| Cognitive control is critical to navigating through a constantly changing environment. The processes employed allow us to inhibit habitual behaviors and make adjustments to behavior and cognition after error. The stop signal task is widely employed to study these behaviors and with the use of functional magnetic resonance imaging (fMRI), we are able to examine the neural processes underlying the component processes, which include response inhibition and error and saliency processing. In Chapter 2, we examined the differences between post-conflict control, as it differs by error and non-error conflict. Saliency processing is defined as the contrast between stop trials (successful and unsuccessful) and go trials. This measure captures the salience of the presentation of the stop signal, as well as aspects of response inhibition and conflict between habitual action and response.;The component processes of cognitive control have long been implicated in many different clinical disorders. In Chapter 3, we studied how obesity interacts with these cognitive control processes. We found that while obese women showed decreased activation during saliency processing in the insula, inferior parietal cortex, and supplementary motor area, they did not have any changes in response inhibition or error processing. Many clinical disorders, including obesity, show high trait impulsivity, and the degree of impulsivity also varies between healthy controls. Previous studies have also shown that measures of cognitive control captured by the stop signal task might be related to traditional ratings of impulsivity, such as the Barratt Impulsiveness Scale. We investigated how variations in Barratt impulsivity within the healthy population affected the component processes of cognitive control (Chapter 4). We again found that activations in the insula and middle frontal cortex decreased only for the saliency processing contrast and with increasing impulsivity, which would align with fmdings in many of these disorders. Furthermore, these regions were connected to an attentional network that also inversely correlated to Barratt impulsivity.;Methylphenidate, a common treatment for ADHD, acts by blocking the norepinephrine and dopamine transporters and thereby likely increasing catecholaminergic signaling to improve the deficits seen in this disorder. To better understand how this medication may work, we examined how methylphenidate affects cognitive control processes in healthy adults. Similar to the previous findings, methylphenidate increased activations during saliency processing in caudate, motor areas, inferior parietal cortex and cerebellum.;Taken altogether, these findings show that saliency processing is particularly susceptible to different clinical states, with alterations in signaling in attention- and motor-related brain areas. |
