The effect of advance information about the sequence of a to-be-signaled motor response on corticospinal excitability during the foreperiod.

We investigated the effect of advance information about the sequence of a to-be-signaled motor response on corticospinal excitability during the foreperiod in healthy humans. Advance information about the sequence of a to-be-signaled motor response was provided by a precue signal 600 ms before a response signal during a warned choice reaction task. The precue signal indicated the sequence of one of three to-be-signaled motor responses: simple, repetitive, or sequential motor responses. The amplitude of the motor-evoked potential (MEP) decreased significantly 100 ms before the response signal in both the first dorsal interosseous (FDI) and abductor pollicis brevis (APB) muscles, but a significant decrease was present only in the APB muscle 300 ms before the response signal. The decrease in the MEP amplitude 100 ms before the response signal induced by the precue signal indicating the repetitive motor response was significantly smaller than that induced by the precue signal indicating the simple or sequential motor response in the FDI muscle, and was significantly smaller than that induced by the precue signal indicating the sequential motor response in the APB muscle. The decrease in corticospinal excitability in the middle foreperiod is larger when the advance information about a to-be-signaled motor response is unrelated to the muscle tested, and the decrease in the late foreperiod is affected by advance information about the sequence of a to-be-signaled motor response.