A method of placing a mouthpiece for delivering non-invasive neuromodulation in a patient's mouth, the method comprising: providing a mouthpiece to the patient, the mouthpiece comprising: an elongated housing having an anterior region with a substantially constant first width and a posterior region with a substantially constant second width, the elongated housing having a non-planar exterior top surface and a transition region connecting the anterior region and posterior region, the transition region having a width that varies smoothly between the first width and the second width; a positioning pad attached to the top surface of the housing such that, in use, the patient can bite down on the positioning pad to secure a position of the mouthpiece in which the posterior region of the mouthpiece rests behind the patient's teeth; a first locator disposed along the anterior region of the positioning pad, the first locator engaging the patient's upper teeth to securely position the mouthpiece in the patient's mouth; a printed circuit board mounted to a bottom portion of the elongated housing, the printed circuit board having a plurality of electrodes for delivering subcutaneous local electrical stimulation to the patient's tongue, wherein the center of gravity of the mouthpiece is located in the posterior region; and a second locator traversing an anterior region of the printed circuit board, the second locator mechanically coupling to the patient's lower teeth to securely position the mouthpiece in the patient's mouth; placing a portion of the mouthpiece in the patient's mouth; manually adjusting the mouthpiece until the posterior region of the mouthpiece rests behind the patient's teeth; and securing the position of the mouthpiece by the patient biting down on the positioning pad. providing a mouthpiece to the patient, the mouthpiece comprising: an elongated housing having an anterior region with a substantially constant first width and a posterior region with a substantially constant second width, the elongated housing having a non-planar exterior top surface and a transition region connecting the anterior region and posterior region, the transition region having a width that varies smoothly between the first width and the second width; a positioning pad attached to the top surface of the housing such that, in use, the patient can bite down on the positioning pad to secure a position of the mouthpiece in which the posterior region of the mouthpiece rests behind the patient's teeth; a first locator disposed along the anterior region of the positioning pad, the first locator engaging the patient's upper teeth to securely position the mouthpiece in the patient's mouth; a printed circuit board mounted to a bottom portion of the elongated housing, the printed circuit board having a plurality of electrodes for delivering subcutaneous local electrical stimulation to the patient's tongue, wherein the center of gravity of the mouthpiece is located in the posterior region; and a second locator traversing an anterior region of the printed circuit board, the second locator mechanically coupling to the patient's lower teeth to securely position the mouthpiece in the patient's mouth; an elongated housing having an anterior region with a substantially constant first width and a posterior region with a substantially constant second width, the elongated housing having a non-planar exterior top surface and a transition region connecting the anterior region and posterior region, the transition region having a width that varies smoothly between the first width and the second width; a positioning pad attached to the top surface of the housing such that, in use, the patient can bite down on the positioning pad to secure a position of the mouthpiece in which the posterior region of the mouthpiece rests behind the patient's teeth; a first locator disposed along the anterior region of the positioning pad, the first locator engaging the patient's upper teeth to securely position the mouthpiece in the patient's mouth; a printed circuit board mounted to a bottom portion of the elongated housing, the printed circuit board having a plurality of electrodes for delivering subcutaneous local electrical stimulation to the patient's tongue, wherein the center of gravity of the mouthpiece is located in the posterior region; and a second locator traversing an anterior region of the printed circuit board, the second locator mechanically coupling to the patient's lower teeth to securely position the mouthpiece in the patient's mouth; placing a portion of the mouthpiece in the patient's mouth; manually adjusting the mouthpiece until the posterior region of the mouthpiece rests behind the patient's teeth; and securing the position of the mouthpiece by the patient biting down on the positioning pad.