While chronic visual symptom complaints are common among Veterans with a history of mild traumatic brain injury (mTBI), research is still ongoing to characterize the pattern of visual deficits that is most strongly associated with mTBI and specifically, the impact of blast-related mTBI on visual functioning. One area that has not been well explored is the potential impact of blast mTBI on refractive error. While myopic shifts have been documented following head injuries in civilian populations, posttraumatic myopic shifts have not been explored in participants with military mTBI. This study investigated the impact of blast mTBIs on a range of visual function measures including distance acuity and refractive error, in a well-characterized cohort of thirty-one Post-9/11 veterans for whom detailed clinical interviews regarding military and TBI history were available. Seventeen participants had a history of blast-related mTBI (blast mTBI + group) while 14 did not (blast mTBI- group). Results show an increased frequency of convergence insufficiency and myopia in the blast mTBI + group relative to the blast mTBI- group. Linear regression analyses further show that deficits in distance acuity and refractive error are associated with the number of blast mTBIs during military service but not the number of non-blast mTBIs or the number of lifetime non-blast TBIs and cannot be accounted for by PTSD. These results are consistent with long-lasting damage following blast mTBI to subcortical visual structures that support both vergence movements and the accommodative functions needed to see clearly objects at varying distances.
A major obstacle in understanding and treating posttraumatic stress disorder (PTSD) is its clinical and neurobiological heterogeneity. To address this barrier, the field has become increasingly interested in identifying subtypes of PTSD based on dysfunction in neural networks alongside cognitive impairments that may underlie the development and maintenance of symptoms. The current study aimed to determine if subtypes of PTSD, based on normative-based cognitive dysfunction across multiple domains, have unique neural network signatures.
In a sample of 271 veterans (90% male) that completed both neuropsychological testing and resting-state fMRI, two complementary, whole-brain functional connectivity analyses explored the link between brain functioning, PTSD symptoms, and cognition.
At the network level, PTSD symptom severity was associated with reduced negative coupling between the limbic network (LN) and frontal-parietal control network (FPCN), driven specifically by the dorsolateral prefrontal cortex and amygdala Hubs of Dysfunction. Further, this relationship was uniquely moderated by executive function (EF). Specifically, those with PTSD and impaired EF had the strongest marker of LN-FPCN dysregulation, while those with above-average EF did not exhibit PTSD-related dysregulation of these networks.
These results suggest that poor executive functioning, alongside LN-FPCN dysregulation, may represent a neurocognitive subtype of PTSD.
The objective of this study is to examine whether metabolic syndrome (MetS), the clustering of 3 or more cardiovascular risk factors, disrupts the resting-state functional connectivity (FC) of the large-scale cortical brain networks. Resting-state functional magnetic resonance imaging data were collected from seventy-eight middle-aged and older adults living with and without MetS (27 MetS; 51 non-MetS). FC maps were derived from the time series of intrinsic activity in the large-scale brain networks by correlating the spatially averaged time series with all brain voxels using a whole-brain seed-based FC approach. Participants with MetS showed hyperconnectivity across the core brain regions with evidence of loss of modularity when compared with non-MetS individuals. Furthermore, patterns of higher between-network MetS-related effects were observed across most of the seed regions in both right and left hemispheres. These findings indicate that MetS is associated with altered intrinsic communication across core neural networks and disrupted between-network connections across the brain due to the co-occurring vascular risk factors in MetS.
Studies suggest looming motion represents a special class of attentional capture stimulus due to behavioural urgency: the need to act upon objects moving toward us in an environment. In particular, one theory suggests that faster reaction times to targets cued by looming relative to receding motion are driven by post-attentional, motor-priming processes beyond the attentional capture effects seen with other stimulus qualities such as colour pop-out. The present study tested this theory using a relative size judgment task where targets were precued by looming and receding optic flow fields. Results show systematic increases in the perceived size of targets that were cued by looming flow fields, consistent with previous attentional capture studies using onset cues. These results challenge theories attributing behavioural changes from looming motion to motor-priming alone.
Functional brain markers of suicidality can help identify at-risk individuals and uncover underlying neurocognitive mechanism(s). Although some converging evidence has implicated dysfunction in several brain networks, suicide-related neuroimaging markers are inconsistent across studies, due to heterogeneity of neuroimaging approaches, clinical populations, and experimental methods.
The current study aimed to address these limitations by examining resting-fMRI connectivity in a sample of post-9/11 veterans with a past suicide attempt (SA; n = 16) compared to a psychiatric control group (PC; n = 124) with no SA history but comparable past and present symptomatology, as well as a trauma control group (TC; n = 66) of trauma-exposed healthy controls. We used both a novel graph-analytic and seed-based approach to characterize SA-related connectivity differences across brain networks.
First, the graph-analytic approach identified the right amygdala and a region in the cognitive control network (right middle temporal gyrus; MTG) as regional SA-related hubs of dysfunction (HoD), or regions that exhibited a high number of SA-related connections. Aberrant SA-related connectivity between these hubs spanned multiple networks, including the cognitive control, default mode and visual networks. Second, the seed-based connectivity analysis that identifies SA-related differences in the strength of neural connections across the whole brain further implicated the right amygdala.
Small sample size and potential underreporting of SA.
These two analytic approaches preliminarily suggest that the right amygdala and right MTG may be specific neural markers of SA that can be differentiated from neural markers of psychopathology more broadly.
A recent study used functional neuroimaging and cognitive tasks to identify posttraumatic stress disorder (PTSD) subtypes. Specifically, this study found that a subgroup of patients with verbal memory impairment had a unique neural signature, namely, decreased ventral attention network (VAN) resting-state functional connectivity, and these same individuals responded poorly to psychotherapy. Although this represents one of the first studies to propose a neurocognitive subtype of PTSD and has far-reaching translational potential, the generalizability and specificity of the observed neural network and cognitive domain remain unclear. We attempted to conceptually replicate and extend these findings in a similar cohort of combat-exposed veterans (n = 229) tested using a standardized battery of neuropsychological tests and a priori criteria for cognitive impairments. First, we conducted identical and complementary analyses to determine whether subjects with PTSD and neuropsychologically defined verbal memory deficits exhibited the VAN connectivity biomarker. Second, we examined whether cognitive deficits in other domains implicated in PTSD (executive functioning and attention) exhibited the VAN signature. Across multiple measures of verbal memory, we did not find that the subgroup of individuals with PTSD and memory impairments had lower VAN connectivity. However, a subgroup of individuals with PTSD and attentional impairments did have lower VAN connectivity, suggesting that the original subtype could have been related to attention and not memory impairments. Overall, our findings suggest that the previously identified memory-impaired PTSD subtype may not generalize. Further consideration of neuropsychological methods will be important for neurocognitive markers to be implemented clinically.
Returning veterans often face multiple concurrent psychiatric and behavioral conditions that negatively impact reintegration into civilian life and are associated with functional disability. Understanding how conditions interact to negatively impact functioning is an important step toward developing holistic treatment approaches optimized for this population. This study utilized a cross‐sectional and prospective longitudinal cohort design, applying regression algorithms to understand the relative contribution of common clinical issues to functional disability in U.S. veterans who served after the September 11, 2001 (9/11), terror attacks. Community‐dwelling post‐9/11 veterans (N = 397) completed detailed assessments, including common clinical condition diagnoses, combat experience, and demographics, which were used to predict functional disability (World Health Organization Disability Assessment Schedule); 205 participants were reassessed approximately 1–2 years after enrollment. Regression analyses showed a strong association between the predictor variables and functional disability, f2 = 1.488. Validation analyses showed a high prediction ability of functional disability to independent samples, r = .719, and across time in the same individuals, r = .780. The strongest predictors included current posttraumatic stress disorder, depressive disorder, sleep disturbance, and pain diagnoses. These results demonstrate the importance of considering multiple common co‐occurring conditions when assessing functional disability in post‐9/11 veterans and suggest that certain syndromes contribute the most unique information to predicting functional disability with high confidence. As most U.S. veterans utilize private healthcare systems, these results have clinical utility for both Veterans Affairs and civilian healthcare practitioners in assessing and monitoring functional disability in post‐9/11 veterans over time.
Metabolic syndrome (MetS) is a clustering of three or more cardiovascular risk factors (RF), including hypertension, obesity, high cholesterol, or hyperglycemia. MetS and its component RFs are more prevalent in older age, and can be accompanied by alterations in brain structure. Studies have shown altered functional connectivity (FC) in samples with individual RFs as well as in clinical populations that are at higher risk to develop MetS. These studies have indicated that the default mode network (DMN) may be particularly vulnerable, yet little is known about the overall impact of MetS on FC in this network.
In this study, we evaluated the integrity of FC to the DMN in participants with MetS relative to non‐MetS individuals. Using a seed‐based connectivity analysis approach, resting‐state functional MRI (fMRI) data were analyzed, and the FC measures among the DMN seed (isthmus of the cingulate) and rest of the brain voxels were estimated.
Participants with MetS demonstrated reduced positive connectivity between the DMN seed and left superior frontal regions, and reduced negative connectivity between the DMN seed and left superior parietal, left postcentral, right precentral, right superior temporal and right superior parietal regions, after accounting for age‐ and sex‐effects.
Our results suggest that MetS is associated with alterations in FC between the DMN and other regions of the brain. Furthermore, these results indicate that the overall burden of vascular RFs associated with MetS may, in part, contribute to the pathophysiology underlying aberrant FC in the DMN.
Rapid shifts of involuntary attention have been shown to induce mislocalizations of nearby objects. One pattern of mislocalization, termed the Attentional Repulsion Effect (ARE), occurs when the onset of peripheral pre-cues lead to perceived shifts of subsequently presented stimuli away from the cued location. While the standard ARE configuration utilizes vernier lines, to date, all previous ARE studies have only assessed distortions along one direction and tested one spatial dimension (i.e., position or shape). The present study assessed the magnitude of the ARE using a novel stimulus configuration. Across three experiments participants judged which of two rectangles on the left or right side of the display appeared wider or taller. Pre-cues were used in Experiments 1 and 2. Results show equivalent perceived expansions in the width and height of the pre-cued rectangle in addition to baseline asymmetries in left/right relative size under no-cue conditions. Altering cue locations led to shifts in the perceived location of the same rectangles, demonstrating distortions in perceived shape and location using the same stimuli and cues. Experiment 3 demonstrates that rectangles are perceived as larger in the periphery compared to fixation, suggesting that eye movements cannot account for results from Experiments 1 and 2. The results support the hypothesis that the ARE reflects a localized, symmetrical warping of visual space that impacts multiple aspects of spatial and object perception.
Objective: It is increasingly recognized that trauma victims, particularly Veterans, have co-occurring psychological and physical conditions that impact cognition, especially the domains of sustained attention and executive functioning. Although previous work has generally attempted to isolate the unique cognitive effects of common combat-related comorbidities, less work has been done to examine how these conditions co-occur, and whether unique cognitive signatures accompany certain clinical combinations. Method: To address this gap, we examined how several deployment-related conditions were associated with performance on a well-validated measure of sustained attention (i.e., gradual onset continuous performance task [gradCPT]) and a battery of standard neuropsychological measures in 123 Veterans from the Translational Research Center for TBI and Stress Disorders. Initially, a Principal component analysis was conducted to investigate how comorbid conditions grouped together. Results: Several sustained attention measures from the gradCPT were differentially associated with four unique combinations of trauma-related pathology. Specifically, a somatic component representing the combination of current pain, sleep disturbance, and mild traumatic brain injury was associated with a higher rate of failures of attentional engagement. On the other hand, a comorbid posttraumatic stress disorder (PTSD) and mood disorder component (moodPTSD), as well as a substance use disorder component, were associated with higher rates of inhibitory control failures. Increased attentional instability was associated with moodPTSD as well as an anxiety disorder component. In contrast, the cognitive effects of deployment-related trauma were not observed on standard neuropsychological measures. Conclusion: These findings suggest that unique combinations of trauma-related pathology have dissociable effects on sustained attentional control.
Novel paradigms have allowed for more precise measurements of sustained attention ability and fluctuations in sustained attention over time, as well as the neural basis of fluctuations and lapses in performance. However, in recent years, concerns have arisen over the replicability of neuroimaging studies and psychology more broadly, particularly given the typically small sample sizes. One recently developed paradigm, the gradual-onset continuous performance task (gradCPT) has been validated behaviorally in large samples of participants. Yet neuroimaging studies investigating the neural basis of performance on this task have only been collected in small samples. The present study completed both a robust replication of the original neuroimaging findings and extended previous results from the gradCPT task using a large sample of 140 Veteran participants. Results replicate findings that fluctuations in attentional stability are tracked over time by BOLD activity in task positive (e.g., dorsal and ventral attention networks) and task negative (e.g., default network) regions. Extending prior results, we relate this coupling between attentional stability and on-going brain activity to overall sustained attention ability and demonstrate that this coupling strength, along with across-network coupling, could be used to predict individual differences in performance. Additionally, the results extend previous findings by demonstrating that temporal dynamics across the default and dorsal attention networks are associated with lapse-likelihood on subsequent trials. This study demonstrates the reliability of the gradCPT, and underscores the utility of this paradigm in understanding attentional fluctuations, as well as individual variation and deficits in sustained attention.
Visual spatial attention is a critical process that allows for the selection and enhanced processing of relevant objects and locations. While studies have shown attentional modulations of perceived location and the representation of distance information across multiple objects, there remains disagreement regarding what influence spatial attention has on the underlying structure of visual space. The present study utilized a method of magnitude estimation in which participants must judge the location of briefly presented targets within the boundaries of their individual visual fields in the absence of any other objects or boundaries. Spatial uncertainty of target locations was used to assess perceived locations across distributed and focused attention conditions without the use of external stimuli, such as visual cues. Across two experiments we tested locations along the cardinal and 45° oblique axes. We demonstrate that focusing attention within a region of space can expand the perceived size of visual space; even in cases where doing so makes performance less accurate. Moreover, the results of the present studies show that when fixation is actively maintained, focusing attention along a visual axis leads to an asymmetrical stretching of visual space that is predominantly focused across the central half of the visual field, consistent with an expansive gradient along the focus of voluntary attention. These results demonstrate that focusing sustained attention peripherally during active fixation leads to an asymmetrical expansion of visual space within the central visual field.
Interpersonal early life trauma (I‐ELT) is associated with a myriad of functional impairments in adulthood, increased risk of drug addiction, and neuropsychiatric disorders. While deficits in emotional regulation and amygdala functioning are well characterized, deficits in general cognitive functioning have also been documented. However, the neural underpinnings of cognitive dysfunction in adults with a history of I‐ELT and the potential relationship between amygdala‐based functional connectivity and behavioral performance are currently poorly understood. This study examined how I‐ELT affects the cognitive and neural mechanisms supporting sustained attention.
A total of 66 Veterans (18 with and 48 without a history of I‐ELT) completed a nonemotional sustained attention task during functional MRI.
The individuals with I‐ELT showed significant impairments in sustained attention (i.e., higher error rates, greater response variability). This cohort exhibited increased amygdala functional connectivity with the prefrontal cortex and decreased functional connectivity with the parahippocampal gyrus when compared to those without I‐ELT. These connections were significantly correlated with individual differences in sustained attention performance. Notably, classification analyses revealed that the pattern of amygdala connectivity across the whole brain was able to classify I‐ELT status with 70% accuracy.
These results provide evidence of a lasting negative impact for those with a history of I‐ELT on sustained attention ability. They also highlight a critical role for amygdala functioning in cognitive control and sustained attention for those with a history of I‐ELT, which may underlie the observed attention deficits in clinical assessments and cognitive tests involving both emotional and nonemotional stimuli.
Models of attention often distinguish among attention subtypes, with classic models separating orienting, switching, and sustaining functions. Compared with other forms of attention, the neurophysiological basis of sustaining attention has received far less notice, yet it is known that momentary failures of sustained attention can have far‐ranging negative effects in healthy individuals, and lasting sustained attention deficits are pervasive in clinical populations. In recent years, however, there has been increased interest in characterizing moment‐to‐moment fluctuations in sustained attention, in addition to the overall vigilance decrement, and understanding how these neurocognitive systems change over the life span and across various clinical populations. The use of novel neuroimaging paradigms and statistical approaches has allowed for better characterization of the neural networks supporting sustained attention and has highlighted dynamic interactions within and across multiple distributed networks that predict behavioral performance. These advances have also provided potential biomarkers to identify individuals with sustained attention deficits. These findings have led to new theoretical models explaining why sustaining focused attention is a challenge for individuals and form the basis for the next generation of sustained attention research, which seeks to accurately diagnose and develop theoretically driven treatments for sustained attention deficits that affect a variety of clinical populations.
Sustained attention is a fundamental cognitive function underlyingmany activities in daily life including workplace safety, but its natural variation throughout the day is incompletely characterized. To examine time-of-day variation, we collected a large online data set (N = 6,363) with participation throughout the day and around the world on the gradual-onset continuous performance task, a sensitive measure of sustained attention. This allowed us to examine accuracy, attentional stability, and strategy. Results show that both accuracy and attentional stability peak between 9:00 and 11:00 a.m. and progressively decline throughout the day, whereas strategy is more stable.
Studies have shown that individuals with hemianopia tend to bisect a line toward their blind, contralesional visual field, termed the hemianopic line bisection error (HLBE). One theory proposes that the HLBE is a perceptual distortion resulting from expansion of the central region of visual space. If true, perceptual expansions of the central regions in the intact hemifield should also be present and observable across different tasks. We tested this hypothesis using a peripheral localization task to assess localization and midpoint estimation along the horizontal axis of the visual field. In this task, participants judged the location of a target dot presented inside a Goldmann perimeter relative to their perceived visual field boundary. In Experiment 1, we tested neurologically healthy participants on the peripheral localization task as well as a novel midpoint assessment task in which participants reported their perceived midpoint along the horizontal axis of their left and right visual fields. The results revealed consistency in individual biases across the two tasks. We then used the peripheral localization task to test whether two patients with hemianopia showed a selective expansion of central visual space. For these patients, three axes were tested: the spared temporal horizontal axis and the upper and lower vertical axes. The results support the notion that the HLBE is due to expansion of perceived space along the spared temporal axis. Together, the results of both experiments validate the use of these novel paradigms for exploring perceptual asymmetries in both healthy individuals and patients with visual field loss.
Normal and abnormal differences in sustained visual attention have long been of interest to scientists, educators, and clinicians. Still lacking, however, is a clear understanding of how sustained visual attention varies across the broad sweep of the human life span. In the present study, we filled this gap in two ways. First, using an unprecedentedly large 10,430-person sample, we modeled age-related differences with substantially greater precision than have prior efforts. Second, using the recently developed gradual-onset continuous performance test (gradCPT), we parsed sustained-attention performance over the life span into its ability and strategy components. We found that after the age of 15 years, the strategy and ability trajectories saliently diverge. Strategy becomes monotonically more conservative with age, whereas ability peaks in the early 40s and is followed by a gradual decline in older adults. These observed life-span trajectories for sustained attention are distinct from results of other life-span studies focusing on fluid and crystallized intelligence.
It has previously been reported that visual crowding of a target by flankers is stronger in the upper visual field than in the lower, and this finding has been attributed to greater attentional resolution in the lower hemifield (He, Cavanagh, & Intriligator, 1996). Here we show that the upper/lower asymmetry in visual crowding can be explained by natural variations in the borders of each individual's visual field. Specifically, asymmetry in crowding along the vertical meridian can be almost entirely accounted for by replacing the conventional definition of visual field location, in units of degrees of visual angle, with a definition based on the ratio of the extents of an individual's upper and lower visual field. We also show that the upper/lower crowding asymmetry is eliminated when stimulus eccentricity is expressed in units of percentage of visual field extent but is present when the conventional measure of visual angle is used. We further demonstrate that the relationship between visual field extent and perceptual asymmetry is most evident when participants are able to focus their attention on the target location. These results reveal important influences of visual field boundaries on visual perception, even for visual field locations far from those boundaries.
A new illusion, called the configural shape illusion (CSI), is described in which the apparent shape of an object (the ‘‘target’’) is systematically distorted by the presence of an adjacent shape (the ‘‘inducer’’) that is distinct from, but perceptually grouped with, the target. The target is selectively elongated in a direction consistent with the extension of the larger configuration that includes both target and inducer. Experiments 1 and 2 show that the CSI magnitude varies systematically with factors known to influence grouping strength between configural elements, including proximity, good continuation, positional alignment, lightness similarity, hue similarity, and common fate. Experiments 3 through 5 examine the influence of relative inducer size and target size on illusion magnitude.We suggest that the CSI is caused by edge assimilation modulated by similarity between the target and inducer arising from population coding of edge positions. This assimilation account fits well with previous explanations of one-dimensional illusions of linear extent (e.g., the Muller-Lyer and Baldwin illusions), which are extended to account for the present two-dimensional illusion of shape.