To act or not to act. Neural correlates of executive control of learned motor behavior.

Successful behavior requires contextual modulation of learned "programs", that is, the retrieval or nonretrieval (inhibition) of behavioral elements depending on situative context. Here we report neural correlates of these elementary aspects of behavior as identified with functional magnetic resonance imaging (fMRI). Inhibition of a "ready-to-go" behavioral program was represented in the brain by reduction of net synaptic activity in the cerebro-cerebellar pathway. The metabolic correlate of inhibition was a multifocal (premotor, primary sensorimotor, superior parietal, cingulate cortex, and cerebellum) decrease of the blood oxygenation level-dependent (BOLD) signal to below the resting state (negative BOLD) with a concomitant decrease of motor cortical excitability. The reverse was true for retrieval. We propose that contextual modulation of learned behavioral programs depends on an interplay of focal increases and decreases of neural activity and that the inhibitory changes are reflected by negative BOLD responses in an extended cerebro-cerebellar network of sensorimotor structures.