| Popis: |
During the fixed foreperiod (4 sec) of two reaction time experiments, using 80 subjects, Hoffman reflexes were simultaneously evoked in both legs in a pseudorandom order at 13 different measuring points. The purpose of the study was to investigate the time course of amplitude changes in both legs, in muscles both involved and not involved in the response. In Experiment 1, subjects responded after the imperative signal by a plantar flexion of either the right or left foot. Thus, reflexes were evoked via the motoneuron pool relevant for the response and via the contralateral irrelevant pool. In Experiment 2, subjects pressed a button with either the right or the left index finger. Thus, reflexes were evoked via motoneurons, irrelevant for the response. Reflex amplitudes during the foreperiod were larger than during the intertrial interval (ITI). An early increase was found at 100–200 msec after the warning signal. Thereafter, amplitudes decreased but remained larger than during the ITI. After 1,000 msec, a steady increase was found, with the largest amplitudes near the end of the foreperiod. Amplitude changes were not different for relevant and irrelevant muscles. It was concluded that the second increase might be part of a motor preparation process. |
