The functional role of the ventral premotor cortex in a visually paced finger tapping task: a TMS study

The accurate control of timed actions is a fundamental aspect of our daily activities. Repetitive movements can be either self-paced or synchronized with an external stimulus. Finger tapping (FT) is a suitable task to study the mechanisms of motor timing in both conditions. The neuronal network supporting motor timing in FT tasks comprises the lateral cerebellum, the lateral and mesial premotor areas as well as parietal sites. It has been suggested that lateral premotor cortices (PMC) are involved in time representation and sensorimotor transformations needed for synchronization. Most studies have focused on the dorsal aspect of PMC (dPMC) whereas the ventral PMC (vPMC) function has been poorly investigated. Here we used an online transcranial magnetic stimulation (TMS) protocol to probe the role of vPMC in an FT task, as compared to a functionally relevant site (dPMC) and an unrelated one. According to the synchronization-continuation paradigm, subjects had to synchronize their tapping to a periodic continuous visual stimulus, and then continue without the external pacer. Two different visual pacers were used: a tapping finger and a hinged tilting bar. We show that TMS reduced the synchronization error when delivered to the vPMC. This effect was larger when the more abstract hinged tilting bar was used as a pacer instead of the finger. No effects were observed in the continuation phase. We hereby offer the first online-TMS evidence of the involvement of vPMC in visually cued FT tasks.