Human information processing is characterized by bottlenecks that constrain throughput. These bottlenecks limit both what we can perceive and what we can act on in multitask settings. Although perceptual and response limitations are often attributed to independent information processing bottlenecks, it has recently been suggested that a common attentional limitation may be responsible for both. To date, however, evidence supporting the existence of such a "unified" bottleneck has been mixed. Here, we tested the unified bottleneck hypothesis using time-resolved fMRI. Experiment 1 isolated brain regions involved in the response selection bottleneck that limits speeded dual-task performance. These same brain regions were not only engaged by a perceptual encoding task in Experiment 2, their activity also tracked delays to a speeded decision-making task caused by concurrent perceptual encoding (Experiment 3). We conclude that a unified attentional bottleneck, including the inferior frontal junction, superior medial frontal cortex, and bilateral insula, temporally limits operations as diverse as perceptual encoding and decision-making.attention | attentional blink | psychological refractory period A lthough the human brain computes a rich representation of the sensory world, it does not have sufficient processing power to fully analyze all of the information it receives (1). Attentional mechanisms must therefore select important aspects of the environment for additional processing while filtering out less salient information (e.g., ref.2). Although attention makes the vast amount of sensory information impinging on our senses manageable, it does so at a cost, for it results in bottlenecks that can both block awareness of, and disrupt decision-making for, behaviorally relevant events. These limitations are most evident in dual-task settings, as the concurrent performance of two or more tasks usually leads to impairment in at least one of the tasks.Evidence supporting the view that attention to one event can block awareness of another comes from the attentional blink (AB) paradigm, in which participants report two-typically visual-targets (T1 and T2) presented in a rapid stream of distractors. The AB refers to the profound deficit in the explicit perception of T2 when that target follows T1 by ≈200-500 ms (3, 4). Although a number of hypotheses have been proposed to explain the AB (5), several lines of evidence suggest that deploying attention to consciously encode an initial target can constrain awareness of additional targets (6). Moreover, the duration of the attentional blink is modulated by the encoding load of T1 (7). Based on such findings, it has been proposed that the attentional demands of encoding information into working memory constitutes a bottleneck in information processing (henceforth, the encoding bottleneck; ref. 8).Unlike the AB, where capacity limitations manifest as a failure of awareness, the psychological refractory period (PRP) paradigm exposes the serial nature of decisional processes. In it, p...

Growing evidence suggests that coordinated activity within specific functional brain networks supports cognitive ability, and that abnormalities in brain connectivity may underlie cognitive deficits observed in neuropsychiatric diseases, such as schizophrenia. Two functional networks, the fronto-parietal network (FPN) and cingulo-opercular network (CON), are hypothesized to support top-down control of executive functioning, and have therefore emerged as potential drivers of cognitive impairment in disease-states. Graph theoretic analyses of functional connectivity data can characterize network topology, allowing the relationships between cognitive ability and network integrity to be examined. In the current study we applied graph analysis to pseudo-resting state data in 54 healthy subjects and 46 schizophrenia patients, and measured overall cognitive ability as the shared variance in performance from tasks of episodic memory, verbal memory, processing speed, goal maintenance, and visual integration. We found that, across all participants, cognitive ability was significantly positively associated with the local and global efficiency of the whole brain, FPN, and CON, but not with the efficiency of a comparison network, the auditory network. Additionally, the participation coefficient of the right anterior insula, a major hub within the CON, significantly predicted cognition, and this relationship was independent of CON global efficiency. Surprisingly, we did not observe strong evidence for group differences in any of our network metrics. These data suggest that functionally efficient task control networks support better cognitive ability in both health and schizophrenia, and that the right anterior insula may be a particularly important hub for successful cognitive performance across both health and disease.

A longstanding debate in working memory (WM) is whether information is maintained in a central, capacity-limited storage system or whether there are domain-specific stores for different modalities. This question is typically addressed by determining whether concurrent storage of 2 different memory arrays produces interference. Prior studies using this approach have shown at least some cost to maintaining 2 memory arrays that differed in perceptual modalities. However, it is not clear whether these WM costs resulted from competition for a central, capacity-limited store or from other potential sources of dual-task interference, such as task preparation and coordination, overlap in representational content (e.g., object vs. space based), or cognitive strategies (e.g., verbalization, chunking of the stimulus material in a higher order structure). In the present study we assess dual-task costs during the concurrent performance of a visuospatial WM task and an auditory object WM task when such sources of interference are minimized. The results show that performance of these 2 WM tasks are independent from each another, even at high WM load. Only when we introduced a common representational format (spatial information) to both WM tasks did dual-task performance begin to suffer. These results are inconsistent with the notion of a domain-independent storage system, and suggest instead that WM is constrained by multiple domain-specific stores and central executive processes. Evidently, there is nothing intrinsic about the functional architecture of the human mind that prevents it from storing 2 distinct representations in WM, as long as these representations do not overlap in any functional domain.

Neurobiological theories of awareness propose divergent accounts of the spatial extent of brain changes that support conscious perception. Whereas focal theories posit mostly local regional changes, global theories propose that awareness emerges from the propagation of neural signals across a broad extent of sensory and association cortex. Here we tested the scalar extent of brain changes associated with awareness using graph theoretical analysis applied to functional connectivity data acquired at ultra-high field while subjects performed a simple masked target detection task. We found that awareness of a visual target is associated with a degradation of the modularity of the brain's functional networks brought about by an increase in intermodular functional connectivity. These results provide compelling evidence that awareness is associated with truly global changes in the brain's functional connectivity.awareness | graph theory | functional connectivity | consciousness T hree broad classes of models have been proposed to explain the neural basis of awareness, with these classes primarily differing on the predicted extent of neural information changes associated with conscious perception. According to focal theories, awareness results from local changes in neural activity in either the perceptual substrates (1-3) or in higher-level nodes of information processing pathways (4). By contrast, network-level theories posit that awareness is tightly associated with activation of parietofrontal attention networks of the brain (5-11). Finally, global models propose that awareness results from widespread changes in the activation state (12-15) and functional connectivity (16-19) of the brain. Though there is strong experimental support for network-level theories, there is scant experimental evidence in favor of truly sweeping, widespread changes in brain activity with conscious perception despite the fact that global scale models have recently come to prominence in the theoretical landscape of this field.Using a graph theoretical approach applied to ultra-high-field fMRI data, here we experimentally tested a key tenet of global theories: the widespread emergence of large-scale functional connectivity with awareness. Graph theory analyses are ideal tools to test global models of awareness because they can provide concise measures of the integration and segregation of interconnected nodes of a system (20). Applied to functional imaging data, we treat individual brain regions of interest (ROIs) as nodes, functional connectivity between ROIs as edges, and functional brain networks as interconnected modules of nodes. When examining a large set of ROIs that encompass the different networks of the human cerebral cortex (21, 22), we can apply graph theory analyses to estimate the extent to which key measures of global information processing are altered by the state of awareness. This approach has been previously applied to study differences in cognitive states (23)(24)(25)(26)(27)(28)(29)(30)(31). Although recent studies have t...

Previous work suggests that individuals with schizophrenia display accelerated aging of white matter integrity, however, it is still unknown whether functional brain networks also decline at an elevated rate in schizophrenia. Given the known degradation of functional connectivity and the normal decline in cognitive functioning throughout healthy aging, we aimed to test the hypothesis that efficiency of large-scale functional brain networks supporting overall cognition, as well as integrity of hub nodes within those networks, show evidence of accelerated aging in schizophrenia. Using pseudo-resting state data in 54 healthy controls and 46 schizophrenia patients, in which task-dependent signal from 3 tasks was regressed out to approximate resting-state data, we observed a significant diagnosis by age interaction in the prediction of both global and local efficiency of the cingulo-opercular network, and of the local efficiency of the fronto-parietal network, but no interaction when predicting both default mode network and whole brain efficiency. We also observed a significant diagnosis by age interaction for the node degree of the right anterior insula, left dorsolateral prefrontal cortex, and dorsal anterior cingulate cortex. All interactions were driven by stronger negative associations between age and network metrics in the schizophrenia group than the healthy controls. These data provide evidence that is consistent with accelerated aging of large-scale functional brain networks in schizophrenia that support higher-order cognitive ability.

Task-based connectivity studies facilitate the understanding of how the brain functions during cognition, which is commonly impaired in schizophrenia (SZ). Our aim was to investigate functional connectivity during a working memory task in SZ. We hypothesized that the task-negative (default mode) network and the cognitive control (frontoparietal) network would show dysconnectivity. Twenty-five SZ patient and 31 healthy control scans were collected using the customized 3T Siemens Skyra MRI scanner, previously used to collect data for the Human Connectome Project. Blood oxygen level dependent signal during the 0-back and 2-back conditions were extracted within a network-based parcelation scheme. Average functional connectivity was assessed within five brain networks: frontoparietal (FPN), default mode (DMN), cingulo-opercular (CON), dorsal attention (DAN), and ventral attention network; as well as between the DMN or FPN and other networks. For within-FPN connectivity, there was a significant interaction between n-back condition and group (p = 0.015), with decreased connectivity at 0-back in SZ subjects compared to controls. FPN-to-DMN connectivity also showed a significant condition × group effect (p = 0.003), with decreased connectivity at 0-back in SZ. Across groups, connectivity within the CON and DAN were increased during the 2-back condition, while DMN connectivity with either CON or DAN were decreased during the 2-back condition. Our findings support the role of the FPN, CON, and DAN in working memory and indicate that the pattern of FPN functional connectivity differs between SZ patients and control subjects during the course of a working memory task.

Early identification and treatment are associated with improved outcomes in bipolar disorder (BPD) and schizophrenia (SCZ). Screening for the presence of these disorders usually involves time-intensive interviews that may not be practical in settings where mental health providers are limited. Thus, individuals at earlier stages of illness are often not identified. The Washington Early Recognition Center Affectivity and Psychosis (WERCAP) screen is a self-report questionnaire originally developed to identify clinical risk for developing bipolar or psychotic disorders. The goal of the current study was to investigate the utility of the WERCAP Screen and two complementary questionnaires, the WERC Stress Screen and the WERC Substance Screen, in identifying individuals with established SCZ or BPD. Participants consisted of 35 BPD and 34 SCZ patients, as well as 32 controls (CON), aged 18–30 years. Univariate analyses were used to test for score differences between groups. Logistic regression and receiver operating characteristic (ROC) curves were used to identify diagnostic predictors. Significant group differences were found for the psychosis section of the WERCAP (pWERCAP; p < 0.001), affective section of the WERCAP (aWERCAP; p = 0.001), and stress severity (p = 0.027). No significant group differences were found in the rates of substance use as measured by the WERC Substance Screen (p = 0.267). Only the aWERCAP and pWERCAP scores were useful predictors of diagnostic category. ROC curve analysis showed the optimal cut point on the aWERCAP to identify BPD among our participant groups was a score of >20 [area under the curve (AUC): 0.87; sensitivity: 0.91; specificity: 0.71], while that for the pWERCAP to identify SCZ was a score of >13 (AUC: 0.89; sensitivity: 0.88; specificity: 0.82). These results indicate that the WERCAP Screen may be useful in screening individuals for BPD and SCZ and that identifying stress and substance-use severity can be rapidly done using self-report questionnaires. Larger studies in undiagnosed individuals will be needed to test the WERCAP Screen’s ability to identify mania or psychosis in the community.

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