Most systems use pulse modulation, with or without other supplementary modulating signals. A gating signal is produced based on a carrier current and three modulating signals. These variations are controlled by both the frequency and the amplitude of the modulating wave. Endocannabinoids are molecules that can relieve pain by modulating nociceptive neurons. The organ of Corti is also capable of modulating the auditory signal. A radio device, responsible for modulating and transmitting the signal; and a digital controller. Studies have also found that testosterone facilitates aggression by modulating vasopressin receptors in the hypothalamus. These space vectors are then used to approximate the modulating signal. This apparently has the effect of modulating autonomic reactivity to stimulation. The VIP also plays a pivotal role in modulating oscillations. The neurotransmitter serotonin seems to play an important role in modulating future discounting. It is used in capillary electrophoresis for modulating peptide mobility. As with all radio, this is done by the modulating and demodulation of carrier waves. The SET domain is a 130-amino acid sequence involved in modulating gene activities. In addition there are regulatory T cells which have a role in modulating immune response.