Effects of target probability on motor preparation and execution

The aim of the present study was to assess the effects of motor target probability on the associations between pro-active motor preparation as reflected by negative slow potentials (NSPs), motor execution as reflected by response-related potentials (RRPs), and performance monitoring as reflected by correct response negativity (Nc). It was hypothesized that if ongoing increases/decreases in preparation induced by target expectation modulate motor execution and monitoring, there would be an association between the effects of motor target probability on NSPs and RRPs/Nc. Electroencephalographic (EEG) signals were recorded in young adults while they produced simultaneous responses with the two hands to Go trials in auditory Go/NoGo tasks with different target probabilities (P = 0.15, P = 0.50, and P = 0.85). NSPs and RRPs were analyzed at the midline and bilateral motor regions. Nc was analyzed at medial frontal electrodes. It was found that the effects of probability on NSPs were lateralized: At the left motor cortex NSPs were expressed for the low and high probabilities, mirroring response speeding, whereas at the right motor region NSPs were not pronounced for higher (P = 0.50 and P = 0.85) probabilities. Bi-lateral RRPs were larger for low- than equal- and high-probability targets and correlated positively with left-hemisphere NSPs but negatively with right-hemisphere NSPs. Nc did not depend on target probability. The lateral and functional NSP/RRP asymmetry and their correlations suggest that the interaction between movement preparation and execution is modulated by hemispheric specialization in motor control such that movement execution in enhanced inhibition context is potentiated by the left hemisphere, and movement execution in response generation context is controlled by proactive inhibition in the right hemisphere. The effects of target probability on performance monitoring are not clearly demonstrated by Nc analysis in Go/NoGo tasks.