1. A device comprising: a control unit; and a plurality of stimulation units configured to be implanted in the body of a patient and generate optical stimuli, wherein the optical stimuli reset the phase of the neuronal activity of the neurons during the stimulation of neurons exhibiting abnormally synchronous and oscillatory neuronal activity, and wherein the control unit is configured to actuate the stimulation units such that at least two of the stimulation units reset the phases of the respectively stimulated neurons at different times.