Destruction of the paraventricular nucleus (PVN) with electrolytic lesions has been shown to produce hyperphagia (overeating) in rats. Injections of local anesthetic into the PVN may also stimulate eating. Likewise, injections of NE into the PVN also produce feeding in rats. What does this information suggest about the effect of NE on the firing rate of neurons in the PVN? A general principle relating changes in the rate of neural firing to changes in the rate of a specific behavior (such as feeding) can be derived from this information. What is this principle?