Highly Specific Role of Hypocretin (Orexin) Neurons: Differential Activation as a Function of Diurnal Phase, Operant Reinforcement versus Operant Avoidance and Light Level , m1 _& b6 K' m5 [5 B E! X, w% E7 f7 C3 x/ p# ]! L: W8 C http://www.jneurosci.org/content ... c-9352-54142c85a5f7