This study was carried out to investigate the influence of pre-movement tonic contraction on the Contingent Negative Variation (CNV) and Flexor Carpi Radialis (FCR) H reflex between the warning (WS) and response signal (RS) (foreperiod : FP) . Two levels of contraction were designed and the accompanying FCR Electromyography (EMG) was directly returned to the subject to sustain constant contraction. The subjects were 10 normal volunteers. Either small or middle (7.9±5.6% or 16.0±6.3% of the standard FCR EMG) contraction was sustained and the isometric wrist flexion movement was performed as quickly as possible following the RS.
EMG Reaction time (RT) in the small contracting condition was shorter than that in the resting condition (nothing performed during the foreperiod) in almost all subjects, but in the middle contracting condition EMG RT was not similar. The CNV amplitude for the late period of the FP, which was considered to be related to the motor preparation, was larger in the middle contracting condition than in the resting condition, although the small contracting condition was similar to the resting condition. The H reflex amplitude for the late period of the FP tended to be smaller than the control level in the small and middle contracting conditions, but it was not significant. However, in over half of the subjects, whose CNV amplitude for the late period of the FP increased linearly depending on the conditions, the H reflex amplitude was smaller than the control level in both contracting conditions, but it was not linear. These results indicate that the modulation of the EMG RT was not directly associated with the CNV or H reflex amplitudes for the late period of the FP, and a functional difference in the set for the RS between the spinal and the upper level of the central nervous system was present.