Time-of-day variations in different measures of sleepiness (MSLT, pupillography, and SSS) and their interrelations

The aim of the present study is to analyze how well physiological measures of sleepiness derived from pupillography and the Multiple Sleep Latency Test correlate with a subjective measure, the Stanford Sleepiness Scale (SSS) score. The results are based on data from 12 healthy participants, who underwent these tests every 2 hr from 7:00 a.m. until 11:00 p.m. Sleep latencies were correlated with four different variables derived from pupillography and the SSS score. The results indicate that the physiologically based variables correspond very well. This is reflected by similar patterns of time-of-day variations, a good agreement at the group level, and correlations at the individual level, whereas the SSS shows a quite different pattern of variation. The two physiological measures of sleepiness seem to reflect the same aspect of the level of tonic central nervous activation, which is not correlated with the subjective feeling of sleepiness.     

The pathway controlling the pupillary light reflex in urodeles

Although the photomechanical response of the iris in amphibians has been characterized, the central pathway of reflex control is unknown. We investigated this pathway by electrophysiological and anatomical techniques in urodeles. Sustained responding neurons in the pretectum were localized and characterized. Three neuron types were found and compared with tonic neurons in mammals. They were driven by the contralateral retina and their dendrites arborized in the pretectal neuropil. The localization of cell bodies resulted in the identification of a physiological nucleus comparable with the nucleus praetectalis olivaris. It was shown that the tonic neurons project ipsi- and contralaterally to the oculomotor region, where axons terminate in deep layers of the stratum album. Using horseradish peroxidase transport the ciliary ganglion in urodeles was identified. It occurs in ontogenesis parallel to the first detectable pupillary light reflex corresponding to the onset of metamorphosis.