Abstract: An implantable helical electrode assembly configured to fit around a nerve for electrically triggering or measuring an action potential or for blocking conduction in nerve tissue. A multiconductor flexible cable connects the electrode to an implanted signal receiver, and the assembly may include multiple individual flexible ribbon electrodes each partially embedded in a portion of the peripheral surface of a helically formed dielectric support matrix. The spiral configuration of the assembly is easy to install around a nerve bundle during surgical implantation, and the resiliency of the assembly minimizes the risk of damage to nerve tissue. The tissue-contacting surface of each electrode is roughened to increase the electrode surface area.