Slow wave sleep in crayfish

Abstract

Clear evidence of sleep in invertebrates is still meager. Defined as a distinct state of reduced activity, arousability, attention, and initiative, it is well established in mammals, birds, reptiles, and teleosts. It is commonly defined by additional electroencephalographic criteria that are only well established in mammals and to some extent in birds. Sleep states similar to those in mammals, except for electrical criteria, seem to occur in some invertebrates, based on behavior and some physiological observations. Currently the most compelling evidence for sleep in invertebrates (evidence that meets most standard criteria for sleep) has been obtained in the fruit fly Drosophila melanogaster. However, in mammals, sleep is also characterized by a brain state different from that at rest but awake. The electrophysiological slow wave criterion for this state is not seen in Drosophila or in honey bees. Here, we show that, in crayfish, a behavioral state with elevated threshold for vibratory stimulation is accompanied by a distinctive form of slow wave electrical activity of the brain, quite different from that during waking rest. Therefore, crayfish can attain a sleep state comparable to that of mammals.

Fig. 1.

Crayfish in several positions. (A) Side view of an aquarium with three crayfish, one of them lying on one side (right) and two standing up (left). (B) Drawing of crayfish standing up. (C) Drawing of crayfish lying on one side.

Fig. 2.

Parameters of crayfish behaviors. (A) Time-hours at which a crayfish is walking around its aquarium. The black bar indicates night hours. (B) Vibratory intensity-duration threshold curves while crayfish behavior is active (curves 1–7), standing up motionless (curves 8–11), and lying on one side against the surface of the water (curve 12; isolated points also correspond to this condition). (C) Time-hours at which a crayfish lies on a side against the surface of the water. A and C show an example of 12 recorded cases.

Fig. 3.

Spontaneous electrical activity of a crayfish. (A) Records obtained from the brain of a crayfish walking around its aquarium. (B and C) Records from the brain while lying asleep on one side against the surface of the water and from scaphognathites. The corresponding power spectra (0–20 Hz) of the records shown in A–C are in frames D–F. Note the different power scales.

Fig. 4.

Time spent by crayfish lying on one side (sleeping) during a 24-h period (12 light/12 dark). Black bands above show the dark period. Filled circles are mean (± SE) values of sleep duration per hour during 7 control days. Open circles show first 24 h of recovery after sleep deprivation, starting at 1200 h. Data are from the same crayfish.