Are mesopontine cholinergic neurons either necessary or sufficient components of the ascending reticular activating system?

The reticular activating system is thought to be composed of one or more thalamo-cortical afferents whose activation results in desynchronization of the electroencephalogram. In recent years, a strong body of correlative evidence has accumulated suggesting that mesopontine cholinergic neurons are a key component of the reticular activating system. However, despite intense study, several critical predictions of the hypothesis remain unfulfilled, and it is still not possible to conclude that mesopontine cholinergic neuronal activity is either necessary or sufficient for generation of desynchrony. Specific criteria required to satisfy this hypothesis are put forth, and potential experimental approaches required are outlined. Such rigorous treatment of this issue will assist in maintaining the rapid pace of advance in this field.