The weakly electric fish Apteronotus has developed a clock unparalleled in its accuracy among biological oscillators. The fundamental goal of this project is to quantify the regularity of this biological oscillator and determine the neuronal basis of its extreme regularity. The kiloHertz oscillator studied is the pacemaker nucleus of the weakly electric fish Apteronotus leptorhynchus. The pacemaker nucleus, a brainstem network of about 150 synchronously firing neurons, is the command center for the oscillating electric organ discharge produced by neurons in the fish's tail. The resulting electric field is dectected by electroreceptors on the fish's body. Any objects in the environment will modulate the electric field and therefore will be 'electrically visible' to the fish. We have found that not only the electric organ discharge but also individual neurons in the intact pacemaker nucleus are regular to submicrosecond resolution. Further experiments will investigate the network and cellular basis of the regularity of the pacemaking in this nucleus.