POSITION-SELECTIVE ACTIVATION OF PERIPHERAL-NERVE FIBERS WITH A CUFF ELECTRODE

The degree of spatial selectivity which can be obtained with longitudi nal dot tripoles in an insulating cuff was quantified in terms of the overlap between fiber populations activated by different tripoles. Pre vious studies have failed to take into account the relative influences of transverse current and longitudinal current on position-selective activation, and furthermore have not controlled for the differing sens itivities of large and small nerve fibers to electrical stimuli, In th is study, these factors were taken into account, Transverse current fr om an anode positioned opposite the stimulating cathode was found to i mprove spatial selectivity, and selectivity was enhanced when the rati o of transverse current to longitudinal current was increased, Large f ibers were excited before small fibers, irrespective of fiber position , indicating a combination of position and size selectivity.