Common neural substrates for visual working memory and attention

Functional mapping of the human insula: Data from electrical stimulations

Electrical stimulations of the insula performed during stereo-electro-encephalography (SEEG) reproduce the ictal symptoms observed during the development of insular seizures and are also a unique opportunity to provide a functional mapping of the insular cortex. We provide here a functional mapping of the insular cortex obtained by electrical stimulation, based on our previous work and a review of literature. The most frequent responses to insula stimulation were somatosensory sensations followed by visceral responses. Then, in decreasing order of frequency, auditory sensations, vestibular illusions, speech impairment, gustato-olfactory sensations and motor reactions were evoked. A bipolar organization could be evidenced with a posterior part assigned to somatosensory functions and notably to pain perception; and an anterior part assigned to visceral functions. Although some degree of spatial segregation could be evidenced, there was a clear spatial overlap between the representations of the different types of responses. These data provide a better understanding of physiological insular functions, insula seizures semiology and a prediction of post-surgical deficits. Insula is the only cortical region where stimulations demonstrate such a multi-modal representation, perhaps supporting its integrative functions of polymodal inputs.

Brain Oscillatory Correlates of Visual Short-Term Memory Errors

Brain dynamics of memory formation were explored during encoding and retention intervals of a visual working memory task. EEG data were acquired while subjects were exposed to grayscale images of widely known object categories (e.g., "luggage," "chair," and "car"). Following a short delay, two probes were shown to test memory accuracy. Oscillatory portraits of successful and erroneous memories were contrasted. Where significant differences were identified, oscillatory traits of false memories (i.e., when a novel probe item of the same category is recognized as familiar) were compared with those of successful and erroneous memories. Spectral analysis revealed theta (6-8 Hz) power over occipital channels for encoding of successful and false memories that was smaller when compared to other types of memory errors. The reduced theta power indicates successful encoding and reflects the efficient activation of the underlying neural assemblies. Prominent alpha-beta (10-26 Hz) activity belonging to the right parieto-occipital channels was identified during the retention interval. It was found to be larger for false memories and errors than that of correctly answered trials. High levels of alpha-beta oscillatory activity for errors correspond to poor maintenance leading to inefficient allocation of WM resources. In case of false memories, this would imply necessary cognitive effort to manage the extra semantic and perceptual load induced by the encoded stimuli.

Topographical memory for newly-learned maps is differentially affected by route-based versus landmark-based learning: a functional MRI study

Humans rely on topographical memory to encode information about spatial aspects of environments. However, even though people adopt different strategies when learning new maps, little is known about the impact of those strategies on topographical memory, and their neural correlates. To examine that issue, we presented participants with 40 unfamiliar maps, each of which displayed one major route and three landmarks. Half were instructed to memorize the maps by focusing on the route, whereas the other half memorized the maps by focusing on the landmarks. One day later, the participants were tested on their ability to distinguish previously studied 'old' maps from completely unfamiliar 'new' maps under conditions of high and low working memory load in the functional MRI scanner. Viewing old versus new maps was associated with relatively greater activation in a distributed set of regions including bilateral inferior temporal gyrus - an important region for recognizing visual objects. Critically, whereas the performance of participants who had followed a route-based strategy dropped to chance level under high working memory load, participants who had followed a landmark-based strategy performed at above chance levels under both high and low working memory load - reflected by relatively greater activation in the left inferior parietal lobule (i.e. rostral part of the supramarginal gyrus known as area PFt). Our findings suggest that landmark-based learning may buffer against the effects of working memory load during recognition, and that this effect is represented by the greater involvement of a brain region implicated in both topographical and working memory.

Testing the efforts model of simultaneous interpreting: An ERP study

We utilized the event-related potential (ERP) technique to study neural activity associated with different levels of working memory (WM) load during simultaneous interpretation (SI) of continuous prose. The amplitude of N1 and P1 components elicited by task-irrelevant tone probes was significantly modulated as a function of WM load but not the direction of interpretation. Furthermore, the latency of the P1 increased significantly with WM load. The WM load effect on N1 latency, however, did not reach significance. Larger negativity under lower WM loads suggests that more attention is available to process the source message, providing the first electrophysiological evidence in support of the Efforts Model of SI. Relationships between the direction of interpretation and median WM load are also discussed.

Dance training is superior to repetitive physical exercise in inducing brain plasticity in the elderly

Animal research indicates that a combination of physical activity and sensory enrichment has the largest and the only sustaining effect on adult neuroplasticity. Dancing has been suggested as a human homologue to this combined intervention as it poses demands on both physical and cognitive functions. For the present exploratory study, we designed an especially challenging dance program in which our elderly participants constantly had to learn novel and increasingly difficult choreographies. This six-month-long program was compared to conventional fitness training matched for intensity. An extensive pre/post-assessment was performed on the 38 participants (63-80 y), covering general cognition, attention, memory, postural and cardio-respiratory performance, neurotrophic factors and-most crucially-structural MRI using an exploratory analysis. For analysis of MRI data, a new method of voxel-based morphometry (VBM) designed specifically for pairwise longitudinal group comparisons was employed. Both interventions increased physical fitness to the same extent. Pronounced differences were seen in the effects on brain volumes: Dancing compared to conventional fitness activity led to larger volume increases in more brain areas, including the cingulate cortex, insula, corpus callosum and sensorimotor cortex. Only dancing was associated with an increase in plasma BDNF levels. Regarding cognition, both groups improved in attention and spatial memory, but no significant group differences emerged. The latter finding may indicate that cognitive benefits may develop later and after structural brain changes have taken place. The present results recommend our challenging dance program as an effective measure to counteract detrimental effects of aging on the brain.

Thirst-Dependent Activity of the Insular Cortex Reflects its Emotion-Related Subdivision: A Cerebral Blood Flow Study

Recent studies investigating neural correlates of human thirst have identified various subcortical and telencephalic brain areas. The experience of thirst represents a homeostatic emotion and a state that slowly evolves over time. Therefore, the present study aims at systematically examining cerebral perfusion during the parametric progression of thirst. We measured subjective thirst ratings, serum parameters and cerebral blood flow in 20 healthy subjects across four different thirst stages: intense thirst, moderate thirst, subjective satiation and physiological satiation. Imaging data revealed dehydration-related perfusion differences in previously identified brain areas, such as the anterior cingulate cortex, the middle temporal gyrus and the insular cortex. However, significant differences across all four thirst stages (including the moderate thirst level), were exclusively found in the posterior insular cortex. The subjective thirst ratings over the different thirst stages, however, were associated with perfusion differences in the right anterior insula. These findings add to our understanding of the insular cortex as a key player in human thirst - both on the level of physiological dehydration and the level of the subjective thirst experience.

Strategic inhibition of distractors with visual working memory contents after involuntary attention capture

Previous research has suggested that visual working memory (VWM) contents had a guiding effect on selective attention, and once participants realized that the distractors shared the same information with VWM contents in the search task, they would strategically inhibit the potential distractors with VWM contents. However, previous behavioral studies could not reveal the way how distractors with VWM contents are inhibited strategically. By employing the eye-tracking technique and a dual-task paradigm, we manipulated the probability of memory items occurring as distractors to explore this issue. Consistent with previous behavioral studies, the results showed that the inhibitory effect occurred only in the high-probability condition, while the guiding effect emerged in the low-probability condition. More importantly, the eye-movement results indicated that in the high-probability condition, once few (even one) distractors with VWM contents were captured at first, all the remaining distractors with VWM contents would be rejected as a whole. However, in the low-probability condition, attention could be captured by the majority of distractors with VWM contents. These results suggested that the guiding effect of VWM contents on attention is involuntary in the early stage of visual search. After the completion of this involuntary stage, the guiding effect of task-irrelevant VWM contents on attention could be strategically controlled.

Social attention directs working memory maintenance

Visual working memory (vWM) performance is enhanced when a memorized object is cued after encoding. This so-called retro-cue effect is typically observed with a predictive (80% valid), retrospective cue. The current study examined whether a nonpredictive (50% valid) retro-cue can similarly enhance internal memory representations in cases where the cue conveys social signals. To this end, gaze cues were presented during the retention interval of a change-detection task, which are capable to engender a mutual attentional focus of two individuals towards one location. In line with our prediction, Experiment 1 demonstrated that a polygon presented at the gazed-at location was remembered better than that at both non-gazed and gazed-away locations. Experiments 2 and 3 showed that low-level motion cues did not elicit attentional orienting in a comparable manner as the gaze cue, and these differences in cuing were found to be reliable and independent of memory load. Furthermore, the gaze retro-cue effect disappeared when the face was inverted (Experiment 4). In sum, these results clearly show that sharing the focus of another individual establishes a point of reference from which visual information is restored with priority, suggesting that a gaze retro-cue leads to social attention, thus, modulating vWM maintenance in a reflexive, automatic manner.

Development of a Ternary Near-Infrared Spectroscopy Brain-Computer Interface: Online Classification of Verbal Fluency Task, Stroop Task and Rest

The majority of proposed NIRS-BCIs has considered binary classification. Studies considering high-order classification problems have yielded average accuracies that are less than favorable for practical communication. Consequently, there is a paucity of evidence supporting online classification of more than two mental states using NIRS. We developed an online ternary NIRS-BCI that supports the verbal fluency task (VFT), Stroop task and rest. The system utilized two sessions dedicated solely to classifier training. Additionally, samples were collected prior to each period of online classification to update the classifier. Using a continuous-wave spectrometer, measurements were collected from the prefrontal and parietal cortices while 11 able-bodied adult participants were cued to perform one of the two cognitive tasks or rests. Each task was used to indicate the desire to select a particular letter on a scanning interface, while rest avoided selection. Classification was performed using 25 iteration of bagging with a linear discriminant base classifier. Classifiers were trained on 10-dimensional feature sets. The BCI's classification decision was provided as feedback. An average online classification accuracy of [Formula: see text]% was achieved, representing an ITR of [Formula: see text] bits/min. The results demonstrate that online communication can be achieved with a ternary NIRS-BCI that supports VFT, Stroop task and rest. Our findings encourage continued efforts to enhance the ITR of NIRS-BCIs.

Neural Representation of Working Memory Content Is Modulated by Visual Attentional Demand

Recent theories assert that visual working memory (WM) relies on the same attentional resources and sensory substrates as visual attention to external stimuli. Behavioral studies have observed competitive tradeoffs between internal (i.e., WM) and external (i.e., visual) attentional demands, and neuroimaging studies have revealed representations of WM content as distributed patterns of activity within the same cortical regions engaged by perception of that content. Although a key function of WM is to protect memoranda from competing input, it remains unknown how neural representations of WM content are impacted by incoming sensory stimuli and concurrent attentional demands. Here, we investigated how neural evidence for WM information is affected when attention is occupied by visual search-at varying levels of difficulty-during the delay interval of a WM match-to-sample task. Behavioral and fMRI analyses suggested that WM maintenance was impacted by the difficulty of a concurrent visual task. Critically, multivariate classification analyses of category-specific ventral visual areas revealed a reduction in decodable WM-related information when attention was diverted to a visual search task, especially when the search was more difficult. This study suggests that the amount of available attention during WM maintenance influences the detection of sensory WM representations.

Distinct Top-down and Bottom-up Brain Connectivity During Visual Perception and Imagery

Research suggests that perception and imagination engage neuronal representations in the same visual areas. However, the underlying mechanisms that differentiate sensory perception from imagination remain unclear. Here, we examine the directed coupling (effective connectivity) between fronto-parietal and visual areas during perception and imagery. We found an increase in bottom-up coupling during perception relative to baseline and an increase in top-down coupling during both perception and imagery, with a much stronger increase during imagery. Modulation of the coupling from frontal to early visual areas was common to both perception and imagery. Furthermore, we show that the experienced vividness during imagery was selectively associated with increases in top-down connectivity to early visual cortex. These results highlight the importance of top-down processing in internally as well as externally driven visual experience.

The effects of changes in object location on object identity detection: A simultaneous EEG-fMRI study

Object identity and location are bound together to form a unique integration that is maintained and processed in visual working memory (VWM). Changes in task-irrelevant object location have been shown to impair the retrieval of memorial representations and the detection of object identity changes. However, the neural correlates of this cognitive process remain largely unknown. In the present study, we aim to investigate the underlying brain activation during object color change detection and the modulatory effects of changes in object location and VWM load. To this end we used simultaneous electroencephalography (EEG) and functional magnetic resonance imaging (fMRI) recordings, which can reveal the neural activity with both high temporal and high spatial resolution. Subjects responded faster and with greater accuracy in the repeated compared to the changed object location condition, when a higher VWM load was utilized. These results support the spatial congruency advantage theory and suggest that it is more pronounced with higher VWM load. Furthermore, the spatial congruency effect was associated with larger posterior N1 activity, greater activation of the right inferior frontal gyrus (IFG) and less suppression of the right supramarginal gyrus (SMG), when object location was repeated compared to when it was changed. The ERP-fMRI integrative analysis demonstrated that the object location discrimination-related N1 component is generated in the right SMG.

Neuronal population coding of perceived and memorized visual features in the lateral prefrontal cortex

The primate lateral prefrontal cortex (LPFC) encodes visual stimulus features while they are perceived and while they are maintained in working memory. However, it remains unclear whether perceived and memorized features are encoded by the same or different neurons and population activity patterns. Here we record LPFC neuronal activity while monkeys perceive the motion direction of a stimulus that remains visually available, or memorize the direction if the stimulus disappears. We find neurons with a wide variety of combinations of coding strength for perceived and memorized directions: some neurons encode both to similar degrees while others preferentially or exclusively encode either one. Reading out the combined activity of all neurons, a machine-learning algorithm reliably decode the motion direction and determine whether it is perceived or memorized. Our results indicate that a functionally diverse population of LPFC neurons provides a substrate for discriminating between perceptual and mnemonic representations of visual features.

Neurons in the lateral prefrontal cortex are known to encode visual features as well as maintain them in working memory. Here the authors report that LPFC neurons encode both perceived and memorized visual features in diverse combinations and the population activity reliably decodes as well as differentiates between these two representations.

Neural Coding for Instruction-Based Task Sets in Human Frontoparietal and Visual Cortex

Task preparation has traditionally been thought to rely upon persistent representations of instructions that permit their execution after delays. Accumulating evidence suggests, however, that accurate retention of task knowledge can be insufficient for successful performance. Here, we hypothesized that instructed facts would be organized into a task set; a temporary coding scheme that proactively tunes sensorimotor pathways according to instructions to enable highly efficient "reflex-like" performance. We devised a paradigm requiring either implementation or memorization of novel stimulus-response mapping instructions, and used multivoxel pattern analysis of neuroimaging data to compare neural coding of instructions during the pretarget phase. Although participants could retain instructions under both demands, we observed striking differences in their representation. To-be-memorized instructions could only be decoded from mid-occipital and posterior parietal cortices, consistent with previous work on visual short-term memory storage. In contrast, to-be-implemented instructions could also be decoded from frontoparietal "multiple-demand" regions, and dedicated visual areas, implicated in processing instructed stimuli. Neural specificity in the latter moreover correlated with performance speed only when instructions were prepared, likely reflecting the preconfiguration of instructed decision circuits. Together, these data illuminate how the brain proactively optimizes performance, and help dissociate neural mechanisms supporting task control and short-term memory storage.

Vibrotactile Discrimination Training Affects Brain Connectivity in Profoundly Deaf Individuals

Early auditory deprivation has serious neurodevelopmental and cognitive repercussions largely derived from impoverished and delayed language acquisition. These conditions may be associated with early changes in brain connectivity. Vibrotactile stimulation is a sensory substitution method that allows perception and discrimination of sound, and even speech. To clarify the efficacy of this approach, a vibrotactile oddball task with 700 and 900 Hz pure-tones as stimuli [counterbalanced as target (T: 20% of the total) and non-target (NT: 80%)] with simultaneous EEG recording was performed by 14 profoundly deaf and 14 normal-hearing (NH) subjects, before and after a short training period (five 1-h sessions; in 2.5–3 weeks). A small device worn on the right index finger delivered sound-wave stimuli. The training included discrimination of pure tone frequency and duration, and more complex natural sounds. A significant P300 amplitude increase and behavioral improvement was observed in both deaf and normal subjects, with no between group differences. However, a P3 with larger scalp distribution over parietal cortical areas and lateralized to the right was observed in the profoundly deaf. A graph theory analysis showed that brief training significantly increased fronto-central brain connectivity in deaf subjects, but not in NH subjects. Together, ERP tools and graph methods depicted the different functional brain dynamic in deaf and NH individuals, underlying the temporary engagement of the cognitive resources demanded by the task. Our findings showed that the index-fingertip somatosensory mechanoreceptors can discriminate sounds. Further studies are necessary to clarify brain connectivity dynamics associated with the performance of vibrotactile language-related discrimination tasks and the effect of lengthier training programs.

Object files across eye movements: Previous fixations affect the latencies of corrective saccades

One of the factors contributing to a seamless visual experience is object correspondence-that is, the integration of pre- and postsaccadic visual object information into one representation. Previous research had suggested that before the execution of a saccade, a target object is loaded into visual working memory and subsequently is used to locate the target object after the saccade. Until now, studies on object correspondence have not taken previous fixations into account. In the present study, we investigated the influence of previously fixated information on object correspondence. To this end, we adapted a gaze correction paradigm in which a saccade was executed toward either a previously fixated or a novel target. During the saccade, the stimuli were displaced such that the participant's gaze landed between the target stimulus and a distractor. Participants then executed a corrective saccade to the target. The results indicated that these corrective saccades had lower latencies toward previously fixated than toward nonfixated targets, indicating object-specific facilitation. In two follow-up experiments, we showed that presaccadic spatial and object (surface feature) information can contribute separately to the execution of a corrective saccade, as well as in conjunction. Whereas the execution of a corrective saccade to a previously fixated target object at a previously fixated location is slowed down (i.e., inhibition of return), corrective saccades toward either a previously fixated target object or a previously fixated location are facilitated. We concluded that corrective saccades are executed on the basis of object files rather than of unintegrated feature information.

Working memory load influences perceptual ambiguity by competing for fronto-parietal attentional resources

A visual stimulus is defined as ambiguous when observers perceive it as having at least two distinct and spontaneously alternating interpretations. Neuroimaging studies suggest an involvement of a right fronto-parietal network regulating the balance between stable percepts and the triggering of alternative interpretations. As spontaneous perceptual reversals may occur even in the absence of attention to these stimuli, we investigated neural activity patterns in response to perceptual changes of ambiguous Necker cube under different amounts of working memory load using a dual-task design. We hypothesized that the same regions that process working memory load are involved in perceptual switching and confirmed the prediction that perceptual reversals led to fMRI responses that linearly depended on load. Accordingly, posterior Superior Parietal Lobule, anterior Prefrontal and Dorsolateral Prefrontal cortices exhibited differential BOLD signal changes in response to perceptual reversals under working memory load. Our results also suggest that the posterior Superior Parietal Lobule may be directly involved in the emergence of perceptual reversals, given that it specifically reflects both perceptual versus real changes and load levels. The anterior Prefrontal and Dorsolateral Prefrontal cortices, showing a significant interaction between reversal levels and load, might subserve a modulatory role in such reversals, in a mirror symmetric way: in the former activation is suppressed by the highest loads, and in the latter deactivation is reduced by highest loads, suggesting a more direct role of the aPFC in reversal generation.

The role of working memory and declarative memory in trace conditioning

Translational assays of cognition that are similarly implemented in both lower and higher-order species, such as rodents and primates, provide a means to reconcile preclinical modeling of psychiatric neuropathology and clinical research. To this end, Pavlovian conditioning has provided a useful tool for investigating cognitive processes in both lab animal models and humans. This review focuses on trace conditioning, a form of Pavlovian conditioning typified by the insertion of a temporal gap (i.e., trace interval) between presentations of a conditioned stimulus (CS) and an unconditioned stimulus (US). This review aims to discuss pre-clinical and clinical work investigating the mnemonic processes recruited for trace conditioning. Much work suggests that trace conditioning involves unique neurocognitive mechanisms to facilitate formation of trace memories in contrast to standard Pavlovian conditioning. For example, the hippocampus and prefrontal cortex (PFC) appear to play critical roles in trace conditioning. Moreover, cognitive mechanistic accounts in human studies suggest that working memory and declarative memory processes are engaged to facilitate formation of trace memories. The aim of this review is to integrate cognitive and neurobiological accounts of trace conditioning from preclinical and clinical studies to examine involvement of working and declarative memory.

Delayed match-to-sample in working memory: A BrainMap meta-analysis

Working memory (WM), or the ability to temporarily store and manipulate information, is one of the most widely studied constructs in cognitive psychology. Since its inception, it has become one of the leading explanations for how humans are able to operate on a cognitive level. The current study probed the neural networks underlying one of the most commonly used tasks, delayed match-to-sample (DMTS), to study WM. An activation likelihood estimation (ALE) analysis of 42 functional neuroimaging studies (626 participants) was conducted to demonstrate neural network engagement during DMTS. Results demonstrated strong convergence in brain regions commonly associated with the working memory construct (i.e., dorsolateral prefrontal cortex, fusiform gyrus, and posterior parietal cortex). However, neural activation in two regions frequently attributed to WM were absent from this meta-analysis: the anterior cingulate and the rostral prefrontal cortex, suggesting that these regions may be more sensitive to task or stimuli characteristics. In a post-hoc analysis, we deconstructed the DMTS meta-analysis to examine nonverbal versus verbal stimuli, and found notable neurofunctional differences such that DMTS using nonverbal stimuli consistently engaged the right middle frontal gyrus (BA 6/46) and precuneus (BA 7) more so than verbal stimuli based DMTS. These results provide a foundation for future models of functional connectivity that may elucidate subtle differences in working memory attributable to pathological processes.

Mapping of the Underlying Neural Mechanisms of Maintenance and Manipulation in Visuo-Spatial Working Memory Using An n-back Mental Rotation Task: A Functional Magnetic Resonance Imaging Study

Mapping of the underlying neural mechanisms of visuo-spatial working memory (WM) has been shown to consistently elicit activity in right hemisphere dominant fronto-parietal networks. However to date, the bulk of neuroimaging literature has focused largely on the maintenance aspect of visuo-spatial WM, with a scarcity of research into the aspects of WM involving manipulation of information. Thus, this study aimed to compare maintenance-only with maintenance and manipulation of visuo-spatial stimuli (3D cube shapes) utilizing a 1-back task while functional magnetic resonance imaging (fMRI) scans were acquired. Sixteen healthy participants (9 women, M = 23.94 years, SD = 2.49) were required to perform the 1-back task with or without mentally rotating the shapes 90° on a vertical axis. When no rotation was required (maintenance-only condition), a right hemispheric lateralization was revealed across fronto-parietal areas. However, when the task involved maintaining and manipulating the same stimuli through 90° rotation, activation was primarily seen in the bilateral parietal lobe and left fusiform gyrus. The findings confirm that the well-established right lateralized fronto-parietal networks are likely to underlie simple maintenance of visuo-spatial stimuli. The results also suggest that the added demand of manipulation of information maintained online appears to require further neural recruitment of functionally related areas. In particular mental rotation of visuospatial stimuli required bilateral parietal areas, and the left fusiform gyrus potentially to maintain a categorical or object representation. It can be concluded that WM is a complex neural process involving the interaction of an increasingly large network.

The Focus of Attention in Visual Working Memory: Protection of Focused Representations and Its Individual Variation

Visual working memory can be modulated according to changes in the cued task relevance of maintained items. Here, we investigated the mechanisms underlying this modulation. In particular, we studied the consequences of attentional selection for selected and unselected items, and the role of individual differences in the efficiency with which attention is deployed. To this end, performance in a visual working memory task as well as the CDA/SPCN and the N2pc, ERP components associated with visual working memory and attentional processes, were analysed. Selection during the maintenance stage was manipulated by means of two successively presented retrocues providing spatial information as to which items were most likely to be tested. Results show that attentional selection serves to robustly protect relevant representations in the focus of attention while unselected representations which may become relevant again still remain available. Individuals with larger retrocueing benefits showed higher efficiency of attentional selection, as indicated by the N2pc, and showed stronger maintenance-associated activity (CDA/SPCN). The findings add to converging evidence that focused representations are protected, and highlight the flexibility of visual working memory, in which information can be weighted according its relevance.

Top-Down Activation of Spatiotopic Sensory Codes in Perceptual and Working Memory Search

A critical requirement of an efficient cognitive system is the selection and prioritization of relevant information. This occurs when selecting specific items from our sensory inputs, which then receive preferential status at subsequent levels of processing. Many everyday tasks also require us to select internal representations, such as a relevant item from memory. We show that both of these types of search are underpinned by the spatiotopic activation of sensory codes, using both fMRI and MEG data. When individuals searched for perceived and remembered targets, the MEG data highlighted a sensor level electrophysiological effect that reflects the contralateral organization of the visual system-namely, the N2pc. The fMRI data were used to identify a network of frontoparietal areas common to both types of search, as well as the early visual areas activated by the search display. We then combined fMRI and MEG data to explore the temporal dynamics of functional connections between the frontoparietal network and the early visual areas. Searching for a target item resulted in significantly enhanced phase-phase coupling between the frontoparietal network and the visual areas contralateral to the perceived or remembered location of that target. This enhancement of spatially specific phase-phase coupling occurred before the N2pc effect and was significantly associated with it on a trial-by-trial basis. The combination of these two imaging modalities suggests that perceptual and working memory search are underpinned by the synchronization of a frontoparietal network and the relevant sensory cortices.

Chronic spatial working memory deficit associated with the superior longitudinal fasciculus: a study using voxel-based lesion-symptom mapping and intraoperative direct stimulation in right prefrontal glioma surgery

OBJECTIVE Although the right prefrontal region is regarded as a silent area, chronic deficits of the executive function, including working memory (WM), could occur after resection of a right prefrontal glioma. This may be overlooked by postoperative standard examinations, and the disabilities could affect the patient's professional life. The right prefrontal region is a part of the frontoparietal network and is subserved by the superior longitudinal fasciculus (SLF); however, the role of the SLF in spatial WM is unclear. This study investigated a persistent spatial WM deficit in patients who underwent right prefrontal glioma resection, and evaluated the relationship between the spatial WM deficit and the SLF. METHODS Spatial WM was examined in 24 patients who underwent prefrontal glioma resection (right, n = 14; left, n = 10) and in 14 healthy volunteers using a spatial 2-back task during the long-term postoperative period. The neural correlates of spatial WM were evaluated using lesion mapping and voxel-based lesion-symptom mapping. In addition, the spatial 2-back task was performed during surgery under direct subcortical electrical stimulation in 2 patients with right prefrontal gliomas. RESULTS Patients with a right prefrontal lesion had a significant chronic spatial WM deficit. Voxel-based lesion-symptom mapping analysis revealed a significant correlation between spatial WM deficit and the region that overlapped the first and second segments of the SLF (SLF I and SLF II). Two patients underwent awake surgery and had difficulties providing the correct responses in the spatial 2-back task with direct subcortical electrical stimulation on the SLF I, which was preserved and confirmed by postoperative diffusion tensor imaging tractography. These patients exhibited no spatial WM deficits during the postoperative immediate and long-term periods. CONCLUSIONS Spatial WM deficits may persist in patients who undergo resection of the tumor located in the right prefrontal brain parenchyma. Injury to the dorsal frontoparietal subcortical white matter pathway, i.e., the SLF I or SLF I and II, could play a causal role in this chronic deficit. A persistent spatial WM deficit, without motor and language deficits, could affect the professional life of the patient. In such cases, awake surgery would be useful to detect the spatial WM network with appropriate task during tumor exploration.

Organization principles in visual working memory: Evidence from sequential stimulus display

Although the mechanisms of visual working memory (VWM) have been studied extensively in recent years, the active property of VWM has received less attention. In the current study, we examined how VWM integrates sequentially presented stimuli by focusing on the role of Gestalt principles, which are important organizing principles in perceptual integration. We manipulated the level of Gestalt cues among three or four sequentially presented objects that were memorized. The Gestalt principle could not emerge unless all the objects appeared together. We distinguished two hypotheses: a perception-alike hypothesis and an encoding-specificity hypothesis. The former predicts that the Gestalt cue will play a role in information integration within VWM; the latter predicts that the Gestalt cue will not operate within VWM. In four experiments, we demonstrated that collinearity (Experiment 1) and closure (Experiment 2) cues significantly improved VWM performance, and this facilitation was not affected by the testing manner (Experiment 3) or by adding extra colors to the memorized objects (Experiment 4). Finally, we re-established the Gestalt cue benefit with similarity cues (Experiment 5). These findings together suggest that VWM realizes and uses potential Gestalt principles within the stored representations, supporting a perception-alike hypothesis.

ERP markers of target selection discriminate children with high vs. low working memory capacity

Selective attention enables enhancing a subset out of multiple competing items to maximize the capacity of our limited visual working memory (VWM) system. Multiple behavioral and electrophysiological studies have revealed the cognitive and neural mechanisms supporting adults’ selective attention of visual percepts for encoding in VWM. However, research on children is more limited. What are the neural mechanisms involved in children’s selection of incoming percepts in service of VWM? Do these differ from the ones subserving adults’ selection? Ten-year-olds and adults used a spatial arrow cue to select a colored item for later recognition from an array of four colored items. The temporal dynamics of selection were investigated through EEG signals locked to the onset of the memory array. Both children and adults elicited significantly more negative activity over posterior scalp locations contralateral to the item to-be-selected for encoding (N2pc). However, this activity was elicited later and for longer in children compared to adults. Furthermore, although children as a group did not elicit a significant N2pc during the time-window in which N2pc was elicited in adults, the magnitude of N2pc during the “adult time-window” related to their behavioral performance during the later recognition phase of the task. This in turn highlights how children’s neural activity subserving attention during encoding relates to better subsequent VWM performance. Significant differences were observed when children were divided into groups of high vs. low VWM capacity as a function of cueing benefit. Children with large cue benefits in VWM capacity elicited an adult-like contralateral negativity following attentional selection of the to-be-encoded item, whereas children with low VWM capacity did not. These results corroborate the close coupling between selective attention and VWM from childhood and elucidate further the attentional mechanisms constraining VWM performance in children.

Towards a ternary NIRS-BCI: single-trial classification of verbal fluency task, Stroop task and unconstrained rest

OBJECTIVE

The majority of near-infrared spectroscopy (NIRS) brain-computer interface (BCI) studies have investigated binary classification problems. Limited work has considered differentiation of more than two mental states, or multi-class differentiation of higher-level cognitive tasks using measurements outside of the anterior prefrontal cortex. Improvements in accuracies are needed to deliver effective communication with a multi-class NIRS system. We investigated the feasibility of a ternary NIRS-BCI that supports mental states corresponding to verbal fluency task (VFT) performance, Stroop task performance, and unconstrained rest using prefrontal and parietal measurements.

APPROACH

Prefrontal and parietal NIRS signals were acquired from 11 able-bodied adults during rest and performance of the VFT or Stroop task. Classification was performed offline using bagging with a linear discriminant base classifier trained on a 10 dimensional feature set.

MAIN RESULTS

VFT, Stroop task and rest were classified at an average accuracy of 71.7% ± 7.9%. The ternary classification system provided a statistically significant improvement in information transfer rate relative to a binary system controlled by either mental task (0.87 ± 0.35 bits/min versus 0.73 ± 0.24 bits/min).

SIGNIFICANCE

These results suggest that effective communication can be achieved with a ternary NIRS-BCI that supports VFT, Stroop task and rest via measurements from the frontal and parietal cortices. Further development of such a system is warranted. Accurate ternary classification can enhance communication rates offered by NIRS-BCIs, improving the practicality of this technology.

The Neural Dynamics of Fronto-Parietal Networks in Childhood Revealed using Magnetoencephalography

Our ability to hold information in mind is limited, requires a high degree of cognitive control, and is necessary for many subsequent cognitive processes. Children, in particular, are highly variable in how, trial-by-trial, they manage to recruit cognitive control in service of memory. Fronto-parietal networks, typically recruited under conditions where this cognitive control is needed, undergo protracted development. We explored, for the first time, whether dynamic changes in fronto-parietal activity could account for children's variability in tests of visual short-term memory (VSTM). We recorded oscillatory brain activity using magnetoencephalography (MEG) as 9- to 12-year-old children and adults performed a VSTM task. We combined temporal independent component analysis (ICA) with general linear modeling to test whether the strength of fronto-parietal activity correlated with VSTM performance on a trial-by-trial basis. In children, but not adults, slow frequency theta (4-7 Hz) activity within a right lateralized fronto-parietal network in anticipation of the memoranda predicted the accuracy with which those memory items were subsequently retrieved. These findings suggest that inconsistent use of anticipatory control mechanism contributes significantly to trial-to-trial variability in VSTM maintenance performance.

Differences in fMRI intersubject correlation while viewing unedited and edited videos of dance performance

Intersubject correlation (ISC) analysis of functional magnetic resonance imaging (fMRI) data provides insight into how continuous streams of sensory stimulation are processed by groups of observers. Although edited movies are frequently used as stimuli in ISC studies, there has been little direct examination of the effect of edits on the resulting ISC maps. In this study we showed 16 observers two audiovisual movie versions of the same dance. In one experimental condition there was a continuous view from a single camera (Unedited condition) and in the other condition there were views from different cameras (Edited condition) that provided close up views of the feet or face and upper body. We computed ISC maps for each condition, as well as created a map that showed the difference between the conditions. The results from the Unedited and Edited maps largely overlapped in the occipital and temporal cortices, although more voxels were found for the Edited map. The difference map revealed greater ISC for the Edited condition in the Postcentral Gyrus, Lingual Gyrus, Precentral Gyrus and Medial Frontal Gyrus, while the Unedited condition showed greater ISC in only the Superior Temporal Gyrus. These findings suggest that the visual changes associated with editing provide a source of correlation in maps obtained from edited film, and highlight the utility of using maps to evaluate the difference in ISC between conditions.

Single-trial classification of near-infrared spectroscopy signals arising from multiple cortical regions

Near-infrared spectroscopy (NIRS) brain-computer interface (BCI) studies have primarily made use of measurements taken from a single cortical area. In particular, the anterior prefrontal cortex has been the key area used for detecting higher-level cognitive task performance. However, mental task execution typically requires coordination between several, spatially-distributed brain regions. We investigated the value of expanding the area of interrogation to include NIRS measurements from both the prefrontal and parietal cortices to decode mental states. Hemodynamic activity was monitored at 46 locations over the prefrontal and parietal cortices using a continuous-wave near-infrared spectrometer while 11 able-bodied adults rested or performed either the verbal fluency task (VFT) or Stroop task. Offline classification was performed for the three possible binary problems using 25 iterations of bagging with a linear discriminant base classifier. Classifiers were trained on a 10 dimensional feature set. When all 46 measurement locations were considered for classification, average accuracies of 80.4±7.0%, 82.4±7.6%, and 82.8±5.9% in differentiating VFT vs rest, Stroop vs rest and VFT vs Stroop, respectively, were obtained. Relative to using measurements from the anterior PFC alone, an overall average improvement of 11.3% was achieved. Utilizing NIRS measurements from the prefrontal and parietal cortices can be of value in classifying mental states involving working memory and attention. NIRS-BCI accuracies may be improved by incorporating measurements from several, distinct cortical regions, rather than a single area alone. Further development of an NIRS-BCI supporting combinations of VFT, Stroop task and rest states is also warranted.

The working memory Ponzo illusion: Involuntary integration of visuospatial information stored in visual working memory

Visual working memory (VWM) has been traditionally viewed as a mental structure subsequent to visual perception that stores the final output of perceptual processing. However, VWM has recently been emphasized as a critical component of online perception, providing storage for the intermediate perceptual representations produced during visual processing. This interactive view holds the core assumption that VWM is not the terminus of perceptual processing; the stored visual information rather continues to undergo perceptual processing if necessary. The current study tests this assumption, demonstrating an example of involuntary integration of the VWM content, by creating the Ponzo illusion in VWM: when the Ponzo illusion figure was divided into its individual components and sequentially encoded into VWM, the temporally separated components were involuntarily integrated, leading to the distorted length perception of the two horizontal lines. This VWM Ponzo illusion was replicated when the figure components were presented in different combinations and presentation order. The magnitude of the illusion was significantly correlated between VWM and perceptual versions of the Ponzo illusion. These results suggest that the information integration underling the VWM Ponzo illusion is constrained by the laws of visual perception and similarly affected by the common individual factors that govern its perception. Thus, our findings provide compelling evidence that VWM functions as a buffer serving perceptual processes at early stages.

Rivalry of homeostatic and sensory-evoked emotions: Dehydration attenuates olfactory disgust and its neural correlates

Neural correlates have been described for emotions evoked by states of homeostatic imbalance (e.g. thirst, hunger, and breathlessness) and for emotions induced by external sensory stimulation (such as fear and disgust). However, the neurobiological mechanisms of their interaction, when they are experienced simultaneously, are still unknown. We investigated the interaction on the neurobiological and the perceptional level using subjective ratings, serum parameters, and functional magnetic resonance imaging (fMRI) in a situation of emotional rivalry, when both a homeostatic and a sensory-evoked emotion were experienced at the same time. Twenty highly dehydrated male subjects rated a disgusting odor as significantly less repulsive when they were thirsty. On the neurobiological level, we found that this reduction in subjective disgust during thirst was accompanied by a significantly reduced neural activity in the insular cortex, a brain area known to be considerably involved in processing of disgust. Furthermore, during the experience of disgust in the satiated condition, we observed a significant functional connectivity between brain areas responding to the disgusting odor, which was absent during the stimulation in the thirsty condition. These results suggest interference of conflicting emotions: an acute homeostatic imbalance can attenuate the experience of another emotion evoked by the sensory perception of a potentially harmful external agent. This finding offers novel insights with regard to the behavioral relevance of biologically different types of emotions, indicating that some types of emotions are more imperative for behavior than others. As a general principle, this modulatory effect during the conflict of homeostatic and sensory-evoked emotions may function to safeguard survival.

Practopoiesis: or how life fosters a mind

The mind is a biological phenomenon. Thus, biological principles of organization should also be the principles underlying mental operations. Practopoiesis states that the key for achieving intelligence through adaptation is an arrangement in which mechanisms laying at a lower level of organization, by their operations and interaction with the environment, enable creation of mechanisms laying at a higher level of organization. When such an organizational advance of a system occurs, it is called a traverse. A case of traverse is when plasticity mechanisms (at a lower level of organization), by their operations, create a neural network anatomy (at a higher level of organization). Another case is the actual production of behavior by that network, whereby the mechanisms of neuronal activity operate to create motor actions. Practopoietic theory explains why the adaptability of a system increases with each increase in the number of traverses. With a larger number of traverses, a system can be relatively small and yet, produce a higher degree of adaptive/intelligent behavior than a system with a lower number of traverses. The present analyses indicate that the two well-known traverses - neural plasticity and neural activity - are not sufficient to explain human mental capabilities. At least one additional traverse is needed, which is named anapoiesis for its contribution in reconstructing knowledge e.g., from long-term memory into working memory. The conclusions bear implications for brain theory, the mind-body explanatory gap, and developments of artificial intelligence technologies.

Consolidation time affects performance and neural activity during visual working memory

We tested the effects of variation of stimulus onset asynchrony (SOA) on visual working memory (WM) performance across different load levels and the underlying brain activation patterns using functional magnetic resonance imaging (fMRI) in 48 healthy participants. Participants were instructed to memorise arrays of coloured squares and had to perform a match/non-match judgement on a probe stimulus after a jittered delay. We presented visual pattern masks at four SOAs after the offset of the memory array (100 ms, 200 ms, 400 ms, and 800 ms). Memory performance decreased with increased load and shortened SOA. Brain activation data showed significant effects of load (during encoding and retrieval), SOA (retrieval) and an interaction of load by SOA (encoding), mainly in frontal and parietal areas. There was also a direct relationship between successfully stored items and activation in the right inferior parietal lobule and the left middle frontal gyrus. The neurobehavioral results suggest that the frontal regions, together with the inferior parietal lobe, are associated with successful WM performance, especially under the most challenging conditions of high load and short SOAs.

Does shape discrimination by the mouth activate the parietal and occipital lobes? - near-infrared spectroscopy study

A cross-modal association between somatosensory tactile sensation and parietal and occipital activities during Braille reading was initially discovered in tests with blind subjects, with sighted and blindfolded healthy subjects used as controls. However, the neural background of oral stereognosis remains unclear. In the present study, we investigated whether the parietal and occipital cortices are activated during shape discrimination by the mouth using functional near-infrared spectroscopy (fNIRS). Following presentation of the test piece shape, a sham discrimination trial without the test pieces induced posterior parietal lobe (BA7), extrastriate cortex (BA18, BA19), and striate cortex (BA17) activation as compared with the rest session, while shape discrimination of the test pieces markedly activated those areas as compared with the rest session. Furthermore, shape discrimination of the test pieces specifically activated the posterior parietal cortex (precuneus/BA7), extrastriate cortex (BA18, 19), and striate cortex (BA17), as compared with sham sessions without a test piece. We concluded that oral tactile sensation is recognized through tactile/visual cross-modal substrates in the parietal and occipital cortices during shape discrimination by the mouth.

Brain Mechanisms of Social Threat Effects on Working Memory

Social threat can have adverse effects on cognitive performance, but the brain mechanisms underlying its effects are poorly understood. We investigated the effects of social evaluative threat on working memory (WM), a core component of many important cognitive capabilities. Social threat impaired WM performance during an N-back task and produced widespread reductions in activation in lateral prefrontal cortex and intraparietal sulcus (IPS), among other regions. In addition, activity in frontal and parietal regions predicted WM performance, and mediation analyses identified regions in the bilateral IPS that mediated the performance-impairing effects of social threat. Social threat also decreased connectivity between the IPS and dorsolateral prefrontal cortex, while increasing connectivity between the IPS and the ventromedial prefrontal cortex, a region strongly implicated in the generation of autonomic and emotional responses. Finally, cortisol response to the stressor did not mediate WM impairment but was rather associated with protective effects. These results provide a basis for understanding interactions between social and cognitive processes at a neural systems level.

Cortical Representations of Cognitive Control and Working Memory Are Dependent Yet Non-Interacting

Cognitive control (CC) and working memory (WM) are concurrently necessary for adaptive human behavior. These processes are thought to rely on similar neural mechanisms, yet little is known of the potential competitive or cooperative brain dynamics that support their concurrent engagement during complex behavioral tasks. Here, statistical interactions (synergy/competition) and dependencies (correlations) in brain function related to CC and WM were measured using functional magnetic resonance imaging. Twenty-five healthy adults performed a novel factorial cognitive paradigm, in which a 2-back verbal WM task was combined with the multisource interference task. Overlapping main effects in neural activation were evident in all regions of the "cognitive control network," together with robust behavioral main effects. However, no significant behavioral or cortical interaction effects were apparent. Conversely, robust positive correlations between the 2 main effects were evident within many components of the network. The results offer robust evidence that the neural representations of WM and CC are statistically dependent, but do not compete. These findings support the notion that CC and WM demands may be dynamically and flexibly encoded within a common brain network to support the efficient production of adaptive behavior across diverse task contexts.

Neural effects of cognitive control load on auditory selective attention

Whether and how working memory disrupts or alters auditory selective attention is unclear. We compared simultaneous event-related potentials (ERP) and functional magnetic resonance imaging (fMRI) responses associated with task-irrelevant sounds across high and low working memory load in a dichotic-listening paradigm. Participants performed n-back tasks (1-back, 2-back) in one ear (Attend ear) while ignoring task-irrelevant speech sounds in the other ear (Ignore ear). The effects of working memory load on selective attention were observed at 130-210ms, with higher load resulting in greater irrelevant syllable-related activation in localizer-defined regions in auditory cortex. The interaction between memory load and presence of irrelevant information revealed stronger activations primarily in frontal and parietal areas due to presence of irrelevant information in the higher memory load. Joint independent component analysis of ERP and fMRI data revealed that the ERP component in the N1 time-range is associated with activity in superior temporal gyrus and medial prefrontal cortex. These results demonstrate a dynamic relationship between working memory load and auditory selective attention, in agreement with the load model of attention and the idea of common neural resources for memory and attention.

The When and Where of Working Memory Dysfunction in Early-Onset Schizophrenia-A Functional Magnetic Resonance Imaging Study

Behavioral evidence indicates that working memory (WM) in schizophrenia is already impaired at the encoding stage. However, the neurophysiological basis of this primary deficit remains poorly understood. Using event-related fMRI, we assessed differences in brain activation and functional connectivity during the encoding, maintenance and retrieval stages of a visual WM task with 3 levels of memory load in 17 adolescents with early-onset schizophrenia (EOS) and 17 matched controls. The amount of information patients could store in WM was reduced at all memory load levels. During encoding, activation in left ventrolateral prefrontal cortex (VLPFC) and extrastriate visual cortex, which in controls positively correlated with the amount of stored information, was reduced in patients. Additionally, patients showed disturbed functional connectivity between prefrontal and visual areas. During retrieval, right inferior VLPFC hyperactivation was correlated with hypoactivation of left VLPFC in patients during encoding. Visual WM encoding is disturbed by a failure to adequately engage a visual-prefrontal network critical for the transfer of perceptual information into WM. Prefrontal hyperactivation appears to be a secondary consequence of this primary deficit. Isolating the component processes of WM can lead to more specific neurophysiological markers for translational efforts seeking to improve the treatment of cognitive dysfunction in schizophrenia.