Methods for treating medical disorders, such as migraine or other primary headaches, or fibromyalgia, by electrical stimulation of a nerve. The method comprises applying a first stimulus to a patient having a medical condition and measuring a first baseline physiological response from the patient. An electrical impulse is applied to a nerve within the patient and second stimulus is applied to the patient. A second physiological response evoked by the second stimulus is measured and compared to the first baseline physiological response. The methods may be used to optimize the placement of a stimulator, to test whether a patient is a suitable candidate for treatment using nerve stimulation, and/or to select the stimulation parameters that optimize acute or chronic treatment.