How are we able to prevent ourselves from being distracted? How can we overcome our compulsions, tics and inappropriate urges? These are questions about cognitive control. A good understanding of the psychological and neural mechanisms underlying such control is of paramount importance for many aspects of everyday life as well as for basic science. A fruitful way to study cognitive control is to examine how people stop already initiated responses. Stopping an already initiated response could be an experimental model for the way in which we stop all kinds of urges in everyday life. Recent research suggests that stopping is achieved by several key "nodes" in the brain. It is likely that communication between the nodes occurs via long-range connections (white matter tracts). With support from the National Science Foundation, Dr. Adam Aron and his research team will test this idea of a network of long-range connections underlying stopping behavior. The approach is twofold: first, to use a form of neuroimaging to measure the strength of the connections in a sample of healthy young adults, and to examine how variations in the strength of the connections relates to individual differences in the behavioral ability to stop; second, to image the connections in patients with specific brain injuries. If particular connections are key for stopping, then damage to these connections will produce problems with stopping even when the key brain "nodes" themselves are intact. Overall, these studies will harness recently-developed methods for the analysis of brain connections to reveal novel information about how the network of connections between key brain regions underlies human control. They are in keeping with recent developments in cognitive neuroscience which emphasize the importance of connections rather than just brain regions themselves.
The funded work will complement activities in Dr. Aron's laboratory which already have an impact on science education at multiple stages, including outreach activities in San Diego area schools, hosting of minority students in the lab and undergraduate and graduate teaching. The work adds unique educational value by introducing new scientific components into Dr. Aron's lab and department: these include the study of patients with brain lesions and methods for analyzing brain connections. Overall, the planned experiments could yield information about the neural architecture of stopping that has implications for diverse domains such as human development, jurisprudence and neuropsychiatry. Alterations in brain connections, perhaps related to developmental delays, disease, or injury, could lead to deficits in inhibiting inappropriate actions. Various neuropsychiatric disorders, such as attention deficits, tic disorders, over-eating and substance abuse may relate to alterations in the brain connections underlying stopping.
How are we able to prevent ourselves from making inappropriate responses? This is an important ability in everyday life. It is also an ability that is weakly formed in children and adolescents, and it can also be impaired in various neurological and psychiatric disorders, leading to impulsivity and distraction. One way that we control our inappropriate responses is by using our goals to target particular response tendencies before, or as, they occur. For example, when crossing a road we monitor for particular objects, and when they come into sight, we quickly change our behavior (stop or change) because that is prepared. Consistent with this, previous research has identified a brain network that includes regions important for higher-level cognition such as goals (the prefrontal cortex) and regions important for action (the basal ganglia). The current study tries to better understand this network by asking how damage to key nodes of the network affects the ability to control particular responses. To do this we studied patients with stroke that affected the prefrontal cortex, and also matched healthy controls. In the patients we also quantified the connections between prefrontal cortex and the basal ganglia using a type of neuroimaging that looks at white matter. We found that damage to two regions in the prefrontal cortex affected the ability to stop inappropriate responses when a stopping signal occurred, and also that damage to one of these also impaired the ability of people to slow down when stopping was likely (i.e. to be cautious). Furthermore, we found that damage to this latter prefrontal region led to reductions in the strength of connection between this region and the lower-level motor system (basal ganglia). Thus a brain lesion to one region has remote effects on the wider network even if it does not directly impinge those other parts of the network. These results partly confirm our understanding of critical brain regions for self-control in humans, and add a novel insight that damage to one part reverberates throughout the network.