Lesion 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.

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 insula's 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.

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.

In the presence of threatening stimuli, post-traumatic stress disorder (PTSD) can manifest as hypervigilance for threat and disrupted attentional control. PTSD patients have shown exaggerated interference effects on tasks using trauma-related or threat stimuli. In studies of PTSD, faces with negative expressions are often used as threat stimuli, yet angry and fearful facial expressions may elicit different responses. The modified Eriksen flanker task, or the emotional face flanker, has been used to examine response interference. We compared 23 PTSD patients and 23 military controls on an emotional face flanker task using angry, fearful and neutral expressions. Participants identified the emotion of a central target face flanked by faces with either congruent or incongruent emotions. As expected, both groups showed slower reaction times (RTs) and decreased accuracy on emotional target faces, relative to neutral. Unexpectedly, both groups showed nearly identical interference effects on fearful and neutral target trials. However, post hoc testing suggested that PTSD patients showed faster RTs than controls on congruent angry faces (target and flanker faces both angry) relative to incongruent, although this finding should be interpreted with caution. This possible RT facilitation effect with angry, but not fearful faces, also correlated positively with self-report measures of PTSD symptoms. These results suggest that PTSD patients may be more vigilant for, or primed to respond to, the appearance of angry faces, relative to fearful, but further study is needed.