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RESEARCH PRODUCT

Chapter 9 The effects of a prepulse on the StartReact phenomenon

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Publisher Summary This chapter presents a study to investigate whether the inhibitory effects of the prepulse are different in the condition of motor preparation with respect to that of unexpectancy and whether the inhibition of the startle reaction by a prepulse is associated with the inhibition of the StartReact phenomenon. The chapter demonstrates that the procedure could help in ascertaining whether reflex and volitional components are actually combined in the StartReact phenomenon. Eight healthy volunteers, six men and two women, aged between 25 and 52 years were investigated and the startle reaction was recorded with surface electrodes over the right orbicularis oculi muscle and, in two of the subjects, also over the sternocleidomastoid muscle. The electromyographical (EMG) activity related to the voluntary action was recorded from the wrist extensor muscles. The most important finding of this study is that although a prepulse stimulus had an inhibitory effect on the startle reaction even during preparation for a motor task, the effect was limited to the startle reaction itself and did not influence the startle-induced reaction time acceleration or StartReact phenomenon. This is consistent with the idea that the startle reaction and the StartReact phenomenon are two different effects of a startling auditory stimulus (SAS), with probably different physiological mechanisms.