Current investigations focus on the use of new or neglected physiological parameters to study sleep. In human subjects, techniques were developed for measuring and quantifying facial muscle activity with less than 0.5 microvolts of noise. This activity is of interest because the nuclei innervating the facial muscles are in the brain stem. Levels of facial muscle activity during sleep are being compared in good and poor sleepers; personality correlates of this activity are also under investigation. Another human study focuses on the measurement of periorbital spike potentials, thought to reflect PGO activity, in relation to goodness of sleep, personality patterns, an psychopathology. Current animal work focuses on the measurement of spike potentials in the ventral hippocampus. These spikes are of interest because they may be an electrophysiological feature to sleep present in both mammals and reptiles and because they may be an indicator of "arousal" during both sleep and wakefulness.