Chronic recording is possible from nerve fibers which have grown through holes in an insulating medium (regeneration electrodes) or which are enclosed by an insulating sheath (cuff
electrodes). Use of three electrodes in a balanced configuration permits good rejection
of electromyographic (EMG) signals and other sources of electrical interference (fluorescent lights, 60 Hz signals from the mains, etc.). Equations are derived and tested for predicting the
amplitude and form of the signals expected for a given cuff length and diameter. These equations can be used to design electrode units optimally for a given application. Finally, the use of transformers permits the neural signals to be carefully matched to the recording apparatus
and further optimizes the neural signal-to-noise and signal-to-EMG ratios. Use of these methods in several physiological and clinical applications, as well as potential abuses, are discussed.