Components of verbal working memory: evidence from neuroimaging

Recovery of Verbal Working Memory Depends on Left Hemisphere White Matter Tracts

Researchers propose that the recovery of language function following stroke depends on the recruitment of perilesional regions in the left hemisphere and/or homologous regions in the right hemisphere (Kiran, 2012). Many investigations of recovery focus on changes in gray matter regions (e.g., Turkeltaub et al., 2011), whereas relatively few examine white matter tracts (e.g., Schlaug et al., 2009) and none address the role of these tracts in the recovery of verbal working memory (WM). The present study addressed these gaps, examining the role of left vs. right hemisphere tracts in the longitudinal recovery of phonological and semantic WM. For 24 individuals with left hemisphere stroke, we assessed WM performance within one week of stroke (acute timepoint) and at more than six months after stroke (chronic timepoint). To address whether recovery depends on the recruitment of left or right hemisphere tracts, we assessed whether changes in WM were related to the integrity of five white matter tracts in the left hemisphere which had been implicated previously in verbal WM and their right hemisphere analogues. Behavioral results showed significant improvement in semantic but not phonological WM from the acute to chronic timepoints. Improvements in semantic WM significantly correlated with tract integrity as measured by functional anisotropy in the left direct segment of the arcuate fasciculus, inferior fronto-occipital fasciculus and inferior longitudinal fasciculus. The results confirm the role of white matter tracts in language recovery and support the involvement of the left rather than right hemisphere in the recovery of semantic WM.

Brain activation patterns in patients with post-stroke cognitive impairment during working memory task: a functional near-infrared spectroscopy study

Objective

To explore the activation patterns in the frontal cortex of patients with post-stroke cognitive impairment during the execution of working memory tasks.

Methods

15 patients with post-stroke cognitive impairment, 17 patients without cognitive impairment, and 15 healthy controls of similar age and sex were included. All participants under-went immediate recall task testing and near-infrared spectroscopy imaging to measure frontal cortex activation during the task.

Results

The healthy control group performed the best in the immediate recall task, followed by the post-stroke non-cognitive impairment group. The post-stroke cognitive impairment group had the poorest performance. The near-infrared spectroscopy results revealed that during the immediate recall task, the healthy control group primarily activated the left frontal lobe region. In contrast, post-stroke patients exhibited reduced activation in the left frontal lobe and increased activation in the right frontal cortex, particularly in the right frontopolar and orbitofrontal regions, with the post-stroke cognitive impairment group displaying the most pronounced changes.

Conclusion

Patients with post-stroke cognitive impairment exhibit reduced activation in the left prefrontal cortex during the working memory tasks. They rely on compensatory activation in the right prefrontal cortex, particularly in the frontopolar and orbitofrontal cortex, to successfully complete the task.

Cognitive brain activity before and after surgery in meningioma patients

Neuropsychological studies have demonstrated that meningioma patients frequently exhibit cognitive deficits before surgery and show only limited improvement after surgery. Combining neuropsychological with functional imaging measurements can shed more light on the impact of surgery on cognitive brain function. We aimed to evaluate whether surgery affects cognitive brain activity in such a manner that it may mask possible changes in cognitive functioning measured by neuropsychological tests. Twenty-three meningioma patients participated in a fMRI measurement using a verbal working memory task as well as three neuropsychological tests focused on working memory, just before and 3 months after surgery. A region of interest based fMRI analysis was used to examine cognitive brain activity at these timepoints within the central executive network and default mode network. Neuropsychological assessment showed impaired cognitive functioning before as well as 3 months after surgery. Neuropsychological test scores, in-scanner task performance as well as brain activity within the central executive and default mode network were not significantly different between both timepoints. Our results indicate that surgery does not significantly affect cognitive brain activity in meningioma patients the first few months after surgery. Therefore, the lack of cognitive improvement after surgery is not likely the result of compensatory processes in the brain. Cognitive deficits that are already present before surgery appear to be persistent after surgery and a considerable recovery period. Our study shows potential leads that comprehensive cognitive evaluation can be of added value so that cognitive functioning may become a more prominent factor in clinical decision making.

Neural mechanisms of sentence production: a volumetric study of primary progressive aphasia

Studies on the neural bases of sentence production have yielded mixed results, partly due to differences in tasks and participant types. In this study, 101 individuals with primary progressive aphasia (PPA) were evaluated using a test that required spoken production following an auditory prime (Northwestern Assessment of Verbs and Sentences-Sentence Production Priming Test, NAVS-SPPT), and one that required building a sentence by ordering word cards (Northwestern Anagram Test, NAT). Voxel-Based Morphometry revealed that gray matter (GM) volume in left inferior/middle frontal gyri (L IFG/MFG) was associated with sentence production accuracy on both tasks, more so for complex sentences, whereas, GM volume in left posterior temporal regions was exclusively associated with NAVS-SPPT performance and predicted by performance on a Digit Span Forward (DSF) task. Verb retrieval deficits partly mediated the relationship between L IFG/MFG and performance on the NAVS-SPPT. These findings underscore the importance of L IFG/MFG for sentence production and suggest that this relationship is partly accounted for by verb retrieval deficits, but not phonological loop integrity. In contrast, it is possible that the posterior temporal cortex is associated with auditory short-term memory ability, to the extent that DSF performance is a valid measure of this in aphasia.

The neural substrates of transdiagnostic cognitive-linguistic heterogeneity in primary progressive aphasia

BACKGROUND

Clinical variants of primary progressive aphasia (PPA) are diagnosed based on characteristic patterns of language deficits, supported by corresponding neural changes on brain imaging. However, there is (i) considerable phenotypic variability within and between each diagnostic category with partially overlapping profiles of language performance between variants and (ii) accompanying non-linguistic cognitive impairments that may be independent of aphasia magnitude and disease severity. The neurobiological basis of this cognitive-linguistic heterogeneity remains unclear. Understanding the relationship between these variables would improve PPA clinical/research characterisation and strengthen clinical trial and symptomatic treatment design. We address these knowledge gaps using a data-driven transdiagnostic approach to chart cognitive-linguistic differences and their associations with grey/white matter degeneration across multiple PPA variants.

METHODS

Forty-seven patients (13 semantic, 15 non-fluent, and 19 logopenic variant PPA) underwent assessment of general cognition, errors on language performance, and structural and diffusion magnetic resonance imaging to index whole-brain grey and white matter changes. Behavioural data were entered into varimax-rotated principal component analyses to derive orthogonal dimensions explaining the majority of cognitive variance. To uncover neural correlates of cognitive heterogeneity, derived components were used as covariates in neuroimaging analyses of grey matter (voxel-based morphometry) and white matter (network-based statistics of structural connectomes).

RESULTS

Four behavioural components emerged: general cognition, semantic memory, working memory, and motor speech/phonology. Performance patterns on the latter three principal components were in keeping with each variant's characteristic profile, but with a spectrum rather than categorical distribution across the cohort. General cognitive changes were most marked in logopenic variant PPA. Regardless of clinical diagnosis, general cognitive impairment was associated with inferior/posterior parietal grey/white matter involvement, semantic memory deficits with bilateral anterior temporal grey/white matter changes, working memory impairment with temporoparietal and frontostriatal grey/white matter involvement, and motor speech/phonology deficits with inferior/middle frontal grey matter alterations.

CONCLUSIONS

Cognitive-linguistic heterogeneity in PPA closely relates to individual-level variations on multiple behavioural dimensions and grey/white matter degeneration of regions within and beyond the language network. We further show that employment of transdiagnostic approaches may help to understand clinical symptom boundaries and reveal clinical and neural profiles that are shared across categorically defined variants of PPA.

Positive emotion up-regulation is resistant to working memory load: An electrocortical investigation of reappraisal and savoring

Studies of emotion regulation to-date have mostly focused on negative emotion down-regulation, leaving positive emotion up-regulation poorly understood, particularly regarding factors that may modulate its success. While reappraisal and savoring have been shown to be effective at increasing electrocortical and subjective response to pictures in controlled laboratory settings, it remains unclear whether individuals can effectively enact these techniques to willfully increase positive emotions in everyday life when faced with other concurrent distractions/demands. Here, we used the late positive potential (LPP), an electrocortical measure that is larger for emotional compared to neutral stimuli, to assess the effect of working memory (WM) load on individuals' ability to reappraise or savor positive pictures. Seventy-six participants were randomly assigned to use either reappraisal or savoring to up-regulate positive emotion to pictures. Following training, participants engaged in a positive emotion up-regulation task interspersed with high and low WM load trials, while EEG was recorded. Frequentist and Bayesian statistics showed that although high WM load seemed to consume resources and reduced picture processing overall, it did not interfere with the enhancement of the LPP via positive emotion up-regulation. Nonetheless, WM performance (especially on high-load trials) was worse when participants were engaged in positive emotion up-regulation. Therefore, while both techniques appear to be effective under concurrent WM load, positive emotion up-regulation may interfere with other ongoing tasks.

Strategies, debates, and adversarial collaboration in working memory: The 51st Bartlett Lecture

Frederic Bartlett championed the importance of individual strategy differences when remembering details of events. I will describe how long-running theoretical debates in the area of working memory may be resolved by considering differences across participants in the strategies that they use when performing cognitive tasks, and through adversarial collaboration between rival laboratories. In common with the established view within experimental cognitive psychology, I assume that adults have a range of cognitive functions, evolved for everyday life. However, I will present evidence showing that these functions can be engaged selectively for laboratory tasks, and that how they are deployed may differ between and within individuals for the same task. Reliance on aggregate data, while treating inter- and intra-participant variability in data patterns as statistical noise, may lead to misleading conclusions about theoretical principles of cognition, and of working memory in particular. Moreover, different theoretical perspectives may be focused on different levels of explanation and different theoretical goals rather than being mutually incompatible. Yet researchers from contrasting theoretical frameworks pursue science as a competition, rarely do researchers from competing labs work in collaboration, and debates self-perpetuate. These approaches to research can stall debate resolution and generate ever-increasing scientific diversity rather than scientific progress. The article concludes by describing a recent extended adversarial collaboration (the WoMAAC project) focused on theoretical contrasts in working memory, and illustrates how this approach to conducting research may help resolve scientific debate and facilitate scientific advance.

Cognitive neuroscience perspective on memory: overview and summary

This paper explores memory from a cognitive neuroscience perspective and examines associated neural mechanisms. It examines the different types of memory: working, declarative, and non-declarative, and the brain regions involved in each type. The paper highlights the role of different brain regions, such as the prefrontal cortex in working memory and the hippocampus in declarative memory. The paper also examines the mechanisms that underlie the formation and consolidation of memory, including the importance of sleep in the consolidation of memory and the role of the hippocampus in linking new memories to existing cognitive schemata. The paper highlights two types of memory consolidation processes: cellular consolidation and system consolidation. Cellular consolidation is the process of stabilizing information by strengthening synaptic connections. System consolidation models suggest that memories are initially stored in the hippocampus and are gradually consolidated into the neocortex over time. The consolidation process involves a hippocampal-neocortical binding process incorporating newly acquired information into existing cognitive schemata. The paper highlights the role of the medial temporal lobe and its involvement in autobiographical memory. Further, the paper discusses the relationship between episodic and semantic memory and the role of the hippocampus. Finally, the paper underscores the need for further research into the neurobiological mechanisms underlying non-declarative memory, particularly conditioning. Overall, the paper provides a comprehensive overview from a cognitive neuroscience perspective of the different processes involved in memory consolidation of different types of memory.

The relationship between diurnal cortisol slope and cognitive development among children maltreated as infants

Little is known about the role of hypothalamic-pituitary-adrenal (HPA) axis functioning for children's cognitive development, especially among vulnerable groups. The current study explores the relationship between diurnal cortisol slope and cognitive outcomes among children at the ages of 5 and 6 who have been maltreated as infants and involved with child protective services, using data from the National Survey of Child and Adolescent Well-Being (NSCAW) I (N=158). Multiple regression analyses showed that a greater decline in salivary cortisol from morning to evening was positively associated with scores on applied problems and expressive communication, even after adjustment for confounding. It was also associated with lower odds of cognitive disability. There were null associations with letter-word identification, passage comprehension, auditory comprehension, matrices, and vocabulary. Results suggest that children involved with child protective services as infants, and thus exposed early to likely 'toxic' levels of stressors, may face dysregulation of the HPA axis and particular difficulties in some aspects of cognitive function. Potential explanations and implications for policy are discussed.

Transcranial direct current stimulation during a prolonged cognitive task: the effect on cognitive and shooting performances in professional female basketball players

The negative effect of prolonged cognitive demands on psychomotor skills in athletes has been demonstrated. Transcranial direct current stimulation (tDCS) could be used to mitigate this effect. This study examined the effects of tDCS over the left dorsolateral prefrontal cortex (DLPFC) during a 30-min inhibitory Stroop task on cognitive and shooting performances of professional female basketball players. Following a randomised, double-blinded, sham-controlled, cross-over design, players were assigned to receive anodal tDCS (a-tDCS, 2 mA for 20 min) or sham-tDCS in two different sessions. Data from 8 players were retained for analysis. Response Time decreased significantly over time (p < 0.001; partial η² = 0.44; no effect of condition, or condition vs. time interaction). No difference in mean accuracy and shooting performance was observed between tDCS conditions. The results suggest that a-tDCS exert no additional benefits in reducing the negative effects of prolonged cognitive demands on technical performance compared to sham (placebo).Practitioner summary: Prolonged cognitive demands can negatively affect the athletes' performance. We tested whether transcranial direct current stimulation (tDCS) over the left dorsolateral prefrontal cortex (DLPFC) could attenuate these effects on cognitive and shooting performance in professional female basketball players. However, tDCS did not exert any additional benefits compared to sham.Abbreviations: tDCS: transcranial direct current stimulation; a-tDCS: anodal transcranial direct current stimulation; PFC: prefrontal cortex; DLPFC: dorsolateral prefrontal cortex; PCT: prolonged cognitive task; TT: time trial; RT: response time; NASA-TLX: National Aeronautics and Space Administration Task Load Index; RPE: ratings of perceived exertion; CR-10 scale: category rating scale; EEG: electroencephalogram; AU: arbitrary units.

Foreign speech sound discrimination and associative word learning lead to a fast reconfiguration of resting-state networks

Learning new words in an unfamiliar language is a complex endeavor that requires the orchestration of multiple perceptual and cognitive functions. Although the neural mechanisms governing word learning are becoming better understood, little is known about the predictive value of resting-state (RS) metrics for foreign word discrimination and word learning attainment. In addition, it is still unknown which of the multistep processes involved in word learning have the potential to rapidly reconfigure RS networks. To address these research questions, we used electroencephalography (EEG), measured forty participants, and examined scalp-based power spectra, source-based spectral density maps and functional connectivity metrics before (RS1), in between (RS2) and after (RS3) a series of tasks which are known to facilitate the acquisition of new words in a foreign language, namely word discrimination, word-referent mapping and semantic generalization. Power spectra at the scalp level consistently revealed a reconfiguration of RS networks as a function of foreign word discrimination (RS1 vs. RS2) and word learning (RS1 vs. RS3) tasks in the delta, lower and upper alpha, and upper beta frequency ranges. Otherwise, functional reconfigurations at the source level were restricted to the theta (spectral density maps) and to the lower and upper alpha frequency bands (spectral density maps and functional connectivity). Notably, scalp RS changes related to the word discrimination tasks (difference between RS2 and RS1) correlated with word discrimination abilities (upper alpha band) and semantic generalization performance (theta and upper alpha bands), whereas functional changes related to the word learning tasks (difference between RS3 and RS1) correlated with word discrimination scores (lower alpha band). Taken together, these results highlight that foreign speech sound discrimination and word learning have the potential to rapidly reconfigure RS networks at multiple functional scales.

Working memory processing deficit associated with a nonlinear response pattern of the anterior cingulate cortex in first-episode and drug-naïve schizophrenia

Impaired working memory (WM) is a core neuropsychological dysfunction of schizophrenia, however complex interactions among the information storage, information processing and attentional aspects of WM tasks make it difficult to uncover the psychophysiological mechanisms of this deficit. Thirty-six first-episode and drug-naïve schizophrenia and 29 healthy controls (HCs) were enrolled in this study. Here, we modified a WM task to isolate components of WM storage and WM processing, while also varying the difficulty level (load) of the task to study regional differences in load-specific activation using mixed effects models, and its relationship to distributed gene expression. Comparing patients with HCs, we found both attentional deficits and WM deficits, with WM processing being more impaired than WM storage in patients. In patients, but not controls, a linear modulation of brain activation was observed mainly in the frontoparietal and dorsal attention networks. In controls, an inverted U-shaped response pattern was identified in the left anterior cingulate cortex. The vertex of this inverted U-shape was lower in patients than controls, and a left-shifting axis of symmetry was associated with better WM performance in patients. Both the above linear and U-shaped modulation effects were associated with the expressions of the genes enriched in the dopamine neurotransmitter system across all cortical brain regions. These findings indicate that a WM processing deficit is evident in schizophrenia from an early stage before antipsychotic treatment, and associated with a dopamine pathway related aberration in nonlinear response pattern at the cingulate cortex when processing WM load.

The effect of backpack weight on the performance of basic short-term/working memory tasks while walking along a pre-determined route

This study investigated possible backpack weight effects on the performance of three basic short-term/working memory (STM/WM) tasks conducted concurrently with the physical task of route walking. The STM/WM tasks were the Corsi block-tapping, digit span, and 3-back tasks, and, were employed to examine the visuo-spatial sketchpad, phonological loop and central executive components of the WM system. Four backpack weight levels (0%, 15%, 25% and 40% of body mass) were considered. Thirty participants conducted the three experimental tasks requiring physical-cognitive multitasking. Data analyses revealed that: (1) increased backpack weight resulted in decreases in the performance of the Corsi block-tapping and the 3-back task, but (2) backpack weight did not significantly affect the digit span task performance. The study results suggest that reducing backpack weight could benefit the performance of various cognitive tasks during route walking. The study findings may be useful for the ergonomics design of body-worn equipment and human-system interfaces.Practitioner summary: This study examined the backpack weight effects on the performance of three basic short-term/working memory tasks conducted concurrently with the physical task of route walking. The study revealed that reducing backpack weight could benefit various cognitive tasks during physical-cognitive multitasking, especially cognitive tasks that require visuospatial processing and executive control.

White Matter Correlates of Domain-Specific Working Memory

Prior evidence suggests domain-specific working memory (WM) buffers for maintaining phonological (i.e., speech sound) and semantic (i.e., meaning) information. The phonological WM buffer’s proposed location is in the left supramarginal gyrus (SMG), whereas semantic WM has been related to the left inferior frontal gyrus (IFG), the middle frontal gyrus (MFG), and the angular gyrus (AG). However, less is known about the white matter correlates of phonological and semantic WM. We tested 45 individuals with left hemisphere brain damage on single word processing, phonological WM, and semantic WM tasks and obtained T1 and diffusion weighted neuroimaging. Virtual dissections were performed for each participants’ arcuate fasciculus (AF), inferior fronto-occipital fasciculus (IFOF), inferior longitudinal fasciculus (ILF), middle longitudinal fasciculus (MLF), and uncinate fasciculus (UF), which connect the proposed domain-specific WM buffers with perceptual or processing regions. The results showed that the left IFOF and the posterior segment of the AF were related to semantic WM performance. Phonological WM was related to both the left ILF and the whole AF. This work informs our understanding of the white matter correlates of WM, especially semantic WM, which has not previously been investigated. In addition, this work helps to adjudicate between theories of verbal WM, providing some evidence for separate pathways supporting phonological and semantic WM.

Does high-definition transcranial direct current stimulation change brain electrical activity in professional female basketball players during free-throw shooting?

Differentiated brain activation in high-performance athletes supports neuronal mechanisms relevant to sports performance. Preparation for the motor action involves cortical and sub-cortical regions that can be non-invasively modulated by electrical current stimulation. This study aimed to investigate the effect of high-definition transcranial direct current stimulation (HD-tDCS) on electrical brain activity in professional female basketball players during free-throw shooting. Successful free-throw shooting (n = 2,361) from seven professional female basketball players was analyzed during two experimental conditions (HD-tDCS cathodic and sham) separated by 72 h. Three spectral bio-markers, Power Ratio Index (PRI), Delta Alpha Ratio (DAR), and Theta Beta Ratio (TBR) were measured (electroencephalography [EEG] Brain Products). Multi-channel HD-tDCS was applied for 20 min, considering current location and intensity for cathodic stimulation: FCC1h, AFF5h, AFF1h (-0.5 mA each), and FCC5h (ground). The within EEG analyses (pre and post HD-tDCS) of frontal channels (Fp1, Fp2, F3, F4, FC1, FC3) for 1 second epoch pre-shooting, showed increases in PRI (p < 0.001) and DAR (p < 0.001) for HD-tDCS cathodic condition, and in TBR for both conditions (cathodic, p = 0.01; sham, p = 0.002). Sub-group analysis divided the sample into less (n = 3; LSG) and more (n = 4; MSG) stable free-throw-shooting performers and revealed that increases in pre to post HD-tDCS in PRI only occurred for the LSG. These results suggest that the effect of HD-tDCS may induce changes in slow frontal frequency brain activities and that this alteration seems to be greater for players demonstrating a less stable free-throw shooting performance.

Age-Specific Activation Patterns and Inter-Subject Similarity During Verbal Working Memory Maintenance and Cognitive Reserve

Cognitive Reserve (CR), according to a recent consensus definition of the NIH-funded Reserve and Resilience collaboratory, is constituted by any mechanism contributing to cognitive performance beyond, or interacting with, brain structure in the widest sense. To identity multivariate activation patterns fulfilling this postulate, we investigated a verbal Sternberg fMRI task and imaged 181 people with age coverage in the ranges 20-30 (44 participants) and 55-70 (137 participants). Beyond task performance, participants were characterized in terms of demographics, and neuropsychological assessments of vocabulary, episodic memory, perceptual speed, and abstract fluid reasoning. Participants studied an array of either one, three, or six upper-case letters for 3 s (=encoding phase), then a blank fixation screen was presented for 7 s (=maintenance phase), to be probed with a lower-case letter to which they responded with a differential button press whether the letter was part of the studied array or not (=retrieval phase). We focused on identifying maintenance-related activation patterns showing memory load increases in pattern score on an individual participant level for both age groups. We found such a pattern that increased with memory load for all but one person in the young participants (p < 0.001), and such a pattern for all participants in the older group (p < 0.001). Both patterns showed broad topographic similarities; however, relationships to task performance and neuropsychological characteristics were markedly different and point to individual differences in Cognitive Reserve. Beyond the derivation of group-level activation patterns, we also investigated the inter-subject spatial similarity of individual working memory rehearsal patterns in the older participants' group as a function of neuropsychological and task performance, education, and mean cortical thickness. Higher task accuracy and neuropsychological function was reliably associated with higher inter-subject similarity of individual-level activation patterns in older participants.

Finding Cortical Subregions Regarding the Dorsal Language Pathway Based on the Structural Connectivity

Although the language-related fiber pathways in the human brain, such as the superior longitudinal fasciculus (SLF) and arcuate fasciculus (AF), are already well-known, understanding more sophisticated cortical regions connected by the fiber tracts is essential to scrutinize the structural connectivity of language circuits. With the regions of interest that were selected based on the Brainnetome atlas, the fiber orientation distribution estimation method for tractography was used to produce further elaborate connectivity information. The results indicated that both fiber bundles had two distinct connections with the prefrontal cortex (PFC). The SLF-II and dorsal AF are mainly connected to the rostrodorsal part of the inferior parietal cortex (IPC) and lateral part of the fusiform gyrus with the inferior frontal junction (IFJ), respectively. In contrast, the SLF-III and ventral AF were primarily linked to the anterior part of the supramarginal gyrus and superior part of the temporal cortex with the inferior frontal cortex, including the Broca's area. Moreover, the IFJ in the PFC, which has rarely been emphasized as a language-related subregion, also had the strongest connectivity with the previously known language-related subregions among the PFC; consequently, we proposed that these specific regions are interconnected via the SLF and AF within the PFC, IPC, and temporal cortex as language-related circuitry.

Distributed networks for auditory memory differentially contribute to recall precision

Re-directing attention to objects in working memory can enhance their representational fidelity. However, how this attentional enhancement of memory representations is implemented across distinct, sensory and cognitive-control brain network is unspecified. The present fMRI experiment leverages psychophysical modelling and multivariate auditory-pattern decoding as behavioral and neural proxies of mnemonic fidelity. Listeners performed an auditory syllable pitch-discrimination task and received retro-active cues to selectively attend to a to-be-probed syllable in memory. Accompanied by increased neural activation in fronto-parietal and cingulo-opercular networks, valid retro-cues yielded faster and more perceptually sensitive responses in recalling acoustic detail of memorized syllables. Information about the cued auditory object was decodable from hemodynamic response patterns in superior temporal sulcus (STS), fronto-parietal, and sensorimotor regions. However, among these regions retaining auditory memory objects, neural fidelity in the left STS and its enhancement through attention-to-memory best predicted individuals' gain in auditory memory recall precision. Our results demonstrate how functionally discrete brain regions differentially contribute to the attentional enhancement of memory representations.

Modulation of threat extinction by working memory load: An event-related potential study

Distraction is typically discouraged during exposure therapy for anxiety, because it is thought to interfere with extinction learning by diverting attention away from anxiety-provoking stimuli. Working memory load is one form of distraction that might interfere with extinction learning. Alternatively, working memory load might reduce threat responding and benefit extinction learning by engaging prefrontal brain regions that have a reciprocal relationship with brain circuits involved in threat detection and processing. Prior work examining the effect of working memory load on threat extinction has been limited and has found mixed results. Here, we used the late positive potential (LPP), an event-related potential that is larger for threatening compared to non-threatening stimuli to assess the effect of working memory load on threat extinction. After acquisition, 38 participants performed three blocks of an extinction task interspersed with low and high working memory load trials. Results showed that overall, the LPP was reduced under high compared to low working memory load, and that working memory load slowed extinction learning. Results provide empirical evidence in support of limiting distraction during exposure therapy in order to optimize extinction learning efficiency.

Clinical insight and cognitive functioning as mediators in the relationships between symptoms of psychosis, depression, and suicide ideation in first-episode psychosis

First-episode psychosis (FEP) is a particularly high-risk period for suicide. Literature suggests poor cognitive functioning may serve as a protective factor, while investigations of clinical insight reveal a complex relationship with suicide outcomes. This study examined the mediating role of cognition and clinical insight in the relationships between positive and negative symptoms, depression, and subsequent suicide ideation among individuals in FEP. Data were obtained from the Recovery After an Initial Schizophrenia Episode project. Participants (n = 404) included adolescents and adults in FEP between the ages of 15 and 40. Measurement utilized the Calgary Depression Rating Scale, Positive and Negative Syndrome Scale, and Brief Assessment of Cognition in Schizophrenia. Structural equation modeling was used to examine the mediation model. The likelihood of experiencing suicide ideation was significantly decreased when working memory was stronger (b = -0.034, SE = 0.02, OR = 0.967, p < .05), and significantly increased when clinical insight was stronger (b = 0.191, SE = 0.08, OR = 1.21, p < .01), positive symptoms were greater (b = 0.422, SE = 0.20, OR = 1.52, p < .05) and depressive symptoms were greater (b = 0.545, SE = 0.15, OR = 1.70, p < .001). Clinical insight and working memory functioned as mediators in the relationships between depression, positive symptoms, negative symptoms, and suicide ideation. Findings suggest it is essential that clinicians have awareness of insight being a risk factor for suicide ideation and balance therapeutic efforts to strengthen clinical insight and cognition in psychosocial treatments with suicide risk assessment and prevention methods.

Frequency-Specific Changes of Amplitude of Low-Frequency Fluctuations in Patients with Acute Basal Ganglia Ischemic Stroke

Objective. The purpose of this study was to investigate the characteristics of different frequency bands in the spontaneous brain activity among patients with acute basal ganglia ischemic stroke (BGIS). Methods. In the present study, thirty-four patients with acute BGIS and forty-four healthy controls were examined by resting-state functional magnetic resonance imaging (rs-fMRI) from May 2019 to December 2020. Two amplitude methods including amplitude of low-frequency fluctuations (ALFF) and fractional ALFF (fALFF) calculated in three frequency bands (conventional frequency band: 0.01-0.08 Hz; slow-5 frequency band: 0.01-0.027 Hz; and slow-4 frequency band: 0.027-0.073 Hz) were conducted to evaluate the spontaneous brain activity in patients with acute BGIS and healthy controls (HCs). Gaussian Random Field Theory (GRF, voxel $p<0.01$ and cluster $p<0.05$ ) correction was applied. The correlation analyses were performed between clinical scores and altered metrics values. Results. Compared to HCs, patients with acute BGIS showed decreased ALFF in the right supramarginal gyrus (SMG) in the conventional and slow-4 bands, increased fALFF in the right middle frontal gyrus (MFG) in the conventional and slow-4 bands, and increased fALFF in the bilateral caudate in the slow-5 frequency band. The fALFF value of the right caudate in the slow-5 frequency band was negatively correlated with the clinical scores. Conclusion. In conclusion, this study showed the alterations in ALFF and fALFF in three frequency bands between patients with acute BGIS and HCs. The results reflected that the abnormal LFO amplitude might be related with different frequency bands and promoted our understanding of pathophysiological mechanism in acute BGIS.

Neurophysiological Verbal Working Memory Patterns in Children: Searching for a Benchmark of Modality Differences in Audio/Video Stimuli Processing

Exploration of specific brain areas involved in verbal working memory (VWM) is a powerful but not widely used tool for the study of different sensory modalities, especially in children. In this study, for the first time, we used electroencephalography (EEG) to investigate neurophysiological similarities and differences in response to the same verbal stimuli, expressed in the auditory and visual modality during the n-back task with varying memory load in children. Since VWM plays an important role in learning ability, we wanted to investigate whether children elaborated the verbal input from auditory and visual stimuli through the same neural patterns and if performance varies depending on the sensory modality. Performance in terms of reaction times was better in visual than auditory modality (p = 0.008) and worse as memory load increased regardless of the modality (p < 0.001). EEG activation was proportionally influenced by task level and was evidenced in theta band over the prefrontal cortex (p = 0.021), along the midline (p = 0.003), and on the left hemisphere (p = 0.003). Differences in the effects of the two modalities were seen only in gamma band in the parietal cortices (p = 0.009). The values of a brainwave-based engagement index, innovatively used here to test children in a dual-modality VWM paradigm, varied depending on n-back task level (p = 0.001) and negatively correlated (p = 0.002) with performance, suggesting its computational effectiveness in detecting changes in mental state during memory tasks involving children. Overall, our findings suggest that auditory and visual VWM involved the same brain cortical areas (frontal, parietal, occipital, and midline) and that the significant differences in cortical activation in theta band were more related to memory load than sensory modality, suggesting that VWM function in the child's brain involves a cross-modal processing pattern.

Contributions of Brain Function and Structure to Three Different Domains of Cognitive Control in Normal Aging

Cognitive control involves the flexible allocation of mental resources during goal-directed behavior and comprises three correlated but distinct domains-inhibition, shifting, and working memory. The work of Don Stuss and others has demonstrated that frontal and parietal cortices are crucial to cognitive control, particularly in normal aging, which is characterized by reduced control mechanisms. However, the structure-function relationships specific to each domain and subsequent impact on performance are not well understood. In the current study, we examined both age and individual differences in functional activity associated with core domains of cognitive control in relation to fronto-parietal structure and task performance. Participants (n = 140, aged 20-86 years) completed three fMRI tasks: go/no-go (inhibition), task switching (shifting), and n-back (working memory), in addition to structural and diffusion imaging. All three tasks engaged a common set of fronto-parietal regions; however, the contributions of age, brain structure, and task performance to functional activity were unique to each domain. Aging was associated with differences in functional activity for all tasks, largely in regions outside common fronto-parietal control regions. Shifting and inhibition showed greater contributions of structure to overall decreases in brain activity, suggesting that more intact fronto-parietal structure may serve as a scaffold for efficient functional response. Working memory showed no contribution of structure to functional activity but had strong effects of age and task performance. Together, these results provide a comprehensive and novel examination of the joint contributions of aging, performance, and brain structure to functional activity across multiple domains of cognitive control.

Changes in theta and alpha oscillatory signatures of attentional control in older and middle age

BACKGROUND

Recent behavioural research has reported age-related changes in the costs of refocusing attention from a temporal (rapid serial visual presentation) to a spatial (visual search) task. Using magnetoencephalography, we have now compared the neural signatures of attention refocusing between three age groups (19-30, 40-49 and 60+ years) and found differences in task-related modulation and cortical localisation of alpha and theta oscillations. Efficient, faster refocusing in the youngest group compared to both middle age and older groups was reflected in parietal theta effects that were significantly reduced in the older groups. Residual parietal theta activity in older individuals was beneficial to attentional refocusing and could reflect preserved attention mechanisms. Slowed refocusing of attention, especially when a target required consolidation, in the older and middle-aged adults was accompanied by a posterior theta deficit and increased recruitment of frontal (middle-aged and older groups) and temporal (older group only) areas, demonstrating a posterior to anterior processing shift. Theta but not alpha modulation correlated with task performance, suggesting that older adults' stronger and more widely distributed alpha power modulation could reflect decreased neural precision or dedifferentiation but requires further investigation. Our results demonstrate that older adults present with different alpha and theta oscillatory signatures during attentional control, reflecting cognitive decline and, potentially, also different cognitive strategies in an attempt to compensate for decline.

Working memory load reduces the electrocortical processing of positive pictures

To date, the emotion regulation literature has focused primarily on the down-regulation of negative emotion, with far fewer studies interrogating the mechanisms at work in positive emotion regulation. This body of work has suggested that nonaffective mechanisms, such as cognitive load have a role to play in reducing emotional response. For example, the late positive potential (LPP), which tracks attention to salient stimuli, is reduced when task-irrelevant negative and neutral stimuli are presented under high compared with low working memory load. Using positive stimuli, working memory load has been shown to reduce the LPP elicited by positive words and faces but has not previously been shown to modulate the LPP elicited by positive scenes. Emotional scenes are the predominant type of stimuli used in the broader emotion regulation literature, are more arousing than faces, and have been shown to more strongly modulate the LPP. Here, 41 participants performed a working memory task interspersed with the presentation of positive and neutral scenes, while electroencephalography was recorded. Results showed that the LPP was increased for positive compared with neutral pictures and reduced on high-load compared to low-load trials. Working memory performance was worse on high-load compared with low-load trials, although it was not significantly correlated with the LPP, and picture type did not affect working memory performance. Results bridge to the willful emotion regulation literature to increase understanding of the mechanisms underlying positive emotion regulation, which has been relatively unexamined.

Disruption of the Prefrontal Cortex Improves Implicit Contextual Memory-Guided Attention: Combined Behavioral and Electrophysiological Evidence

Many studies have shown that the dorsolateral prefrontal cortex (DLPFC) plays an important role in top-down cognitive control over intentional and deliberate behavior. However, recent studies have reported that DLPFC-mediated top-down control interferes with implicit forms of learning. Here we used continuous theta-burst stimulation (cTBS) combined with electroencephalography to investigate the causal role of DLPFC in implicit contextual memory-guided attention. We aimed to test whether transient disruption of the DLPFC would interfere with implicit learning performance and related electrical brain activity. We applied neuronavigation-guided cTBS to the DLPFC or to the vertex as a control region prior to the performance of an implicit contextual learning task. We found that cTBS applied over the DLPFC significantly improved performance during implicit contextual learning. We also noted that beta-band (13-19 Hz) oscillatory power was reduced at fronto-central channels about 140 to 370 ms after visual stimulus onset in cTBS DLPFC compared with cTBS vertex. Taken together, our results provide evidence that DLPFC-mediated top-down control interferes with contextual memory-guided attention and beta-band oscillatory activity.

A functional MRI study of presurgical cognitive deficits in glioma patients

Background

The main goal of this functional MRI (fMRI) study was to examine whether cognitive deficits in glioma patients prior to treatment are associated with abnormal brain activity in either the central executive network (CEN) or default mode network (DMN).

Methods

Forty-six glioma patients, and 23 group-matched healthy controls (HCs) participated in this fMRI experiment, performing an N-back task. Additionally, cognitive profiles of patients were evaluated outside the scanner. A region of interest–based analysis was used to compare brain activity in CEN and DMN between groups. Post hoc analyses were performed to evaluate differences between low-grade glioma (LGG) and high-grade glioma (HGG) patients.

Results

In-scanner performance was lower in glioma patients compared to HCs. Neuropsychological testing indicated cognitive impairment in LGG as well as HGG patients. fMRI results revealed normal CEN activation in glioma patients, whereas patients showed reduced DMN deactivation compared to HCs. Brain activity levels did not differ between LGG and HGG patients.

Conclusions

Our study suggests that cognitive deficits in glioma patients prior to treatment are associated with reduced responsiveness of the DMN, but not with abnormal CEN activation. These results suggest that cognitive deficits in glioma patients reflect a reduced capacity to achieve a brain state necessary for normal cognitive performance, rather than abnormal functioning of executive brain regions. Solely focusing on increases in brain activity may well be insufficient if we want to understand the underlying brain mechanism of cognitive impairments in patients, as our results indicate the importance of assessing deactivation.

Working Memory Capacities Neurally Dissociate: Evidence from Acute Stroke

Substantial behavioral evidence implies the existence of separable working memory (WM) components for maintaining phonological and semantic information. In contrast, only a few studies have addressed the neural basis of phonological versus semantic WM using functional neuroimaging and none has used a lesion-symptom mapping (LSM) approach. Here, we address this gap, reporting a multivariate LSM study of phonological and semantic WM for 94 individuals at the acute stage of left hemisphere stroke. Testing at the acute stage avoids issues of brain reorganization and the adoption of patient strategies for task performance. The LSM analyses for each WM component controlled for the other WM component and semantic and phonological knowledge at the single word level. For phonological WM, the regions uncovered included the supramarginal gyrus, argued to be the site of phonological storage, and several cortical and subcortical regions plausibly related to inner rehearsal. For semantic WM, inferior frontal regions and the angular gyrus were uncovered. The findings thus provide converging evidence for separable systems for phonological and semantic WM that are distinguished from the systems supporting long-term knowledge representations in those domains.

Maintenance vs. Manipulation in Auditory Verbal Working Memory in the Elderly: New Insights Based on Temporal Dynamics of Information Processing in the Millisecond Time Range

Working memory (WM) is a limited-capacity cognitive system that allows the storage and use of a limited amount of information for a short period of time. Two WM processes can be distinguished: maintenance (i.e., storing, monitoring, and matching information) and manipulation (i.e., reordering and updating information). A number of studies have reported an age-related decline in WM, but the mechanisms underlying this deterioration need to be investigated. Previous research, including studies conducted in our laboratory, revealed that age-related cognitive deficits are related to decreased millisecond timing, i.e., the ability to perceive and organize incoming events in time. The aim of the current study was: (1) to identify in the elderly the brain network involved in the maintenance and manipulation WM processes; and (2) to use an fMRI task to investigate the relation between the brain activity associated with these two processes and the efficiency of temporal information processing (TIP) on a millisecond level reflected by psychophysical indices. Subjects were 41 normal healthy elderly people aged from 62 to 78 years. They performed: (1) an auditory verbal n-back task for assessing WM efficiency in an MRI scanner; and (2) a psychophysical auditory temporal-order judgment (TOJ) task for assessing temporal resolution in the millisecond domain outside the scanner. The n-back task comprised three conditions (0-, 1-, and 2-back), which allowed maintenance (1- vs. 0-back comparisons) and manipulation (2- vs. 1-back comparisons) processes to be distinguished. Results revealed the involvement of a similar brain network in the elderly to that found in previous studies. However, during maintenance processes, we found relatively limited and focused activations, which were significantly extended during manipulation. A novel result of our study, never reported before, is an indication of significant moderate correlations between the efficiency of WM and TIP. These correlations were found only for manipulation but not for maintenance. Our results confirmed the hypothesis that manipulation in the elderly is a dynamic process requiring skilled millisecond timing with high temporal resolution. We conclude that millisecond timing contributes to WM manipulation in the elderly, but not to maintenance.

SERIAL-ORDER recall in working memory across the cognitive spectrum of Parkinson's disease and neuroimaging correlates

We sought to determine if Parkinson's disease (PD) with mild cognitive impairment (MCI) is associated with a greater SERIAL-ORDER (mental manipulation) than ANY-ORDER (auditory span, storage) deficit in working memory (WM). We investigated WM combining neuropsychological measures with the study of brain functional connectivity. A cohort of 160 patients with idiopathic PD, classified as PD-MCI (n = 87) or PD with normal cognition (PD-NC; n = 73), and 70 matched healthy controls were studied. Verbal WM was assessed with the Backward Digit Span Task (BDT; Lamar et al., 2007, Neuropsychologia, 45, 245), measuring SERIAL-ORDER and ANY-ORDER recall. Resting-state MRI data were collected for 15 PD-MCI, 15 PD-NC and 30 controls. Hypothesis-driven seed-based functional connectivity of the dorsolateral prefrontal cortex (DLPFC) was compared between the three groups and correlated with BDT performance. We found the main effect of the test (impairment in SERIAL ORDER > ANY ORDER) and group ((NC = PD-NC) > PD-MCI) in BDT performance that was even more pronounced in SERIAL ORDER when controlling for ANY ORDER variability but not vice versa. Furthermore, PD-MCI compared to other groups were characterized by the functional disconnection between the bilateral DLPFC and the cerebellum. In functional correlations, DLPFC connectivity was positively related to both SERIAL- and ANY-ORDER performance. In conclusion, PD-MCI patients evidenced greater SERIAL-ORDER (manipulation and cognitive control) than ANY-ORDER (storage) working memory impairment than PD-NC and controls with a disrupted DLPFC resting-state connectivity that was also related to the verbal WM performance.

Functional MRI investigation of verbal working memory in adults with anorexia nervosa

Literature regarding verbal working memory (vWM) in anorexia nervosa (AN) has been inconsistent due to a misunderstanding of the key components of vWM and introduction of confounding stimuli. Furthermore, there are no studies looking at how brain function in people with AN relates to vWM performance. The present study used functional magnetic resonance imaging (fMRI) with a letter n-back paradigm to study the effect of increasing vWM task difficulty on cortical functioning in the largest AN sample to date (n = 31). Although the AN group had low BMI and higher anxious and depressive symptomology compared to age-matched controls (HC), there were no between-group differences in accuracy and speed at any task difficulty. fMRI data revealed no regions exhibiting significant differences in activation when groups were compared at each difficulty separately and no regions showing group x condition interaction. Although there was a trend towards lower accuracy as duration of illness increased, this was not correlated with activity in regions associated with vWM. These findings indicate that vWM in AN is as efficient and performed using the same cognitive strategy as HC, and that there may not be a need for therapies to pursue remediation of this particular neurocognitive faculty.

Processing of Targets and Non-targets in Verbal Working Memory

In this study we used functional MRI (fMRI) to examine whether defining a stimulus as a target affects brain activation associated with a verbal working memory (WM) task. Seventeen healthy right-handed volunteers performed a Sternberg task with three consonants as memory set. We performed a region of interest based fMRI analysis to examine differences in brain activity patterns between targets and non-targets. Non-target brain activity was subtracted from target activity and hemispheric and fronto-parietal differences were tested by conducting a MANOVA. Participants responded correctly to 97.5% of the stimuli. The fMRI results showed a hemisphere by fronto-parietal location interaction, where targets evoked increased activity in the right frontal regions compared to non-targets, whereas the left frontal task activation did not differ between targets and non-targets. In the parietal regions, targets evoked increased activity compared to non-targets in the lateral anterior, but not the medial posterior part. Our study revealed that defining a stimulus as a target within a verbal WM task evokes an increase in brain activity in right frontal brain regions, compared to non-targets. Our results suggest an important hemispheric differentiation in target processing, in which the right frontal cortex is predominantly involved in processes associated with target stimuli. The left frontal cortex does not differentiate between processing target and non-target stimuli, suggesting involvement in WM processes that are independent of stimulus type. Parietal, the lateral anterior part is predominantly involved in target processing, while the medial posterior part does not differentiate between target and non-target processing.

Working memory predictors of mathematics across the middle primary school years

BACKGROUND

Work surrounding the relationship between visuospatial working memory (WM) and mathematics performance is gaining significant traction as a result of a focus on improving academic attainment.

AIMS

This study examined the relative contributions of verbal and visuospatial simple and complex WM measures to mathematics in primary school children aged 6-10 years.

SAMPLE

A sample of 111 children in years 2-5 were assessed (M_age  = 100.06 months, SD = 14.47).

METHOD

Children were tested individually on all memory measures, followed by a separate mathematics testing session as a class group in the same assessment wave.

RESULTS AND CONCLUSIONS

Results revealed an age-dependent relationship, with a move towards visuospatial influence in older children. Further analyses demonstrated that backward word span and backward matrices contributed unique portions of variance of mathematics, regardless of the regression model specified. We discuss possible explanations for our preliminary findings in relation to the existing literature alongside their implications for educators and further research.

Frontal volume as a potential source of the comorbidity between attention-deficit/hyperactivity disorder and reading disorders

Prefrontal volume reductions commonly are demonstrated in ADHD, but the literature examining prefrontal volume in reading disorders (RD) is scant despite their also having executive functioning (EF) deficits. Furthermore, only a few anatomical studies have examined the frontal lobes in comorbid RD/ADHD, though they have EF deficits similar to RD and ADHD. Hence, we examined frontal gyri volume in children with RD, ADHD, RD/ADHD and controls, as well as their relationship to EF for gyri found to differ between groups. We found right inferior frontal (RIF) volume was smaller in ADHD, and smaller volume was related to worse behavioral regulation. Left superior frontal (LSF) volume was larger in RD than ADHD, and its size was negatively related to basic reading ability. Left middle frontal (LMF) volume was largest in RD/ADHD overall. Further, its volume was not related to basic reading nor behavioral regulation but was related to worse attentional control, suggesting some specificity in its EF relationship. When examining hypotheses on the etiology of RD/ADHD, RD/ADHD was commensurate with ADHD in RIF volume and both RD and ADHD in LSF volume (being midway between the groups), consistent with the common etiology hypothesis. Nevertheless, they also had an additional gyrus affected: LMF, consistent with the cognitive subtype hypothesis in its specificity to RD/ADHD. The few other frontal aMRI studies on RD/ADHD supported both hypotheses as well. Given this, future research should continue to focus on frontal morphology in its endeavors to find neurobiological contributors to the comorbidity between RD and ADHD.

The effect of response frequency on cognitive brain activity during an alertness task

A required response forces the brain to react overtly on a stimulus. This may be a factor that influences cognitive activity during a task, as it could facilitate for instance alertness, especially in tasks that are relatively easy. In the current article, we therefore tested the hypothesis that response frequency affects cognitive brain activity in an alertness task. In this 3T functional MRI study, healthy volunteers performed a continuous performance task with three conditions with increasing response frequency. Only scans during presentation of non-targets were analyzed, to exclude activity related to the change in frequency in response selection and motor responses between conditions. To evaluate changes in cognitive brain activity, a network analysis was performed based on two main networks including regions with task-induced activation and task-induced deactivation. We tested for differences in brain activity as an effect of target frequency. Performance results indicated no effect of target frequency on accuracy or reaction time. During non-targets, we found significant signal changes in TID for all three conditions, whereas TIA showed no significant signal changes in any condition. Target frequency did not have a significant effect on the level of signal change at network level, as well as at individual region level. Our study showed predominantly deactivation during non-responses in all three task conditions. Furthermore, our results indicate that response frequency does not influence brain activity during an alertness task. Our results provide additional information relevant for the understanding of the neurophysiological implementation of cognitive control or alertness.

The Methodological Quality of Short-Term/Working Memory Treatments in Poststroke Aphasia: A Systematic Review

Purpose The aims of this systematic review are to provide a critical overview of short-term memory (STM) and working memory (WM) treatments in stroke aphasia and to systematically evaluate the internal and external validity of STM/WM treatments. Method A systematic search was conducted in February 2014 and then updated in December 2016 using 13 electronic databases. We provided descriptive characteristics of the included studies and assessed their methodological quality using the Risk of Bias in N-of-1 Trials quantitative scale ( Tate et al., 2015 ), which was completed by 2 independent raters. Results The systematic search and inclusion/exclusion procedure yielded 17 single-case or case-series studies with 37 participants for inclusion. Nine studies targeted auditory STM consisting of repetition and/or recognition tasks, whereas 8 targeted attention and WM, such as attention process training including n-back tasks with shapes and clock faces as well as mental math tasks. In terms of their methodological quality, quality scores on the Risk of Bias in N-of-1 Trials scale ranged from 4 to 17 ( M = 9.5) on a 0-30 scale, indicating a high risk of bias in the reviewed studies. Effects of treatment were most frequently assessed on STM, WM, and spoken language comprehension. Transfer effects on communication and memory in activities of daily living were tested in only 5 studies. Conclusions Methodological limitations of the reviewed studies make it difficult, at present, to draw firm conclusions about the effects of STM/WM treatments in poststroke aphasia. Further studies with more rigorous methodology and stronger experimental control are needed to determine the beneficial effects of this type of intervention. To understand the underlying mechanisms of STM/WM treatment effects and how they relate to language functioning, a careful choice of outcome measures and specific hypotheses about potential improvements on these measures are required. Future studies need to include outcome measures of memory functioning in everyday life and psychosocial functioning more generally to demonstrate the ecological validity of STM and WM treatments.

Anodal Transcranial Direct Current Stimulation Induces High Gamma-Band Activity in the Left Dorsolateral Prefrontal Cortex During a Working Memory Task: A Double-Blind, Randomized, Crossover Study

Transcranial direct current stimulation (tDCS) has been shown to have mixed effects on working memory (WM) capacity in healthy individuals. Different stimulation paradigms may account for these discrepancies, with certain features being favored. To determine the effect in the context of anodal tDCS, we investigated whether anodal tDCS induced cortical oscillatory changes during a WM task. Specifically, we tested whether anodal offline tDCS over the left prefrontal cortex (PFC) enhances WM capacity by modulating the oscillatory activity in the left dorsolateral PFC (DLPFC) using magnetoencephalography (MEG). This study employed a double-blind, randomized, crossover design, in which 24 healthy right-handed participants conducted MEG recordings during a 3-back task after administration of 2 mA tDCS or sham stimulation as a placebo. Our results showed that the effect of tDCS did not appear in the behavioral indices—WM accuracy (d′) or reaction time (RT). From the results of the time-frequency analysis, significant event-related synchronization (ERS) in the high-gamma band (82–84 Hz) of the left DLPFC was found under the tDCS condition; however, ERS was not correlated with WM capacity. Furthermore, we calculated the modulation index (MI), which indicates the strength of phase-amplitude coupling (PAC). tDCS significantly decreased MI of the left DLPFC, representing the theta-gamma PAC during the n-back task using color names as verbal stimuli. Our results suggest that although tDCS increased the gamma-band oscillation indicating greater neural activity in the left DLPFC, it did not lead to an improvement of WM capacity; this may be due to the inability of gamma-band oscillation to couple with the task-induced theta wave. WM capacity might not increase unless theta-gamma PAC is not enhanced by tDCS.

Effects of backpack weight on the performance of basic short-term/working memory tasks during flat-surface standing

This study empirically investigated the effects of backpack weight on the performance of three basic short-term/working memory (STM/WM) tasks during flat-surface standing. Four levels of backpack weight were considered: 0, 15, 25 and 40% of the body weight. The three STM/WM tasks were the Corsi block, digit span and 3-back tasks, corresponding to the visuo-spatial sketchpad, phonological loop and central executive of WM, respectively. Thirty participants conducted the STM/WM tasks while standing with loaded backpack. Major study findings were that (1) increased backpack weight adversely affected the scores of all three STM/WM tasks; and, (2) the adverse effect of backpack weight was less pronounced for the phonological loop STM task than the other STM/WM tasks. The study findings may help understand and predict the impacts of body-worn equipment weight on the worker's mental task performance for various work activities requiring simultaneous performance of mental and physical tasks. Practitioner summary: The current study empirically examined the effects of backpack weight on the performance of three basic STM/WM tasks. The study findings entail that reduces the weight of body-worn equipment can positively impact the worker's mental task performance in addition to reducing the worker's bodily stresses. Abbreviations: ACC: anterior cingulate cortex; AP: anterior-posterior; BW: body weight; CoP: centre of pressure; C-S: central executive working memory task and standing; DLPFC: dorsolateral prefrontal cortex; HIP: human information processing; ML: medio-lateral; PMC: premotor cortex; P-S: phonological loop short-term memory task and standing; SMA: supplementary motor area; STM: short-term memory; VLPFC: ventrolateral prefrontal cortex; V-S: visuo-spatial short-term memory task and standing; WM: working memory.

Abnormal neural response to phonological working memory demands in persistent developmental stuttering

Persistent developmental stuttering is a neurological disorder that commonly manifests as a motor problem. Cognitive theories, however, hold that poorly developed cognitive skills are the origins of stuttering. Working memory (WM), a multicomponent cognitive system that mediates information maintenance and manipulation, is known to play an important role in speech production, leading us to postulate that the neurophysiological mechanisms underlying stuttering may be associated with a WM deficit. Using functional magnetic resonance imaging, we aimed to elucidate brain mechanisms in a phonological WM task in adults who stutter and controls. A right-lateralized compensatory mechanism for a deficit in the rehearsal process and neural disconnections associated with the central executive dysfunction were found. Furthermore, the neural abnormalities underlying the phonological WM were independent of memory load. This study demonstrates for the first time the atypical neural responses to phonological WM in PWS, shedding new light on the underlying cause of stuttering.

As Time Goes by: A rTMS Study on Age-Related Changes in Sentence Comprehension

It is well established that off-line sentence judgment tasks (oSJTs) typically rely on phonological working memory (WM), beyond specific linguistic processing. Nevertheless, empirical findings suggest that a juvenile level of performance in an oSJT could be associated with the recruitment of age-specific additional supportive neural network in healthy aging. In particular, in one of our previous study, healthy elderlies showed the additional activation of associative visual cortices when compared with young controls. We suggested that age-related hyperactivations, during an auditory sentence judgment task, might represent the neurofunctional correlate of the recruitment of compensatory strategies that are necessary to maintain a juvenile level of performance. To explicitly test this hypothesis we adopted repetitive transcranial magnetic stimulation (rTMS). Twelve healthy elderlies and 12 young participants were engaged in an off-line semantic plausibility judgment task while rTMS was delivered over: (1) the left inferior frontal gyrus (LIFG; i.e., a core region of the WM network); (2) the precuneus; and (3) a Control Site (vertex). Results showed a significant main effect of Stimulation Site and a significant Group-by-Stimulation Site interaction effect. In particular, the rTMS stimulation of the LIFG slowed down reaction times (RTs) both in young and healthy elderly participants, while only healthy elderlies showed an increment of RTs during the stimulation of the precuneus. Taken together our results further support the idea that the maintenance of a juvenile level of performance in graceful aging may be associated with task-specific compensatory processes that would manifest them-selves, from the neurofunctional point of view, by the recruitment of additional neural supportive regions.

Load modulates the alpha and beta oscillatory dynamics serving verbal working memory

A network of predominantly left-lateralized brain regions has been linked to verbal working memory (VWM) performance. However, the impact of memory load on the oscillatory dynamics serving VWM is far less understood. To further investigate this, we had 26 healthy adults perform a high-load (6 letter) and low-load (4 letter) variant of a VWM task while undergoing magnetoencephalography (MEG). MEG data were evaluated in the time-frequency domain and significant oscillatory responses spanning the encoding and maintenance phases were reconstructed using a beamformer. To determine the impact of load on the neural dynamics, the resulting images were examined using paired-samples t-tests and virtual sensor analyses. Our results indicated stronger increases in frontal theta activity in the high- relative to low-load condition during early encoding. Stronger decreases in alpha/beta activity were also observed during encoding in bilateral posterior cortices during the high-load condition, and the strength of these load effects increased as encoding progressed. During maintenance, stronger decreases in alpha activity in the left inferior frontal gyrus, middle temporal gyrus, supramarginal gyrus, and inferior parietal cortices were detected during high- relative to low-load performance, with the strength of these load effects remaining largely static throughout maintenance. Finally, stronger increases in occipital alpha activity were observed during maintenance in the high-load condition, and the strength of these effects grew stronger with time during the first half of maintenance, before dissipating during the latter half of maintenance. Notably, this was the first study to utilize a whole-brain approach to statistically evaluate the temporal dynamics of load-related oscillatory differences during encoding and maintenance processes, and our results highlight the importance of spatial, temporal, and spectral specificity in this regard.

Functional Near-Infrared Spectroscopy Recordings of Visuospatial Working Memory Processes. Part II: A Replication Study in Children on Sensitivity and Mental-Ability-Induced Differences in Functional Activation

In a previous study in young adults, we showed that hemodynamic changes as measured by functional near-infrared spectroscopy (fNIRS) were sensitive for identifying visuospatial working memory (WM)-related functional brain activation in the prefrontal cortex. This functional activation, however, could not be verified for participants with far-above-average mental ability, suggesting different cognitive processes adopted by this group. The present study was designed to confirm these findings in 11- to 13-year-old children by applying the same study design, experimental task, fNIRS setup, and statistical approach. We successfully replicated the earlier findings on sensitivity of fNIRS with regard to visuospatial WM-specific task demands in our children sample. Likewise, mental-ability-induced differences in functional activation were even more pronounced in the children compared with in the young adults. By testing a children sample, we were able to not only replicate our previous findings based on adult participants but also generalize the validity of these findings to children. This latter aspect seems to be of particular significance considering the relatively large number of fNIRS studies on WM performance in children.

The Validity of Functional Near-Infrared Spectroscopy Recordings of Visuospatial Working Memory Processes in Humans

Functional near infrared spectroscopy (fNIRS) is increasingly used for investigating cognitive processes. To provide converging evidence for the validity of fNIRS recordings in cognitive neuroscience, we investigated functional activation in the frontal cortex in 43 participants during the processing of a visuospatial working memory (WM) task and a sensory duration discrimination (DD) task functionally unrelated to WM. To distinguish WM-related processes from a general effect of increased task demand, we applied an adaptive approach, which ensured that subjective task demand was virtually identical for all individuals and across both tasks. Our specified region of interest covered Brodmann Area 8 of the left hemisphere, known for its important role in the execution of WM processes. Functional activation, as indicated by an increase of oxygenated and a decrease of deoxygenated hemoglobin, was shown for the WM task, but not in the DD task. The overall pattern of results indicated that hemodynamic responses recorded by fNIRS are sensitive to specific visuospatial WM capacity-related processes and do not reflect a general effect of increased task demand. In addition, the finding that no such functional activation could be shown for participants with far above-average mental ability suggested different cognitive processes adopted by this latter group.

Neural Correlates of Temporal Complexity and Synchrony during Audiovisual Correspondence Detection

We often perceive real-life objects as multisensory cues through space and time. A key challenge for audiovisual integration is to match neural signals that not only originate from different sensory modalities but also that typically reach the observer at slightly different times. In humans, complex, unpredictable audiovisual streams lead to higher levels of perceptual coherence than predictable, rhythmic streams. In addition, perceptual coherence for complex signals seems less affected by increased asynchrony between visual and auditory modalities than for simple signals. Here, we used functional magnetic resonance imaging to determine the human neural correlates of audiovisual signals with different levels of temporal complexity and synchrony. Our study demonstrated that greater perceptual asynchrony and lower signal complexity impaired performance in an audiovisual coherence-matching task. Differences in asynchrony and complexity were also underpinned by a partially different set of brain regions. In particular, our results suggest that, while regions in the dorsolateral prefrontal cortex (DLPFC) were modulated by differences in memory load due to stimulus asynchrony, areas traditionally thought to be involved in speech production and recognition, such as the inferior frontal and superior temporal cortex, were modulated by the temporal complexity of the audiovisual signals. Our results, therefore, indicate specific processing roles for different subregions of the fronto-temporal cortex during audiovisual coherence detection.

Left Inferior Frontal Gyrus Sensitivity to Phonetic Competition in Receptive Language Processing: A Comparison of Clear and Conversational Speech

The speech signal is rife with variations in phonetic ambiguity. For instance, when talkers speak in a conversational register, they demonstrate less articulatory precision, leading to greater potential for confusability at the phonetic level compared with a clear speech register. Current psycholinguistic models assume that ambiguous speech sounds activate more than one phonological category and that competition at prelexical levels cascades to lexical levels of processing. Imaging studies have shown that the left inferior frontal gyrus (LIFG) is modulated by phonetic competition between simultaneously activated categories, with increases in activation for more ambiguous tokens. Yet, these studies have often used artificially manipulated speech and/or metalinguistic tasks, which arguably may recruit neural regions that are not critical for natural speech recognition. Indeed, a prominent model of speech processing, the dual-stream model, posits that the LIFG is not involved in prelexical processing in receptive language processing. In the current study, we exploited natural variation in phonetic competition in the speech signal to investigate the neural systems sensitive to phonetic competition as listeners engage in a receptive language task. Participants heard nonsense sentences spoken in either a clear or conversational register as neural activity was monitored using fMRI. Conversational sentences contained greater phonetic competition, as estimated by measures of vowel confusability, and these sentences also elicited greater activation in a region in the LIFG. Sentence-level phonetic competition metrics uniquely correlated with LIFG activity as well. This finding is consistent with the hypothesis that the LIFG responds to competition at multiple levels of language processing and that recruitment of this region does not require an explicit phonological judgment.