Changes of human blink reflex magnitude during a three second fixed foreperiod

Blink reflexes were evoked at distinct times during a 3 sec foreperiod (FP) between a warning stimulus (WS) and a reaction signal (RS). Sixteen well-trained, right-handed subjects participated in the experiment. Following RS, they reacted instantaneously with a blink of the right eye. In the electrically evoked blink reflex, an early ipsilateral component (R1) with a latency of +/- 10 msec and a late bilateral component (R2) with a latency of +/- 25-40 msec could be distinguished. The peak-to-peak amplitude of R1 and the integral of R2 were computed. In the beginning of FP, R1 was enlarged as compared to control values. Toward the end of FP, a continuous rise of R1 amplitudes was seen. This increment was most pronounced in the muscle involved in the reaction following RS. R2 was inhibited immediately after WS, while no significant inhibition could be seen near the end of FP. The conclusion is that the facilitation of R1 and the disinhibition of R2 towards the end of FP reflect the preparation on the reaction after RS. The extra increment of R1 might be due to a selective extra preparation of the motoneurons of the involved muscle, although an effect of motor dominance cannot be excluded.