A method for continuously monitoring the electrical threshold of single intraspinal nerve fibers

A method is described for the determination and continuous monitoring of the electrical threshold of single primary afferent fibres within the spinal cord of the cat. The centre barrels of multibarrel micropipettes, filled with 3.6 M NaCl, were used as stimulating electrodes, impulses in single afferents were recorded peripherally and a firing index of 50% was maintained by using a feedback circuit to regulate the amplitude of the stimulating pulses (0.2-0.3 msec duration, less than 2 microA).