Modelling neural correlates of working memory: a coordinate-based meta-analysis

Temporal dynamics of visual working memory

The involvement of the human cerebellum in working memory has been well established in the last decade. However, the cerebro-cerebellar network for visual working memory is not as well defined. Our previous fMRI study showed superior and inferior cerebellar activations during a block design visual working memory task, but specific cerebellar contributions to cognitive processes in encoding, maintenance and retrieval have not yet been established. The current study examined cerebellar contributions to each of the components of visual working memory and presence of cerebellar hemispheric laterality was investigated. 40 young adults performed a Sternberg visual working memory task during fMRI scanning using a parametric paradigm. The contrast between high and low memory load during each phase was examined. We found that the most prominent activation was observed in vermal lobule VIIIb and bilateral lobule VI during encoding. Using a quantitative laterality index, we found that left-lateralized activation of lobule VIIIa was present in the encoding phase. In the maintenance phase, there was bilateral lobule VI and right-lateralized lobule VIIb activity. Changes in activation in right lobule VIIIa were present during the retrieval phase. The current results provide evidence that superior and inferior cerebellum contributes to visual working memory, with a tendency for left-lateralized activations in the inferior cerebellum during encoding and right-lateralized lobule VIIb activations during maintenance. The results of the study are in agreement with Baddeley's multi-component working memory model, but also suggest that stored visual representations are additionally supported by maintenance mechanisms that may employ verbal coding.

Brain activation during visual working memory correlates with behavioral mobility performance in older adults

Functional mobility and cognitive function often decline with age. We previously found that functional mobility as measured by the Timed Up and Go Test (TUG) was associated with cognitive performance for visually-encoded (i.e., for location and face) working memory (WM) in older adults. This suggests a common neural basis between TUG and visual WM. To elucidate this relationship further, the present study aimed to examine the neural basis for the WM-mobility association. In accordance with the well-known neural compensation model in aging, we hypothesized that "attentional" brain activation for easy WM would increase in participants with lower mobility. The data from 32 healthy older adults were analyzed, including brain activation during easy WM tasks via functional Magnetic Resonance Imaging (fMRI) and mobility performance via both TUG and a simple walking test. WM performance was significantly correlated with TUG but not with simple walking. Some prefrontal brain activations during WM were negatively correlated with TUG performance, while positive correlations were found in subcortical structures including the thalamus, putamen and cerebellum. Moreover, activation of the subcortical regions was significantly correlated with WM performance, with less activation for lower WM performers. These results indicate that older adults with lower mobility used more cortical (frontal) and fewer subcortical resources for easy WM tasks. To date, the frontal compensation has been proposed separately in the motor and cognitive domains, which have been assumed to compensate for dysfunction of the other brain areas; however, such dysfunction was less clear in previous studies. The present study observed such dysfunction as degraded activation associated with lower performance, which was found in the subcortical regions. We conclude that a common dysfunction-compensation activation pattern is likely the neural basis for the association between visual WM and functional mobility.

From Brain Maps to Cognitive Ontologies: Informatics and the Search for Mental Structure

A major goal of cognitive neuroscience is to delineate how brain systems give rise to mental function. Here we review the increasingly large role informatics-driven approaches are playing in such efforts. We begin by reviewing a number of challenges conventional neuroimaging approaches face in trying to delineate brain-cognition mappings--for example, the difficulty in establishing the specificity of postulated associations. Next, we demonstrate how these limitations can potentially be overcome using complementary approaches that emphasize large-scale analysis--including meta-analytic methods that synthesize hundreds or thousands of studies at a time; latent-variable approaches that seek to extract structure from data in a bottom-up manner; and predictive modeling approaches capable of quantitatively inferring mental states from patterns of brain activity. We highlight the underappreciated but critical role for formal cognitive ontologies in helping to clarify, refine, and test theories of brain and cognitive function. Finally, we conclude with a speculative discussion of what future informatics developments may hold for cognitive neuroscience.

Brain activation during associative short-term memory maintenance is not predictive for subsequent retrieval

Performance on working memory (WM) tasks may partially be supported by long-term memory (LTM) processing. Hence, brain activation recently being implicated in WM may actually have been driven by (incidental) LTM formation. We examined which brain regions actually support successful WM processing, rather than being confounded by LTM processes, during the maintenance and probe phase of a WM task. We administered a four-pair (faces and houses) associative delayed-match-to-sample (WM) task using event-related functional MRI (fMRI) and a subsequent associative recognition LTM task, using the same stimuli. This enabled us to analyze subsequent memory effects for both the WM and the LTM test by contrasting correctly recognized pairs with incorrect pairs for either task. Critically, with respect to the subsequent WM effect, we computed this analysis exclusively for trials that were forgotten in the subsequent LTM recognition task. Hence, brain activity associated with successful WM processing was less likely to be confounded by incidental LTM formation. The subsequent LTM effect, in contrast, was analyzed exclusively for pairs that previously had been correctly recognized in the WM task, disclosing brain regions involved in successful LTM formation after successful WM processing. Results for the subsequent WM effect showed no significantly activated brain areas for WM maintenance, possibly due to an insensitivity of fMRI to mechanisms underlying active WM maintenance. In contrast, a correct decision at WM probe was linked to activation in the “retrieval success network” (anterior and posterior midline brain structures). The subsequent LTM analyses revealed greater activation in left dorsolateral prefrontal cortex and posterior parietal cortex in the early phase of the maintenance stage. No supra-threshold activation was found during the WM probe. Together, we obtained clearer insights in which brain regions support successful WM and LTM without the potential confound of the respective memory system.

Multimodal connectivity of motor learning-related dorsal premotor cortex

The dorsal premotor cortex (dPMC) is a key region for motor learning and sensorimotor integration, yet we have limited understanding of its functional interactions with other regions. Previous work has started to examine functional connectivity in several brain areas using resting state functional connectivity (RSFC) and meta-analytical connectivity modelling (MACM). More recently, structural covariance (SC) has been proposed as a technique that may also allow delineation of functional connectivity. Here, we applied these three approaches to provide a comprehensive characterization of functional connectivity with a seed in the left dPMC that a previous meta-analysis of functional neuroimaging studies has identified as playing a key role in motor learning. Using data from two sources (the Rockland sample, containing resting state data and anatomical scans from 132 participants, and the BrainMap database, which contains peak activation foci from over 10,000 experiments), we conducted independent whole-brain functional connectivity mapping analyses of a dPMC seed. RSFC and MACM revealed similar connectivity maps spanning prefrontal, premotor, and parietal regions, while the SC map identified more widespread frontal regions. Analyses indicated a relatively consistent pattern of functional connectivity between RSFC and MACM that was distinct from that identified by SC. Notably, results indicate that the seed is functionally connected to areas involved in visuomotor control and executive functions, suggesting that the dPMC acts as an interface between motor control and cognition.

Identifying neural correlates of visual consciousness with ALE meta-analyses

Neural correlates of consciousness (NCC) have been a topic of study for nearly two decades. In functional imaging studies, several regions have been proposed to constitute possible candidates for NCC, but as of yet, no quantitative summary of the literature on NCC has been done. The question whether single (striate or extrastriate) regions or a network consisting of extrastriate areas that project directly to fronto-parietal regions are necessary and sufficient neural correlates for visual consciousness is still highly debated [e.g., Rees et al., 2002, Nat Rev. Neurosci 3, 261-270; Tong, 2003, Nat Rev. Neurosci 4, 219-229]. The aim of this work was to elucidate this issue and give a synopsis of the present state of the art by conducting systematic and quantitative meta-analyses across functional magnetic resonance imaging (fMRI) studies using several standard paradigms for conscious visual perception. In these paradigms, consciousness is operationalized via perceptual changes, while the visual stimulus remains invariant. An activation likelihood estimation (ALE) meta-analysis was performed, representing the best approach for voxel-wise meta-analyses to date. In addition to computing a meta-analysis across all paradigms, separate meta-analyses on bistable perception and masking paradigms were conducted to assess whether these paradigms show common or different NCC. For the overall meta-analysis, we found significant clusters of activation in inferior and middle occipital gyrus; fusiform gyrus; inferior temporal gyrus; caudate nucleus; insula; inferior, middle, and superior frontal gyri; precuneus; as well as in inferior and superior parietal lobules. These results suggest a subcortical-extrastriate-fronto-parietal network rather than a single region that constitutes the necessary NCC. The results of our exploratory paradigm-specific meta-analyses suggest that this subcortical-extrastriate-fronto-parietal network might be differentially activated as a function of the paradigms used to probe for NCC.

ANIMA: A data-sharing initiative for neuroimaging meta-analyses

Meta-analytic techniques allow cognitive neuroscientists to pool large amounts of data across many individual task-based functional neuroimaging experiments. These methods have been aided by the introduction of online databases such as Brainmap.org or Neurosynth.org, which collate peak activation coordinates obtained from thousands of published studies. Findings from meta-analytic studies typically include brain regions which are consistently activated across studies for specific contrasts, investigating cognitive or clinical hypotheses. These regions can be subsequently used as the basis for seed-based connectivity analysis, or formally compared to neuroimaging data in order to help interpret new findings. To facilitate such approaches, we have developed a new online repository of meta-analytic neuroimaging results, named the Archive of Neuroimaging Meta-analyses (ANIMA). The ANIMA platform consists of an intuitive online interface for querying, downloading, and contributing data from published meta-analytic studies. Additionally, to aid the process of organizing, visualizing, and working with these data, we present an open-source desktop application called Volume Viewer. Volume Viewer allows users to easily arrange imaging data into composite stacks, and save these sessions as individual files, which can also be uploaded to the ANIMA database. The application also allows users to perform basic functions, such as computing conjunctions between images, or extracting regions-of-interest or peak coordinates for further analysis. The introduction of this new resource will enhance the ability of researchers to both share their findings and incorporate existing meta-analytic results into their own research.

Neuroticism and conscientiousness respectively constrain and facilitate short-term plasticity within the working memory neural network

Individual differences in cognitive efficiency, particularly in relation to working memory (WM), have been associated both with personality dimensions that reflect enduring regularities in brain configuration, and with short‐term neural plasticity, that reflects task‐related changes in brain connectivity. To elucidate the relationship of these two divergent mechanisms, we tested the hypothesis that personality dimensions, which reflect enduring aspects of brain configuration, inform about the neurobiological framework within which short‐term, task‐related plasticity, as measured by effective connectivity, can be facilitated or constrained. As WM consistently engages the dorsolateral prefrontal (DLPFC), parietal (PAR), and anterior cingulate cortex (ACC), we specified a WM network model with bidirectional, ipsilateral, and contralateral connections between these regions from a functional magnetic resonance imaging dataset obtained from 40 healthy adults while performing the 3‐back WM task. Task‐related effective connectivity changes within this network were estimated using Dynamic Causal Modelling. Personality was evaluated along the major dimensions of Neuroticism, Extraversion, Openness to Experience, Agreeableness, and Conscientiousness. Only two dimensions were relevant to task‐dependent effective connectivity. Neuroticism and Conscientiousness respectively constrained and facilitated neuroplastic responses within the WM network. These results suggest individual differences in cognitive efficiency arise from the interplay between enduring and short‐term plasticity in brain configuration. Hum Brain Mapp 36:4158–4163, 2015. © 2015 The Authors Human Brain Mapping Published by Wiley Periodicals, Inc.

Neurogenetic variations in norepinephrine availability enhance perceptual vividness

Emotionally salient aspects of the world are experienced with greater perceptual vividness than mundane ones; however, such emotionally enhanced vividness (EEV) may be experienced to different degrees for different people. We examined whether BOLD activity associated with a deletion variant of the ADRA2b gene coding for the α2b adrenoceptor modulates EEV in humans. Relative to noncarriers, ADRA2b deletion carriers showed higher levels of perceptual vividness, with the ventromedial prefrontal cortex (VMPFC) showing greater modulation by EEV. Deletion carriers were also more sensitive to the featural salience of the images, suggesting a more pervasive role of norepinephrine in perceptual encoding. Path analysis revealed that, whereas a simple model by which the amygdala modulated the lateral occipital complex best characterized EEV-related activity in noncarriers, contributions of an additional VMPFC pathway best characterized deletion carriers. Thus, common norepinephrine-related neurogenetic differences enhance the subjective vividness of perceptual experience and its emotional enhancement.

Development of common neural representations for distinct numerical problems

How the brain develops representations for abstract cognitive problems is a major unaddressed question in neuroscience. Here we tackle this fundamental question using arithmetic problem solving, a cognitive domain important for the development of mathematical reasoning. We first examined whether adults demonstrate common neural representations for addition and subtraction problems, two complementary arithmetic operations that manipulate the same quantities. We then examined how the common neural representations for the two problem types change with development. Whole-brain multivoxel representational similarity (MRS) analysis was conducted to examine common coding of addition and subtraction problems in children and adults. We found that adults exhibited significant levels of MRS between the two problem types, not only in the intraparietal sulcus (IPS) region of the posterior parietal cortex (PPC), but also in ventral temporal-occipital, anterior temporal and dorsolateral prefrontal cortices. Relative to adults, children showed significantly reduced levels of MRS in these same regions. In contrast, no brain areas showed significantly greater MRS between problem types in children. Our findings provide novel evidence that the emergence of arithmetic problem solving skills from childhood to adulthood is characterized by maturation of common neural representations between distinct numerical operations, and involve distributed brain regions important for representing and manipulating numerical quantity. More broadly, our findings demonstrate that representational analysis provides a powerful approach for uncovering fundamental mechanisms by which children develop proficiencies that are a hallmark of human cognition.

Functional networks and structural connectivity of visuospatial and visuoperceptual working memory

Neural correlates of working memory (WM) in healthy subjects have been extensively investigated using functional MRI (fMRI). However it still remains unclear how cortical areas forming part of functional WM networks are also connected by white matter fiber bundles, and whether DTI measures, used as indices of microstructural properties and directionality of these connections, can predict individual differences in task performance. fMRI data were obtained from 23 healthy young subjects while performing one visuospatial (square location) and one visuoperceptual (face identification) 2-back task. Diffusion tensor imaging (DTI) data were also acquired. We used independent component analysis (ICA) of fMRI data to identify the main functional networks involved in WM tasks. Voxel-wise DTI analyses were performed to find correlations between structural white matter and task performance measures, and probabilistic tracking of DTI data was used to identify the white matter bundles connecting the nodes of the functional networks. We found that functional recruitment of the fusiform and the inferior frontal cortex was specific for the visuoperceptual working memory task, while there was a high overlap in brain activity maps in parietal and middle frontal areas for both tasks. Axial diffusivity and fractional anisotropy, of the tracts connecting the fusiform with the inferior frontal areas correlated with processing speed in the visuoperceptual working memory task. Although our findings need to be considered as exploratory, we conclude that both tasks share a highly-overlapping pattern of activity in areas of frontal and parietal lobes with the only differences in activation between tasks located in the fusiform and inferior frontal regions for the visuoperceptual task. Moreover, we have found that the DTI measures are predictive of the processing speed.

Transfer of training from one working memory task to another: behavioural and neural evidence

N-back working memory (WM) tasks necessitate the maintenance and updating of dynamic rehearsal sets during performance. The delayed matching-to-sample (dMTS) task is another WM task, which in turn involves the encoding, maintenance, and retrieval of stimulus representations in sequential order. Because both n-back and dMTS engage WM function, we hypothesized that compared to a control task not taxing WM, training on the n-back task would be associated with better performance on dMTS by virtue of training a shared mental capacity. We tested this hypothesis by randomly assigning subjects (N = 43) to train on either the n-back (including 2-back and 3-back levels) or an active control task. Following training, dMTS was administered in the fMRI scanner. The n-back group performed marginally better than the active control group on dMTS. In addition, although the n-back group improved more on the less difficult 2-back level than the more difficult 3-back level across training sessions, it was improvement on the 3-back level that accounted for 21% of the variance in dMTS performance. For the control group, improvement in training across sessions was unrelated to dMTS performance. At the neural level, greater activation in the left inferior frontal gyrus, right posterior parietal cortex, and the cerebellum distinguished the n-back group from the control group in the maintenance phase of dMTS. Degree of improvement on the 3-back level across training sessions was correlated with activation in right lateral prefrontal and motor cortices in the maintenance phase of dMTS. Our results suggest that although n-back training is more likely to improve performance in easier blocks, it is improvement in more difficult blocks that is predictive of performance on a target task drawing on WM. In addition, the extent to which training on a task can transfer to another task is likely due to the engagement of shared cognitive capacities and underlying neural substrates—in this case WM.

Co-activation Probability Estimation (CoPE): An approach for modeling functional co-activation architecture based on neuroimaging coordinates

Recent progress in functional neuroimaging has prompted studies of brain activation during various cognitive tasks. Coordinate-based meta-analysis has been utilized to discover the brain regions that are consistently activated across experiments. However, within-experiment co-activation relationships, which can reflect the underlying functional relationships between different brain regions, have not been widely studied. In particular, voxel-wise co-activation, which may be able to provide a detailed configuration of the co-activation network, still needs to be modeled. To estimate the voxel-wise co-activation pattern and deduce the co-activation network, a Co-activation Probability Estimation (CoPE) method was proposed to model within-experiment activations for the purpose of defining the co-activations. A permutation test was adopted as a significance test. Moreover, the co-activations were automatically separated into local and long-range ones, based on distance. The two types of co-activations describe distinct features: the first reflects convergent activations; the second represents co-activations between different brain regions. The validation of CoPE was based on five simulation tests and one real dataset derived from studies of working memory. Both the simulated and the real data demonstrated that CoPE was not only able to find local convergence but also significant long-range co-activation. In particular, CoPE was able to identify a 'core' co-activation network in the working memory dataset. As a data-driven method, the CoPE method can be used to mine underlying co-activation relationships across experiments in future studies.

The neuroplastic effect of working memory training in healthy volunteers and patients with schizophrenia: Implications for cognitive rehabilitation

We conducted an activation likelihood estimation (ALE) meta-analysis to quantitatively review the existing working memory (WM) training studies that investigated neural activation changes both in healthy individuals and patients with schizophrenia. ALE analysis of studies in healthy individuals indicates a widespread distribution of activation changes with WM training in the frontal and parietal regions, especially the dorsolateral prefrontal cortex, the medial frontal cortex and the precuneus, as well as subcortical regions such as the insula and the striatum. WM training is also accompanied by activation changes in patients with schizophrenia, mainly in the dorsolateral prefrontal cortex, the precuneus and the fusiform gyrus. Our results demonstrate that WM training is accompanied by changes in neural activation patterns in healthy individuals, which may provide the basis for understanding neuroplastic changes in patients with schizophrenia.

Multimodal connectivity mapping of the human left anterior and posterior lateral prefrontal cortex

Working memory is essential for many of our distinctly human abilities, including reasoning, problem solving, and planning. Research spanning many decades has helped to refine our understanding of this high-level function as comprising several hierarchically organized components, some which maintain information in the conscious mind, and others which manipulate and reorganize this information in useful ways. In the neocortex, these processes are likely implemented by a distributed frontoparietal network, with more posterior regions serving to maintain volatile information, and more anterior regions subserving the manipulation of this information. Recent meta-analytic findings have identified the anterior lateral prefrontal cortex, in particular, as being generally engaged by working memory tasks, while the posterior lateral prefrontal cortex was more strongly associated with the cognitive load required by these tasks. These findings suggest specific roles for these regions in the cognitive control processes underlying working memory. To further characterize these regions, we applied three distinct seed-based methods for determining cortical connectivity. Specifically, we employed meta-analytic connectivity mapping across task-based fMRI experiments, resting-state BOLD correlations, and VBM-based structural covariance. We found a frontoparietal pattern of convergence which strongly resembled the working memory networks identified in previous research. A contrast between anterior and posterior parts of the lateral prefrontal cortex revealed distinct connectivity patterns consistent with the idea of a hierarchical organization of frontoparietal networks. Moreover, we found a distributed network that was anticorrelated with the anterior seed region, which included most of the default mode network and a subcomponent related to social and emotional processing. These findings fit well with the internal attention model of working memory, in which representation of information is processed according to an anteroposterior gradient of abstract-to-concrete representations.

Resting state signatures of domain and demand-specific working memory performance

Working memory (WM) is one of the key constructs in understanding higher-level cognition. We examined whether patterns of activity in the resting state of individual subjects are correlated with their off-line working and short-term memory capabilities. Participants completed a resting-state fMRI scan and off-line working and short-term memory (STM) tests with both verbal and visual materials. We calculated fractional amplitude of low frequency fluctuations (fALFF) from the resting state data, and also computed connectivity between seeds placed in frontal and parietal lobes. Correlating fALFF values with behavioral measures showed that the fALFF values in a widespread fronto-parietal network during rest were positively correlated with a combined memory measure. In addition, STM showed a significant correlation with fALFF within the right angular gyrus and left middle occipital gyrus, whereas WM was correlated with fALFF values within the right IPS and left dorsomedial cerebellar cortex. Furthermore, verbal and visuospatial memory capacities were associated with dissociable patterns of low-frequency fluctuations. Seed-based connectivity showed correlations with the verbal WM measure in the left hemisphere, and with the visual WM measure in the right hemisphere. These findings contribute to our understanding of how differences in spontaneous low-frequency fluctuations at rest are correlated with differences in cognitive performance.

Spatiotemporal oscillatory dynamics during the encoding and maintenance phases of a visual working memory task

Many electrophysiology studies have examined neural oscillatory activity during the encoding, maintenance, and/or retrieval phases of various working memory tasks. Together, these studies have helped illuminate the underlying neural dynamics, although much remains to be discovered and some findings have not replicated in subsequent work. In this study, we examined the oscillatory dynamics that serve visual working memory operations using high-density magnetoencephalography (MEG) and advanced time-frequency and beamforming methodology. Specifically, we recorded healthy adults while they performed a high-load, Sternberg-type working memory task, and focused on the encoding and maintenance phases. We found significant 9-16 Hz desynchronizations in the bilateral occipital cortices, left dorsolateral prefrontal cortex (DLPFC), and left superior temporal areas throughout the encoding phase. Our analysis of the dynamics showed that the left DLPFC and superior temporal desynchronization became stronger as a function of time during the encoding period, and was sustained throughout most of the maintenance phase until sharply decreasing in the milliseconds preceding retrieval. In contrast, desynchronization in occipital areas became weaker as a function of time during encoding and eventually evolved into a strong synchronization during the maintenance period, consistent with previous studies. These results provide clear evidence of dynamic network-level processes during the encoding and maintenance phases of working memory, and support the notion of a dynamic pattern of functionally-discrete subprocesses within each working memory phase. The presence of such dynamic oscillatory networks may be a potential source of inconsistent findings in this literature, as neural activity within these networks changes dramatically with time.

Intraparietal regions play a material general role in working memory: Evidence supporting an internal attentional role

Determining the role of intraparietal sulcus (IPS) regions in working memory (WM) remains a topic of considerable interest and lack of clarity. One group of hypotheses, the internal attention view, proposes that the IPS plays a material general role in maintaining information in WM. An alternative viewpoint, the pure storage account, proposes that the IPS in each hemisphere maintains material specific (e.g., left--phonological; right--visuospatial) information. Yet, adjudication between competing theoretical perspectives is complicated by divergent findings from different methodologies and their use of different paradigms, perhaps most notably between functional magnetic resonance imaging (fMRI) and electroencephalography (EEG). For example, fMRI studies typically use full field stimulus presentations and report bilateral IPS activation, whereas EEG studies direct attention to a single hemifield and report a contralateral bias in both hemispheres. Here, we addressed this question by applying a regions-of-interest fMRI approach to elucidate IPS contributions to WM. Importantly, we manipulated stimulus type (verbal, visuospatial) and the cued hemifield to assess the degree to which IPS activations reflect stimulus specific or stimulus general processing consistent with the pure storage or internal attention hypotheses. These data revealed significant contralateral bias along regions IPS0-5 regardless of stimulus type. Also present was a weaker stimulus-based bias apparent in stronger left lateralized activations for verbal stimuli and stronger right lateralized activations for visuospatial stimuli. However, there was no consistent stimulus-based lateralization of activity. Thus, despite the observation of stimulus-based modulation of spatial lateralization this pattern was bilateral. As such, although it is quantitatively underspecified, our results are overall more consistent with an internal attention view that the IPS plays a material general role in refreshing the contents of WM.

n-back task performance and corresponding brain-activation patterns in women with restrictive and bulimic eating-disorder variants: preliminary findings

Eating disorder (ED) variants characterized by "binge-eating/purging" symptoms differ from "restricting-only" variants along diverse clinical dimensions, but few studies have compared people with these different eating-disorder phenotypes on measures of neurocognitive function and brain activation. We tested the performances of 19 women with "restricting-only" eating syndromes and 27 with "binge-eating/purging" variants on a modified n-back task, and used functional magnetic resonance imaging (fMRI) to examine task-induced brain activations in frontal regions of interest. When compared with "binge-eating/purging" participants, "restricting-only" participants showed superior performance. Furthermore, in an intermediate-demand condition, "binge-eating/purging" participants showed significantly less event-related activation than did "restricting-only" participants in a right posterior prefrontal region spanning Brodmann areas 6-8-a region that has been linked to planning of motor responses, working memory for sequential information, and management of uncertainty. Our findings suggest that working memory is poorer in eating-disordered individuals with binge-eating/purging behaviors than in those who solely restrict food intake, and that observed performance differences coincide with interpretable group-based activation differences in a frontal region thought to subserve planning and decision making.

Co-Activation-Based Parcellation of the Lateral Prefrontal Cortex Delineates the Inferior Frontal Junction Area

The inferior frontal junction (IFJ) area, a small region in the posterior lateral prefrontal cortex (LPFC), has received increasing interest in recent years due to its central involvement in the control of action, attention, and memory. Yet, both its function and anatomy remain controversial. Here, we employed a meta-analytic parcellation of the left LPFC to show that the IFJ can be isolated based on its specific functional connections. A seed region, oriented along the left inferior frontal sulcus (IFS), was subdivided via cluster analyses of voxel-wise whole-brain co-activation patterns. The ensuing clusters were characterized by their unique connections, the functional profiles of associated experiments, and an independent topic mapping approach. A cluster at the posterior end of the IFS matched previous descriptions of the IFJ in location and extent and could be distinguished from a more caudal cluster involved in motor control, a more ventral cluster involved in linguistic processing, and 3 more rostral clusters involved in other aspects of cognitive control. Overall, our findings highlight that the IFJ constitutes a core functional unit within the frontal lobe and delineate its borders. Implications for the IFJ's role in human cognition and the organizational principles of the frontal lobe are discussed.

The effect of ANK3 bipolar-risk polymorphisms on the working memory circuitry differs between loci and according to risk-status for bipolar disorder

Polymorphisms at the rs10994336 and rs9804190 loci of the Ankyrin 3 (ANK3) gene have been strongly associated with increased risk for bipolar disorder (BD). However, their potential pathogenetic effect on BD-relevant neural circuits remains unknown. We examined the effect of BD-risk polymorphisms at rs10994336 and rs9804190 on the working memory (WM) circuit using functional magnetic resonance imaging (fMRI) data obtained from euthymic patients with BD (n = 41), their psychiatrically healthy first-degree relatives (n = 25) and unrelated individuals without personal or family history of psychiatric disorders (n = 46) while performing the N-back task. In unrelated healthy individuals, the rs10994336-risk-allele was associated with reduced activation of the ventral visual cortical components of the WM circuit while the rs9804190-risk-allele was associated with inefficient hyperactivation of the prefrontal cortical components of the WM. In patients and their healthy relatives, risk alleles at either loci were associated with hyperactivation in the ventral anterior cingulate cortex. Additionally, Rs9804190-risk-allele carriers with BD evidenced abnormal hyperactivation within the posterior cingulate cortex. This study provides new insights on the neurogenetic correlates of allelic variation at different genome-wide supported BD-risk associated ANK3 loci that support their involvement in BD and highlight the modulatory influence of increased background genetic risk for BD.

Gray matter atrophy in narcolepsy: An activation likelihood estimation meta-analysis

The authors reviewed the literature on the use of voxel-based morphometry (VBM) in narcolepsy magnetic resonance imaging (MRI) studies via the use of a meta-analysis of neuroimaging to identify concordant and specific structural deficits in patients with narcolepsy as compared with healthy subjects. We used PubMed to retrieve articles published between January 2000 and March 2014. The authors included all VBM research on narcolepsy and compared the findings of the studies by using gray matter volume (GMV) or gray matter concentration (GMC) to index differences in gray matter. Stereotactic data were extracted from 8 VBM studies of 149 narcoleptic patients and 162 control subjects. We applied activation likelihood estimation (ALE) technique and found significant regional gray matter reduction in the bilateral hypothalamus, thalamus, globus pallidus, extending to nucleus accumbens (NAcc) and anterior cingulate cortex (ACC), left mid orbital and rectal gyri (BAs 10 and 11), right inferior frontal gyrus (BA 47), and the right superior temporal gyrus (BA 41) in patients with narcolepsy. The significant gray matter deficits in narcoleptic patients occurred in the bilateral hypothalamus and frontotemporal regions, which may be related to the emotional processing abnormalities and orexin/hypocretin pathway common among populations of patients with narcolepsy.

Semantic retrieval over time in the aging brain: Structural evidence of hippocampal contribution

This study investigates relationship between regional cerebral volumes and performances over time of a categorical fluency task, in a sample of older adults (n = 316). Using voxel-wise technique, the relationship between local grey matter volume and Isaacs Set Test (IST) scores at its early (first 15 sec) and late (last 15 sec) phase production was analyzed with a linear regression model adjusting for age, sex, educational level, ApoEɛ4 allele, handedness and Grey Matter atrophy. Lower early IST scores were associated with smaller volumes in bilateral inferior frontal gyri and in right thalamus, whereas lower late IST scores were associated to smaller left inferior parietal gyrus and left anterior hippocampus. An analysis based on automatic segmentation of hippocampus confirmed the latest relationship which cannot be attributed to the correlation of each variable with global cognitive impairment because it remained when MMSE was accounted for. We observed a switch from frontal to temporo-parietal regions as words retrieval become more difficult over time. Automatic speech production of the early phase of the category fluency task is dependent on executive networks integrity whereas controlled speech production of the late phase is dependent on memory networks integrity, including left hippocampus. These results are concordant with recent imaging studies expanding the implication of hippocampus to semantic memory performances and they underlie the need to consider verbal fluency task over time.

Continuous theta burst stimulation over the left dorsolateral prefrontal cortex decreases medium load working memory performance in healthy humans

The dorsolateral prefrontal cortex (DLPFC) plays a key role in working memory. Evidence indicates that transcranial magnetic stimulation (TMS) over the DLPFC can interfere with working memory performance. Here we investigated for how long continuous theta-burst stimulation (cTBS) over the DLPFC decreases working memory performance and whether the effect of cTBS on performance depends on working memory load. Forty healthy young subjects received either cTBS over the left DLPFC or sham stimulation before performing a 2-, and 3-back working memory letter task. An additional 0-back condition served as a non-memory-related control, measuring general attention. cTBS over the left DLPFC significantly impaired 2-back working memory performance for about 15 min, whereas 3-back and 0-back performances were not significantly affected. Our results indicate that the effect of left DLPFC cTBS on working memory performance lasts for roughly 15 min and depends on working memory load.

A meta-analysis of changes in brain activity in clinical depression

Insights into neurobiological mechanisms of depression are increasingly being sought via brain imaging studies. Our aim was to quantitatively summarize overlap and divergence in regions of altered brain activation associated with depression under emotionally valenced compared to cognitively demanding task conditions, and with reference to intrinsic functional connectivity. We hypothesized differences reflective of task demands. A co-ordinate-based meta-analysis technique, activation likelihood estimation, was used to analyze relevant imaging literature. These studies compared brain activity in depressed adults relative to healthy controls during three conditions: (i) emotionally valenced (cognitively easy) tasks (n = 29); (ii) cognitively demanding tasks (n = 15); and (iii) resting conditions (n = 21). The meta-analyses identified five, eight, and seven significant clusters of altered brain activity under emotion, cognition, and resting conditions, respectively, in depressed individuals compared to healthy controls. Regions of overlap and divergence between pairs of the three separate meta-analyses were quantified. There were no significant regions of overlap between emotion and cognition meta-analyses, but several divergent clusters were found. Cognitively demanding conditions were associated with greater activation of right medial frontal and insula regions while bilateral amygdala was more significantly altered during emotion (cognitively undemanding) conditions; consistent with task demands. Overlap was present in left amygdala and right subcallosal cingulate between emotion and resting meta-analyses, with no significant divergence. Our meta-analyses highlight alteration of common brain regions, during cognitively undemanding emotional tasks and resting conditions but divergence of regions between emotional and cognitively demanding tasks. Regions altered reflect current biological and system-level models of depression and highlight the relationship with task condition and difficulty.

Predicting learning plateau of working memory from whole-brain intrinsic network connectivity patterns

Individual learning performance of cognitive function is related to functional connections within ‘task-activated' regions where activities increase during the corresponding cognitive tasks. On the other hand, since any brain region is connected with other regions and brain-wide networks, learning is characterized by modulations in connectivity between networks with different functions. Therefore, we hypothesized that learning performance is determined by functional connections among intrinsic networks that include both task-activated and less-activated networks. Subjects underwent resting-state functional MRI and a short period of training (80–90 min) in a working memory task on separate days. We calculated functional connectivity patterns of whole-brain intrinsic networks and examined whether a sparse linear regression model predicts a performance plateau from the individual patterns. The model resulted in highly accurate predictions (R² = 0.73, p = 0.003). Positive connections within task-activated networks, including the left fronto-parietal network, accounted for nearly half (48%) of the contribution ratio to the prediction. Moreover, consistent with our hypothesis, connections of the task-activated networks with less-activated networks showed a comparable contribution (44%). Our findings suggest that learning performance is potentially constrained by system-level interactions within task-activated networks as well as those between task-activated and less-activated networks.

Neural correlates during working memory processing in major depressive disorder

BACKGROUND

Functional magnetic resonance imaging (fMRI) studies in major depressive disorder (MDD) have revealed cortical-limbic-subcortical dysfunctions during working memory (WM) processing, but the results are inconsistent and it is unclear to what extent these findings are influenced by demographic, clinical characteristics and task performance of patients. The present study conducted a quantitative coordinate-based meta-analysis of fMRI data to investigate the hypothesized dysfunction in the neural correlates during WM processing in MDD.

METHODS

A systematic research was conducted for fMRI studies during WM processing comparing MDD patients with healthy controls (HC). Meta-analysis was performed using effect size signed differential mapping (ES-SDM). Meta-regression analyses with age, sex and medication as factors were performed in MDD group.

RESULTS

Functional MRI data of 160 MDD patients and 203 HC from 13 WM experiments across 11 studies were included in this meta-analysis. In the pooled meta-analysis of all included studies, significant increased activation during WM in the left lateral prefrontal cortex, left precentral gyrus, left insula, right superior temporal and right supramarginal areas, and significant decreased activity in the right precentral gyrus, right precuneus and right insula were observed in MDD compared with controls. In the subgroup analysis of the studies with matched task performance, MDD subgroup showed hyperactivation only in the left prefrontal cortex and hypoactivation in the regions similar to the pooled analysis. The meta-regression with age, sex and medication showed no significance in MDD group.

CONCLUSIONS

Regardless of differences in task performance between groups, patients with MDD showed consistent functional abnormalities in the cortical-limbic-subcortical circuitry during WM processing. Distinct patterns of neural engagement may reflect compensatory neural strategies to potential dysfunction in MDD.

Is functional integration of resting state brain networks an unspecific biomarker for working memory performance?

Is there one optimal topology of functional brain networks at rest from which our cognitive performance would profit? Previous studies suggest that functional integration of resting state brain networks is an important biomarker for cognitive performance. However, it is still unknown whether higher network integration is an unspecific predictor for good cognitive performance or, alternatively, whether specific network organization during rest predicts only specific cognitive abilities. Here, we investigated the relationship between network integration at rest and cognitive performance using two tasks that measured different aspects of working memory; one task assessed visual-spatial and the other numerical working memory. Network clustering, modularity and efficiency were computed to capture network integration on different levels of network organization, and to statistically compare their correlations with the performance in each working memory test. The results revealed that each working memory aspect profits from a different resting state topology, and the tests showed significantly different correlations with each of the measures of network integration. While higher global network integration and modularity predicted significantly better performance in visual-spatial working memory, both measures showed no significant correlation with numerical working memory performance. In contrast, numerical working memory was superior in subjects with highly clustered brain networks, predominantly in the intraparietal sulcus, a core brain region of the working memory network. Our findings suggest that a specific balance between local and global functional integration of resting state brain networks facilitates special aspects of cognitive performance. In the context of working memory, while visual-spatial performance is facilitated by globally integrated functional resting state brain networks, numerical working memory profits from increased capacities for local processing, especially in brain regions involved in working memory performance.

Assessing dynamic brain graphs of time-varying connectivity in fMRI data: application to healthy controls and patients with schizophrenia

Graph theory-based analysis has been widely employed in brain imaging studies, and altered topological properties of brain connectivity have emerged as important features of mental diseases such as schizophrenia. However, most previous studies have focused on graph metrics of stationary brain graphs, ignoring that brain connectivity exhibits fluctuations over time. Here we develop a new framework for accessing dynamic graph properties of time-varying functional brain connectivity in resting-state fMRI data and apply it to healthy controls (HCs) and patients with schizophrenia (SZs). Specifically, nodes of brain graphs are defined by intrinsic connectivity networks (ICNs) identified by group independent component analysis (ICA). Dynamic graph metrics of the time-varying brain connectivity estimated by the correlation of sliding time-windowed ICA time courses of ICNs are calculated. First- and second-level connectivity states are detected based on the correlation of nodal connectivity strength between time-varying brain graphs. Our results indicate that SZs show decreased variance in the dynamic graph metrics. Consistent with prior stationary functional brain connectivity works, graph measures of identified first-level connectivity states show lower values in SZs. In addition, more first-level connectivity states are disassociated with the second-level connectivity state which resembles the stationary connectivity pattern computed by the entire scan. Collectively, the findings provide new evidence about altered dynamic brain graphs in schizophrenia, which may underscore the abnormal brain performance in this mental illness.

Functional connectivity mapping of regions associated with self- and other-processing

Neuroscience literature increasingly suggests a conceptual self composed of interacting neural regions, rather than independent local activations, yet such claims have yet to be investigated. We, thus, combined task-dependent meta-analytic connectivity modeling (MACM) with task-independent resting-state (RS) connectivity analysis to delineate the neural network of the self, across both states. Given psychological evidence implicating the self's interdependence on social information, we also delineated the neural network underlying conceptual other-processing. To elucidate the relation between the self-/other-networks and their function, we mined the MACM metadata to generate a cognitive-behavioral profile for an empirically identified region specific to conceptual self, the pregenual anterior cingulate (pACC), and conceptual other, posterior cingulate/precuneus (PCC/PC). Mining of 7,200 published, task-dependent, neuroimaging studies, using healthy human subjects, yielded 193 studies activating the self-related seed and were conjoined with RS connectivity analysis to delineate a differentiated self-network composed of the pACC (seed) and anterior insula, relative to other functional connectivity. Additionally, 106 studies activating the other-related seed were conjoined with RS connectivity analysis to delineate a differentiated other-network of PCC/PC (seed) and angular gyrus/temporoparietal junction, relative to self-functional connectivity. The self-network seed related to emotional conflict resolution and motivational processing, whereas the other-network seed related to socially oriented processing and contextual information integration. Notably, our findings revealed shared RS connectivity between ensuing self-/other-networks within the ventromedial prefrontal cortex and medial orbitofrontal cortex, suggesting self-updating via integration of self-relevant social information. We, therefore, present initial neurobiological evidence corroborating the increasing claims of an intricate self-network, the architecture of which may promote social value processing.

Letter and Colour Matching Tasks: Parametric Measures of Developmental Working Memory Capacity

We investigated the mediating role of interference in developmental assessments of working memory (WM) capacity across childhood, adolescence, and young adulthood. One hundred and forty-two participants completed two versions of visuospatial (colour matching task, CMT) and verbal (letter matching task, LMT) WM tasks, which systematically varied cognitive load in a high and low interference condition. Results showed similar developmental trajectories across high interference contexts (CMT- and LMT-Complex) and divergent developmental growth patterns across low interference contexts (CMT- and LMT-Simple). Performance on tasks requiring greater cognitive control was in closer agreement with developmental predictions relative to simple recall guided tasks that rely solely on the storage components of WM. These findings suggest that developmental WM capacity, as measured by the CMT and LMT paradigms, can be better quantified using high interference contexts, in both content domains, and demonstrate steady increases in WM through to mid-adolescence.

Effects of overnight fasting on working memory-related brain network: an fMRI study

Glucose metabolism serves as the central source of energy for the human brain. Little is known about the effects of blood glucose level (BGL) on higher-order cognitive functions within a physiological range (e.g., after overnight fasting). In this randomized, placebo-controlled, double blind study, we assessed the impact of overnight fasting (14 h) on brain activation during a working memory task. We sought to mimic BGLs that occur naturally in healthy humans after overnight fasting. After standardized periods of food restriction, 40 (20 male) healthy participants were randomly assigned to receive either glucagon to balance the BGL or placebo (NaCl). A parametric fMRI paradigm, including 2-back and 0-back tasks, was used. Subclinically low BGL following overnight fasting was found to be linked to reduced involvement of the bilateral dorsal midline thalamus and the bilateral basal ganglia, suggesting high sensitivity of those regions to minimal changes in BGLs. Our results indicate that overnight fasting leads to physiologically low levels of glucose, impacting brain activation during working memory tasks even when there are no differences in cognitive performance.

Three key regions for supervisory attentional control: evidence from neuroimaging meta-analyses

The supervisory attentional system has been proposed to mediate non-routine, goal-oriented behaviour by guiding the selection and maintenance of the goal-relevant task schema. Here, we aimed to delineate the brain regions that mediate these high-level control processes via neuroimaging meta-analysis. In particular, we investigated the core neural correlates of a wide range of tasks requiring supervisory control for the suppression of a routine action in favour of another, non-routine one. Our sample comprised n=173 experiments employing go/no-go, stop-signal, Stroop or spatial interference tasks. Consistent convergence across all four paradigm classes was restricted to right anterior insula and inferior frontal junction, with anterior midcingulate cortex and pre-supplementary motor area being consistently involved in all but the go/no-go task. Taken together with lesion studies in patients, our findings suggest that the controlled activation and maintenance of adequate task schemata relies, across paradigms, on a right-dominant midcingulo-insular-inferior frontal core network. This also implies that the role of other prefrontal and parietal regions may be less domain-general than previously thought.

Sex differences in cognitive regulation of psychosocial achievement stress: brain and behavior

Although cognitive regulation of emotion has been extensively examined, there is a lack of studies assessing cognitive regulation in stressful achievement situations. This study used functional magnetic resonance imaging in 23 females and 20 males to investigate cognitive downregulation of negative, stressful sensations during a frequently used psychosocial stress task. Additionally, subjective responses, cognitive regulation strategies, salivary cortisol, and skin conductance response were assessed. Subjective response supported the experimental manipulation by showing higher anger and negative affect ratings after stress regulation than after the mere exposure to stress. On a neural level, right middle frontal gyrus (MFG) and right superior temporal gyrus (STG) were more strongly activated during regulation than nonregulation, whereas the hippocampus was less activated during regulation. Sex differences were evident: after regulation females expressed higher subjective stress ratings than males, and these ratings were associated with right hippocampal activation. In the nonregulation block, females showed greater activation of the left amygdala and the right STG during stress than males while males recruited the putamen more robustly in this condition. Thus, cognitive regulation of stressful achievement situations seems to induce additional stress, to recruit regions implicated in attention integration and working memory and to deactivate memory retrieval. Stress itself is associated with greater activation of limbic as well as attention areas in females than males. Additionally, activation of the memory system during cognitive regulation of stress is associated with greater perceived stress in females. Sex differences in cognitive regulation strategies merit further investigation that can guide sex sensitive interventions for stress-associated disorders.

Differential associations between impulsivity and risk-taking and brain activations underlying working memory in adolescents

Increased impulsivity and risk-taking are common during adolescence and relate importantly to addictive behaviors. However, the extent to which impulsivity and risk-taking relate to brain activations that mediate cognitive processing is not well understood. Here we examined the relationships between impulsivity and risk-taking and the neural correlates of working memory. Neural activity was measured in 18 adolescents (13-18 years) while they engaged in a working memory task that included verbal and visuospatial components that each involved encoding, rehearsal and recognition stages. Risk-taking and impulsivity were assessed using the Balloon Analogue Risk Task (BART) and the adolescent version of the Barratt Impulsiveness Scale-11 (BIS-11A), respectively. We found overlapping as well as distinct regions subserving the different stages of verbal and visuospatial working memory. In terms of risk-taking, we found a positive correlation between BART scores and activity in subcortical regions (e.g., thalamus, dorsal striatum) recruited during verbal rehearsal, and an inverse correlation between BART scores and cortical regions (e.g., parietal and temporal regions) recruited during visuospatial rehearsal. The BIS-11A evidenced that motor impulsivity was associated with activity in regions recruited during all stages of working memory, while attention and non-planning impulsivity was only associated with activity in regions recruited during recognition. In considering working memory, impulsivity and risk-taking together, both impulsivity and risk-taking were associated with activity in regions recruited during rehearsal; however, during verbal rehearsal, differential correlations were found. Specifically, positive correlations were found between: (1) risk-taking and activity in subcortical regions, including the thalamus and dorsal striatum; and, (2) motor impulsivity and activity in the left inferior frontal gyrus, insula, and dorsolateral prefrontal cortex. Therefore these findings suggest that while there may be some overlap in the neural correlates of working memory and their relationship to impulsivity and risk-taking, there are also important differences in these constructs and their relationship to the stages of working memory during adolescence.

The long-term effects of prenatal nicotine exposure on verbal working memory: an fMRI study of young adults

BACKGROUND

Using functional magnetic resonance imaging (fMRI), the long-term effects of prenatal nicotine exposure on verbal working memory were investigated in young adults. Participants were members of the Ottawa Prenatal Prospective Study, a longitudinal study that collected a unique body of information on participants from infancy to young adulthood. This allowed for the measurement of an unprecedented number of potentially confounding drug exposure variables including: prenatal marijuana and alcohol exposure and current marijuana, nicotine and alcohol use.

METHODS

Twelve young adults with prenatal nicotine exposure and 13 non-exposed controls performed a 2-Back working memory task while fMRI blood oxygen level-dependent responses were examined. Despite similar task performance, participants with more prenatal nicotine exposure demonstrated significantly greater activity in several regions of the brain that typically subserve verbal working memory including the middle frontal gyrus, precentral gyrus, the inferior parietal lobe and the cingulate gyrus.

RESULTS

These results suggest that prenatal nicotine exposure contributes to altered neural functioning during verbal working memory that continues into adulthood. Working memory is critical for a wide range of cognitive skills such as language comprehension, learning and reasoning.

CONCLUSION

Thus, these findings highlight the need for continued educational programs and public awareness campaigns to reduce tobacco use among pregnant women.

Spectrotemporal dynamics of the EEG during working memory encoding and maintenance predicts individual behavioral capacity

We investigated the effect of memory load on encoding and maintenance of information in working memory. Electroencephalography (EEG) signals were recorded while participants performed a modified Sternberg visual memory task. Independent component analysis (ICA) was used to factorise the EEG signals into distinct temporal activations to perform spectrotemporal analysis and localisation of source activities. We found 'encoding' and 'maintenance' operations were correlated with negative and positive changes in α-band power, respectively. Transient activities were observed during encoding of information in the bilateral cuneus, precuneus, inferior parietal gyrus and fusiform gyrus, and a sustained activity in the inferior frontal gyrus. Strong correlations were also observed between changes in α-power and behavioral performance during both encoding and maintenance. Furthermore, it was also found that individuals with higher working memory capacity experienced stronger neural oscillatory responses during the encoding of visual objects into working memory. Our results suggest an interplay between two distinct neural pathways and different spatiotemporal operations during the encoding and maintenance of information which predict individual differences in working memory capacity observed at the behavioral level.

Structural and functional imaging of the hippocampus in young people at familial risk of depression

BACKGROUND

Major depression is associated with abnormalities in the function and structure of the hippocampus. However, it is unclear whether these abnormalities might also be present in people 'at risk' of illness.

METHOD

We studied 62 young people (mean age 18.8 years) at familial risk of depression (FH+) but who had never been depressed themselves. Participants underwent magnetic resonance imaging to assess hippocampal structure and neural responses to a task designed to activate hippocampal memory networks. Magnetic resonance spectroscopy was used to measure levels of a combination of glutamine and glutamate (Glx) in the right hippocampus. A total of 59 matched controls with no history of mood disorder in a first-degree relative underwent the same investigations.

RESULTS

Hippocampal volume did not differ between FH+ participants and controls; however, relative to controls, during the memory task, FH+ participants showed increased activation in brain regions encompassing the insular cortices, putamen and pallidum as well as the dorsal anterior cingulate cortex (ACC). FH+ participants also had increased hippocampal levels of Glx.

CONCLUSIONS

Euthymic individuals with a parental history of depression demonstrate increased activation of hippocampal-related neural networks during a memory task, particularly in brain regions involved in processing the salience of stimuli. Changes in the activity of the ACC replicate previous findings in FH+ participants using different psychological tasks; this suggests that task-related abnormalities in the ACC may be a marker of vulnerability to depression. Increased levels of Glx in the hippocampus might also represent a risk biomarker but follow-up studies will be required to test these various possibilities.

A meta-analysis of fMRI studies in healthy relatives of patients with schizophrenia

OBJECTIVE

Genetically at-risk yet healthy relatives of patients with schizophrenia, sharing an important part of the genetic susceptibility to the disease, allow the study of neuroimaging endophenotypes. The aim of our study was to perform a meta-analysis of whole-brain functional magnetic resonance imaging (fMRI) studies that compared adult healthy relatives of patients with schizophrenia and controls.

METHODS

Twenty-one whole-brain fMRI studies were included (17 using cognitive tasks and four using emotional tasks), published between 2003 and 2013. These studies included 467 healthy relatives of patients with schizophrenia and 768 controls. To conduct the statistical analysis, we used the effect-size signed differential mapping software, a voxel-based meta-analytic approach.

RESULTS

In healthy relatives of patients with schizophrenia, we observed a general pattern of overactivation across the 21 fMRI studies in right-sided frontal, parietal and temporal regions compared to controls. This pattern was accompanied by an underactivation in the cingulate gyrus. Our analyses showed a very similar pattern during purely cognitive tasks; during emotional tasks, healthy relatives additionally overactivated the left parahippocampal gyrus.

CONCLUSIONS

This fMRI pattern of prefrontal overactivation and hypoactivation of the cingulate gyrus may represent a candidate endophenotype for schizophrenia.

Hyper-coupling between working memory task-evoked activations and amplitude of spontaneous fluctuations in first-episode schizophrenia

Working memory (WM) deficit is an important component of impaired cognition in schizophrenia. However, between-studies inconsistencies as to the specific functional substrate imply that inter-individual variability (IIV) in the WM performance is associated with IIV in brain activity in schizophrenia. To examine the neural substrate of this WM IIV, we studied whether the neural mechanisms that underlie individual differences in WM capacity are the same in schizophrenia patients and healthy people. We correlated the IIV of the task-evoked brain activity and task performance during an n-back WM task with the IIV of the moment-to-moment variability in intrinsic resting-state activity, as measured by the amplitude of low-frequency fluctuations (ALFFs) and further compared this relationship between 17 patients with first-episode schizophrenia (FES) and 18 healthy controls. Between-group comparisons of the correlation patterns indicated aberrant ALFF-WM activation correlations and ALFF-WM performance correlations in the FES patients, but no significant changes were detected in any single measurement of these three characteristics. Specifically, we found increased positive ALFF-WM activation correlations in the bilateral lateral prefrontal cortices, posterior parietal cortices and fusiform gyri in the FES patients. We also observed significant increases in positive ALFF-WM performance correlations in the bilateral ventromedial prefrontal cortices in the FES patients. This hyper-coupling between the ALFF and fMRI measures during a WM task may indicate that it was difficult for the patients to detach themselves from one state to transition to another and suggests that the inefficient cortical function in schizophrenia stems from the intrinsic functional architecture of the brain.

Dissociable patterns in the control of emotional interference in adults with attention-deficit/hyperactivity disorder (ADHD) and in adults with alcohol dependence

Objectives

To effectively manage current task demands, attention must be focused on task-relevant information while task-irrelevant information is rejected. However, in everyday life, people must cope with emotions, which may interfere with actual task demands and may challenge functional attention allocation. Control of interfering emotions has been associated with the proper functioning of the dorsolateral prefrontal cortex (DLPFC). As DLPFC dysfunction is evident in subjects with ADHD and in subjects with alcohol dependence, the current study sought to examine the bottom-up effect of emotional distraction on task performance in both disorders.

Methods

Male adults with ADHD (n = 22), male adults with alcohol dependence (n = 16), and healthy controls (n = 30) performed an emotional working memory task (n-back task). In the background of the task, we presented neutral and negative stimuli that varied in emotional saliency.

Results

In both clinical groups, a working memory deficit was evident. Moreover, both clinical groups displayed deficient emotional interference control. The n-back performance of the controls was not affected by the emotional distractors, whereas that of subjects with ADHD deteriorated in the presence of low salient distractors, and that of alcoholics did not deteriorate until high salient distractors were presented. Subsequent to task performance, subjects with ADHD accurately recognized more distractors than did alcoholics and controls. In alcoholics, picture recognition accuracy was negatively associated with n-back performance, suggesting a functional association between the ability to suppress emotional distractors and successful task performance. In subjects with ADHD, performance accuracy was negatively associated with ADHD inattentive symptoms, suggesting that inattention contributes to the performance deficit.

Conclusions

Subjects with ADHD and alcoholics both display an emotional interference control deficit, which is especially pronounced in subjects with ADHD. Beyond dysfunctional attention allocation processes, a more general attention deficit seems to contribute to the more pronounced performance deficit pattern in ADHD.

Attempted and successful compensation in preclinical and early manifest neurodegeneration - a review of task FMRI studies

Several models of neural compensation in healthy aging have been suggested to explain brain activity that aids to sustain cognitive function. Applying recently suggested criteria of "attempted" and "successful" compensation, we reviewed existing literature on compensatory mechanisms in preclinical Huntington's disease (HD) and amnestic mild cognitive impairment (aMCI). Both disorders constitute early stages of neurodegeneration ideal for examining compensatory mechanisms and developing targeted interventions. We strived to clarify whether compensation criteria derived from healthy aging populations can be applied to early neurodegeneration. To concentrate on the close coupling of cognitive performance and brain activity, we exclusively addressed task fMRI studies. First, we found evidence for parallels in compensatory mechanisms between healthy aging and neurodegenerative disease. Several studies fulfilled criteria of attempted compensation, while reports of successful compensation were largely absent, which made it difficult to conclude on. Second, comparing working memory studies in preclinical HD and aMCI, we identified similar compensatory patterns across neurodegenerative disorders in lateral and medial prefrontal cortex. Such patterns included an inverted U-shaped relationship of neurodegeneration and compensatory activity spanning from preclinical to manifest disease. Due to the lack of studies systematically targeting all criteria of compensation, we propose an exemplary study design, including the manipulation of compensating brain areas by brain stimulation. Furthermore, we delineate the benefits of targeted interventions by non-invasive brain stimulation, as well as of unspecific interventions such as physical activity or cognitive training. Unambiguously detecting compensation in early neurodegenerative disease will help tailor interventions aiming at sustained overall functioning and delayed clinical disease onset.

Clinical utility of the N-back task in functional neuroimaging studies of working memory

INTRODUCTION

N-back tasks are commonly used in functional neuroimaging studies to identify the neural mechanisms supporting working memory (WM). Despite widespread use, the clinical utility of these tasks is not well specified. This study compared N-back performance during functional magnetic resonance imaging (fMRI) with task data acquired outside of the scanner as a measure of reliability across environment. N-back task validity was examined in relation to performance and rater-based measures used clinically to assess working memory.

METHOD

Forty-three healthy adults completed verbal and object N-back tasks during fMRI scanning and outside the scanner. Task difficulty was varied parametrically (0, 1, and 2-back conditions). Order of N-back task completion was stratified by modality (verbal/object) and environment. Participants completed the Digit Span (DS) and provided self-ratings using the Behavior Rating Inventory of Executive Function (BRIEF-WM).

RESULTS

Mean verbal and object N-back accuracy was above 95% across load conditions; task difficulty was effectively manipulated across load conditions. Performance accuracy did not significantly differ by environment. N-back reaction time was slower during fMRI (F = 6.52, p = .01, ηp(2) = .13); participants were faster when initially completing tasks outside the scanner (ηp(2) = .10-.15). Verbal 2-back accuracy was significantly related to DS performance (r = .36, p = .02). N-back performance was not related to BRIEF-WM.

CONCLUSIONS

Our results provide evidence for reliability of N-back accuracy during fMRI scanning; however, reliability of reaction time data is affected by order of task presentation. Data regarding construct validity are inconsistent and emphasize the need to consider clinical utility of behavioral measures in the design and interpretation of functional neuroimaging studies.

Functional Specialization and Flexibility in Human Association Cortex

The association cortex supports cognitive functions enabling flexible behavior. Here, we explored the organization of human association cortex by mathematically formalizing the notion that a behavioral task engages multiple cognitive components, which are in turn supported by multiple overlapping brain regions. Application of the model to a large data set of neuroimaging experiments (N = 10 449) identified complex zones of frontal and parietal regions that ranged from being highly specialized to highly flexible. The network organization of the specialized and flexible regions was explored with an independent resting-state fMRI data set (N = 1000). Cortical regions specialized for the same components were strongly coupled, suggesting that components function as partially isolated networks. Functionally flexible regions participated in multiple components to different degrees. This heterogeneous selectivity was predicted by the connectivity between flexible and specialized regions. Functionally flexible regions might support binding or integrating specialized brain networks that, in turn, contribute to the ability to execute multiple and varied tasks.

Anterior and posterior subareas of the dorsolateral frontal cortex in socially relevant decisions based on masked affect expressions

Socially-relevant decisions are based on clearly recognizable but also not consciously accessible affective stimuli. We studied the role of the dorsolateral frontal cortex (DLFC) in decision-making on masked affect expressions using functional magnetic resonance imaging. Our paradigm permitted us to capture brain activity during a pre-decision phase when the subjects viewed emotional expressions below the threshold of subjective awareness, and during the decision phase, which was based on verbal descriptions as the choice criterion. Using meta-analytic connectivity modeling, we found that the preparatory phase of the decision was associated with activity in a right-posterior portion of the DLFC featuring co-activations in the left-inferior frontal cortex. During the subsequent decision a right-anterior and more dorsal portion of the DLFC became activated, exhibiting a different co-activation pattern. These results provide evidence for partially independent sub-regions within the DLFC, supporting the notion of dual associative processes in intuitive judgments.

Curbing craving: behavioral and brain evidence that children regulate craving when instructed to do so but have higher baseline craving than adults

Although one third of children and adolescents are overweight or obese, developmental changes in food craving and the ability to regulate craving remain poorly understood. We addressed this knowledge gap by examining behavioral and neural responses to images of appetizing unhealthy foods in individuals ages 6 through 23 years. On close trials (assessing unregulated craving), participants focused on a pictured food's appetitive features. On far trials (assessing effortful regulation), participants focused on a food's visual features and imagined that it was farther away. Across conditions, older age predicted less craving, less striatal recruitment, greater prefrontal activity, and stronger frontostriatal coupling. When effortfully regulating their responses to the images, all participants reported less craving and exhibited greater recruitment of lateral prefrontal cortex and less recruitment of ventromedial prefrontal cortex. Greater body mass predicted less regulation-related prefrontal activity, particularly among children. These results suggest that children experience stronger craving than adults but can also effectively regulate craving. Moreover, the mechanisms underlying regulation may differ for heavy and lean children.

Anterior and posterior subareas of the dorsolateral frontal cortex in socially relevant decisions based on masked affect expressions

Socially-relevant decisions are based on clearly recognizable but also not consciously accessible affective stimuli. We studied the role of the dorsolateral frontal cortex (DLFC) in decision-making on masked affect expressions using functional magnetic resonance imaging. Our paradigm permitted us to capture brain activity during a pre-decision phase when the subjects viewed emotional expressions below the threshold of subjective awareness, and during the decision phase, which was based on verbal descriptions as the choice criterion. Using meta-analytic connectivity modeling, we found that the preparatory phase of the decision was associated with activity in a right-posterior portion of the DLFC featuring co-activations in the left-inferior frontal cortex. During the subsequent decision a right-anterior and more dorsal portion of the DLFC became activated, exhibiting a different co-activation pattern. These results provide evidence for partially independent sub-regions within the DLFC, supporting the notion of dual associative processes in intuitive judgments.