Functional dissociation of temporal processing mechanisms during speech production and hand movement: An ERP study

Skilled motor actions are mediated by neural mechanisms that incorporate sensory feedback for driving or suppressing movement with remarkable temporal precision. The predictive coding model proposes that the brain performs this function by establishing an internal representation of timing to accelerate movement response time. However, it is unclear whether different neural mechanisms are involved in temporal processing of movement initiation and cessation. The present study examined how temporal information is encoded for initiation and cessation of speech and hand movement. Event-related potentials (ERPs) were recorded while young healthy subjects performed speech and hand movement initiation and cessation in response to temporally predictable and unpredictable visual stimuli. We found that predictable stimuli elicited faster movement in both speech and hand modalities, with shorter reaction times associated with movement cessation compared with initiation. Analysis of ERPs revealed that premotor neural activities were significantly attenuated before speech initiation and hand movement initiation and cessation for temporally predictable vs. unpredictable conditions, but an opposite pattern was observed for speech cessation. In addition, we observed that the premotor ERPs were significantly modulated during speech initiation vs. cessation, but no such effect was found during hand movement. Finally, we found that the premotor ERPs were strongly correlated with motor reaction time during movement initiation and cessation for speech and hand modalities only in response to temporally predictable stimuli. These findings indicate that premotor ERPs reflect a temporal predictive code for planning of movement initiation and cessation and highlight functional dissociation of temporal processing mechanisms in speech and hand motor systems.