Do rats sleep with their eyes closed? - briefly
Rats close their eyes while sleeping, although a thin translucent membrane (the nictitating membrane) may still be faintly visible. This eye closure occurs during both REM and non‑REM sleep phases.
Do rats sleep with their eyes closed? - in detail
Rats possess a thin, translucent nictitating membrane that covers the eye, but they also have functional upper and lower eyelids capable of full closure. During the resting phase, the eyelids typically shut completely, similar to most mammals. Electrophysiological recordings show that rats enter both non‑rapid eye movement (NREM) and rapid eye movement (REM) sleep while their eyes are closed, indicating that eyelid closure is not limited to a single sleep stage.
Observations from laboratory studies provide additional detail:
- NREM sleep – characterized by slow‑wave brain activity; eyes remain fully closed, and the animal is largely unresponsive to external stimuli.
- REM sleep – marked by bursts of brain activity and muscle atonia; despite rapid eye movements beneath the closed lids, the outer eyelids stay shut.
- Micro‑arousals – brief awakenings may involve partial opening of the lids, but the default state during sustained sleep is full closure.
Anatomical examinations reveal that the palpebral muscles in rats are well‑developed, allowing rapid blinking and sustained closure. The nictitating membrane can be drawn across the eye for protection, but it does not replace the function of the primary eyelids during sleep.
Field observations of wild rats corroborate laboratory findings: nocturnal activity ceases at daylight, and individuals found in burrows exhibit closed eyes, often with the nictitating membrane partially visible. Video monitoring in controlled environments confirms that even during deep sleep, rats do not keep their eyes open.
In summary, rats close their eyes while sleeping, employing both eyelids and, when needed, the nictitating membrane for ocular protection. This behavior aligns with mammalian sleep physiology and is documented across multiple experimental and natural settings.