Anodal block, a local block of nerve conduction caused by hyperpolarization of the nerve cell membrane under the anode, has been described when the anode is inadvertently placed between the cathode and recording electrode. This phenomenon has been documented in animal studies but not in humans.
In this investigation, the measured latencies and amplitudes in median nerve motor and sensory conduction, and the H-reflex studies were not significantly different when the anode placed proximally or distally to the cathode. However, when orthodromic sensory conduction studies were performed with anode-active recording electrode and gradually increasing intensities of stimulation, prolonged latencies were observed with low intensities. Furthermore, moderate stimuli intensities led to double peak potentials, most prominently displayed with a 4 cm anode-cathode separation. With further increases in intensity of the stimulation, the double peak potentials disappeared and the latencies shorten.
