Eye movements during the waking-sleep cycle of the encéphale isolé semichronic cat preparation

In 'semichronic encéphale isolé (EI) cats' the spatio-temporal characteristics of eye displacements were measured with the scleral coil technique, in the dark, during active wakefulness, slow wave sleep and activated sleep. To active waking (AW) there corresponded spatial patterns of ocular movements with a clear-cut monotonous back and forth orientation in the horizontal or slightly oblique plane. Most often the AW patterns showed a periodic behaviour resulting in a true nystagmoid shape since slow, drifting deviations of the eyes were regularly followed by counter-saccades, whose speed very seldom exceeded 100 deg/sec. As slow wave sleep (SS) supervened, this fixed pattern disappeared, being replaced by large, disjunctive, slow (less than 10 deg/sec) deviations with a prevailing vertical orientation. At SS deepest stage the eyes remained still most of the time and always elevated well above the level of direct forward gaze (up to 30--35 degrees). The rare residual movements slowed down more and more, eventually acquiring the characteristics of disjunctive drifts. At the onset of activated sleep (AS) the eyes moved in a downward direction, even reaching a position at 10--15 degrees below the centre of gaze. From this position the globes started to move in the upward direction and executed loop shaped trajectories with the major axis oriented vertically. The loop paths nearly always returned to their original position and only after displaying several loops did the eyes pass, through a slow horizontal deviation, to a new position from which they executed another series of loops over and over again. The fastest phase of the loop pattern corresponded to the upward component (up to 55 deg/sec), in contrast with waking saccades, whose maximal speed was achieved when they were executed over a horizontal or slightly oblique plane. In sharp contrast with disjunctive eye deviations of SS, the AS ocular movements were always conjugated like waking saccades. Both the maximal velocity and the relationship between maximal velocity and amplitude consistently differentiated, however, the fastest (upward) component of AS loop patterns from the quickest (horizontal) AW saccades, the former resulting as if they were somewhat filtered saccades. Nevertheless, the occurrence of a fixed directional orientation in space of a non-random loop-shaped eye movement pattern during AS, must be considered a reflection of well coordinated central oculomotor activity such as that occurring in AW, even if the intrinsic organizations differ from each other.