Interference severity in nerve cuff recordings due to muscle source relative proximity

The output signal-to-interference (ENG/EMG) ratio of amplifier configurations connected to tripolar nerve cuff electrodes is affected by systematic interface errors which severely degrade neural recordings. These errors are contained in the term "cuff imbalance" and known causes include inhomogeneous tissue growth after cuff implantation and cuff manufacturing tolerances. In this paper we report on an additional contribution to cuff imbalance that stems from variations in orientation and distance (both factors contained here in the term proximity) of the tripolar cuff relative to the external interference source (represented here by a dipole). Interference amplitude is also shown to depend on proximity of the muscle to the cuff