A useful, physiological tool for assessing the arousal level in humans: averaged photopalpebral reflex

The averaged photopalpebral reflex (PPR) was bipolarly recorded from electrodes placed on the upper and lower palpebrae in male university students. In a drowsy state which was defined by the monitored EEG, the latencies of PPR were significantly prolonged and the amplitude reduced. In contrast, the latencies were shortened by immersing their hands in ice water which greatly aroused the subjects. The central stimulant, methylphenidate 10 mg, significantly shortened the latencies and diazepam 5 mg possessing anxiolytic and hypnotic actions significantly prolonged them. When the recording of PPR was repeated consecutively five times, the amplitude was easily reduced but the latencies were relatively stable. From these results, it is confirmed that the latencies of PPR are prolonged in a lowered arousal level and shortened in a more aroused state. This indicates that PPR could be a useful index to assess objectively the arousal level of humans and hence could be a useful tool for investigations of psychophysiology and psychopharmacology.