Associate Professor, Department of Psychological and Brain Sciences, Zanvyl Krieger Mind/Brain Institute
I am interested in the neurophysiological mechanisms that underlie decision-making and self-control, two essential functions of higher executive processes. To this end, in my lab we record the activity of single neurons in awake animals that are engaged in decision-making. This allows us to identify the types of signals that neurons in specific parts of the brain represent and the computations they carry out. I will also study human subjects in the same tasks with the help of fMRI. These parallel experiments will provide comparative information about decision processes in human and non-human primates. The results of one set of experiments will guide the design and the interpretation of results in the other set of experiments. This parallel approach will combining the strength of these two very different techniques.
In recent years, I have investigated neural mechanisms of the initiation and suppression of actions using the countermanding paradigm - a task that infrequently requires subjects to withhold a movement in response to a stop signal and an analysis that provides an estimate of the time needed to cancel a partially prepared movement. We chose fast eye movements (saccades) as the actions that needed to be controlled, because eye movements are relatively simple movements that are still under voluntary control. In the course of these experiments we detected signals that begin to explain how the consequences of actions are recognized and how subsequent actions might be influenced (Stuphorn et al., 2000; Ito et al., 2003; Schall et al., 2002).
A number of areas in the frontal cortex are involved in the control of fast eye movements in the countermanding task. We recorded in three of them: the frontal eye field (FEF), the supplementary eye field (SEF) and anterior cingulate cortex (ACC) and found that the FEF on the one hand and the SEF and the ACC on the other hand seem to belong to two different functional systems. FEF generates signals sufficient to select targets and initiate the generation of eye movements. It represents therefore an essential node in the network that ultimately controls gaze. The two medial frontal areas, ACC and SEF, seem not to be directly involved in the primary control of eye movements (Stuphorn et al., 2000; Ito et al., 2003). Instead, they seem to monitor performance, registering whether the actions that are produced lead to the desired consequences or not. These findings led to the working hypothesis that the medial frontal cortex might be part of an secondary executive control system. The results of SEF microstimulation indicate that supervisory control signals bias the ongoing response selection in the oculomotor system and thus close the loop between the two control systems (Stuphorn et al., 2002). This additional control enables the agent to achieve a more adaptive match between behavior and the ever-changing demands of the environmental setting.