Rethinking Cognitive Load: A Default-Mode Network Perspective

Intervention effect of exercise on working memory in patients with depression: a systematic review

Background

This article aims to systematically evaluate the intervention effect of exercise on working memory in patients with depression.

Methods

Six Chinese and English databases were searched for randomized controlled trials (RCTs) about exercise on working memory in patients with depression. PEDro scale was adopted to evaluate the methodological quality of the included articles, GRADEpro scale was employed to evaluate the level of evidence for outcomes, and the Metafor Package in R 4.4.1 was used to analyze the combined effect size, subgroup analyses and publication bias.

Results

A total of 15 studies were included. The meta-analysis indicated that exercise had a statistically significant effect on working memory in patients with depression, with an effect size of 0.16 (95% CI [0.03-0.28], p = 0.02). Exercise type (F(3,34) = 1.99, p = 0.13), intervention content (F(1,36) = 1.60, p = 0.22), and exercise duration (F(1,36) = 0.05, p = 0.83) did not moderate the effect, whereas exercise intensity showed a moderating effect (F(2,35) = 8.83, p < 0.01). There was evidence of publication bias in the study results (t = 2.52, p = 0.02).

Conclusion

Exercise can improve the working memory of patients with depression, and its moderating effect is the best when having low-intensity and moderate-intensity. Research plan was registered in international system evaluation platform PROSPERO (https://www.crd.york.ac.uk/PROSPERO/) (CRD42023475325).

Inner sense of rhythm: percussionist brain activity during rhythmic encoding and synchronization

Introduction

The main objective of this research is to explore the core cognitive mechanisms utilized by exceptionally skilled percussionists as they navigate complex rhythms. Our specific focus is on understanding the dynamic interactions among brain regions, respectively, related to externally directed cognition (EDC), internally directed cognition (IDC), and rhythm processing, defined as the neural correlates of rhythm processing (NCRP).

Methods

The research involved 26 participants each in the percussionist group (PG) and control group (CG), who underwent task-functional magnetic resonance imaging (fMRI) sessions focusing on rhythm encoding and synchronization. Comparative analyses were performed between the two groups under each of these conditions.

Results

Rhythmic encoding showed decreased activity in EDC areas, specifically in the right calcarine cortex, left middle occipital gyrus, right fusiform gyrus, and left inferior parietal lobule, along with reduced NCRP activity in the left dorsal premotor, right sensorimotor cortex, and left superior parietal lobule. During rhythmic synchronization, there was increased activity in IDC areas, particularly in the default mode network, and in NCRP areas including the left inferior frontal gyrus and bilateral putamen. Conversely, EDC areas like the right dorsolateral prefrontal gyrus, right superior temporal gyrus, right middle occipital gyrus, and bilateral inferior parietal lobule showed decreased activity, as did NCRP areas including the bilateral dorsal premotor cortex, bilateral ventral insula, bilateral inferior frontal gyrus, and left superior parietal lobule.

Discussion

PG's rhythm encoding is characterized by reduced cognitive effort compared to CG, as evidenced by decreased activity in brain regions associated with EDC and the NCRP. Rhythmic synchronization reveals up-regulated IDC, down-regulated EDC involvement, and dynamic interplay among regions with the NCRP, suggesting that PG engages in both automatic and spontaneous processing simultaneously. These findings provide valuable insights into expert performance and present opportunities for improving music education.

Behavioural Synchronisation between Dogs and Humans: Unveiling Interspecific Motor Resonance?

Dogs' behavioural synchronisation with humans is of growing scientific interest. However, studies lack a comprehensive exploration of the neurocognitive foundations of this social cognitive ability. Drawing parallels from the mechanisms underlying behavioural synchronisation in humans, specifically motor resonance and the recruitment of mirror neurons, we hypothesise that dogs' behavioural synchronisation with humans is underpinned by a similar mechanism, namely interspecific motor resonance. Based on a literature review, we argue that dogs possess the prerequisites for motor resonance, and we suggest that interspecific behavioural synchronisation relies on the activation of both human and canine mirror neurons. Furthermore, interspecific behavioural studies highlight certain characteristics of motor resonance, including motor contagion and its social modulators. While these findings strongly suggest the potential existence of interspecific motor resonance, direct proof remains to be established. Our analysis thus paves the way for future research to confirm the existence of interspecific motor resonance as the neurocognitive foundation for interspecific behavioural synchronisation. Unravelling the neurocognitive mechanisms underlying this behavioural adjustment holds profound implications for understanding the evolutionary dynamics of dogs alongside humans and improving the day-to-day management of dog-human interactions.

A dual process model of spontaneous conscious thought

In the present article, I review theory and evidence on the psychological mechanisms of mind wandering, paying special attention to its relation with executive control. I then suggest applying a dual-process framework (i.e., automatic vs. controlled processing) to mind wandering and goal-directed thought. I present theoretical arguments and empirical evidence in favor of the view that mind wandering is based on automatic processing, also considering its relation to the concept of working memory. After that, I outline three scenarios for an interplay between mind wandering and goal-directed thought during task performance (parallel automatic processing, off-task thought substituting on-task thought, and non-disruptive mind wandering during controlled processing) and address the ways in which the mind-wandering and focused-attention spells can terminate. Throughout the article, I formulate empirical predictions. In conclusion, I discuss how automatic and controlled processing may be balanced in human conscious cognition.

Neural processing of bottom-up perception of biological motion under attentional load

Considering its importance for one's survival and social significance, biological motion (BM) perception is assumed to occur automatically. Previous behavioral results showed that task-irrelevant BM in the periphery interfered with task performance at the fovea. Under selective attention, BM perception is supported by a network of regions including the occipito-temporal (OTC), parietal, and premotor cortices. Retinotopy studies that use BM stimulus showed distinct maps for its processing under and away from selective attention. Based on these findings, we investigated how bottom-up perception of BM would be processed in the human brain under attentional load when it was shown away from the focus of attention as a task-irrelevant stimulus. Participants (N = 31) underwent an fMRI study in which they performed an attentionally demanding visual detection task at the fovea while intact or scrambled point light displays of BM were shown at the periphery. Our results showed the main effect of attentional load in fronto-parietal regions and both univariate activity maps and multivariate pattern analysis results support the attentional load modulation on the task-irrelevant peripheral stimuli. However, this effect was not specific to intact BM stimuli and was generalized to motion stimuli as evidenced by the motion-sensitive OTC involvement during the presence of dynamic stimuli in the periphery. These results confirm and extend previous work by showing that task-irrelevant distractors can be processed by stimulus-specific regions when there are enough attentional resources available. We discussed the implications of these results for future studies.

Exercise habits and mental health: Exploring the significance of multimodal imaging markers

Engaging in regular physical activity and establishing exercise habits is known to have multifaceted benefits extending beyond physical health to cognitive and mental well-being. This study explores the intricate relationship between exercise habits, brain imaging markers, and mental health outcomes. While extensive evidence supports the positive impact of exercise on cognitive functions and mental health, recent advancements in multimodal imaging techniques provide a new dimension to this exploration. By using a cross-sectional multimodal brain-behavior statistic in participants with different exercise habits, we aim to unveil the intricate mechanisms underlying exercise's influence on cognition and mental health, including the status of depression, anxiety, and quality of life. This integration of exercise science and imaging promises to substantiate cognitive benefits on mental health and uncover functional and structural changes underpinning these effects. This study embarks on a journey to explore the significance of multimodal imaging metrics (i.e., structural and functional metrics) in deciphering the intricate interplay between exercise habits and mental health, enhancing the comprehension of how exercise profoundly shapes psychological well-being. Our analysis of group comparisons uncovered a strong association between regular exercise habits and improved mental well-being, encompassing factors such as depression, anxiety levels, and overall life satisfaction. Additionally, individuals who engaged in exercise displayed enhanced brain metrics across different modalities. These metrics encompassed greater gray matter volume within the left frontal regions and hippocampus, improved white matter integrity in the frontal-occipital fasciculus, as well as more robust functional network configurations in the anterior segments of the default mode network. The interplay between exercise habits, brain adaptations, and mental health outcomes underscores the pivotal role of an active lifestyle in nurturing a resilient and high-functioning brain, thus paving the way for tailored interventions and improved well-being.

Aberrant dynamic functional network connectivity in type 2 diabetes mellitus individuals

An increasing number of recent brain imaging studies are dedicated to understanding the neuro mechanism of cognitive impairment in type 2 diabetes mellitus (T2DM) individuals. In contrast to efforts to date that are limited to static functional connectivity, here we investigate abnormal connectivity in T2DM individuals by characterizing the time-varying properties of brain functional networks. Using group independent component analysis (GICA), sliding-window analysis, and k-means clustering, we extracted thirty-one intrinsic connectivity networks (ICNs) and estimated four recurring brain states. We observed significant group differences in fraction time (FT) and mean dwell time (MDT), and significant negative correlation between the Montreal Cognitive Assessment (MoCA) scores and FT/MDT. We found that in the T2DM group the inter- and intra-network connectivity decreases and increases respectively for the default mode network (DMN) and task-positive network (TPN). We also found alteration in the precuneus network (PCUN) and enhanced connectivity between the salience network (SN) and the TPN. Our study provides evidence of alterations of large-scale resting networks in T2DM individuals and shed light on the fundamental mechanisms of neurocognitive deficits in T2DM.

Identification and effective connections of core networks in patients with temporal lobe epilepsy and cognitive impairment: Granger causality analysis and multivariate pattern analysis

OBJECTIVE

This study aimed to explore effective connectivity (EC) of the core networks in cognition impairment associated with temporal lobe epilepsy (CI-TLE) by applying resting state and Granger causality analysis (REST-GCA). The specific brain regions that played a critical role in classification were assessed using multivariate pattern analysis (MVPA).

METHODS

Thirty-two patients with CI-TLE and 29 healthy controls who were matched based on age and gender underwent functional magnetic resonance imaging (fMRI).

RESULTS

REST-GCA revealed that patients with CI-TLE displayed decreased GC values in the following brain areas: from the posterior cingulate cortex (PCC) to the left fusiform gyrus (lFFG) and the right parahippocampal gyrus (rPPG); from the right dorsal prefrontal cortex (rDPFC) to the left superior parietal lobule (lSPL); from the left amygdala (lAG) to the PCC. Inhibitory EC was observed from the rDPFC to the PCC compared to HCs. The GC values increased from the right dorsal prefrontal cingulate cortex (rdACC) to the PCC and from the right dorsal forebrain insula (rDAI) to the right middle temporal gyrus (rMTG) in the CI-TLE patients. MVPA showed that the classification yielded an accuracy of 81.91% (78.12%, specificity =85.71%).

CONCLUSION

Our observations indicated that the abnormal EC between the frontal and parietal regions might be associated with the pathophysiological mechanism of CI-TLE. These results also indicated that EC might be play a role as a potential discriminative pattern to detect CI-TLE in patients.

Gradual Loss of Social Group Support during Competition Activates Anterior TPJ and Insula but Deactivates Default Mode Network

Group forming behaviors are common in many species to overcome environmental challenges. In humans, bonding, trust, group norms, and a shared past increase consolidation of social groups. Being a part of a social group increases resilience to mental stress; conversely, its loss increases vulnerability to depression. However, our knowledge on how social group support affects brain functions is limited. This study observed that default mode network (DMN) activity reduced with the loss of social group support from real-life friends in a challenging social competition. The loss of support induced anterior temporoparietal activity followed by anterior insula and the dorsal attentional network activity. Being a part of a social group and having support provides an environment for high cognitive functioning of the DMN, while the loss of group support acts as a threat signal and activates the anterior temporoparietal junction (TPJ) and insula regions of salience and attentional networks for individual survival.

Static and dynamic functional connectome reveals reconfiguration profiles of whole-brain network across cognitive states

Assessment of functional connectivity (FC) has revealed a great deal of knowledge about the macroscale spatiotemporal organization of the brain network. Recent studies found task-versus-rest network reconfigurations were crucial for cognitive functioning. However, brain network reconfiguration remains unclear among different cognitive states, considering both aggregate and time-resolved FC profiles. The current study utilized static FC (sFC, i.e., long timescale aggregate FC) and sliding window-based dynamic FC (dFC, i.e., short timescale time-varying FC) approaches to investigate the similarity and alterations of edge weights and network topology at different cognitive loads, particularly their relationships with specific cognitive process. Both dFC/sFC networks showed subtle but significant reconfigurations that correlated with task performance. At higher cognitive load, brain network reconfiguration displayed increased functional integration in the sFC-based aggregate network, but faster and larger variability of modular reorganization in the dFC-based time-varying network, suggesting difficult tasks require more integrated and flexible network reconfigurations. Moreover, sFC-based network reconfigurations mainly linked with the sensorimotor and low-order cognitive processes, but dFC-based network reconfigurations mainly linked with the high-order cognitive process. Our findings suggest that reconfiguration profiles of sFC/dFC networks provide specific information about cognitive functioning, which could potentially be used to study brain function and disorders.

Flexible integration and segregation of large-scale networks during adaptive control

Adaptive control characterizes the dynamic adjustment of cognitive control to changing environmental demand, and has obtained growing interests in its neural mechanism for the past two decades. Recent years, interpreting network reconfiguration in terms of integration and segregation has been proved to shed light on neural structure underlying various cognitive tasks. However, the relationship between network architecture and adaptive control remains unclear. Here, we quantified the network integration (global efficiency, participation coefficient, inter-subnetwork efficiency) and segregation (local efficiency, modularity) in the whole-brain and analyzed how these graph theory metrics were modulated by adaptive control. The results showed that the integration of the cognitive control network (the fronto-parietal network, FPN), the visual network (VIN) and the sensori-motor network (SMN) was significantly improved when conflict was rare, so as to cope with the incongruent trials of high cognitive control demands. Additionally, as the conflict proportion increased, the segregation of the cingulo-opercular network (CON) and the default mode network (DMN) significantly enhanced, which may contribute to specialized functioning or automatic processing, and help to solve conflict in a less resource-intensive mode. Finally, using graph metrics as features, the multivariate classifier reliably predicted the context condition. These results demonstrate how large-scale brain networks support adaptive control through flexible integration and segregation.

Age-related reduction in trait anxiety: Behavioral and neural evidence of automaticity in negative facial emotion processing

Trait anxiety diminishes with age, which may result from age-related decline in registering salient emotional stimuli and/or enhancement in emotion regulation. We tested the hypotheses in 88 adults 21 to 85 years of age and studied with fMRI of the Hariri task. Age-related decline in stimulus registration would manifest in delayed reaction time (RT) and diminished saliency circuit activity in response to emotional vs. neutral stimuli. Enhanced control of negative emotions would manifest in diminished limbic/emotional circuit and higher prefrontal cortical (PFC) responses to negative emotion. The results showed that anxiety was negatively correlated with age. Age was associated with faster RT and diminished activation of the medial PFC, in the area of the dorsal and rostral anterior cingulate cortex (dACC/rACC) - a hub of the saliency circuit - during matching of negative but not positive vs. neutral emotional faces. A slope test confirmed the differences in the regressions. Further, age was not associated with activation of the PFC in whole-brain regression or in region-of-interest analysis of the dorsolateral PFC, an area identified from meta-analyses of the emotion regulation literature. Together, the findings fail to support either hypothesis; rather, the findings suggest age-related automaticity in processing negative emotions as a potential mechanism of diminished anxiety. Automaticity results in faster RT and diminished anterior cingulate activity in response to negative but not positive emotional stimuli. In support, analyses of psychophysiological interaction demonstrated higher dACC/rACC connectivity with the default mode network, which has been implicated in automaticity in information processing. As age increased, individuals demonstrated faster RT with higher connectivity during matching of negative vs. neutral images. Automaticity in negative emotion processing needs to be investigated as a mechanism of age-related reduction in anxiety.

Autistic traits shape neuronal oscillations during emotion perception under attentional load modulation

Emotional content is particularly salient, but situational factors such as cognitive load may disturb the attentional prioritization towards affective stimuli and interfere with their processing. In this study, 31 autistic and 31 typically developed children volunteered to assess their perception of affective prosodies via event-related spectral perturbations of neuronal oscillations recorded by electroencephalography under attentional load modulations induced by Multiple Object Tracking or neutral images. Although intermediate load optimized emotion processing by typically developed children, load and emotion did not interplay in children with autism. Results also outlined impaired emotional integration emphasized in theta, alpha and beta oscillations at early and late stages, and lower attentional ability indexed by the tracking capacity. Furthermore, both tracking capacity and neuronal patterns of emotion perception during task were predicted by daily-life autistic behaviors. These findings highlight that intermediate load may encourage emotion processing in typically developed children. However, autism aligns with impaired affective processing and selective attention, both insensitive to load modulations. Results were discussed within a Bayesian perspective that suggests atypical updating in precision between sensations and hidden states, towards poor contextual evaluations. For the first time, implicit emotion perception assessed by neuronal markers was integrated with environmental demands to characterize autism.

A Role for Uncertainty in the Neural Distinction Between Social and Nonsocial Thought

Neuroimaging research has identified a network of brain regions that is consistently more engaged when people think about the minds of other people than when they engage in nonsocial tasks. Activations in this "mentalizing network" are sometimes interpreted as evidence for the domain-specificity of cognitive processes supporting social thought. Here, we examine the alternative possibility that at least some activations in the mentalizing network may be explained by uncertainty. A reconsideration of findings from existing functional MRI studies in light of new data from independent raters suggests that (a) social tasks used in past studies have higher levels of uncertainty than their nonsocial comparison tasks and (b) activation in a key brain region associated with social cognition, the dorsomedial prefrontal cortex (DMPFC), may track with the degree of uncertainty surrounding both social and nonsocial inferences. These observations suggest that the preferential DMPFC response observed consistently in social scenarios may reflect the engagement of domain-general processes of uncertainty reduction, which points to avenues for future research into the core cognitive mechanisms supporting typical and atypical social thought.

Cortical connectivity gradients and local timescales during cognitive states are modulated by cognitive loads

Although resting-state fMRI studies support that human brain is topographically organized regarding localized and distributed processes, it is still unclear about the task-modulated cortical hierarchy in terms of distributed functional connectivity and localized timescales. To address, current study investigated the effect of cognitive load on cortical connectivity gradients and local timescales in the healthy brain using resting state fMRI as well as 1- and 2-back working memory task fMRI. The results demonstrated that (1) increased cognitive load was associated with lower principal gradient in transmodal cortices, higher principal gradient in primary cortices, decreased decay rate and reduced timescale variability; (2) global properties including gradient variability, timescale decay rate, timescale variability and network topology were all modulated by cognitive load, with timescale variability related to behavioral performance; and (3) at 2-back state, the timescale variability was indirectly and negatively linked with global network integration, which was mediated by gradient variability. In conclusion, current study provides novel evidence for load-modulated cortical connectivity gradients and local timescales during cognitive states, which could contribute to better understanding about cognitive load theory and brain disorders with cognitive dysfunction.

Intrinsic brain activity reorganization contributes to long-term compensation of higher-order hearing abilities in single-sided deafness

Single-sided deafness (SSD) is an extreme case of partial hearing deprivation and results in a significant decline in higher-order hearing abilities, including sound localization and speech-in-noise recognition. Clinical studies have reported that patients with SSD recover from these higher-order hearing abilities to some extent over time. Neuroimaging studies have observed extensive brain functional plasticity in patients with SSD. However, studies investigating the role of plasticity in functional compensation, particularly those investigating the relationship between intrinsic brain activity alterations and higher-order hearing abilities, are still limited. In this study, we used resting-state functional MRI to investigate intrinsic brain activity, measured by the amplitude of low-frequency fluctuation (ALFF), in 19 patients with left SSD, 17 patients with right SSD, and 21 normal hearing controls (NHs). All patients with SSD had durations of deafness longer than 2 years. Decreased ALFF values in the bilateral precuneus (PCUN), lingual gyrus, and left middle frontal gyrus were observed in patients with SSD compared with the values of NHs. Longer durations of deafness were correlated with better hearing abilities, as well as higher ALFF values in the left inferior parietal lobule, the angular gyrus, the middle occipital gyrus, the bilateral PCUN, and the posterior cingulate gyrus. Moreover, we observed a generally consistent trend of correlation between ALFF values and higher-order hearing abilities in specific brain areas in patients with SSD. That is, better abilities were correlated with lower ALFF values in the frontal regions and higher ALFF values in the PCUN and surrounding parietal-occipital areas. Furthermore, mediation analysis revealed that the ALFF values in the PCUN were a significant mediator of the relationship between the duration of deafness and higher-order hearing abilities. Our study reveals significant plasticity of intrinsic brain activity in patients with SSD and suggests that reorganization of intrinsic brain activity may be one of the compensatory mechanisms that facilitate improvement in higher-order hearing abilities in these patients over time.

Associations of cognitive impairment in patients with schizophrenia with genetic features and with schizophrenia-related structural and functional brain changes

Cognitive impairment is highly prevalent in patients with major psychiatric disorders (MPDs), including schizophrenia (SCZ), bipolar disorder, major depressive disorder, in whom it can be highly disruptive to community functioning and worsen prognosis. Previously, genetic factors and cognitive impairments in MPD patients have been examined mostly in isolated circuits rather than in the whole brain. In the present study, genetic, neuroimaging, and psychometric approaches were combined to investigate the relationship among genetic factors, alterations throughout the brain, and cognitive impairments in a large cohort of patients diagnosed with SCZ, with a reference healthy control (HC) group. Single nucleotide polymorphisms (SNPs) in SCZ-risk genes were found to be strongly related to cognitive impairments as well as to gray matter volume (GMV) and functional connectivity (FC) alterations in the SCZ group. Annotating 136 high-ranking SNPs revealed 65 affected genes (including PPP1R16B, GBBR2, PDE4B, CANCNA1C, SLC12AB, SATB2, MAG12, and SATB2). Only one, a PDE4B SNP (rs1006737), correlated with GMV (r = 0:19 p = 0.015) and FC (r = 0.21, p = 0.0074) in SCZ patients. GMV and FC alterations correlated with one another broadly across brain regions. Moreover, the present data demonstrate three-way SNP-FC-GMV associations in patients with SCZ, thus providing clues regarding potential genetic bases of cognition impairments in SCZ. SNP-FC-GMV relationships correlated with visual learning and reasoning dimensions of cognition. These data provide evidence that SCZ-related cognitive impairments may reflect genetically underlain whole-brain structural and functional alterations.

A new multimodality fusion classification approach to explore the uniqueness of schizophrenia and autism spectrum disorder

Schizophrenia (SZ) and autism spectrum disorder (ASD) sharing overlapping symptoms have a long history of diagnostic confusion. It is unclear what their differences at a brain level are. Here, we propose a multimodality fusion classification approach to investigate their divergence in brain function and structure. Using brain functional network connectivity (FNC) calculated from resting-state fMRI data and gray matter volume (GMV) estimated from sMRI data, we classify the two disorders using the main data (335 SZ and 380 ASD patients) via an unbiased 10-fold cross-validation pipeline, and also validate the classification generalization ability on an independent cohort (120 SZ and 349 ASD patients). The classification accuracy reached up to 83.08% for the testing data and 72.10% for the independent data, significantly better than the results from using the single-modality features. The discriminative FNCs that were automatically selected primarily involved the sub-cortical, default mode, and visual domains. Interestingly, all discriminative FNCs relating to the default mode network showed an intermediate strength in healthy controls (HCs) between SZ and ASD patients. Their GMV differences were mainly driven by the frontal gyrus, temporal gyrus, and insula. Regarding these regions, the mean GMV of HC fell intermediate between that of SZ and ASD, and ASD showed the highest GMV. The middle frontal gyrus was associated with both functional and structural differences. In summary, our work reveals the unique neuroimaging characteristics of SZ and ASD that can achieve high and generalizable classification accuracy, supporting their potential as disorder-specific neural substrates of the two entwined disorders.

Subcortical control of the default mode network: Role of the basal forebrain and implications for neuropsychiatric disorders

The precise interplay between large-scale functional neural systems throughout the brain is essential for performance of cognitive processes. In this review we focus on the default mode network (DMN), one such functional network that is active during periods of quiet wakefulness and believed to be involved in introspection and planning. Abnormalities in DMN functional connectivity and activation appear across many neuropsychiatric disorders, including schizophrenia. Recent evidence suggests subcortical regions including the basal forebrain are functionally and structurally important for regulation of DMN activity. Within the basal forebrain, subregions like the ventral pallidum may influence DMN activity and the nucleus basalis of Meynert can inhibit switching between brain networks. Interactions between DMN and other functional networks including the medial frontoparietal network (default), lateral frontoparietal network (control), midcingulo-insular network (salience), and dorsal frontoparietal network (attention) are also discussed in the context of neuropsychiatric disorders. Several subtypes of basal forebrain neurons have been identified including basal forebrain parvalbumin-containing or somatostatin-containing neurons which can regulate cortical gamma band oscillations and DMN-like behaviors, and basal forebrain cholinergic neurons which might gate access to sensory information during reinforcement learning. In this review, we explore this evidence, discuss the clinical implications on neuropsychiatric disorders, and compare neuroanatomy in the human vs rodent DMN. Finally, we address technological advancements which could help provide a more complete understanding of modulation of DMN function and describe newly identified BF therapeutic targets that could potentially help restore DMN-associated functional deficits in patients with a variety of neuropsychiatric disorders.

Brain Network Topology and Structural–Functional Connectivity Coupling Mediate the Association Between Gut Microbiota and Cognition

Increasing evidence indicates that gut microbiota can influence cognition via the gut–brain axis, and brain networks play a critical role during the process. However, little is known about how brain network topology and structural–functional connectivity (SC–FC) coupling contribute to gut microbiota-related cognition. Fecal samples were collected from 157 healthy young adults, and 16S amplicon sequencing was used to assess gut diversity and enterotypes. Topological properties of brain structural and functional networks were acquired by diffusion tensor imaging (DTI) and resting-state functional magnetic resonance imaging (fMRI data), and SC–FC coupling was further calculated. 3-Back, digit span, and Go/No-Go tasks were employed to assess cognition. Then, we tested for potential associations between gut microbiota, complex brain networks, and cognition. The results showed that gut microbiota could affect the global and regional topological properties of structural networks as well as node properties of functional networks. It is worthy of note that causal mediation analysis further validated that gut microbial diversity and enterotypes indirectly influence cognitive performance by mediating the small-worldness (Gamma and Sigma) of structural networks and some nodal metrics of functional networks (mainly distributed in the cingulate gyri and temporal lobe). Moreover, gut microbes could affect the degree of SC–FC coupling in the inferior occipital gyrus, fusiform gyrus, and medial superior frontal gyrus, which in turn influence cognition. Our findings revealed novel insights, which are essential to provide the foundation for previously unexplored network mechanisms in understanding cognitive impairment, particularly with respect to how brain connectivity participates in the complex crosstalk between gut microbiota and cognition.

A voxel-level brain-wide association study of cortisol at 8 a.m.: Evidence from Cushing's disease

Cortisol, the end product of the hypothalamic–pituitary–adrenal axis, regulates cognitive function and emotion processing. Cushing's disease, which is characterized by a unique excess of cortisol upon clinical diagnosis, serve as an excellent in vivo “hyperexpression” model to investigate the neurobiological mechanisms of cortisol in the human brain. Previous studies have shown the association between cortisol and functional connectivity within an a priori brain network. However, the whole-brain connectivity pattern that accompanies endogenous cortisol variation is still unclear, as are its associated genetic underpinnings. Here, using resting-state functional magnetic resonance imaging in 112 subjects (60 patients with Cushing's disease and 52 healthy subjects), we performed a voxel-level brain-wide association analysis to investigate the functional connectivity pattern associated with a wide variation in cortisol levels at 8 a.m. The results showed that the regions associated with cortisol as of 8 a.m. were primarily distributed in brain functional hubs involved in self-referential processing, such as the medial prefrontal cortex, anterior and posterior cingulate cortex, and caudate. We also found that regions in the middle temporal, inferior parietal and ventrolateral prefrontal cortex, which is important for social communication tasks, and in the visual and supplementary motor cortex, which is involved in primary sensorimotor perception, were adversely affected by excessive cortisol. The connectivity between these regions was also significantly correlated with neuropsychiatric profiles, such anxiety and depression. Finally, combined neuroimaging and transcriptome analysis showed that functional cortisol-sensitive brain variations were significantly coupled to regional expression of glucocorticoid and mineralocorticoid receptors. These findings reveal cortisol-biased functional signatures in the human brain and shed light on the transcriptional regulation constraints on the cortisol-related brain network.

The role of inhibitory control and ADHD symptoms in the occurrence of involuntary thoughts about the past and future: An individual differences study

In everyday life, people often experience involuntary thoughts about their personal past and future events in response to incidental cues in the environment. Yet, despite the abundance of such cues, our consciousness is not constantly flooded by these involuntary autobiographical memories (IAMs) and involuntary future thoughts (IFTs). The main goal of the present study was to further investigate the possibility that cognitive inhibitory control keeps these involuntary cognitions at bay. To test this inhibition hypothesis, we conducted a large-scale study (n = 157) in which groups of participants with different levels of inhibitory control (low, medium, high) and individuals with ADHD spectrum symptoms were engaged in a laboratory vigilance task in which the frequency of IFTs and IAMs was assessed. Contrary to predictions, although participants across groups differed significantly in terms of their individual inhibitory control capacity, the number of IFTs and IAMs reported during the vigilance task was comparable. In addition, individuals with the ADHD spectrum symptoms did not report more spontaneous thoughts compared to other groups. Together, these findings lend little support for the idea that inhibition is a key mechanism that regulates the occurrence of IAMs and IFTs in everyday life. Other possible mechanisms and avenues for future research are discussed.

The neural correlates of ongoing conscious thought

A core goal in cognitive neuroscience is identifying the physical substrates of the patterns of thought that occupy our daily lives. Contemporary views suggest that the landscape of ongoing experience is heterogeneous and can be influenced by features of both the person and the context. This perspective piece considers recent work that explicitly accounts for both the heterogeneity of the experience and context dependence of patterns of ongoing thought. These studies reveal that systems linked to attention and control are important for organizing experience in response to changing environmental demands. These studies also establish a role of the default mode network beyond task-negative or purely episodic content, for example, implicating it in the level of vivid detail in experience in both task contexts and in spontaneous self-generated experiential states. Together, this work demonstrates that the landscape of ongoing thought is reflected in the activity of multiple neural systems, and it is important to distinguish between processes contributing to how the experience unfolds from those linked to how these experiences are regulated.

Examiners' decision-making processes in observation-based clinical examinations

BACKGROUND

Objective structured clinical examinations (OSCEs) are commonly used to assess the clinical skills of health professional students. Examiner judgement is one acknowledged source of variation in candidate marks. This paper reports an exploration of examiner decision making to better characterise the cognitive processes and workload associated with making judgements of clinical performance in exit-level OSCEs.

METHODS

Fifty-five examiners for exit-level OSCEs at five Australian medical schools completed a NASA Task Load Index (TLX) measure of cognitive load and participated in focus group interviews immediately after the OSCE session. Discussions focused on how decisions were made for borderline and clear pass candidates. Interviews were transcribed, coded and thematically analysed. NASA TLX results were quantitatively analysed.

RESULTS

Examiners self-reported higher cognitive workload levels when assessing a borderline candidate in comparison with a clear pass candidate. Further analysis revealed five major themes considered by examiners when marking candidate performance in an OSCE: (a) use of marking criteria as a source of reassurance; (b) difficulty adhering to the marking sheet under certain conditions; (c) demeanour of candidates; (d) patient safety, and (e) calibration using a mental construct of the 'mythical [prototypical] intern'. Examiners demonstrated particularly higher mental demand when assessing borderline compared to clear pass candidates.

CONCLUSIONS

Examiners demonstrate that judging candidate performance is a complex, cognitively difficult task, particularly when performance is of borderline or lower standard. At programme exit level, examiners intuitively want to rate candidates against a construct of a prototypical graduate when marking criteria appear not to describe both what and how a passing candidate should demonstrate when completing clinical tasks. This construct should be shared, agreed upon and aligned with marking criteria to best guide examiner training and calibration. Achieving this integration may improve the accuracy and consistency of examiner judgements and reduce cognitive workload.

Increased cerebral FDG-PET uptake in type 1 diabetes patients with impaired awareness of hypoglycaemia

Approximately 20% of type 1 diabetes (T1D) patients have an impaired awareness of hypoglyceamia (IAH). IAH represents a risk factor for severe and recurrent hypoglycaemic events, which can lead to brain damage. Because no effective treatments are currently available to prevent IAH in this population, characterising the set of brain alterations associated with IAH may reveal novel preclinical diagnostic or therapeutic strategies. Using state-of-the art neuroimaging techniques, we compared ¹⁸ F-fluorodeoxyglucose-positron emission tomography (FDG-PET) uptake at rest between 10 T1D patients with IAH and nine patients with normal awareness of hypoglycaemia (NAH). T1D-IAH patients showed a pattern of increased FDG-PET uptake with respect to NAH patients (P < .05 corrected). Topographically, glucose metabolism was increased in the frontal and precuneus regions. Importantly, within the IAH group, this abnormal hypermetabolism correlated with IAH severity. This hypermetabolic state appeared to be unrelated to compensatory mechanisms as a result of reduced grey matter density or a neuroinflammatory state. We observed an abnormal increase in FDG-uptake in T1D patients with IAH in brain regions strongly related to cognition. Because this hypermetabolic state correlated with IAH severity, its biological characterisation could reveal new preventive or therapeutic strategies. A possible mechanism could be that glucose transport is increased in hypoglycaemia unawareness to compensate for recurrent hypoglycaemia, although this need to be confirmed in further research.

Dynamic Properties of Human Default Mode Network in Eyes-Closed and Eyes-Open

The default mode network (DMN) reflects spontaneous activity in the resting human brain. Previous studies examined the difference in static functional connectivity (sFC) of the DMN between eyes-closed (EC) and eyes-open (EO) using the resting-state functional magnetic resonance imaging (rs-fMRI) data. However, it remains unclear about the difference in dynamic FC (dFC) of the DMN between EC and EO. To this end, we acquired rs-fMRI data from 19 subjects in two different statues (EC and EO) and selected a seed region-of-interest (ROI) at the posterior cingulate cortex (PCC) to generate the sFC map. We identified the DMN consisting of ten clusters that were significantly correlated with the PCC. By using a sliding-window approach, we analyzed the dFC of the DMN. Then, the Newman's modularity algorithm was applied to identify dFC states based on nodal total connectivity strength in each sliding-window. In addition, graph-theory based network analysis was applied to detect dynamic topological properties of the DMN. We identified three group-level dFC states (State1, 2 and 3) that reflects the strength of dFC within the DMN between EC and EO in different time. The following results were reached: (1) no significant difference in sFC between EC and EO, (2) dFC was lower in State2 but higher in State3 in EC than in EO, (3) lower clustering coefficient, local efficiency, and global efficiency, but higher characteristic path length in State2 in EC than in EO, and (4) lower nodal strength in the precuneus (PCUN), PCC, angular gyrus (ANG), middle temporal gyrus (MTG) and medial prefrontal cortex (MPFC) in State3 in EC. These results suggested different resting statuses, EC and EO, may induce different time-varying neural activity in the DMN.

Age differences in the fronto-striato-parietal network underlying serial ordering

Maintaining the ability to arrange thoughts and actions in an appropriate serial order is crucial for complex behavior. We aimed to investigate age differences in the fronto-striato-parietal network underlying serial ordering using functional magnetic resonance imaging. We exposed 25 young and 27 older healthy adults to a digit ordering task, where they had to reorder and recall sequential digits or simply to recall them. We detected a network comprising of the lateral and medial prefrontal, posterior parietal, and striatal regions. In young adults, the prefrontal and parietal regions were more activated and more strongly connected with the supplementary motor area for "reorder & recall" than "pure recall" trials (psychophysiological interaction, PPI). In older adults, the prefrontal and parietal activations were elevated, but the PPI was attenuated. Individual adults who had a stronger PPI performed more accurately in "reorder & recall" trials. The decreased PPI appeared to be compensated by increased physiological correlations between the prefrontal/parietal cortex and the striatum, and by that between the striatum and the supplementary motor area.

The mental workload of conducting research in assessor cognition

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