| Prefrontal cortex, a heterogeneous region constituting roughly one quarter of the human brain, plays an important role in planning and controlling behavior. The goal of my dissertation research was to use functional magnetic resonance imaging (fMRI) to examine how prefrontal cortex enables us to focus on goal-relevant information and suppress interference. In the first study, I examined the neural substrates underlying the ability to simultaneously perform 2 tasks that have the potential to interfere with one another. This study suggested—in contrast to standard models of executive control—that control was distributed over several brain regions rather than being localized specifically to prefrontal cortex. In the second study, I examined the ability to suppress irrelevant memories during performance of a working memory task. The findings of this study showed that interference resolution was mediated by the same neural circuitry as working memory, and demonstrated that the level of activation of regions within prefrontal cortex predicted the ability to control interference. In the final three studies, I examined the neural substrates underlying the ability to select between competing plans of action to produce the most contextually-appropriate response. The third study demonstrated a functional dissociation between the contributions of prefrontal and parietal cortices to action planning. Parietal cortex appeared to be involved in representing possible plans of action in response to a visual stimulus, whereas prefrontal cortex was specifically engaged when there was a need to select between competing plans of action. The fourth study demonstrated that several prefrontal regions were recruited specifically by stimuli of a particular type. These regions are likely to be involved in processing the distracting information. In contrast, several other prefrontal regions were recruited by response competition regardless of the stimulus type. These regions are likely to be involved in implementing control over interference from different types of stimuli. In the fifth study, I examined the changes in brain activation across childhood which underlie the development of the ability to suppress interference and withhold contextually inappropriate responses. |
