UC San Diego

Using contextual information to prepare to stop behavior is a key aspect of human self-control. For example, a child might chase a ball into the street, without stopping, if she does not know to check for cars. This thesis addresses the neurocognitive basis of how we prepare to stop. In three studies, we used behavioral tasks that require the subject to prepare to stop motor responses. The first study tested the idea that preparing-to-stop changes how outright stopping is achieved - specifically whether it affects task-irrelevant effectors. Accordingly, we used Transcranial Magnetic Stimulation to index the effect of stopping a manual response on a task-irrelevant leg muscle. We found that when subjects slowed down in anticipation of stopping there was less suppression in the leg at the time of stopping than if they did not slow down. Thus, preparing-to-stop promotes selectivity in outright stopping. The second study tested the hypothesis that preparing to stop is implemented via an 'associative/ executive' prefrontal-basal-ganglia circuit that passes through the ventral but not the dorsal subthalamic nucleus (STN). Accordingly, we stimulated either the ventral or dorsal STN in Parkinson's patients and measured the amount of response slowing in anticipation of stopping. Patients off stimulation did not slow as much as healthy controls. Notably, ventral, but not dorsal, stimulation remediated this deficit. This implicates the associative/executive circuit in preparing-to-stop. The third study tested the idea that preparing-to-stop makes outright stopping quicker by 'priming' a cortical mechanism involved in stopping. We recorded electroencephalography (EEG) in subjects while varying the degree of preparation for stopping. We found that preparing-to-stop led to faster stopping and an increased fronto-central EEG signature (the P3) that has previously been mapped to dorsomedial frontal cortex, a known node in stopping-related circuitry. This finding suggests that preparing-to-stop primes the mechanism for outright stopping. Taken together, these studies show that preparing to stop i) promotes selective stopping, ii) is probably implemented via an 'associative/executive' prefrontal-STN circuit, and iii) 'primes' cortical mechanisms to enable quicker stopping. This research speaks to the specialization of the human brain for preparing to control behavior