Activity of eye-movement-related neurons in the region of the interstitial nucleus of Cajal during sleep.

Activity of vertical burst-tonic neurons in the region of the interstitial nucleus of Cajal (INC) in cats that showed a close correlation with spontaneous vertical eye movement during the waking state was compared to that during sleep. All the cells tested maintained high and regular discharge rates similar to those during the waking state when the eye was near the primary position. However, a significant correlation between tonic discharge rates and vertical eye position change seen during the waking state was lost during slow drifting eye movement during sleep, indicating that they are not involved in such eye movement. Upward (or downward) burst-tonic neurons showed bursts (or decreased activity) during upward rapid-eye movements (REMs) accompanied by failure of eye position holding with almost exponential decay during REM sleep. However, the increased (or decreased) activity was not maintained and quickly returned to near-previous discharge rates. Despite the fact that a significant positive correlation was seen between average discharge rates during vertical saccades and tonic rates after saccades for these neurons during the waking state, the same cells lost such a correlation during vertical REMs with eye position holding failure. The close correlation between presence or absence of tonic activity related to preceding bursts of burst-tonic neurons, on the one hand, and holding or failure of vertical eye position after vertical saccades or REMs, on the other, suggests that these neurons receive excitatory and inhibitory burst inputs, and also that they are involved in some aspect of vertical eye position generation, but that the INC region alone cannot convert the burst signals into eye position.