Apparatus is provided, including a control unit (310), adapted to be implanted within a patient (324), and a corkscrew-shaped electrode mount (400), adapted to be implanted in a wall of a stomach of the patient. The corkscrew-shaped electrode mount includes first (404) and second (424) electrodes, at respective sites of the electrode mount, and a controller (420), wirelessly coupled to the control unit. Other embodiments are also described.