Tonic and phasic components of eye movements during REM sleep in the rat

Abstract

Phasic oculomotor activity is one of the features identifying rapid eye movement (REM) sleep. Recently, it has been shown in cats that, despite bursts of complex two-component rapid eye movements, the eyes tend to maintain a nasal and downward rotation during REM sleep. Although the function of eye movements during sleep remains elusive, it is important to know whether the characteristics of eye movements during sleep are species-specific in mammals. In this work, quantitative characteristics of eye movements, recorded by the scleral search coil technique, were studied during wakefulness and sleep in rats. During wakefulness, rats performed conjugated saccades at a very low rate and some eye movements associated to blinking and gnawing. Throughout non-REM sleep, eye movements were slow, mostly unconjugated and the eyes maintained a divergence in the horizontal plane. The beginning of REM sleep was characterized by a convergence and downward rotation of the eyes, which tended to persist until the end of REM sleep. Rapid eye movements, isolated and monocular at the beginning, became complex and organized in high-frequency bursts. These results demonstrate that, despite the difference in extraocular anatomy and visuomotor strategies between frontal- and lateral-eyed species, eye movements during REM sleep in rats are very similar to those described in cats. This suggests that the mechanisms generating eye movements during REM sleep are largely conserved in mammals.

Saccade, search and orient – the neural control of saccadic eye movements

“…Although the precise function of rapid eye movements during sleep has remained elusive, it is important to determine whether similar physiological mechanisms control saccades and rapid eye movements during sleep. Sanchez‐Lopez & Escudero (2011) present original data showing that, at the beginning of REM sleep, normal rodents have a tendency to converge the eyes and rotate them downward in a similar pattern to that observed previously in the cat. These data are important for demonstrating the similarity of the rodent behavior to other animals so that detailed physiological mechanisms of REM sleep can now be pursued.…”

Pupil Size Coupling to Cortical States Protects the Stability of Deep Sleep via Parasympathetic Modulation

“…If used with higher frame rate (>60 Hz), iBip is ideally suited to track the eye movement dynamics during REM sleep ( Figure S2 B; Movie S1 ). Eye movements during tonic and phasic REM periods have been shown to have neural and muscular correlates in adult and developing mammals [ 55 , 56 , 57 ]. Currently, the state-of-the-art rodent eye-tracking systems include implanted coils or electrodes around the eye area [ 57 , 58 ].…”

REM Sleep Rebound as an Adaptive Response to Stressful Situations

“…It is worth mentioning that in human beings the waking threshold is similar between tonic REM sleep stage 2 NREM sleep; however the highest behavioral arousal threshold occurs during phasic REM sleep and stage 4 sleep (Price and Kremen, 1980; Ermis et al, 2010). In rats, tonic and phasic components of REM sleep are present, although not as clearly as in humans (Sanchez-Lopez and Escudero, 2011). …”