Activity of Type I (A and B) and II (C and D) wake-related neurons during AW, QW, non-REM sleep and REM sleep, showing individual (A and C) and mean (± s.e.m.; B and D) discharge rates. Note that both types of neuron exhibited significantly higher discharge rates during AW compared to QW, non-REM and REM sleep. For both types of neuron, discharge rates during QW, non-REM and REM sleep were not significantly different. * P < 0.01.