The effect of monocular deprivation on unihemispheric sleep in light and dark incubated/reared domestic chicks.

Unihemispheric sleep is an aspect of the cerebral lateralization of certain species of birds. During sleep, domestic chicks (Gallus gallus) show brief periods of monocular-unihemispheric sleep (Mo-Un sleep): one eye is open and the connected hemisphere is awaken while the other eye remains shut and the connected hemisphere sleeps. The time spent in Mo-Un sleep was investigated following a brief monocular deprivation (MD) in chicks hatched from eggs incubated in darkness and reared in light (D-L), incubated in light and reared in light (L-L) and incubated in darkness and reared in darkness (D-D). The right eye occluded for 12 h in half of chicks and the left eye in the other half. At the end of MD, the Mo-Un sleep was recorded. The effect of MD (total time and time bias) prevailed in determining the pattern of Mo-Un sleep. Chicks showed more time sleeping with the eye/hemisphere that was in control of visual behaviour during MD and opened more time the eye and awake the hemisphere visually deprived. The Mo-Un pattern was not influenced by incubation, rearing, symmetry/asymmetry of visual pathways and imprinting thereby indicating that Mo-Un sleep pattern depends only on the kind of visual experience during wakefulness.