Highly Specific Role of Hypocretin (Orexin) Neurons: Differential Activation as a Function of Diurnal Phase, Operant Reinforcement versus Operant Avoidance and Light Level ' h/ S7 ^7 A" b, H 0 m2 o! M n% G7 Zhttp://www.jneurosci.org/content ... c-9352-54142c85a5f7