Dissociating the role of the caudate nucleus and dorsolateral prefrontal cortex in the monitoring of events within human working memory

There is evidence that the dorsolateral prefrontal cortex is involved in the monitoring of information held in memory whether it is self-ordered or externally triggered. However, the functional contribution of the caudate nucleus in the monitoring of events has not yet been studied. We have previously proposed that the striatum is involved when a novel self-initiated action needs to be generated. The present study aimed to test the hypothesis that the caudate nucleus is significantly more required when the monitoring is self-ordered as opposed to externally triggered. Self-ordered monitoring refers to keeping track of which items have been selected so far in order to perform the current selection. Externally triggered monitoring refers to keeping track of which items have been selected by an outside source. Thirteen healthy young adults were scanned using functional magnetic resonance imaging while performing a monitoring task with three conditions: self-ordered, externally triggered and recognition. As predicted, a significant increase of activity was found in the dorsolateral prefrontal cortex bilaterally when the self-ordered and externally triggered conditions were compared with the recognition condition. Most importantly, significantly increased activity was found in the right caudate nucleus when comparing the self-ordered with the recognition condition or with the externally triggered condition, but not when comparing the externally triggered with the recognition condition. We suggest that the caudate nucleus is involved in the planning of a self-initiated novel action, especially when no clear indication is given for the response choice, and that this may be the case across different domains of cognition.