The ability to step outside a routine—to select a new response over a habitual one—is a cardinal function of the frontal lobes. A large body of neuroimaging work now exists pointing to increased activation within the anterior cingulate when stimuli evoke competing responses (incongruent trials) relative to when responses converge (congruent trials). However, lesion evidence that the ACC is necessary in this situation is inconsistent. We hypothesized that this may be a consequence of different task procedures (context) used in lesion and neuroimaging studies. The present study attempted to reconcile the lesion and the fMRI findings by having subjects perform clinical and experimental versions of the Stroop task during BOLD fMRI acquisition. We examined the relationship of brain activation patterns, specifically within the anterior cingulate and left dorsolateral frontal regions, to congruent and incongruent trial types in different task presentations or contexts. The results confirmed our hypothesis that ACC activity is relatively specific to unblocked–uncued incongruent Stroop conditions that have not been used in large neuropsychological studies. Moreover, the size of the behavioral Stroop interference effect was significantly correlated with activity in ACC and left dorsolateral regions, although in different directions. The current results are discussed in terms of previous proposals for the functional roles of these regions in activating, monitoring, and task setting, and the relation of these findings to the disparate reports in recent case series is considered.

This study used fMRI to investigate the neural effects of increasing cognitive demands in normal aging and their role for performance. Simple and complex go/no-go tasks were used with two versus eight colored letters as go stimuli, respectively. In both tasks, no-go stimuli could produce high conflict (same letter, different color) or low conflict (colored numbers) with go stimuli. Multivariate partial least square analysis of fMRI data showed that older adults overengaged a cohesive pattern of fronto-parietal regions with no-go stimuli under the specific combination of factors which progressively amplified task demands: high conflict no-go trials in the first phase of the complex task. This early neural overrecruitment was positively correlated with a lower error rate in the older group. Thus, the present data suggest that age-related extra-recruitment of neural resources can be beneficial for performance under taxing task conditions, such as when novel, weak, and complex rules have to be acquired.

There is an inconsistency regarding the relationship between thinking about personal past experiences during autobiographical memory (AM) and thinking about other people's mental states during theory of mind (ToM). Neuroimaging studies of AM and ToM consistently report overlap in the brain regions recruited. Lesion data, however, show that amnesic people with AM impairment can have intact ToM, suggesting that distinct neural mechanisms support these abilities [Rosenbaum, R. S., Stuss, D. T., Levine, B., & Tulving, E. Theory of mind is independent of episodic memory. Science, 318, 1257, 2007]. The current fMRI study examined the functional and neural correlates of remembering one's own experiences in response to personal photos (AM condition) and imagining others' experiences in response to strangers' photos (ToM condition). AM and ToM conditions were matched in terms of content and vividness, and were compared directly and to a common baseline. Analyses revealed common activity within frontal and temporal–parietal regions, yet midline structures exhibited greater activity during AM. More specific analyses of event construction and detail elaboration revealed unique activation of the right hippocampus during AM construction, and of lateral regions, such as the right temporo-parietal junction (TPJ) during ToM elaboration. Moreover, a region of left hippocampus/perirhinal cortex appeared to be driven by event vividness. Thus, differences in AM and ToM emerge when a common baseline is used and temporal dynamics are taken into account. Furthermore, the right TPJ and related lateral regions, and not the hippocampus, may be needed for ToM, given that this ability is intact in amnesic people.

Time processing may shape behavior in several ways, although the underlying neural correlates are still poorly understood. When preparatory intervals between stimuli vary randomly in a block, for instance, responses are faster as the interval gets longer. This effect, known as variable foreperiod (FP) effect, has been attributed to a process monitoring the conditional probability of stimulus occurrence as the interval increases. Previous evidence points to the right dorsolateral prefrontal cortex (DLPFC) as a possible node for this time-monitoring process. The present study addresses this hypothesis with functional magnetic resonance imaging (fMRI). Block-design fMRI was used on 14 young participants while they performed a visual discrimination task with fixed and variable preparatory intervals (FPs) of 1 and 3 sec. In the variable versus fixed FP contrast, the right DLPFC and a visual area were more activated in the subgroup of participants who showed a reliable variable FP effect than in another subgroup who did not show that effect. Only the activation in the right DLPFC was supported by a significant interaction between FP condition (variable vs. fixed) and group. This finding may reflect possible differences in the strategy adopted by the two subgroups of participants while performing the task. Although results suggest that many brain areas may be involved in preparation over time, the role of the right DLPFC is critical to observe the strategically mediated behavioral effects in the variable FP paradigm.

Regions within the frontal and parietal cortex have been implicated as important neural correlates for cognitive control during conflict resolution. Despite the extensive reciprocal connectivity between the cerebellum and these putatively critical cortical areas, a role for the cerebellum in conflict resolution has never been identified. We used a task-switching paradigm that separates processes related to task-set switching and the management of response conflict independent of motor processing. Eleven patients with chronic, focal lesions to the cerebellum and 11 healthy controls were compared. Patients were slower and less accurate in conditions involving conflict resolution. In the absence of response conflict, however, tasks-witching abilities were not impaired in our patients. The cerebellum may play an important role in coordinating with other areas of cortex to modulate active response states. These results are the first demonstration of impaired conflict resolution following cerebellar lesions in the presence of an intact prefrontal cortex.

Inhibitory control is an essential part of behavior. Comprehensive knowledge of the neural underpinnings will shed light on complex behavior, its breakdown in neurological and psychological disorders, and current and future techniques for the pharmacological or structural remediation of disinhibition. This study investigated the neural mechanisms involved in rapid response inhibition. The stop signal task was used to estimate inhibitory speed in a group of neurologically normal control subjects and patients with discrete frontal lobe lesions. Task procedures were controlled to rule out probable confounds related to strategic changes in task effort. The findings indicate that the frontal lobes are necessary for inhibitory control and, furthermore, that the integrity of the right superior medial frontal region is key for rapid inhibitory control under conditions controlling for strategically slow responses, forcing reliance more on a rapid, “kill-switch” inhibitory system. These results are interpreted within an anatomical framework of corticospinal motor control.