Decades of research have been devoted to our ability to control whether we act and which action to make, but no neuroscience research has tested how these two vital cognitive functions work together. This study will be the first to specifically and thoroughly test this, from behavior to brain. The overall hypothesis is that distinct pools of neurons independently implement the two processes. Response inhibition is a form of executive control, exercised when an imminent action needs to be canceled. It has been extensively studied using the stop signal paradigm, and is now diagnostic for many psychiatric and neurological disorders. The task typically requires responding to a choice stimulus, but inhibiting the response when an infrequent stop signal is presented. The difficulty of canceling a response varies with the delay between the choice stimulus and subsequent stop signal, the stop signal delay (SSD). Inhibition is easier for shorter SSDs. The race model explains performance of the task as a race between stochastic GO and STOP processes. If the GO process finishes before the STOP process, a response is made, but if the STOP process finishes first the response is withheld. The model accounts for correct and error response times (RTs) and provides ways to estimate the duration of the covert stopping process. A saccade stop task with rhesus macaques found neuronal correlates of the GO and STOP processes in the frontal eye field (FEF). These neural data refined the race model from a cognitive process model into a brain mechanism model. However, the model and the associated behavior and single neuron data in monkeys addressed saccades to single targets. Nearly all stop signal studies in humans have used choice RT tasks, in which subjects discriminate a choice stimulus to respond. Both cognitive and neural race models lack an account of the categorical decision required by choice RT tasks. The neuronal basis of categorical decision-making has been explored extensively but has made little contact with the neuronal basis of response inhibition. Decision-making studies typically use a two-alternative forced choice task. Drift diffusion models explain decisions as a diffusion process between choice boundaries. Neuronal correlates of the diffusion have been found in FEF. The major research goal of this proposal is to integrate behavioral and neural decision making into the race model of response inhibition.
The aims are (1) to explore neuronal mechanisms underlying response inhibition and decision making by recording neural activity in FEF of macaque monkeys performing a choice RT stop signal task, and (2) to develop a model that integrates response inhibition and decision-making and accounts for behavior and neurophysiology. The first major training goal of this proposal is to expand the applicant's neurophysiological skill set, building on previous experience. The second major training goal is to acquire expertise in cognitive modeling with stochastic accumulators. This research training coupled with professional development activities will build the foundation for the applicant's long-term goal of becoming an independent researcher in visual neuroscience.
The goal of this training plan is to reveal brain activity underlying our ability to make decisions and control our actions, and to develop a model that explains these processes. It is important to understand how behavior relates to brain function, and the proposed research will improve diagnoses and treatment of multiple brain and neuropsychiatric disorders, and will help understand self-control across the lifespan.
| Middlebrooks, Paul G; Schall, Jeffrey D (2014) Response inhibition during perceptual decision making in humans and macaques. Atten Percept Psychophys 76:353-66 |
