Neural correlates of attention bias to threat in post-traumatic stress disorder

Attentional biases have been proposed to contribute to symptom maintenance in posttraumatic stress disorder (PTSD), although the neural correlates of these processes have not been well defined; this was the goal of the present study. We administered an attention bias task, the dot probe, to a sample of 37 (19 control, 18 PTSD+) traumatized African-American adults during fMRI. Compared to controls, PTSD+ participants demonstrated increased activation in the dorsolateral prefrontal cortex (dlPFC) in response to threat cue trials. In addition, attentional avoidance of threat corresponded with increased ventrolateral prefrontal cortex (vlPFC) and dorsal anterior cingulate cortex (dACC) activation in the PTSD group, a pattern that was not observed in controls. These data provide evidence to suggest that relative increases in dlPFC, dACC and vlPFC activation represent neural markers of attentional bias for threat in individuals with PTSD, reflecting selective disruptions in attentional control and emotion processing networks in this disorder.     

Eye movement and electrodermal responses to threat stimuli in post-traumatic stress disorder

A core feature of post-traumatic stress disorder (PTSD) is hypervigilence to threatening material. This study measured processing of threat material in PTSD with simultaneously acquired initial eye movements and electrodermal activity, following presentation of threatening and neutral words. Ten PTSD subjects and 10 controls were presented with 4 words in parafoveal range. On trials in which a threat word was present, PTSD subjects demonstrated initial eye fixations on the threat word more than controls. PTSD subjects also demonstrated more orienting responses on all trials than controls. These results suggest that processing of threat information in PTSD can be usefully investigated with convergent psychophysiological methodologies.     

An electrophysiological study of the locus of the interference effect in a stimulus-response compatibility paradigm

This study investigated the locus of the interference effect in a stimulus-response compatibility task using event-related potentials (ERPs). Ten participants were instructed to respond to stimulus color with the left or right middle finger. Red or blue arrows pointed in the same direction as the response hand on congruent trials and pointed in the opposite direction on incongruent trials. Neutral trials were red or blue horizontal bars. Reaction times (RTs) to incongruent stimuli were significantly longer than RTs to congruent stimuli. The peak latency of the P300 for incongruent stimuli was significantly longer than that for congruent stimuli. In addition, onset of stimulus-locked lateralized readiness potential (LRPs) was significantly later for incongruent stimuli than for congruent stimuli. However, electromyogram (EMG)-locked LRPs for incongruent stimuli showed incorrect preparation. These results suggest that the interference effect might occur at the stage in which stimulus evaluation processes and response-related processes overlap.     

Trait anxiety and conflict monitoring following threat: An ERP study

Threat-related attentional disruptions in anxiety may relate to changes in cognitive control during task processing. The present study examined this question using the N2 event-related brain potential. It was predicted that threat stimuli will selectively influence the N2 for those showing elevated trait anxiety and that reduced N2 may reflect a compensatory process predicting better attention performance. EEG was recorded while 36 participants completed a cued flanker task with threat or nonthreat distracters. N2 amplitudes were greater to incongruent versus congruent flankers. Following threat, high trait anxious participants showed reduced modulation of the N2 by flanker type and greater N2 amplitudes to congruent flankers. Reduced N2 was associated with better attention performance. This study was among the first documenting the emotional modulation of the N2 related to the threat bias and its links with attention interference in anxiety.     

Tobacco smoking and event-related brain potentials in a Stroop task.

Behavioral and event-related brain potential (ERP) measures were used to assess the effects of tobacco smoking on selective attention. Two groups of abstinent smokers performed a Stroop color-naming task. The display color of a stimulus word determined the correct response, whereas word meaning was irrelevant. Meaning was congruent, neutral, or incongruent with respect to color. After completing two blocks of trials under abstinent conditions, subjects received a 15-min break before performing two more blocks. Subjects in the Smoking group (N=12) smoked two cigarettes during the break. Matched Control subjects (N=12) did not smoke during the break. Typical Stroop effects were found, as reaction time (RT) was shortest to congruent words, intermediate to neutral words, and longest to incongruent words. Overall RT decreased after the break equally for the Smoking and Control groups, whereas the magnitude of the Stroop effect was unchanged for either group. P300 amplitude decreased after the break for the Smoking group but not for the Control group, which implied that smoking rather than practice produced component decline. Error rate and P300 latency did not change after the break for either group. The results suggest that tobacco smoking may decrease the availability of general attentional resources required to evaluate colored word stimuli, whereas the specific stimulus processing mechanisms responsible for the Stroop effect are relatively unaffected.     

Event‐related potential indices of congruency sequence effects without feature integration or contingency learning confounds

The congruency effect in Stroop‐like tasks (i.e., increased response time and reduced accuracy in incongruent relative to congruent trials) is often smaller when the previous trial was incongruent as compared to congruent. This congruency sequence effect (CSE) is thought to reflect cognitive control processes that shift attention to the target and/or modulate the response engendered by the distracter differently after incongruent relative to congruent trials. The neural signatures of CSEs are therefore usually attributed to cognitive control processes that minimize distraction from irrelevant stimuli. However, CSEs in previous functional neuroimaging studies were ubiquitously confounded with feature integration and/or contingency learning processes. We therefore investigated whether a neural CSE can be observed without such confounds in a group of healthy young adults (n = 56). To this end, we combined a prime‐probe task that lacks such confounds with high‐density ERPs to identify, for the first time, the neural time course of confound‐minimized CSEs. Replicating recent behavioral findings, we observed strong CSEs in this task for mean response time and mean accuracy. Critically, conceptually replicating prior ERP results from confounded tasks, we also observed a CSE in both the parietal conflict slow potential (conflict SP) and the frontomedial N450. These findings indicate for the first time that neural CSEs as indexed by ERPs can be observed without the typical confounds. More broadly, the present study provides a confound‐minimized protocol that will help future researchers to better isolate the neural bases of control processes that minimize distraction from irrelevant stimuli.     

An experimental investigation of hypervigilance for threat in children and adolescents with post-traumatic stress disorder

BACKGROUND: The present study examined biases in visual attention for emotional material in children and adolescents with post-traumatic stress disorder (PTSD) and healthy controls. METHODS: The participants carried out an attentional deployment task in which probe detection latency data were used to determine the distribution of visual attention for threat-related and depression-related material. RESULTS: The results showed that children and adolescents with PTSD, relative to controls, selectively allocated processing resources towards socially threatening stimuli and away from depression-related stimuli. This attentional avoidance of depression-related information in the PTSD participants declined with age. CONCLUSIONS: The results of the study are interpreted as a consolidation and extension of previous research on attentional bias and emotional disorder in younger participants.     

Pupillary assessment and computational modeling of the Stroop task in depression.

Depressed individuals frequently display disruptions in selective attention, but the time course and specificity of these difficulties are not well-understood. To better understand the nature of attentional disruptions in depression, 28 healthy adults and 23 unmedicated depressed adults completed a Stroop color-naming task using a long inter-stimulus interval and pupil dilation was recorded as a measure of cognitive load. Both groups took longer to name the color for incongruent than congruent trials. Pupil dilation was also larger for incongruent trials than for congruent trials across groups, which suggested that pupil dilation reflected cognitive load on the task. Though the groups did not differ in the magnitude of Stroop effect in pupil dilation, depressed individuals displayed decreased pupil dilation in the seconds following stimuli relative to controls. Computational neural network modeling further suggested that observed effects were consistent with decreased prefrontal cortex activity, associated with decreased cognitive control.     

Congruency, attentional set, and laterality effects with emotional words

The present study investigated the influence of attention and word-emotion congruency on auditory asymmetries with stimuli that include verbal and emotional components. Words were presented dichotically to 80 participants and were pronounced in either congruent or incongruent emotional tones. Participants were asked to identify the presence of a target word or emotion under 1 of 2 conditions. The blocked condition required detection of a word or emotional target in separate blocks. In the randomized condition, the target was changed across trials by means of a postcue. A right-ear advantage (REA) and a left-ear advantage (LEA) were found for word and emotion targets, respectively. However, the finding of a Condition x Stimulus Type x Ear x Congruency interaction indicated that in the randomized condition, a REA was obtained for words when the stimuli were congruent and a LEA was observed for emotions when the stimuli were incongruent. The findings suggest that randomizing the target reduced the influence of the attentional set established by blocking the target. It is likely that this promoted the detection of hemispheric interference in the randomized condition.     

Collision error avoidance: influence of proportion congruency and sensorimotor memory on open-loop grasp control

Grasping behaviour involves the integration of current and historical knowledge about an object, a process that can be influenced by sensory uncertainty. In the present study, participants simultaneously interacted with a visual cue and a haptic cue before reaching to grasp a target object. The visual cue was either congruent (equal in size to haptic cue and target) or incongruent (larger than haptic cue and target). To enhance sensory uncertainty, we manipulated the proportion of congruent trials to be either 80 or 20%. We compared grasp kinematics and forces between congruent and incongruent trials and between the 20 and 80% proportion congruency groups. We also studied the effects of trial history by comparing the performance of congruent and incongruent trials preceded by either the same or opposite trial type. Proportion congruency did not affect temporal kinematics but did affect maximum grip aperture (MGA) as the 80% proportion congruency group used a greater MGA, regardless of trial type. For grasping forces, an interaction effect showed that the 20% proportion congruency group used a greater peak load force on congruent trials. Incongruent trials that followed congruent trials had decreased movement time, increased MGA and increased grasping forces, relative to those that followed incongruent trials. We interpret the data to suggest that the grasp control system integrates multisensory information using flexible, yet specific criteria regarding task constraints. The prevention of collision error (i.e., an inadequate MGA when contacting the target) may be one guiding principle in the control process.     

When cognitive control is calibrated: Event-related potential correlates of adapting to information-processing conflict despite erroneous response preparation

To examine when in the perception-action cycle resolving information-processing conflict modulates signals of the current need for cognitive control, the present work examined event-related potential correlates of response preparation (lateralized readiness potentials; LRPs) and of information-processing conflict (fronto-central N2 responses) on trial n flanker trials, as a function of whether trial n –1 entailed a congruent flanker, an incongruent flanker, or a NoGo cue. Although LRP-indexed erroneous response preparation was substantial on incongruent trials across all levels of trial n –1, N2 amplitudes and behavioral interference effects were attenuated on incongruent trials following NoGo and incongruent (relative to congruent) trials. Even after initial attentional and motor-preparation processes have transpired, then, relatively later control mechanisms appear sufficient to signal a reduced need to engage cognitive control anew.     

Implicit memory bias and trait anxiety: a psychophysiological analysis

The effect of threatening words and anxiety upon implicit memory performance was investigated. It was predicted that anxious individuals would show a bias to threat-related material. In addition, psychophysiological measures were obtained to assess the attentional and encoding processes that might underlie this cognitive bias. Forty participants were equally allocated to high and low trait anxious groups, according to pre-determined cut-offs. All participants were exposed to threat and non-threat words and following a filler task, were asked to complete primed and unprimed wordstems. Implicit memory performance was assessed in terms of accuracy and reaction time for completion. Heart rate and electrodermal responses were measured. Results demonstrated initial increased cardiac deceleration to threat stimuli, subsequent cardiac acceleration to non-threat stimuli, and an implicit memory bias to non-threat material by all participants. These findings are discussed in relation to the 'vigilance-avoidance' model of attention to threat stimuli.     

Dissociative responses to conscious and non-conscious fear impact underlying brain function in post-traumatic stress disorder

BACKGROUND: Dissociative reactions in post-traumatic stress disorder (PTSD) have been regarded as strategic responses that limit arousal. Neuroimaging studies suggest distinct prefrontal responses in individuals displaying dissociative and hyperarousal responses to threat in PTSD. Increased prefrontal activity may reflect enhanced regulation of limbic arousal networks in dissociation. If dissociation is a higher-order regulatory response to threat, there may be differential responses to conscious and automatic processing of threat stimuli. This study addresses this question by examining the impact of dissociation on fear processing at different levels of awareness. METHOD: Functional magnetic resonance imaging (fMRI) with a 1.5-T scanner was used to examine activation to fearful (versus neutral) facial expressions during consciously attended and non-conscious (using backward masking) conditions in 23 individuals with PTSD. Activation in 11 individuals displaying non-dissociative reactions was compared to activation in 12 displaying dissociative reactions to consciously and non-consciously perceived fear stimuli. RESULTS: Dissociative PTSD was associated with enhanced activation in the ventral prefrontal cortex for conscious fear, and in the bilateral amygdala, insula and left thalamus for non-conscious fear compared to non-dissociative PTSD. Comparatively reduced activation in the dissociative group was apparent in dorsomedial prefrontal regions for conscious fear faces. CONCLUSIONS: These findings confirm our hypotheses of enhanced prefrontal activity to conscious fear and enhanced activity in limbic networks to non-conscious fear in dissociative PTSD. This supports the theory that dissociation is a regulatory strategy invoked to cope with extreme arousal in PTSD, but this strategy appears to function only during conscious processing of threat.     

Are object- and space-based attentional biases both important to free-viewing perceptual asymmetries?

In contrast to unilateral neglect patients, who overattend to the right hemispace, normal participants attend more to the left: a phenomenon known as pseudoneglect. Two experiments examined whether pseudoneglect results from object- or space-based attentional biases. Normal participants (n=38, 22) made luminance judgments for two left/right mirror-reversed luminance gradients (greyscales task). The relative lateral position of the greyscales stimuli was manipulated so that object- and space-based coordinates were congruent or incongruent. A baseline condition was also included. A leftward bias, found for the baseline condition, was annulled in the incongruent condition, demonstrating an opposition of object- and space-based biases. The leftward bias was reduced in the congruent condition where object- and space-based biases were expected to be additive. This effect was attributed to extraneous factors, which were avoided in the second experiment by presenting the greyscales stimuli sequentially. Once again, no bias was observed in the incongruent condition where object- and space-based biases were opposed. The leftward bias in the congruent condition was the same as the baseline. The results can be explained by a combination of space- and object-based biases or by space-based biases alone and are discussed with reference to a variety of models, which describe the distribution of attention across space.     

Episodic memory for spatial context biases spatial attention

The study explores the bottom-up attentional consequences of episodic memory retrieval. Individuals studied words (Experiment 1) or pictures (Experiment 2) presented on the left or on the right of the screen. They then viewed studied and new stimuli in the centre of the screen. One-second after the appearance of each stimulus, participants had to respond to a dot presented on the left or on the right of the screen. The dot could follow a stimulus that had been presented, during the study phase, on the same side as the dot (congruent condition), a stimulus that had been presented on the opposite side (incongruent condition), or a new stimulus (neutral condition). Subjects were faster to respond to the dot in the congruent compared to the incongruent condition, with an overall right visual field advantage in Experiment 1. The memory-driven facilitation effect correlated with subjects’ re-experiencing of the encoding context (R responses; Experiment 1), but not with their explicit memory for the side of items’ presentation (source memory; Experiment 2). The results indicate that memory contents are attended automatically and can bias the deployment of attention. The degree to which memory and attention interact appears related to subjective but not objective indicators of memory strength.     

The contextual effect in object detection from picture

Participants detected a target from search stimuli which contained either eight (Experiment 1) or four (Experiment 2) living or nonliving common objects. Objects were represented either as pictures or as words. The target and other stimuli were from a same category, either living or nonliving, in the congruent condition, and were from a different category in the incongruent condition. The results of Experiment 1 showed that picture targets were detected more quickly in the incongruent than in the congruent condition while word targets were detected more quickly in the congruent than in the incongruent condition. These results indicate an interference effect of visual context in picture detection and a facilitation effect of semantic context in word detection. However, Experiment 2 using four stimuli did not show the same contextual effects as Experiment 1, probably because the task became easy.     

Phasic heart period reactions to cued threat and nonthreat stimuli in generalized anxiety disorder

The hallmark of generalized anxiety disorder (GAD) is chronic uncontrollable worry. A preattentive bias toward threat cues and hypervigilance may support this ongoing state of apprehension. A study was conducted to bridge the attentional and physiological underpinnings of GAD by examining phasic heart period (HP) responses to cued threat and nonthreat stimuli. Thirty-three GAD clients and 33 nonanxious control participants engaged in an S1-S2 procedure that employed cued threat and nonthreat word stimuli, during which phasic HP reactions were recorded. As compared with the control group, the GAD group showed (1) smaller cardiac orienting responses and impaired habituation of cardiac orienting to neutral words, (2) HR acceleration in response to threat words, and (3) a conditioned anticipatory HR deceleration to threat words over repeated trials. The cardiac-autonomic underpinnings of GAD appear to rigidly maintain precognitive defensive responses against threat. This portrayal is discussed in the context of an integrative model that depicts diminished global adaptive variability in GAD.     

Impairments of response conflict monitoring and resolution in schizophrenia

BACKGROUND: It has been argued recently that the attentional dysfunction in schizophrenia occurs as a result of an inability to inhibit automatic attentional shifts to compelling external stimuli. However, this hypothesis is based on performance on paradigms that require overt or covert shifts of spatial attention. METHOD: We investigated responses to foveally presented stimuli in patients with schizophrenia and healthy controls as they performed unidimensional and bidimensional versions of the flanker task. In both tasks, centrally presented target stimuli were flanked by peripheral stimuli that were either congruent or incongruent with the behavioural goal of the subject. In the bidimensional task, the flanking stimuli could be congruent and incongruent on multiple stimulus characteristics. RESULTS: On the unidimensional flanker task, the behavioural goal modulated the responses of the schizophrenia group such that response times (RTs) to target stimuli that were flanked by congruent stimuli were faster than RTs to target stimuli flanked by incongruent stimuli. However, on the bidimensional flanker task, the responses of schizophrenia patients were no longer constrained by the behavioural goal and RTs to both congruent and incongruent stimuli were equivalent. CONCLUSIONS: It appears that the attentional dysfunction in schizophrenia may reflect difficulty in resolving multiple and simultaneous response conflicts. These findings suggest a possible role for the anterior cingulate cortex in the attentional impairments associated with schizophrenia.     

Pikachurin interaction with dystroglycan is diminished by defective O-mannosyl glycosylation in congenital muscular dystrophy models and rescued by LARGE overexpression

Visuo-tactile integration occurs in a privileged way in peripersonal space, namely when visual and tactile stimuli are in spatial proximity. Here, we investigated whether crossmodal spatial effects (i.e. stronger crossmodal interactions for spatially congruent compared to incongruent visual and tactile stimuli) are also present when visual stimuli presented near the body are indirectly viewed in a mirror, thus appearing in far space. Participants had to attend to one of their hands throughout a block of stimuli in order to detect infrequent tactile target stimuli at that hand while ignoring tactile targets at the unattended hand, all tactile non-target stimuli, and any visual stimuli. Visual stimuli were presented simultaneously with tactile stimuli, in the same (congruent) or opposite (incongruent) hemispace with respect to the tactile stimuli. In one group of participants the visual stimuli were delivered near the participants' hands and were observed as indirect mirror reflections ('mirror' condition), while in the other group these were presented at a distance from the hands ('far' condition). The main finding was that crossmodal spatial modulations of ERPs recorded over and close to somatosensory cortex were present in the 'mirror' condition but not the 'far' condition. That is, ERPs were enhanced in response to tactile stimuli coupled with spatially congruent versus incongruent visual stimuli when the latter were viewed through a mirror. These effects emerged around 190 ms after stimuli onset, and were modulated by the focus of spatial attention. These results provide evidence that visual stimuli observed in far space via a mirror are coded as near-the-body stimuli according to their known rather than to their perceived location. This suggests that crossmodal interactions between vision and touch may be modulated by previous knowledge of reflecting surfaces (i.e. top-down processing).     

Effects of attention and semantic relation on event-related potentials in a picture-word naming task

The interactive effects of attention and semantic relation on event-related potential (ERP) waveforms were examined during a naming task in which the physical stimulus array was the same across conditions. Superimposed picture-word pairs were presented in which the meaning of the words and pictures was congruent, semantically associated, or incongruent. In separate conditions, participants named words or pictures while ignoring the other stimulus. When words were attended, the superimposed pictures modulated the amplitude of P240 waves at posterior sites compared with when words were presented individually, but had no effect on N450 waves. In contrast, when pictures were attended to, the superimposed incongruent words elicited larger amplitude N450 waves at anterior sites than did congruent words or individually presented pictures. These effects affirm the independent processing of words and pictures during attention and are consistent with automatic and controlled processing of words and pictures, respectively. They also illustrate the endogenous nature of these late ERP waves.