 5000 TOJ trials with naturalistic videos. In each trial, they watched a video of about 10 s comprising two across-context clips, and after a 2-s retention delay, performed a temporal order judgement between two frames extracted from the video. The results show that the monkeys adopt a self-terminating search of ordered frames in their mnemonic representation. The memory replay is forward and temporally compressed, paralleling evidence in humans. Such compression of replay is however not sophisticated enough to allow them to skip over irrelevant information by compressing the encoded video globally. Moreover, we also reveal that the monkeys can segment events using contextual boundaries like humans and such contextual segmentation facilitates their memory recall by an increased rate of information accumulation in a drift diffusion model framework. Memory replay is an elaborate mental process and our demonstration of a time-compressed, forward replay mechanism in the macaque monkeys provides insights into mapping the mechanisms and evolution of episodic memory in our lineage.

Summary Non-human primate neuroimaging is a rapidly growing area of research that promises to transform and scale translational and cross-species comparative neuroscience. Unfortunately, the technological and methodological advances of the past two decades have outpaced the accrual of data, which is particularly challenging given the relatively few centers that have the necessary facilities and capabilities. The PRIMatE Data Exchange (PRIME-DE) addresses this challenge by aggregating independently acquired non-human primate magnetic resonance imaging (MRI) datasets and openly sharing them via the International Neuroimaging Data-sharing Initiative (INDI). Here, we present the rationale, design, and procedures for the PRIME-DE consortium, as well as the initial release, consisting of 25 independent data collections aggregated across 22 sites (total = 217 non-human primates). We also outline the unique pitfalls and challenges that should be considered in the analysis of non-human primate MRI datasets, including providing automated quality assessment of the contributed datasets., Highlights • Openly shared, large non-human primate neuroimaging data resource • Multiple imaging modalities contributed from investigators around the world • Quality assessments of the dataset • Discussed pitfalls and challenges in analyzing the non-human primate MRI data, The PRIMatE Data Exchange (PRIME-DE) consortium is an open science resource for the neuroimaging community aiming to facilitate efforts to map the non-human primate connectome. It aggregates and shares anatomical, functional, and diffusion MRI datasets from laboratories throughout the world.

Visual stimuli are known to activate the auditory cortex of deaf people, presenting evidence of cross-modal plasticity. However, the mechanisms underlying such plasticity are poorly understood. In this functional MRI study, we presented two types of visual stimuli, language stimuli (words, sign language, and lip-reading) and a general stimulus (checkerboard) to investigate neural reorganization in the superior temporal cortex (STC) of deaf subjects and hearing controls. We found that only in the deaf subjects, all visual stimuli activated the STC. The cross-modal activation induced by the checkerboard was mainly due to a sensory component via a feed-forward pathway from the thalamus and primary visual cortex, positively correlated with duration of deafness, indicating a consequence of pure sensory deprivation. In contrast, the STC activity evoked by language stimuli was functionally connected to both the visual cortex and the frontotemporal areas, which were highly correlated with the learning of sign language, suggesting a strong language component via a possible feedback modulation. While the sensory component exhibited specificity to features of a visual stimulus (e.g., selective to the form of words, bodies, or faces) and the language (semantic) component appeared to recruit a common frontotemporal neural network, the two components converged to the STC and caused plasticity with different multivoxel activity patterns. In summary, the present study showed plausible neural pathways for auditory reorganization and correlations of activations of the reorganized cortical areas with developmental factors and provided unique evidence towards the understanding of neural circuits involved in cross-modal plasticity.

In the present study, we searched for causal evidence linking activity in the bilateral primary somatosensory cortex (SI), posterior parietal cortex (PPC), and prefrontal cortex (PFC) with behavioral performance in vibrotactile working memory. Participants performed a vibrotactile delayed matching-to-sample task, while single-pulse transcranial magnetic stimulation (sp-TMS) was applied over these cortical areas at 100, 200, 300, 600, 1600, and 1900 ms after the onset of vibrotactile stimulation (200 ms duration). In our experiments, sp-TMS over the contralateral SI at the early delay (100 and 200 ms) deteriorated the accuracy of task performance, and over the ipsilateral SI at the late delay (1600 and 1900 ms) also induced such deteriorating effects. Furthermore, deteriorating effects caused by sp-TMS over the contralateral DLPFC at the same maintenance stage (1600 ms) were correlated with the effects caused by sp-TMS over the ipsilateral SI, indicating that information retained in the ipsilateral SI during the late delay may be associated with the DLPFC. Taken together, these results suggest that both the contralateral and ipsilateral SIs are involved in tactile WM, and the contralateral DLPFC bridges the contralateral SI and ipsilateral SI for goal-directed action.

Diffusion kurtosis imaging (DKI) is a new method of magnetic resonance imaging (MRI) that provides non-Gaussian information that is not available in conventional diffusion tensor imaging (DTI). DKI requires data acquisition at multiple b-values for parameter estimation; this process is usually time-consuming. Therefore, fewer b-values are preferable to expedite acquisition. In this study, we carefully evaluated various acquisition schemas using different numbers and combinations of b-values. Acquisition schemas that sampled b-values that were distributed to two ends were optimized. Compared to conventional schemas using equally spaced b-values (ESB), optimized schemas require fewer b-values to minimize fitting errors in parameter estimation and may thus significantly reduce scanning time. Following a ranked list of optimized schemas resulted from the evaluation, we recommend the 3b schema based on its estimation accuracy and time efficiency, which needs data from only 3 b-values at 0, around 800 and around 2600 s/mm2, respectively. Analyses using voxel-based analysis (VBA) and region-of-interest (ROI) analysis with human DKI datasets support the use of the optimized 3b (0, 1000, 2500 s/mm2) DKI schema in practical clinical applications.

Iterative Cross-Correlation (ICC) is the most popularly used schema for correcting eddy current (EC)-induced distortion in diffusion-weighted imaging data, however, it cannot process data acquired at high b-values. We analyzed the error sources and affecting factors in parameter estimation, and propose an efficient algorithm by expanding the ICC framework with a number of techniques: (1) Pattern recognition for excluding brain ventricles; (2) ICC with the extracted ventricle for parameter initialization; (3) Gradient-based Entropy Correlation Coefficient (GECC) for optimal and finer registration. Experiments demonstrated that our method is robust with high accuracy and error tolerance, and outperforms other ICC-family algorithms and popular approaches currently in use.

Prefrontal cortex (PFC) has been implicated in modulation of sensory information processing in somatosensory cortex. However, it remains unclear whether or not PFC regulates sensory information in thalamus. In the present study, the effect of PFC stimulation on tactile responses of neurons in the ventrobasal thalamus (VB) of the rat was investigated by single-unit recording. PFC stimulation significantly enhanced the signal-noise ratio (tactile responses/background activities) in 16 out of 66 VB neurons (24.2%) that had receptive fields in fore or hind limbs. Such changes can be classified into three different categories: (1) PFC stimulation not only increased the tactile responses, but also suppressed the background activities of neurons (six neurons, 9.1%); (2) PFC stimulation only increased the tactile responses of neurons (five neurons, 7.6%); (3) PFC stimulation only suppressed the background activities of neurons (five neurons, 7.6%). Our results suggest that PFC also modulates somatosensory information at the thalamic level.

This study explores the cortical cell dynamics of unimodal and cross-modal working memory (WM). Neuronal activity was recorded from parietal areas of monkeys performing delayed match-to-sample tasks with tactile or visual samples. Tactile memoranda (haptic samples) consisted of rods with differing surface features (texture or orientation of ridges) perceived by active touch. Visual memoranda (icons) consisted of striped patterns of differing orientation. In a haptic-haptic task, the animal had to retain through a period of delay the surface feature of the sample rod to select a rod that matched it. In a visual-haptic task, the animal had to retain the icon for the haptic choice of a rod with ridges of the same orientation as the icon's stripes. Units in all areas responded with firing change to one or more task events. Also in all areas, cells responded differently to different sample memoranda. Differential sample coherent firing was present in most areas during the memory period (delay). It is concluded that neurons in somatosensory and association areas of parietal cortex participate in broad networks that represent various task events and stimuli (auditory, motor, proprioceptive, tactile, and visual). Neurons in the same networks take part in retaining in WM the memorandum for each trial, whether it is encoded haptically or visually. The VH association by parietal cells in WM is analogous to the auditory-visual association previously observed in prefrontal cortex. Both illustrate the capacity of cortical neurons to associate sensory information across time and across modalities in accord with the rules of a behavioral task.

Persistent elevated neuronal activity has been identified as the neuronal correlate of working memory. It is generally assumed in the literature and in computational and theoretical models of working memory that memory-cell activity is stable and replicable; however, this assumption may be an artifact of the averaging of data collected across trials, and needs experimental verification. In this study, we introduce a classification scheme to characterize the firing frequency trends of cells recorded from the cortex of monkeys during performance of working memory tasks. We examine the frequency statistics and variability of firing during baseline and memory periods. We also study the behavior of cells on individual trials and across trials, and explore the stability of cellular firing during the memory period. We find that cells from different firing-trend classes possess markedly different statistics. We also find that individual cells show substantial variability in their firing behavior across trials, and that firing frequency also varies markedly over the course of a single trial. Finally, the average frequency distribution is wider, the magnitude of the frequency increases from baseline to memory smaller, and the magnitude of frequency decreases larger than is generally assumed. These results may serve as a guide in the evaluation of current theories of the cortical mechanisms of working memory.

In the present study, causal roles of both the primary somatosensory cortex (SI) and the posterior parietal cortex (PPC) were investigated in a tactile unimodal working memory (WM) task. Individual magnetic resonance imaging-based single-pulse transcranial magnetic stimulation (spTMS) was applied, respectively, to the left SI (ipsilateral to tactile stimuli), right SI (contralateral to tactile stimuli) and right PPC (contralateral to tactile stimuli), while human participants were performing a tactile-tactile unimodal delayed matching-to-sample task. The time points of spTMS were 300, 600 and 900 ms after the onset of the tactile sample stimulus (duration: 200 ms). Compared with ipsilateral SI, application of spTMS over either contralateral SI or contralateral PPC at those time points significantly impaired the accuracy of task performance. Meanwhile, the deterioration in accuracy did not vary with the stimulating time points. Together, these results indicate that the tactile information is processed cooperatively by SI and PPC in the same hemisphere, starting from the early delay of the tactile unimodal WM task. This pattern of processing of tactile information is different from the pattern in tactile-visual cross-modal WM. In a tactile-visual cross-modal WM task, SI and PPC contribute to the processing sequentially, suggesting a process of sensory information transfer during the early delay between modalities.

Working memory is essential to learning and performing sensory-motor behaviors that in many situations require the integration of stimuli of one modality with stimuli of another. In the present study, we focused on the neural mechanisms underlying crossmodal working memory. We hypothesized that in performance of the tactile crossmodal working memory task, there would be sequentially discrete task-correlated neural activities representing the processes of crossmodal working memory. Scalp-recorded event-related potentials were collected from 15 electrodes in humans performing each of four tasks: tactile-tactile unimodal delayed matching-to-sample task, tactile-visual crossmodal delayed matching-to-sample task, tactile unimodal control spatial task, and tactile crossmodal control spatial task. Two positive event-related potential peaks were observed during the delay of the task. One peak (late positive component-1) was at about 330 ms after the onset of the tactile stimulus, and the other (late positive component-2) was at about 600 ms. Late positive component-1 was observed in all four tasks. There was no significant difference in late positive component-1 either between the unimodal tasks, or between the crossmodal tasks, but late positive component-1 was significantly larger in the crossmodal tasks than that in the unimodal tasks, and showed a specific pattern of larger activity over parietal areas than activity over frontal areas. Late positive component-2 was not observed in the unimodal matching task but was observed in all other three tasks over parietal areas. During the late delay (1000 ms-1500 ms), significant differences in negative potentials (late negative component) were found between the tasks. The present study shows sequential changes in event-related potentials during the retention period of working memory tasks. It indicates that in performance of a crossmodal working memory task, there are sequentially discrete neural processes that may represent neural activities related to different cognitive functions, such as crossmodal transfer of information, and the working memory of the stimulus.

Many researchers agree that children's difficulty with fraction and rational numbers is associated with their whole number knowledge, but they disagree on the origin of the whole number bias. This article reviews three explanations of the nature of the bias. These accounts diverge on the questions of whether or not early quantitative representation originates from a numerical-specific cognitive mechanism, and whether or not the early quantitative representation privileges discrete quantity. The review suggests that there does not yet appear to be sufficient evidence to decide among the competing accounts as to the nature of the whole number bias. Yet, in the search for the understanding, two important issues have been brought up with regard to learning and teaching fraction and rational numbers. One question is related to how learning about fraction and rational numbers may be organized in such a way to be less strained for taking advantage of the prior knowledge of whole numbers. The second issue is conc...

Clinical studies show that anxiety and chronic pain are concomitant. The neural basis for the comorbidity is unclear. The prefrontal cortex (PFC) has been recognized as a critical area for affective disorders and chronic pain modulation. In this study, we examined the role of the PFC in the pathogenesis of anxiety associated with chronic pain in a rat model of neuropathic pain with spare nerve injury (SNI). The SNI rats showed apparent anxiety-like behaviors in both open field (OF) test and elevated-plus maze (EPM) test eight weeks after surgery. Thus, the number of entries to the central area in the OF decreased to 45% (±5%, n = 15) of sham control (n = 17), while the overall motor activity (i.e., total distance) was unaffected. In the EPM, the percentage of entries into the open arms significantly (p

Previous studies have shown that neurons of monkey dorsolateral prefrontal cortex (DLPFC) integrate information across modalities and maintain it throughout the delay period of working-memory (WM) tasks. However, the mechanisms of this temporal integration in the DLPFC are still poorly understood. In the present study, to further elucidate the role of the DLPFC in crossmodal WM, we trained monkeys to perform visuo–haptic (VH) crossmodal and haptic–haptic (HH) unimodal WM tasks. The neuronal activity recorded in the DLPFC in the delay period of both tasks indicates that the early-delay differential activity probably is related to the encoding of sample information with different strengths depending on task modality, that the late-delay differential activity reflects the associated (modality-independent) action component of haptic choice in both tasks (that is, the anticipation of the behavioral choice and/or active recall and maintenance of sample information for subsequent action), and that the sustained whole-delay differential activity likely bridges and integrates the sensory and action components. In addition, the VH late-delay differential activity was significantly diminished when the haptic choice was not required. Taken together, the results show that, in addition to the whole-delay differential activity, DLPFC neurons also show early- and late-delay differential activities. These previously unidentified findings indicate that DLPFC is capable of (i) holding the coded sample information (e.g., visual or tactile information) in the early-delay activity, (ii) retrieving the abstract information (orientations) of the sample (whether the sample has been haptic or visual) and holding it in the late-delay activity, and (iii) preparing for behavioral choice acting on that abstract information.

The activity in sensory cortices and the prefrontal cortex (PFC) throughout the delay interval of working memory (WM) tasks reflect two aspects of WM-quality and quantity, respectively. The delay activity in sensory cortices is fine-tuned to sensory information and forms the neural basis of the precision of WM storage, while the delay activity in the PFC appears to represent behavioral goals and filters out irrelevant distractions, forming the neural basis of the quantity of task-relevant information in WM. The PFC and sensory cortices interact through different frequency bands of neuronal oscillation (theta, alpha, and gamma) to fulfill goal-directed behaviors.

Diffusion kurtosis imaging (DKI) is a new model in magnetic resonance imaging (MRI) characterizing restricted diffusion of water molecules in living tissues. We propose a method for fast estimation of the DKI parameters. These parameters – apparent diffusion coefficient (ADC) and apparent kurtosis coefficient (AKC) – are evaluated using an alternative iteration schema (AIS). This schema first roughly estimates a pair of ADC and AKC values from a subset of the DKI data acquired at 3 b -values. It then iteratively and alternately updates the ADC and AKC until they are converged. This approach employs the technique of linear least square fitting to minimize estimation error in each iteration. In addition to the common physical and biological constrains that set the upper and lower boundaries of the ADC and AKC values, we use a smoothing procedure to ensure that estimation is robust. Quantitative comparisons between our AIS methods and the conventional methods of unconstrained nonlinear least square (UNLS) using both synthetic and real data showed that our unconstrained AIS method can significantly accelerate the estimation procedure without compromising its accuracy, with the computational time for a DKI dataset successfully reduced to only 1 or 2min. Moreover, the incorporation of the smoothing procedure using one of our AIS methods can significantly enhance the contrast of AKC maps and greatly improve the visibility of details in fine structures.

Microelectrode recordings of cortical activity in primates performing working memory tasks reveal some cortical neurons exhibiting sustained or graded persistent elevations in firing rate during the period in which sensory information is actively maintained in short-term memory. These neurons are called “memory cells”. Imaging and transcranial magnetic stimulation studies indicate that memory cells may arise from distributed cortical networks. Depending on the sensory modality of the memorandum in working memory tasks, neurons exhibiting memory-correlated patterns of firing have been detected in different association cortices including prefrontal cortex, and primary sensory cortices as well. Here we elaborate on neurophysiological experiments that lead to our understanding of the neuromechanisms of working memory, and mainly discuss findings on widely distributed cortical networks involved in tactile working memory.

Single-unit activity was recorded from the hand areas of the somatosensory cortex of monkeys trained to perform a haptic delayed matching to sample task with objects of identical dimensions but different surface features. During the memory retention period of the task (delay), many units showed sustained firing frequency change, either excitation or inhibition. In some cases, firing during that period was significantly higher after one sample object than after another. These observations indicate the participation of somatosensory neurons not only in the perception but in the short-term memory of tactile stimuli. Neurons most directly implicated in tactile memory are (i) those with object-selective delay activity, (ii) those with nondifferential delay activity but without activity related to preparation for movement, and (iii) those with delay activity in the haptic-haptic delayed matching task but no such activity in a control visuo-haptic delayed matching task. The results indicate that cells in early stages of cortical somatosensory processing participate in haptic short-term memory.

Abacus experts are able to mentally calculate multi-digit numbers rapidly. Some behavioral and neuroimaging studies have suggested a visuospatial and visuomotor strategy during abacus mental calculation. However, no study up to now has attempted to dissociate temporally the visuospatial neural process from the visuomotor neural process during abacus mental calculation. In the present study, an abacus expert performed the mental addition tasks (8-digit and 4-digit addends presented in visual or auditory modes) swiftly and accurately. The 100% correct rates in this expert’s task performance were significantly higher than those of ordinary subjects performing 1-digit and 2-digit addition tasks. ERPs, EEG source localizations, and fMRI results taken together suggested visuospatial and visuomotor processes were sequentially arranged during the abacus mental addition with visual addends and could be dissociated from each other temporally. The visuospatial transformation of the numbers, in which the superior parietal lobule was most likely involved, might occur first (around 380 ms) after the onset of the stimuli. The visuomotor processing, in which the superior/middle frontal gyri were most likely involved, might occur later (around 440 ms). Meanwhile, fMRI results suggested that neural networks involved in the abacus mental addition with auditory stimuli were similar to those in the visual abacus mental addition. The most prominently activated brain areas in both conditions included the bilateral superior parietal lobules (BA 7) and bilateral middle frontal gyri (BA 6). These results suggest a supra-modal brain network in abacus mental addition, which may develop from normal mental calculation networks.

We propose a reconstructed diffusion gradient (RDG) method for spatial normalization of diffusion tensor imaging (DTI) data that warps the raw imaging data and then estimates the associated gradient direction for reconstruction of normalized DTI in the template space. The RDG method adopts the backward mapping strategy for DTI normalization, with a specially designed approach to reconstruct a specific gradient direction in combination with the local deformation force. The method provides a voxel-based strategy to make the gradient direction align with the raw diffusion weighted imaging (DWI) volumes, ensuring correct estimation of the tensors in the warped space and thereby retaining the orientation information of the underlying structure. Compared with the existing tensor reorientation methods, experiments using both simulated and human data demonstrated that the RDG method provided more accurate tensor information. Our method can properly estimate the gradient direction in the template space that has been changed due to image transformation, and subsequently use the warped imaging data to directly reconstruct the warped tensor field in the template space, achieving the same goal as directly warping the tensor image. Moreover, the RDG method also can be used to spatially normalize data using the Q-ball imaging (QBI) model.

Previous studies suggested that primary somatosensory (SI) neurons in well-trained monkeys participated in the haptic–haptic unimodal delayed matching-to-sample (DMS) task. In this study, 585 SI neurons were recorded in monkeys performing a task that was identical to that in the previous studies but without requiring discrimination and active memorization of specific features of a tactile or visual memorandum. A substantial number of those cells significantly changed their firing rate in the delay compared with the baseline, and some of them showed differential delay activity. These firing changes are similar to those recorded from monkeys engaged in active (working) memory. We conclude that the delay activity is not necessarily only observed as was generally thought in the situation of active memorization of different features between memoranda after those features have been actively discriminated. The delay activity observed in this study appears to be an intrinsic property of SI neurons and suggests that there exists a neural network in SI (the primary sensory cortex) for haptic working memory no matter whether the difference in features of memoranda needs to be memorized in the task or not. Over 400 SI neurons were also recorded in monkeys well-trained to discriminate two memoranda in the haptic–haptic DMS task for comparison of delay firing of SI neurons between the two different working memory tasks used in this study. The similarity observed in those two situations suggests that working memory uses already-existing memory apparatus by activating it temporarily. Our data also suggest that, through training (repetitive exposure to the stimulus), SI neurons may increase their involvement in the working memory of the memorandum.

Region-based active contour model (ACM) has been extensively used in medical image segmentation and Chan & Vese's (C-V) model is one of the most popular ACM methods. We propose to incorporate into the C-V model a weighting function to take into consideration the fact that different locations in an image with differing distances from the active contour have differing importance in generating the segmentation result, thereby making it a weighted C-V (WC-V) model. The theoretical properties of the model and our experiments both demonstrate that the proposed WC-V model can significantly reduce the computational cost while improve the accuracy of segmentation over the results using the C-V model.

Neurons in the cortex exhibit a number of patterns that correlate with working memory. Specifically, averaged across trials of working memory tasks, neurons exhibit different firing rate patterns during the delay of those tasks. These patterns include: 1) persistent fixed-frequency elevated rates above baseline, 2) elevated rates that decay throughout the tasks memory period, 3) rates that accelerate throughout the delay, and 4) patterns of inhibited firing (below baseline) analogous to each of the preceding excitatory patterns. Persistent elevated rate patterns are believed to be the neural correlate of working memory retention and preparation for execution of behavioral/motor responses as required in working memory tasks. Models have proposed that such activity corresponds to stable attractors in cortical neural networks with fixed synaptic weights. However, the variability in patterned behavior and the firing statistics of real neurons across the entire range of those behaviors across and within trials of working memory tasks are typical not reproduced. Here we examine the effect of dynamic synapses and network architectures with multiple cortical areas on the states and dynamics of working memory networks. The analysis indicates that the multiple pattern types exhibited by cells in working memory networks are inherent in networks with dynamic synapses, and that the variability and firing statistics in such networks with distributed architectures agree with that observed in the cortex.

In the present study, we examined the neural mechanisms underlying cross-modal working memory by analyzing scalp-recorded event-related potentials (ERPs) from normal human subjects performing tactile-tactile unimodal or tactile-auditory cross-modal delay tasks that consisted of stimulus-1 (S-1, tactile), interval (delay), and stimulus-2 (S-2, tactile or auditory). We hypothesized that there would be sequentially discrete task-correlated changes in ERPs representing neural processes of tactile working memory, and in addition, significant differences would be observed in ERPs between the unimodal task and the cross-modal task. In comparison to the ERP components in the unimodal task, two late positive ERP components (LPC-1 and LPC-2) evoked by the tactile S-1 in the delay of the cross-modal task were enhanced by expectation of the associated auditory S-2 presented at the end of the delay. Such enhancement might represent neural activities involved in cross-modal association between the tactile stimulus and the auditory stimulus. Later in the delay, a late negative component (LNC) was observed. The amplitude of LNC depended on information retained during the delay, and when the same information was retained, this amplitude was not influenced by modality or location of S-2 (auditory S-2 through headphones, or tactile S-2 on the left index finger). LNC might represent the neural activity involved in working memory. The above results suggest that the sequential ERP changes in the present study represent temporally distinguishable neural processes, such as the cross-modal association and cross-modal working memory.

Human tactile discrimination studies have shown that visual stimuli enhance tactile performance. Other studies on event-related potentials showed that somatosensory N140 was enhanced when attention of human subjects was directed to tactile stimuli. Therefore, we hypothesized that N140 would be modulated when human subjects performed tactile cross-modal delay tasks. Scalp-event-related potentials were recorded from normal subjects performing either a tactile-tactile unimodal, or a tactile-visual cross-modal delayed matching-to-sample task. Identical tactile stimuli were used in both tasks. N140 component evoked by the tactile stimuli was enhanced in the cross-modal task. Enhancement of this component was also observed in control cross-modal tasks. The results suggest that tactile-visual cross-modal association affects tactile sensory-perceptual processes in humans.

Cells in the somatosensory cortex of the monkey are known to exhibit sustained elevations of firing frequency during the short-term mnemonic retention of tactile information in a haptic delay task. In this study, we examine the possibility that those firing elevations are accompanied by changes in firing pattern. Patterns are identified by the application of a pattern-searching algorithm to the interspike intervals of spike trains. By sequential use of sets of pattern templates with a range of temporal resolutions, we find patterned activity in the majority of the cells investigated. In general, the degree of patterning significantly increases during active memory. Surrogate analysis suggests that the observed patterns may not be simple linear stochastic functions of instantaneous or average firing frequency. Therefore, during the active retention of a memorandum, the activity of a 'memory cell' may be characterized not only by changes in frequency but also by changes in pattern.

Neurons in the monkey’s anterior parietal cortex (Brodmann’s areas 3a, 3b, 1, and 2) have been reported to retain information from a visual cue that has been associated with a tactile stimulus in a haptic memory task. This cross-modal transfer indicates that neurons in somatosensory cortex can respond to non-tactile stimuli if they are associated with tactile information needed for performance of the task. We hypothesized that neurons in somatosensory cortex would be activated by other non-tactile stimuli signaling the haptic movements—of arm and hand—that the task required. We found such cells in anterior parietal areas. They reacted with short-latency activity changes to an auditory signal (a click) that prompted those movements. Further, some of those cells changed their discharge in temporal correlation with the movements themselves, with the touch of the test objects, and with the short-term memory of those objects for subsequent tactile discrimination. These findings suggest that cells in the somatosensory cortex participate in the behavioral integration of auditory stimuli with other sensory stimuli and with motor acts that are associated with those stimuli.

Recent studies show that cells in the somatosensory cortex are involved in the short-term retention of tactile information. In addition, some somatosensory cells appear to retain visual information that has been associated with the touch of an object. The presence of such cells suggests that nontactile stimuli associated with touch have access to cortical neuron networks engaged in the haptic sense. Thus, we inferred that somatosensory cells would respond to behaviorally associated visual and tactile stimuli. To test this assumption, single units were recorded from the anterior parietal cortex (Brodmann's areas 3a, 3b, 1, and 2) of monkeys performing a visuo-haptic delay task, which required the memorization of a visual cue for a tactile choice. Most cells responding to that cue responded also to the corresponding object presented for tactile choice. Significant correlations were observed in some cells between their differential reactions to tactile objects and their differential reactions to the associated visual cues. Some cells were recorded in both the cross-modal task and a haptic unimodal task, where the animal had to retain a tactile cue for a tactile choice. In most of these cells, correlations were observed between stimulus-related firing in corresponding cue periods of the two tasks. These findings suggest that cells in somatosensory cortex are the components of neuronal networks representing tactile information. Associated visual stimuli may activate such networks through visuo-haptic associations established by behavioral training.