MODULATION OF ELECTRICALLY ELICITED BLINK REFLEX COMPONENTS BY VISUALAND ACOUSTIC PRESTIMULI IN MAN

The effects of a prestimulus on the electrically elicited blink reflex components were investigated in 20 healthy subjects. In the first gro up of 10 subjects (warned group), electric shocks were delivered in is olation or preceded, at an interstimulus interval (ISI) of 0.1 s, 1 s, or 10 s, by a visual or acoustic warning stimulus. In die second grou p of 10 subjects (unwarned group), the electric shocks were delivered either in isolation or preceded, at the same ISI, by visual or acousti c stimuli having no warning value. The modulation of the three blink r eflex components was then analysed. Compared to the baseline condition , the R1 oligosynaptic component was enhanced at 0.1 s and 1 s ISI, in the warned group with the visual prestimulus, but only at 0.1 s after a visual and acoustic prestimulus in the unwarned group. On the contr ary, the polysynaptic responses showed a different course: R2 was sign ificantly reduced at the 0.1 s interval in the warned group with both the prestimuli, and only with the visual prestimulus in the unwarned g roup. The R3 was inhibited at all three intervals with the visual pres timulus, and at the 0.1 s and 1 s with the acoustic one in the warned group, and only at 0.1 s in the unwarned group, both after visual and acoustic prestimuli. The decrement in R2 and R3 observed with the shor test interval was probably related to the prepulse inhibition of start le reflex. Furthermore, only R3 was still inhibited at longer interval s, when the sustained processes of attention may have influenced this component. Perhaps this combination of events represents, in the warne d group, the best preparation for voluntary reflex reaction.