Figure 13.

Firing rate of hypocretin cells in waking and sleep behaviors in freely moving rats. The discharge pattern of a representative hypocretin neuron across the sleep–waking cycle in the freely moving rat. (A) High firing rates are seen during AW (active waking – grooming). (B) Reduced firing rate or cessation of activity is seen in QW (quiet waking) and drowsiness. (C) A further decrease or cessation of firing is seen during SW sleep. (D) Minimal firing rate is seen during the tonic phase of rapid eye movement (REM) sleep. Brief Hcrt cell discharge bursts are correlated with muscle twitches during the phasic events of REM sleep. EMG, electromyogram; EEG, electroencephalogram. (From Mileykovskiy et al.²⁶)