Victoria Ashley

Left inferior frontal gyrus is critical for response inhibition

BackgroundLesion studies in human and non-human primates have linked several different regions of prefrontal cortex (PFC) with the ability to inhibit inappropriate motor responses. However, recent functional neuroimaging studies have specifically implicated right inferior PFC in response inhibition. Right frontal dominance for inhibitory motor control has become a commonly accepted view, although support for this position has not been consistent. Particularly conspicuous is the lack of data on the importance of the homologous region in the left hemisphere. To investigate whether the left inferior frontal gyrus (IFG) is critical for response inhibition, we used neuropsychological methodology with carefully characterized brain lesions in neurological patients.ResultsTwelve individuals with damage in the left IFG and the insula were tested in a Go/NoGo response inhibition task. In alternating blocks, the difficulty of response inhibition was easy (50% NoGo trials) or hard (10% NoGo trials). Controls showed the predicted pattern of faster reaction times and more false alarm errors in the hard condition. Left IFG patients had higher error rates than controls in both conditions, but were more impaired in the hard condition, when a greater degree of inhibitory control was required. In contrast, a patient control group with orbitofrontal cortex lesions showed intact performance.ConclusionRecent neuroimaging studies have focused on a highly specific association between right IFG and inhibitory control. The present results indicate that the integrity of left IFG is also critical for successful implementation of inhibitory control over motor responses. Our findings demonstrate the importance of obtaining converging evidence from multiple methodologies in cognitive neuroscience.

Are the neural correlates of stopping and not going identical? Quantitative meta-analysis of two response inhibition tasks

Neuroimaging studies have utilized two primary tasks to assess motor response inhibition, a major form of inhibitory control: the Go/NoGo (GNG) task and the Stop-Signal Task (SST). It is unclear, however, whether these two tasks engage identical neural systems. This question is critical because assumptions that both tasks are measuring the same cognitive construct have theoretical and practical implications. Many papers have focused on a right hemisphere dominance for response inhibition, with the inferior frontal gyrus (IFG) and the middle frontal gyrus (MFG) receiving the bulk of attention. Others have emphasized the role of the pre-supplementary motor area (pre-SMA). The current study performed separate quantitative meta-analyses using the Activation Likelihood Estimate (ALE) method to uncover the common and distinctive clusters of activity in GNG and SST. Major common clusters of activation were located in the right anterior insula and the pre-SMA. Insular activation was right hemisphere dominant in GNG but more bilaterally distributed in SST. Differences between the tasks were observed in two major cognitive control networks: (1) the fronto-parietal network that mediates adaptive online control, and (2) the cingulo-opercular network implicated in maintaining task set (Dosenbach et al., 2007) and responding to salient stimuli (Seeley et al., 2007). GNG engaged the fronto-parietal control network to a greater extent than SST, with prominent foci located in the right MFG and right inferior parietal lobule. Conversely, SST engaged the cingulo-opercular control network to a greater extent, with more pronounced activations in the left anterior insula and bilateral thalamus. The present results reveal the anterior insulas importance in response inhibition tasks and confirm the role of the pre-SMA. Furthermore, GNG and SST tasks are not completely identical measures of response inhibition, as they engage overlapping but distinct neural circuits.

Time course and specificity of event-related potentials to emotional expressions

To clarify the time course of neural responses to faces with different emotional expressions, we used event-related potential (ERP) and reaction time measures. Faces expressing four different emotions (happy, neutral, fearful, disgusted) and houses were shown in both upright and inverted orientations while subjects performed an immediate-repeats task. Results indicated that upright fearful expressions enhanced the frontocentral P200. However, emotional effects on the N170 and late positive component interacted with face orientation and were not selective for any specific expression. A unique negative component for upright disgust faces was observed at ∼300 ms at occipital regions. These results provide evidence for emotion-specific ERPs associated with fear and disgust, distinct from other non-specific configurational and attentional effects.

Impaired Response Inhibition in Veterans with Post-Traumatic Stress Disorder and Mild Traumatic Brain Injury

Combat veterans with post-traumatic stress disorder (PTSD) can show impairments in executive control and increases in impulsivity. The current study examined the effects of PTSD on motor response inhibition, a key cognitive control function. A Go/NoGo task was administered to veterans with a diagnosis of PTSD based on semi-structured clinical interview using DSM-IV criteria (n = 40) and age-matched control veterans (n = 33). Participants also completed questionnaires to assess self-reported levels of PTSD and depressive symptoms. Performance measures from the patients (error rates and reaction times) were compared to those from controls. PTSD patients showed a significant deficit in response inhibition, committing more errors on NoGo trials than controls. Higher levels of PTSD and depressive symptoms were associated with higher error rates. Of the three symptom clusters, re-experiencing was the strongest predictor of performance. Because the co-morbidity of mild traumatic brain injury (mTBI) and PTSD was high in this population, secondary analyses compared veterans with PTSD+mTBI (n = 30) to veterans with PTSD only (n = 10). Although preliminary, results indicated the two patient groups did not differ on any measure (p > .88). Since cognitive impairments could hinder the effectiveness of standard PTSD therapies, incorporating treatments that strengthen executive functions might be considered in the future. (JINS, 2012, 18, 1-10).

Attentional bias for trauma-related words: exaggerated emotional Stroop effect in Afghanistan and Iraq war veterans with PTSD.

BackgroundPost-traumatic stress disorder (PTSD) involves debilitating symptoms that can disrupt cognitive functioning. The emotional Stroop has been commonly used to examine the impact of PTSD on attentional control, but no published study has yet used it with Afghanistan and Iraq war veterans, and only one previous study has compared groups on habituation to trauma-related words.MethodsWe administered the emotional Stroop, the Beck Depression Inventory (BDI), and the PTSD Checklist (PCL) to 30 veterans with PTSD, 30 military controls, and 30 civilian controls. Stroop word types included Combat, Matched-neutral, Neutral, Positive and Negative.ResultsCompared to controls, veterans with PTSD were disproportionately slower in responding to Combat words. They were also slower and less accurate overall, did not show interference on Negative or Positive words relative to Neutral, and showed a trend for delayed but successful habituation to Combat words. Higher PCL and BDI scores also correlated with larger interference effects.ConclusionsBecause of its specificity in detecting attentional biases to trauma-related words, the emotional Stroop task may serve as a useful pre- and post task with intervention studies of PTSD patients.

Increased response variability as a marker of executive dysfunction in veterans with post-traumatic stress disorder.

The stability of cognitive control processes over time can be indexed by trial-to-trial variability in reaction time (RT). Greater RT variability has been interpreted as an indicator of executive dysfunction, inhibitory inefficiency, and excessive mental noise. Previous studies have demonstrated that combat veterans with post-traumatic stress disorder (PTSD) show substantial impairments in inhibitory control, but no studies have examined response variability in this population. In the current experiment, RT variability in the Go/NoGo response inhibition task was assessed for 45 veterans with PTSD and 34 control veterans using the intra-individual coefficient of variation (ICV) and ex-Gaussian analysis of RT distributions. Despite having mean RTs that were indistinguishable from controls, the PTSD patients had significantly greater RT variability as measured by ICV. More variable RTs were in turn associated with a greater number of false alarm errors in the patients, suggesting that less consistent performers were less successful at inhibiting inappropriate responses. RT variability was also highly correlated with self-reported symptoms of PTSD, depression, and attentional impulsiveness. Furthermore, response variability predicted diagnosis even when controlling for PTSD symptom severity. In turn, PTSD severity was correlated with self-rated attentional impulsiveness. Deficits in the top-down cognitive control processes that cause greater response variability might contribute to the maintenance of PTSD symptomology. Thus, the distractibility issues that cause more variable reaction times might also result in greater distress related to the trauma.

Material-specific interference control is dissociable and lateralized in human prefrontal cortex.

The prefrontal cortex (PFC) plays a key role in the ability to pursue a particular goal in the face of competing alternatives, an ability that is fundamental to higher-order human behavior. Whether this region contributes to cognitive control through material-general mechanisms, or through hemispheric specialization of component abilities, remains unclear. Here we show that left or right ventrolateral PFC damage in humans leads to doubly dissociable deficits in two classic tests of interference control. Patients with damage centered on left ventrolateral prefrontal cortex had exaggerated interference effects in the color-word Stroop, but not the Eriksen flanker task, whereas patients with damage affecting right ventrolateral prefrontal cortex showed the opposite pattern. Thus, effective interference resolution requires either right or left lateral PFC, depending on the nature of the task. This finding supports a lateralized, material-specific account of cognitive control in humans.

Enhanced Attentional Bias Variability in Post-Traumatic Stress Disorder and its Relationship to More General Impairments in Cognitive Control

Hypervigilance towards threat is one of the defining features of post-traumatic stress disorder (PTSD). This symptom predicts that individuals with PTSD will be biased to attend to potential dangers in the environment. However, cognitive tasks designed to assess visual-spatial attentional biases have shown mixed results. A newer proposal suggests that attentional bias is not a static phenomenon, but rather is characterized by fluctuations towards and away from threat. Here, we tested 28 combat Veterans with PTSD and 28 control Veterans on a dot probe task with negative-neutral word pairs. Combat-related words and generically negative words were presented in separate blocks. Replicating previous results, neither group showed a bias to attend towards or away from threat, but PTSD patients showed greater attentional bias variability (ABV), which correlated with symptom severity. However, the cognitive processes indexed by ABV are unclear. The present results indicated that ABV was strongly correlated with standard deviation at the reaction time (RT) level and with excessively long RTs (ex-Gaussian tau) related to cognitive failures. These findings suggest an overall increase in response variability unrelated to threat-related biases in spatial attention, and support a disruption in more general cognitive control processes in PTSD.

Dissociation between working memory performance and proactive interference control in post-traumatic stress disorder

ABSTRACT Deficits in working memory (WM) and cognitive control processes have been reported in post‐traumatic stress disorder (PTSD), in addition to clinical symptoms such as hypervigilance, re‐experiencing, and avoidance of trauma reminders. Given the uncontrollable nature of intrusive memories, an important question is whether PTSD is associated with altered control of interference in WM. Some studies also suggest that episodic memory shows a material‐specific dissociation in PTSD, with greater impairments in verbal memory and relative sparing of nonverbal memory. It is unclear whether this dissociation applies to WM, as no studies have used identical task parameters across material. Here we tested 29 combat Veterans with PTSD and 29 age‐matched control Veterans on a recent probes WM task with words and visual patterns in separate blocks. Participants studied four‐item sets, followed by a probe stimulus that had been presented in the previous set (recent probe) or not (nonrecent probe). Participants with PTSD made more errors than controls, and this decrement was similar for verbal and visual stimuli. Proactive interference from items recently presented, but no longer relevant, was not significantly different in the PTSD group and showed no relationship to re‐experiencing symptom severity. These results demonstrate that PTSD is not reliably associated with increased intrusions of irrelevant representations into WM when non‐emotional stimuli are used. Future studies that use trauma‐related material may provide insight into the flashbacks and intrusive thoughts that plague those with PTSD. HIGHLIGHTSPTSD patients showed lower accuracy on verbal and visual working memory tasks.The decrement was similar for verbal and visual stimuli.PTSD patients did not show greater proactive interference from recent items.Executive components of working memory dissociated from working memory maintenance.Relevant to the literature on memory intrusions, a cardinal feature of PTSD.