Daytime variations in central nervous system activation measured by a pupillographic sleepiness test

Pupil size is regulated exclusively by the autonomic nervous system, and in darkness is proportional to the level of central sympathetic tone. Spontan eous pupillary movements, while at rest in darkness and quiet, were recorde d for a period of 11 min, using infrared video pupillography. Thirteen youn g adults took part in a 30-h experiment lasting from 08.00 h to 14.00 h on the following day. Pupillographic testing and completion of a self-rated sc ale for the estimate of sleepiness were repeated every two hours. Pupillary unrest index (PUI), as a measure of pupil size instability associated with daytime sleepiness, showed the lowest values at 09.00 h, when pupil size w as found to be maximal, and 23.00 h. During the course of the day,amplitude spectrum less than or equal to0.8 Hz and PUI showed increasing values duri ng the afternoon hours, followed by a decrease during the evening. Daytime variations in the pupillary unrest index in healthy normal subjects were fo und to be positively correlated with the level of alertness. These findings are similar to the daytime variations found by the MSLT (multiple sleep la tency test) in young adults.