Overlap and segregation in predorsal premotor cortex activations related to free selection of self-referenced and target-based finger movements

In reaching movements, parietal contributions can be distinguished that are based on representations of external space and body scheme. By functional magnetic resonance imaging, we examined 16 healthy subjects to see whether such segregation similarly exists in the frontal lobes when visuomotor actions are not specified but when free choices are allowed. Free selection was button based (target based) or finger based (self-referenced), with invariant instructions as control. To avoid a visual attention bias, instructions were auditory presented. Statistical parametric mapping revealed that free button selection with the same finger was associated with increased activations in the anterior cingulate cortex (ACC), right posterodorsal prefrontal cortex (PFC) including the rostral extension of the dorsal premotor cortex (pre-PMd), and the anterodorsal PFC. Prefrontal activation related to free finger selection (pressing the same button) was restricted to an anteromedial segment of the posterodorsal PFC/pre-PMd. Bilateral inferior parietal activations were present in both free-choice conditions. Pre-PMd and parietal contributions to free selection support concepts on early-stage action selection in dorsal visuomotor pathways. The rostral-caudal segregation in pre-PMd activations reflected that in anterior direction, frontal processing is gradually less involved in selection of environmental information but increasingly committed to self-referenced selection. ACC particularly contributes to free selection between external goals.