Working memory in preterm‐born adults: Load‐dependent compensatory activity of the posterior default mode network

Premature birth is associated with an increased risk of cognitive performance deficits that are dependent on working memory (WM) load in childhood. Less clear is whether preterm‐born adults show similar WM impairments, or develop compensatory brain mechanisms that help to overcome prematurity‐related functional deficits, for example, by a workload‐dependent over‐recruitment of WM‐typical areas, and/or engagement of alternative brain networks. In this functional magnetic resonance imaging study, 73 adults born very preterm and/or with very low birth weight (VP/VLBW) and 73 term‐born controls (CON, mean age: 26.5 years) performed a verbal N‐Back paradigm with varying workload (0‐back, 1‐back, 2‐back). Generally, both groups showed similar performance accuracy and task‐typical patterns of brain activations (especially in fronto‐cingulo‐parietal, thalamic, and cerebellar areas) and deactivations (especially in mesial frontal and parietal aspects of the default mode network [DMN]). However, VP/VLBW adults showed significantly stronger deactivations (P < 0.05, cluster‐level corrected) than CON in posterior DMN regions, including right ventral precuneus, and right parahippocampal areas (with adjacent cerebellar areas), which were specific for the most demanding 2‐back condition. Consistent with a workload‐dependent effect, VP/VLBW adults with stronger deactivations (1‐back > 2‐back) in the parahippocampal/cerebellar cluster also presented a greater slowing of response latencies with increasing WM load (2‐back > 1‐back), indicative of higher effort. In conclusion, VP/VLBW adults recruited similar anatomical networks as controls during N‐back performance, but showed an enhanced suppression of posterior DMN regions during higher workload, which may reflect a temporary suppression of stimulus‐independent thoughts that helps to maintain adequate task performance with increasing attentional demands. Hum Brain Mapp 36:1121–1137, 2015. © 2014 Wiley Periodicals, Inc.     

Dysregulation of working memory and default‐mode networks in schizophrenia using independent component analysis,an fBIRN and MCIC study

Deficits in working memory (WM) are a consistent neurocognitive marker for schizophrenia. Previous studies have suggested that WM is the product of coordinated activity in distributed functionally connected brain regions. Independent component analysis (ICA) is a data‐driven approach that can identify temporally coherent networks that underlie fMRI activity. We applied ICA to an fMRI dataset for 115 patients with chronic schizophrenia and 130 healthy controls by performing the Sternberg Item Recognition Paradigm. Here, we describe the first results using ICA to identify differences in the function of WM networks in schizophrenia compared to controls. ICA revealed six networks that showed significant differences between patients with schizophrenia and healthy controls. Four of these networks were negatively task‐correlated and showed deactivation across the posterior cingulate, precuneus, medial prefrontal cortex, anterior cingulate, inferior parietal lobules, and parahippocampus. These networks comprise brain regions known as the default‐mode network (DMN), a well‐characterized set of regions shown to be active during internal modes of cognition and implicated in schizophrenia. Two networks were positively task‐correlated, with one network engaging WM regions such as bilateral DLPFC and inferior parietal lobules while the other network engaged primarily the cerebellum. Our results suggest that DLPFC dysfunction in schizophrenia might be lateralized to the left and intrinsically tied to other regions such as the inferior parietal lobule and cingulate gyrus. Furthermore, we found that DMN dysfunction in schizophrenia exists across multiple subnetworks of the DMN and that these subnetworks are individually relevant to the pathophysiology of schizophrenia. In summary, this large multsite study identified multiple temporally coherent networks, which are aberrant in schizophrenia versus healthy controls and suggests that both task‐correlated and task‐anticorrelated networks may serve as potential biomarkers. Hum Brain Mapp, 2009. © 2009 Wiley‐Liss, Inc.     

Functional connections between activated and deactivated brain regions mediate emotional interference during externally directed cognition

Recent evidence shows that task‐deactivations are functionally relevant for cognitive performance. Indeed, higher cognitive engagement has been associated with higher suppression of activity in task‐deactivated brain regions ‐ usually ascribed to the Default Mode Network (DMN). Moreover, a negative correlation between these regions and areas actively engaged by the task is associated with better performance. DMN regions show positive modulation during autobiographical, social, and emotional tasks. However, it is not clear how processing of emotional stimuli affects the interplay between the DMN and executive brain regions. We studied this interplay in an fMRI experiment using emotional negative stimuli as distractors. Activity modulations induced by the emotional interference of negative stimuli were found in frontal, parietal, and visual areas, and were associated with modulations of functional connectivity between these task‐activated areas and DMN regions. A worse performance was predicted both by lower activity in the superior parietal cortex and higher connectivity between visual areas and frontal DMN regions. Connectivity between right inferior frontal gyrus and several DMN regions in the left hemisphere was related to the behavioral performance. This relation was weaker in the negative than in the neutral condition, likely suggesting less functional inhibitions of DMN regions during emotional processing. These results show that both executive and DMN regions are crucial for the emotional interference process and suggest that DMN connections are related to the interplay between externally‐directed and internally‐focused processes. Among DMN regions, superior frontal gyrus may be a key node in regulating the interference triggered by emotional stimuli.     

Facing successfully high mental workload and stressors: An fMRI study

The present fMRI study aimed at highlighting patterns of brain activations and autonomic activity when confronted with high mental workload and the threat of auditory stressors. Twenty participants performed a complex cognitive task in either safe or aversive conditions. Our results showed that increased mental workload induced recruitment of the lateral frontoparietal executive control network (ECN), along with disengagement of medial prefrontal and posterior cingulate regions of the default mode network (DMN). Mental workload also elicited an increase in heart rate and pupil diameter. Task performance did not decrease under the threat of stressors, most likely due to efficient inhibition of auditory regions, as reflected by a large decrement of activity in the superior temporal gyri. The threat of stressors was also accompanied with deactivations of limbic regions of the salience network (SN), possibly reflecting emotional regulation mechanisms through control from dorsal medial prefrontal and parietal regions, as indicated by functional connectivity analyses. Meanwhile, the threat of stressors induced enhanced ECN activity, likely for improved attentional and cognitive processes toward the task, as suggested by increased lateral prefrontal and parietal activations. These fMRI results suggest that measuring the balance between ECN, SN, and DMN recruitment could be used for objective mental state assessment. In this sense, an extra recruitment of task‐related regions and a high ratio of lateral versus medial prefrontal activity may represent a relevant marker of increased but efficient mental effort, while the opposite may indicate a disengagement from the task due to mental overload and/or stressors.     

Default mode of brain function in monkeys

Human neuroimaging has revealed a specific network of brain regions-the default-mode network (DMN)-that reduces its activity during goal-directed behavior. So far, evidence for a similar network in monkeys is mainly indirect, since, except for one positron emission tomography study, it is all based on functional connectivity analysis rather than activity increases during passive task states. Here, we tested whether a consistent DMN exists in monkeys using its defining property. We performed a meta-analysis of functional magnetic resonance imaging data collected in 10 awake monkeys to reveal areas in which activity consistently decreases when task demands shift from passive tasks to externally oriented processing. We observed task-related spatially specific deactivations across 15 experiments, implying in the monkey a functional equivalent of the human DMN. We revealed by resting-state connectivity that prefrontal and medial parietal regions, including areas 9/46d and 31, respectively, constitute the DMN core, being functionally connected to all other DMN areas. We also detected two distinct subsystems composed of DMN areas with stronger functional connections between each other. These clusters included areas 24/32, 8b, and TPOC and areas 23, v23, and PGm, respectively. Such a pattern of functional connectivity largely fits, but is not completely consistent with anatomical tract tracing data in monkeys. Also, analysis of afferent and efferent connections between DMN areas suggests a multisynaptic network structure. Like humans, monkeys increase activity during passive epochs in heteromodal and limbic association regions, suggesting that they also default to internal modes of processing when not actively interacting with the environment.     

Cortical deactivations during gastric fundus distension in health: visceral pain‐specific response or attenuation of ‘default mode’ brain function? A H215O‐PET study

Abstract Gastric distension activates a cerebral network including brainstem, thalamus, insula, perigenual anterior cingulate, cerebellum, ventrolateral prefrontal cortex and potentially somatosensory regions. Cortical deactivations during gastric distension have hardly been reported. To describe brain areas of decreased activity during gastric fundus distension compared to baseline, using data from our previously published study (Gastroenterology, 128, 2005 and 564). H₂¹⁵O‐brain positron emission tomography was performed in 11 healthy volunteers during five conditions (random order): (C₁) no distension (baseline); isobaric distension to individual thresholds for (C₂) first, (C₃) marked, (C₄) unpleasant sensation and (C₅) sham distension. Subtraction analyses were performed (in SPM2) to determine deactivated areas during distension compared to baseline, with a threshold of P_{uncorrected_voxel_level} < 0.001 and P_{corrected_cluster_level} < 0.05. Baseline–maximal distension (C₁–C₄) yielded significant deactivations in: (i) bilateral occipital, lateral parietal and temporal cortex as well as medial parietal lobe (posterior cingulate and precuneus) and medial temporal lobe (hippocampus and amygdala), (ii) right dorsolateral and dorso‐ and ventromedial PFC, (iii) left subgenual ACC and bilateral caudate head. Intragastric pressure and epigastric sensation score correlated negatively with brain activity in similar regions. The right hippocampus/amygdala deactivation was specific to sham. Gastric fundus distension in health is associated with extensive cortical deactivations, besides the activations described before. Whether this represents task‐independent suspension of ‘default mode’ activity (as described in various cognitive tasks) or an visceral pain/interoception‐specific process remains to be elucidated.     

Modulation of the default mode network is task-dependant in chronic schizophrenia patients

The activity of brain regions of the so-called default mode network (DMN) attenuates during the performance of goal-directed tasks. These activity decreases (named task-induced deactivations; TID) are though to reflect the reallocation of cognitive resources from the DMN to areas implicated in the execution of the task. Recently, DMN activity suppression has been studied in schizophrenia patients. Although these works showed that TID are altered in schizophrenia, they also revealed inconsistent findings. We hypothesized that reallocation of resources is altered in schizophrenia patients and is context or task specific. We investigated TID using functional MRI in 26 schizophrenic patients and 13 control subjects while performing two different goal-directed tasks (the Hayling Sentence Completion Test and the N-Back task). Both whole brain and region of interest conjunction analyses were conducted to investigate brain areas commonly deactivated in the two tasks (task unspecific deactivations). Task-unspecific deactivations were not observed in the schizophrenia group, although these were strongly significant in the control group. Differences between patient and control participants were observed in different regions of the DMN depending whether the subjects performed the Hayling or the N-back task. These results suggest that reallocation of cognitive resources is altered in our patient sample. Moreover, TID were task-unspecific indicating that resources reallocation is context dependent in schizophrenia. DMN activity attenuates differently in schizophrenia patients depending on the cognitive processes involved in the task.     

Cognitive and emotional modulation of brain default operation

Goal-directed behavior lowers activity in brain areas that include the medial frontal cortex, the medial and lateral parietal cortex, and limbic and paralimbic brain regions, commonly referred to as the "default network." These activity decreases are believed to reflect the interruption of processes that are ongoing when the mind is in a restful state. Previously, the nature of these processes was probed by varying cognitive task parameters, but the presence of emotional processes, while often assumed, was little investigated. With fMRI, we studied the effect of systematic variations of both cognitive load and emotional stimulus connotation on task-related decreases in the default network by employing an auditory working memory (WM) task with musical sounds. The performance of the WM task, compared to passive listening, lowered the activity in medial and lateral, prefrontal, parietal, temporal, and limbic regions. In a subset of these regions, the magnitude of decrease depended on the memory load; the greater the cognitive load, the larger the magnitude of the observed decrease. Furthermore, in the right amygdala and the left precuneus, areas previously associated with processing of unpleasant dissonant musical sounds, there was an interaction between the experimental condition and the stimulus type. The current results are consistent with the previously reported effect of task difficulty on task-related brain activation decreases. The results also indicate that task-related decreases may be further modulated by the emotional stimulus connotation.     

Default-mode network changes in preclinical Huntington's disease

The default-mode network (DMN) refers to as a set of brain regions which are active when the brain does not engage in a cognitive task and which are deactivated with task-related cognitive effort. Altered function of the DMN has been associated with a decline of cognition in several neurodegenerative diseases and related at-risk conditions. In Huntington's disease, an autosomal dominant inherited neurodegenerative disorder, several studies so far have shown abnormal task-related brain activation patterns even in preclinical carriers of the Huntington's disease gene mutation (preHD). To date, however, the functional integrity of the DMN has not been addressed in this population. The aim of this study was to study the functional connectivity of the DMN in 18 preHD and 18 healthy controls who underwent functional magnetic resonance imaging during an attention task. A group independent component analysis identified spatiotemporally distinct patterns of two DMN subsystems. The spatial distribution of these components in preHD was similar to controls. However, preHD showed lower subsystem-specific connectivity in the anterior medial prefrontal cortex, the left inferior parietal and the posterior cingulate cortex (p<0.05, cluster-corrected). Connectivity between the two DMN subsystems was increased in preHD compared to controls. In preHD individuals lower functional connectivity of the left inferior parietal cortex was associated with shorter reaction times in the attention task. This suggests that some functionally critical regions of the DMN may have to remain active to maintain or optimise cognitive performance in preHD.     

Disrupted default mode network connectivity in male adolescents with conduct disorder

Conduct disorder (CD) is a serious behavioral disorder of childhood and adolescence. The default mode network (DMN) is a brain network which supports self-referential cognitive processes and is typically deactivated during task performance. The aim of this study was to investigate DMN connectivity in male adolescents with pure CD compared to typically-developing controls. Eighteen male adolescents with CD and 18 sex-, age- and education-matched typically-developing (TD) participants were recruited. Current and lifetime psychiatric disorders were assessed using the Chinese version of the Schedule for Affective Disorder and Schizophrenia for School-Age Children-Present and Lifetime Version. Resting state functional magnetic resonance imaging (fMRI) data were obtained using a 3.0 T scanner. Independent components analysis (ICA) was used to investigate functional connectivity between the DMN and related brain regions. DMN activity was observed in medial prefrontal, posterior cingulate, and lateral parietal cortices, and extended to the brainstem. Adolescents with CD showed significantly reduced functional connectivity within the bilateral posterior cingulate cortex (PCC), bilateral precuneus and right superior temporal gyrus relative to TD controls. CD is associated with reduced functional connectivity within the DMN and between the DMN and other regions. These preliminary results suggest that deficits in DMN functional connectivity may serve as a biomarker of CD.     

Effects of working memory training on functional connectivity and cerebral blood flow during rest

Working memory (WM) training (WMT) alters the task-related brain activity and structure of the external attention system (EAS). We investigated whether WMT also alters resting-state brain mechanisms, which are assumed to reflect intrinsic brain activity and connectivity. Our study subjects were subjected to a 4-week WMT program and brain scans before and after the intervention for determining changes of functional connectivity and regional cerebral blood flow during rest (resting-FC/resting-rCBF). Compared with no-intervention, WMT (a) increased resting-FC between the medial prefrontal cortex (mPFC) and precuneus, which are key nodes of the default mode network (DMN), (b) decreased resting-FC between mPFC and the right posterior parietal cortex/right lateral prefrontal cortex (LPFC), which are key nodes of the EAS, and (c) increased resting-rCBF in the right LPFC. However, the training-related decreases in resting-FC between the key DMN node and the nodes of EAS were only observed when the whole brain signal was regressed out in individual analyses, and these changes were not observed when the whole brain signal was not regressed out in individual analyses. Further analyses indicated that these differences may be mediated by a weak but a widespread increase in resting-FC between the nodes of EAS and activity of multiple bilateral areas across the brain. These results showed that WMT induces plasticity in neural mechanisms involving DMN and the EAS during rest and indicated that intrinsic brain activity and connectivity can be affected by cognitive training.     

Common and distinct neural mechanisms of the fundamental dimensions of social cognition

In the present study, we used a valence classification task to investigate the common and distinct neural basis of the two fundamental dimensions of social cognition (agency and communion) using functional magnetic resonance imaging (fMRI). The results showed that several brain areas associated with mentalizing, along with the inferior parietal gyrus in the mirror system, showed overlap in response to both agentic and communal words. These findings suggest that both content categories are related to the neural basis of social cognition; further, several areas in the default mode network (DMN) showed similar deactivations between agency and communion, reflecting task-induced deactivation (TID). In terms of distinct activations, the findings indicated greater deactivations for communal than agentic content in the ventral anterior cingulate (vACC) and medial orbitofrontal cortex (mOFC). Communion also showed greater activation in some visual areas compared to agentic content, including occipital gyrus, lingual gyrus, and fusiform gyrus. These activations may reflect greater allocation of attentional resources to visual areas when processing communal content, or inhibition of cognitive activity irrelevant to task performance. If so, this suggests greater attention and engagement with communion-related content. The present research thus suggests common and differential activations for agency- versus communion-related content.     

Reduced functional coupling in the default‐mode network during self‐referential processing

Activity within the default‐mode network (DMN) is thought to be related to self‐referential processing, such as thinking about one's preferences or personality traits. Although the DMN is generally considered to function as a network, evidence is starting to accumulate that suggests that areas of the DMN are each specialized for different subfunctions of self‐referential processing. Here, we address the issue of functional specialization by investigating changes in coupling between areas of the DMN during self‐referential processing. To this aim, brain activity was assessed during a task in which subjects had to indicate whether a trait adjective described their own personality (self‐referential, Self condition), that of another person (other‐referential, Other condition), or whether the trait was socially desirable (nonreferential, Control condition). To exclude confounding effects of cardiorespiratory processes on activity and functional coupling, we corrected the fMRI signal for these effects. Activity within areas of the DMN was found to be modulated by self‐referential processing. More specifically, during the Self condition compared to the Other and Control condition, activity within the dorsal medial prefrontal cortex, ventral medial prefrontal cortex, and posterior cingulate cortex was increased. Moreover, coupling between areas of the DMN was reduced during the Self condition compared to the Other and Control condition, while coupling between regions of the DMN and regions outside the network was increased. As such, these results provide an indication for functional specialization within the DMN and support the notion that each area of the DMN is involved in different subfunctions of self‐referential processing. Hum Brain Mapp, 2010. © 2010 Wiley‐Liss, Inc.     

Functional connectivity maps based on hippocampal and thalamic dynamics may account for the default‐mode network

The default‐mode network (DMN) has been reported to comprise a set of inter‐connected transmodal cortical areas, including the posterior cingulate cortex (PCC), medial prefrontal cortex, posterior inferior parietal lobule, lateral temporal region and others. However, the subcortical constituents of the DMN are still not clear. This study aimed to examine whether the correlation maps derived from subcortical structures may also account for neural pattern of the DMN. Structural magnetic resonance imaging (MRI) and resting‐state functional MRI scans of 36 subjects were selected from the Rockland sample (Nathan Kline Institute). The hippocampus and thalamus were chosen as subcortical regions of interest (ROIs). Each ROI was partitioned into composite modules which in turn provided simplified and representative dynamics of blood‐oxygen‐level‐dependent (BOLD) signals. PCC‐seeded and ROI‐based correlation maps were compared by conjunction analyses and paired t‐tests (corrected P < 0.05). Our results unveiled that the hippocampus‐, thalamus‐ and PCC‐centred correlation patterns actually overlapped to a substantial degree. Integrating the signals in the thalamus and hippocampus altogether fully explained the PCC‐seeded DMN. Supplementary analyses based on the BOLD dynamics in several subcortical nuclei (caudate, putamen and globus pallidus) were dissimilar to the DMN. The DMN derived from the ROI/seed‐based approach may represent combined limbic and region‐specific informatics (and their closely interacting neural substrates). The possible causes for previous methods of task‐induced deactivation and seed‐based correlation that failed to depict the holistic limbic picture are discussed. The neocortical manifestation of DMN may reflect the limbic information in the transmodal brain regions.     

Impaired temporoparietal deactivation with working memory load in antipsychotic-naïve patients with first-episode schizophrenia

Abstract

Objectives. Neuroimaging studies have shown abnormal task-related deactivations during working memory (WM) in schizophrenia patients with recent emphasis on brain regions within the default mode network. Using fMRI, we tested whether antipsychotic-naïve schizophrenia patients were impaired at deactivating brain regions that do not subserve WM. Methods. Twenty-three antipsychotic-naïve patients with first-episode schizophrenia and 35 healthy individuals underwent whole-brain 3T fMRI scans while performing a verbal N-back task including 0-back (no WM load), 1-back (low WM load), and 2-back (high WM load) conditions. Results. Contrasting the 2-back and 0-back conditions revealed that patients deactivated default mode network regions to a similar degree as controls. However, patients were impaired in deactivating large bilateral clusters centred on the superior temporal gyrus with increasing WM load. These regions activated with the no WM load condition (0-back) in both groups. Conclusions. Because 0-back activation reflects verbal attention processes, patients’ persistent activation in the 1-back and 2-back conditions may reflect an inability to shift cognitive strategy with onset of WM demands. Since patients were antipsychotic-naïve and task performance was equal to controls, we infer that this impaired temporoparietal deactivation may represent a primary dysfunction in schizophrenia.     

Strategic resource allocation in the human brain supports cognitive coordination of object and spatial working memory

The ability to integrate different types of information (e.g., object identity and spatial orientation) and maintain or manipulate them concurrently in working memory (WM) facilitates the flow of ongoing tasks and is essential for normal human cognition. Research shows that object and spatial information is maintained and manipulated in WM via separate pathways in the brain (object/ventral versus spatial/dorsal). How does the human brain coordinate the activity of different specialized systems to conjoin different types of information? Here we used functional magnetic resonance imaging to investigate conjunction‐ versus single‐task manipulation of object (compute average color blend) and spatial (compute intermediate angle) information in WM. Object WM was associated with ventral (inferior frontal gyrus, occipital cortex), and spatial WM with dorsal (parietal cortex, superior frontal, and temporal sulci) regions. Conjoined object/spatial WM resulted in intermediate activity in these specialized areas, but greater activity in different prefrontal and parietal areas. Unique to our study, we found lower temporo‐occipital activity and greater deactivation in temporal and medial prefrontal cortices for conjunction‐ versus single‐tasks. Using structural equation modeling, we derived a conjunction‐task connectivity model that comprises a frontoparietal network with a bidirectional DLPFC‐VLPFC connection, and a direct parietal‐extrastriate pathway. We suggest that these activation/deactivation patterns reflect efficient resource allocation throughout the brain and propose a new extended version of the biased competition model of WM. Hum Brain Mapp, 2011. © 2010 Wiley‐Liss, Inc.     

Biphasic hemodynamic responses influence deactivation and may mask activation in block-design fMRI paradigms

A previous block-design fMRI study revealed deactivation in the hippocampus in the transverse patterning task, specifically designed, on the basis of lesion literature, to engage hippocampal information processing. In the current study, a mixed block/event-related design was used to determine the temporal nature of the signal change leading to the seemingly paradoxical deactivation. All positive activations in the hippocampal-dependent condition, relative to a closely matched control task, were seen to result from positive BOLD transients in the typical 4-7 s poststimulus time range. However, most deactivations, including in the hippocampus and in other "default mode" regions commonly deactivated in cognitive tasks, were attributable to enhanced negative transient signals in a later time range, 10-12 s. This late hemodynamic transient was most pronounced in medial prefrontal cortex. In some regions, the hippocampal-dependent condition enhanced both the early positive and late negative transients to approximately the same degree, resulting in no significant signal change when block analysis is used, despite very different event-related responses. These results imply that delayed negative transients can play a role in determining the presence and sign of brain activation in block-design studies, in which case an event-related analysis can be more sensitive than a block analysis, even if the different conditions occur within blocks. In this case, default mode deactivations are timelocked to stimulus presentation as much as positive activations are, but in a later time range, suggesting a specific role of negative transient signals in task performance.     

Resting state and task‐induced deactivation: A methodological comparison in patients with schizophrenia and healthy controls

Changes in the default mode network (DMN) have been linked to multiple neurological disorders including schizophrenia. The anticorrelated relationship the DMN shares with task‐related networks permits the quantification of this network both during task (task‐induced deactivations: TID) and during periods of passive mental activity (extended rest). However, the effects of different methodologies (TID vs. extended rest) for quantifying the DMN in the same clinical population are currently not well understood. Moreover, several different analytic techniques, including independent component analyses (ICA) and seed‐based correlation analyses, exist for examining functional connectivity during extended resting states. The current study compared both methodologies and analytic techniques in a group of patients with schizophrenia (SP) and matched healthy controls. Results indicated that TID analyses, ICA, and seed‐based correlation all consistently identified the midline (anterior and posterior cingulate gyrus) and lateral parietal cortex as core regions of the DMN, as well as more variable involvement of temporal lobe structures. In addition, SP exhibited increased deactivation during task, as well as decreased functional connectivity with frontal regions and increased connectivity with posterior and subcortical areas during periods of extended rest. The increased posterior and reduced anterior connectivity may partially explain some of the cognitive dysfunction and clinical symptoms that are frequently associated with schizophrenia. Hum Brain Mapp, 2010. © 2009 Wiley‐Liss, Inc.     

Large‐scale reconfiguration of connectivity patterns among attentional networks during context‐dependent adjustment of cognitive control

The ability to adjust our behavior flexibly depending on situational demands and changes in the environment is an important characteristic of cognitive control. Previous studies have proved that this type of adaptive control plays a crucial role in selective attention, but have barely explored whether and how attentional networks support adaptive control. In the present study, a Stroop task with a different proportion of incongruent trials was used to investigate the brain activity and connectivity of six typical attentional control networks (i.e., the fronto‐parietal network (FPN), cingulo‐opercular network (CON), default mode network (DMN), dorsal attention network (DAN), and ventral attention network/salience network (VAN/SN)) in the environment with changing control demand. The behavioral analysis indicated a decreased Stroop interference (incongruent vs. congruent trial response time [RT]) with the increase in the proportion of incongruent trials within a block, indicating that cognitive control was improved there. The fMRI data revealed that the attenuate Stroop interference was accompanied by the activation of frontal and parietal regions, such as bilateral dorsolateral prefrontal cortex and anterior cingulate cortex. Crucially, the improved cognitive control induced by the increased proportion of incongruent trials was associated with the enhanced functional connectivity within the five networks, and a greater connection between CON with the DAN/SN, and between DMN with the CON/DAN/SN. Meanwhile, however, the functional coupling between the FPN and VAN was decreased. These results suggest that flexible regulations of cognitive control are implemented by the large‐scale reconfiguration of connectivity patterns among the attentional networks.     

Long reaction times are associated with delayed brain activity in lewy body dementia

A significant symptom of Lewy body dementia (LBD) is slow cognitive processing or bradyphrenia. In a previous fMRI task‐based study, we found slower responses in LBD, accompanied by greater deactivation in the default mode network. In this study, we investigated the timing and magnitude of the activations and deactivations with respect to reaction time to determine whether the slower responses in LBD were associated with delayed neuronal activity. Using fMRI, we examined the magnitude and latency of activations and deactivations during an event‐related attention task in 32 patients with LBD and 23 healthy controls using predefined regions of interest. Default mode network deactivations did not significantly differ in their timing between groups or task conditions, while the task‐related activations in the parietal, occipital, frontal, and motor cortex were all significantly later in the LBD group. Repeating the analysis with reaction time as a parametric modulator of activation magnitude produced similar findings, with the reaction time modulator being significant in a number of regions including the default mode network, suggesting that the increased deactivation in LBD is partly explained by slower task completion. Our data suggest that the default mode network deactivation is initiated at the start of the task, and remains deactivated until its end, with the increased magnitude of deactivation in LBD reflecting the more prolonged cognitive processing in these patients. These data add substantially to our understanding of the neural origins of bradyphrenia, which will be essential for determining optimum therapeutic strategies for cognitive impairment in LBD. Hum Brain Mapp 39:633–643, 2018. © 2017 The Authors Human Brain Mapping Published by Wiley Periodicals, Inc.