Medial versus lateral prefrontal dissociation in movement selection and inhibitory control

We aimed to test the hypothesis that the cerebral selection of movement includes active suppression of unwanted movements. To that end, a cerebral activation paradigm was used in which index finger flexion was compared with similar movement, made together with fingers 3, 4, 5. Cerebral activations were assessed by positron emission tomography (PET) measurements of cerebral perfusion in 10 healthy subjects, during the two motor tasks and rest. Statistical parametric mapping (SPM) revealed significant increase of (antero)medial prefrontal activity and subtle changes in pallidum and thalamus in the condition of less movement, i.e. isolated index finger flexion contrasted to full-hand flexion. These increases indicated a mechanism of selection mediated by active suppression of unwanted movements. Suppression of all motor responses was inferred from anterolateral prefrontal activation related to rest (with only auditory cues), contrasted to both motor conditions. This segregation of inhibitory functions specifies the complementary character of response selection and inhibitory control, in such a way, that towards the medial prefrontal surface, a transition from general to increasingly selective inhibition allows the internal ordering of action.