In electric fish of the mormyrid family, an efference copy is present in the brain region that receives afferent input from ampullary electroreceptors. The efference copy is elicited by the motor command to fire the electric organ. Its effect is always opposite that the ampullary afferents responding to the electric organ discharge, and it changes to match variations in this afferent input. It probably reduces the central effects of activity in ampullary receptors evoked by the electric organ discharge.