1. An apparatus comprising: an implantable stimulation device to elicit a response in a tissue by delivering one or more stimuli, the stimulation device including a stimulus delivery element to deliver the one or more stimuli to elicit the response; a memory to store a range value identifying a range of values of a stimulation parameter relative to a first value; and a controller to control delivery of the one or more stimuli by the stimulus delivery element accordance with the range value, the stimulation parameter characterizing the one or more stimuli to be delivered by the stimulation device.